# Patent

## Title
Substituted pyridine ligands and related water-soluble catalysts

## Abstract

Versatile Group VIII metathesis catalysts, as can be used in a range of polymerization reactions and other chemical methodologies.

## Background
This application is a continuation in part of and claims priority benefit from application Ser. No. 12/033,471 filed Feb. 19, 2008 now abandoned which was a continuation of application Ser. No. 11/254,947 filed Oct. 20, 2005, and issued as U.S. Pat. No. 7,332,609 on Feb. 19, 2008, which claimed priority from provisional application Ser. No. 60/620,491 filed Oct. 20, 2004—each of which is incorporated herein by reference in its entirety.


The United States government has certain rights to this invention pursuant to Grant Nos. S13200001200000 and N00014-03-1-1000 from the Office of Naval Research, Grant No. DE-FG02-04ER46126 from the Department of Energy and Grant No. NSF-CBET 0553597 from the National Science Foundation, all to the University of Massachusetts.


BACKGROUND OF THE INVENTION
Olefin metathesis is a vital tool in synthetic organic and polymer chemistry. In small molecule chemistry, olefin metathesis represents an effective method to construct elaborate cyclic and heterocyclic molecules, many of which are now being used in pharmaceutical applications. In polymer science, ring-opening and acyclic diene metathesis polymerization provides an effective route to new, highly functional polyolefins. A major limitation of these reactions is a lack of catalyst versatility, particularly concerning catalyst solubility. The vast majority of modern metathesis reactions are performed in organic solvents, typically chlorinated organic solvents. However, as the need for water-based chemistries, materials and processing increases, water-soluble catalysts and their use in polymerization and related synthetic techniques have become an on-going concern in the art.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide metathesis catalyst compounds and/or methods for their use, thereby overcoming various deficiencies and shortcomings of the prior art, including those outlined above. It will be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can meet certain other objectives. Each objective may not apply equally, in all its respects, to every aspect of this invention. As such, the following objects can be viewed in the alternative with respect to any one aspect of this invention.
It is another object of the present invention to provide such compounds directly from commercially-available materials, without resort to multi-step synthetic techniques.
It is an object of the present invention to provide a broad class of compounds having amphiphilic or hydrophilic properties and exhibiting catalytic function over a range of chemistries.
It is an object of this invention to provide a catalytic compound heretofore unknown in the art, for use in either aqueous or organic solution, giving good product yield or polymer conversions without long reaction times.
Accordingly, in conjunction with one or more of the preceding objectives, it can be an object of the present invention to provide one or more metathesis catalyst compounds as can be used in conjunction with a range of synthetic organic and polymer chemistries, including but not limited to cross-metathesis reactions, ring-opening metathesis polymerization reactions and the like, as well as for convenient routes to functionalized polyolefins, and related composites and coating materials, not attainable by conventionally synthetic methods.
Other objects, features, benefits and advantages of the present invention will be apparent from this summary and its descriptions of certain embodiments and will be readily apparent to those skilled in the art having knowledge of catalytic compounds and their use in the realm of synthetic organic chemistry. Such objects, features, benefits and advantages will be apparent from the above as taken into conjunction with the accompanying examples, data, figures and all reasonable inferences to be drawn therefrom, alone or with consideration of the references incorporated herein.
In part, the present invention can comprise a compound of a formula (I)




wherein M can be ruthenium, osmium or another Group VIII metal; X1 and X2 can be independently an anionic ligand, including but not limited to halide ion; L1, L2 and L3 can be independently neutral electron donor ligands, and at least one of L1-L3 can be an N-heterocyclic carbene ligand, and the other L ligand(s) can be independently one of the substituted pyridinyl ligands discussed below; and R1 and R2 can be independently hydrogen, alkyl, substituted alkyl, cyclic alkyl, substituted cyclic alkyl, alkenyl, substituted alkenyl, cyclic alkenyl, substituted cyclic alkenyl, phenyl or substituted phenyl moieties.

As mentioned above, one or two of the neutral electron donor ligands L1-L3 can comprise a pyridinyl moiety coupled to and/or substituted with an oligomeric/polymeric component affording amphiphilic and/or hydrophilic properties and function of the sort described herein, such ligands of a formula (II).




The substituent or component (P) coupled (e.g., without limitation with an alkoxy or triazole moiety) to each such pyridine ligand can include, but is not limited to, acyclic ethers and polyethers such as alkyl ethers and alkyl polyethers, the later including poly(ethylene glycol) (PEG), with a molecular weight and degree of oxa substitution as can vary depending upon end use application. Typically, but without limitation, the molecular weight of any such PEG component can range from about 200 to about 5000 or greater. In certain embodiments, where the repeating glycol unit can be represented by (OCH2CH2)n, n can range from about 2 to about 10 or up to 100 or greater. Regardless, such a PEG component can, opposite the pyridine terminus be substituted with a functional chain-end moiety such as, but not limited to hydroxy, alkyl, alkoxy (ether), carboxylate, and ammonium or substituted ammonium salts. Various other end/functional groups will be well known to those skilled in the art and made aware of this invention, incorporation of which can be achieved through available synthetic methods either before or after coupling with a suitable pyridinyl or other nitrogenous moiety.
Various other polymeric components can be employed depending upon end use application or compatibility with an associated or predetermined solvent system. Associated polymeric components, without regard as to chain length or molecular weight, include but are not limited to: poly(hexaethylene glycol), poly(hexadecylethylene glycol), poly(ε-caprolactone), poly(lactide), poly(glycolide), polyglycidyl, and polypropylene oxide, alone or in combination with one another and/or a PEG component. Accordingly, the present invention includes design, choice or variation of the polymeric component of such a ligand compound depending on a given solvent system. For example, a more hydrophilic polymeric or co-polymeric component (e.g., without limitation, incorporating a phosphoryl choline moiety) could be used in applications involving aqueous systems whereas monomers or polymeric blocks could be included for hydrophobic applications involving organic or mixed solvent systems. Likewise, system solubility can be further modified with ligands comprising multiple polymeric components and/or related substituents. In accordance with this invention, various other pyridinyl ligand components useful in conjunction herewith are described in co-pending application Ser. No. 10/643,015 filed Aug. 18, 2003, the entirety of which is incorporated herein by reference.
With respect to the compounds, composites and/or methods of this invention, the nitrogenous moieties and/or polymeric components can comprise, consist of or consist essentially of any of the aforementioned molecular entities and/or functional groups thereof. Each such moiety or component thereof is distinguishable, characteristically contrasted, and can be practiced in conjunction with the present invention separate and apart from another. Accordingly, it should be understood that the inventive composites, compounds and/or methods, as illustratively disclosed herein, can be practiced or utilized in the absence of any one moiety or component which may or may not be disclosed, referenced or inferred herein, the absence of which may not be specifically disclosed, referenced or inferred herein.
N-heterocyclic carbene (NHC) ligands for metathesis catalysts are well-known in the art. Such a component of catalyst compound I (i.e., one of L1-L3) can be as described more fully in U.S. Pat. No. 6,759,537, the entirety of which is incorporated herein by reference. Without limitation, such components can include the NHC ligands provided in columns 2 and 6-7 of the '537 patent, optionally substituted as shown, each such substituent as can further be substituted with one or more of the moieties and/or functional groups provided therein. In certain embodiments, such a component can comprise a 4,5-dihydroimidazolylidene moiety and can be N-substituted with aryl or substituted aryl moieties. In certain other embodiments, such an N-substituent can be a 2,4,6-trimethylphenyl (i.e., mesityl or mes) moiety.
Likewise, ligands X1 and X2 can, without limitation, include the anionic ligands provided in column 5 of the '537 patent, optionally substituted as shown, each such substituent as can be further substituted with one or more of the moieties and/or functional groups provided therein. In certain embodiments, either or both of X1 and X2 can be halide. In certain other embodiments, one or more of such ligands can be chloride.
Likewise, without limitation, R1 and R2 can be as described in columns 2 and 4-5 of the '537 patent, optionally substituted as shown, each such substituent as can be further substituted with one or more of the moieties and/or functional groups provided therein. In certain embodiments, R1 can be hydrogen and R2 can be selected from C1- about C20 alkyl, alkenyl, and aryl moieties, each whether substituted or non-substituted. In certain other embodiments, R1 can be hydrogen and R2 can be phenyl, such that M is coordinated to benzylidene.
Regardless of ligand identity, M can be, as would be understood by those skilled in the art, a Group VIII transition metal including, but not limited to, ruthenium or osmium. (See, e.g. compounds of a formula III, below.) Alternatively, such metal centers can be considered as formally in the +2 oxidation state, having an electron count of 18 and hexacoordinated. In certain non-limiting embodiments, M can be ruthenium or osmium. Accordingly, without limitation, the present invention can relate to such hexacoordinated ruthenium and osmium catalyst compounds, with the understanding that the terms “compound,” “catalyst,” and “complex.” and plurals thereof, can be used interchangeably, herein.




In part, the present invention can also be directed to a reaction system comprising an amphiphilic hexacoordinated ruthenium or osmium compound of this invention, and at least one alkene compound. Such systems can also comprise one or more fluid medium and/or solvent components, as can be used in conjunction with one or both of such compounds, to facilitate reaction within the content of any particular chemical synthesis or production environment or facility. In certain embodiments, as illustrated below, such a system can comprise two or more acyclic alkene compounds, such that the system can facilitate a cross-metathesis reaction. In certain other embodiments, such a system can comprise cyclic and acyclic alkene compounds, such that the system provides for a ring-opening cross-metathesis reaction.
In certain other embodiments, such a system can comprise a cyclic alkene compound, such that the system provides for a ring-opening metathesis polymerization reaction. In variations of such embodiments, such a system can further comprise a substrate material. As would be understood by those skilled in the art, substituents on such an alkene compound, or such substituents further substituted with one or more functional moieties, can provide for coupling or linking such an alkene compound to a substrate. In certain embodiments, the substrate can be a nanodimensioned particulate, such particulates including, but not limited to, those semi-conductive, luminescent materials known in the art as quantum dots. Such substrates include, but are not limited to, cadmium selenide, cadmium sulfide, cadmium telluride, zinc sulfide, cobalt, and such substrates as can be further provided with a shell, layer or coating thereon (e.g., a cadmium-based nanoparticle, coated with a shell of zinc sulfide or zinc selenide). In such systems, alkene compounds coupled or linked to such a substrate can be cross-linked one with another to provide a corresponding polymeric coating or layer component on the substrate.
As can be related thereto, certain other embodiments of this invention can provide a method of using an N-heterocyclic carbene ruthenium benzylidene catalyst for a ring-opening metathesis reaction in an aqueous medium. Such a method can comprise providing a cyclic alkene compound; and contacting the alkene compound and a corresponding ruthenium catalyst compound of the type described herein, such contact for a time sufficient for reaction of the alkene compound. As demonstrated herein, at least one of the alkene and catalyst compounds can be provided and/or utilized in an aqueous medium. In certain other embodiments, as mentioned above, such an alkene compound can be coupled to a substrate component. Such coupled components can be provided in a substantially hydrophobic medium, such that a catalyst compound in or provided with an aqueous medium can be used to cross-link the substrate-coupled alkene compounds at the media interface. Representative of such embodiments is the operation of a catalyst of this invention on coupled nanoparticulate assemblies or composites at the interface of immiscible fluids, as for instance an oil-water interface where the such nanoparticulate materials can be concentrated.
As discussed above and illustrated elsewhere herein, the pyridine ligands can be polymer-substituted. Accordingly, this invention can also comprise a method of using such ligands to affect the aqueous solubility of an alkylidene/benzylidene carbene metathesis catalyst. Such a method comprises providing a polymer-substituted pyridine ligand component; and contacting the ligand and a Group VIII pentacoordinated or a Group VIII hexacoordinated carbene metathesis catalyst known in the art, such contact sufficient to provide a hexacoordinated Group VIII catalyst compound comprising polymer-substituted pyridine ligand components. The compositional and coordination change afforded by such contact has been found to provide catalyst compounds with improved water solubility and higher metathesis activity than prior water soluble catalysts, as well as amphiphilic or hydrophilic properties, as demonstrated below.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-B. A representative ROMP reaction, in accordance with this invention, with GPC analysis of the polymers obtained: (A) Plot of molecular weight versus monomer/catalyst ratio; and (B) GPC chromatogram of entry 3.
FIGS. 2A-B. Another representative ROMP reaction, in accordance with this invention, with GPC analysis of the polymers obtained with 2A and 2B as described above.
FIGS. 3A-B. TEM images at (A) low magnification of a dried, collapsed nanoparticle capsule; and (B) high resolution showing well dispersed individual nanoparticles.
FIG. 4. GPC-estimated number-average molecular weights (Mn) of polymer 5 as a function of monomer-to-catalyst ratio, and GPC traces (in THF) of polymer 5 recorded on samples prepared using monomer-to-catalyst ratios of 50, 144, and 400.
FIG. 5. Comparative GPC chromatograms of polymer 7, obtained by ROMP of 6 at pH 7 and 1.5 (top), and with added copper (bottom).



DETAILED DESCRIPTIONS OF CERTAIN EMBODIMENTS
With reference to examples 1-8 and FIGS. 1-3, certain embodiments of this invention use poly(ethylene glycol) (PEG)-substituted pyridine molecules as ligands for ruthenium benzylidene catalysts, where the nitrogen of the pyridine group coordinates to the ruthenium metal center of the catalyst. Such PEG-functionalization, or PEGylation, of these ruthenium catalysts gives new water-soluble catalysts that actively polymerize water-soluble cyclic olefins in water. As described below, the synthesis of PEG-substituted pyridines can be accomplished by Mitsunobu coupling of poly(ethylene glycol) diols (i.e., OH at each chain-end) of varying chain length, with 3- or 4-hydroxypyridine. See Scheme 1, below, and various other such substituted pyridine ligands and polymeric components thereof, including but not limited to those described in application Ser. No. 10/643,015 filed Aug. 18, 2003, the entirety of which is incorporated herein by reference. The use of PEG-diols in this coupling step provides a free-hydroxyl group after coordination to the catalyst metal center (i.e., HO-PEG-pyridine-Ru), rendering the new, PEGylated catalysts soluble in water.
Exchange of the tricyclohexylphosphine ligands of the catalyst precursor for these PEG-pyridine ligands can be performed with a 10-fold excess of 1 or 2 (or related compounds with different ethylene glycol chain lengths) in minimal dichloromethane. Removal of dichloromethane in vacuo affords a mixture of 4 and PEG-pyridine starting material as a dark green oil. Dilution of this green oil in water causes precipitation of tricyclohexylphosphine, which is removed easily by centrifugation. Dark green homogeneous solutions of 4 (and e.g. 1 or 2) can then be formed in many solvents, including water, methanol, toluene, and dichloromethane, all of which can be used in metathesis chemistry. Alternatively, catalyst compounds of this invention can be prepared and isolated absent excess PEG-pyridine ligand, as shown in several of the following examples.
NMR spectroscopy (1H, 13C, and 31P) performed on a mixture of 4 and 1 (or 2) in D2O confirms the success of the ligand exchange. The 1H NMR spectrum of the catalyst mixture taken in CDCl3 shows resonances from δ3.5-3.7 ppm, characteristic of the methylene protons of PEG. A singlet at δ19.2 ppm corresponds to the benzylidene proton. This benzylidene proton is 0.07 ppm downfield from the benzylidene proton of 3.
Scheme 2 illustrates, in accordance with one aspect of this invention, the synthesis of a water-soluble metathesis catalyst by ligand exchange chemistry, using a commercially available pentavalent ruthenium catalyst and an excess of PEG-functionalized pyridine. In important advances from previous water-soluble metathesis catalysts, the compounds of this invention are 1) prepared easily and 2) exhibit markedly enhanced reactivity, due to the nature of the pyridine substituent, and 3) have appreciable solubility in neutral water. While there have been a few reports of metathesis chemistry in aqueous solution, the catalysts utilized in these studies required multistep synthetic procedures. An especially useful benefit of this invention lies in the ability to perform a range of aqueous based metathesis chemistries, such as ring opening metathesis polymerization, ring-closing metathesis and cross-metathesis. For these reactions, catalyst activity is important, since high reaction yield with minimal catalyst loading are preferred. The use of these catalysts has also been demonstrated for the polymerization of polar monomers in water. Again, the ability to carry out polymerizations in entirely aqueous media is advantageous, as organic solvents can be eliminated and post-polymerization purification is minimized.
It should also be noted that the catalysts of this invention are also soluble in a number of organic solvents, due to the amphiphilic nature of the polymeric component (e.g., polyethylene glycol) and its influence on solubility. Thus, the present invention provides a broad class of metathesis catalysts, both in terms of chemistries available and reaction media employed.
Accordingly, Catalyst 4 (Scheme 2) was tested for its ability to polymerize cyclic olefins in dichloromethane and found to successfully polymerize cyclooctene and norbornene to full conversion at room temperature in seconds. The average molecular weights of the polymers produced could be controlled easily by adjustment of the monomer-to-catalyst ratios. FIG. 1 shows GPC data for polymers obtained from exo,exo-5,6-bis(methoxycarbonyl)-7-oxabicyclo[2.2.1] hept-2-ene using catalyst 4 in dichloromethane at various monomer-to-catalyst ratios. In all ratios, the corresponding polyolefin was produced with low PDI values (<1.1) and good control over average molecular weight.
FIG. 1 also shows a plot of molecular weight versus monomer-to-catalyst ratio and a gel permeation chromatograph of the polymer prepared using a monomer-to-catalyst ratio of 200:1. The linear correlation of molecular weight and monomer-to-catalyst ratio, combined with the low PDI values of the resulting polymers, provides evidence for the “living” nature of this ROMP using this PEG-substituted ruthenium benzylidene catalyst. These results are in accord with those from the reports by Grubbs and coworkers on 3-bromopyridine-substituted ruthenium catalysts, and contrast the polymerization prior art catalyst 3, which under similar conditions produces polymers with PDI values greater than 1.5.
To test the metathesis activity of catalyst 4 in a completely aqueous environment, a water-soluble PEG-grafted oxanorbornene (FIG. 2) was synthesized by Mitsunobu coupling of exo-oxanorbornene imide in the presence of excess tetraethylene glycol. In neutral water, catalyst 4 failed to polymerize the tricyclic olefin. However, polymerization occurred in aqueous solution at low pH (2 or lower) as evidenced by a rapid increase in solution viscosity immediately after injection of 4. In this case, the presence of a Brønstead acid may activate the catalyst by protonation of PEG-pyridine ligands, which diminishes their ligation capability and increases the reactivity of catalyst 4 toward cyclic olefins.
FIG. 2 provides GPC-derived molecular weight data for the polymer prepared by polymerizations that employed various ratios of monomer to catalyst in water at pH 1.5. The average molecular weight of polymer could be adjusted to higher or lower values by variation of the monomer-to-catalyst ratio in aqueous polymerizations using catalyst 4. However, the estimated molecular weights of the polymers obtained, using GPC with DMF as the mobile phase, were not consistent with theoretical estimations. For example, in polymerization using monomer-to-catalyst ratios of 25:1 (entry 5) and 50:1 (entry 6), the polymers obtained had GPC-estimated Mn values of 67,000 and 116,000 g/mol, respectively. Full monomer conversion was confirmed by 1H NMR spectroscopy recorded in CDCl3, wherein resonances at δ6.5 ppm for the cyclic olefin were not observed. Under ideal conditions of quantitative initiation and absence of termination reactions, Mn values of  ̃10,000 and 20,000 g/mol would have been obtained for entries 5 and 6, respectively. This rather significant discrepancy in theoretical versus experimental molecular weight, along with the relatively broad PDI values (1.3-2.4), suggests that initiation by catalyst 4 under these conditions is incomplete or slow. In contrast, good agreement of theoretical versus experimentally estimated molecular weight (by GPC) was found for the polymerization in dichloromethane.
Relating to certain other embodiments of this invention, molecular monolayers can be constructed on a variety of substrates. As shown herein, when such molecular components or a monolayer thereof bear appropriate functionality, polymerization chemistries can be used to cross-link the components. Relative to flat surfaces or interfaces, the spherical surface of a droplet offers four times the surface area, provides greater access to the surrounding environment, and offers an effective route for encapsulation within a droplet. Nanoparticle assemblies on droplets represent, in many respects, ideal platforms for tuning capsule-environment interactions, as the ligands associated with each nanoparticle provide opportunities for tailored interfacial interactions and chemistries.
A unique aspect associated with interfacial assembly of nanoparticles and fluids is the highly mobile nature of the assembly, which provides rapid diffusion within the interface and fast equilibration of the assembly. For instance, tri-n-octylphosphine oxide (TOPO)-covered CdSe nanoparticles can readily segregate to a toluene/water interface. However, experience with such TOPO-covered CdSe quantum dots reveal this nanoparticle interfacial assembly becomes less stable with increasing temperature (e.g., for effecting reactive chemistry on associated ligands). In this light, the present invention can be seen as an approach to nanoparticle-based materials with improved mechanical integrity.
As demonstrated below, the catalyst compounds of this invention can also be used to effect transformation of interfacial (e.g., fluid-fluid) assemblies to robust nanoparticle capsules and substrate sheets by cross-linking the ligands fixed to a nanoparticle or substrate surface. Success of this invention in such embodiments can be evidenced by operation at room temperature. For instance, nanoparticle assemblies remain intact during the cross-linking process, demonstrating an excellent means of cross-linking nanoparticle assemblies where the nanoparticles are surface-functionalized with cyclic olefins. Previous efforts to cross-link such assemblies presented difficulties associated with the temperatures needed (ca. 60° C.) for the free radical cross-linking method employed. Such elevated temperatures led to some degree of rupture of the capsules due to thermal expansion during cross-linking. In contrast, the metathesis catalysts of this invention are active at room temperature. Moreover, the water-solubility and amphiphilicity of the catalysts provides for cross-linking from the aqueous side of an oil-water interface, and at the interface, and the preparation of well-defined capsules, as polymerization of the excess ligand-covered nanoparticles in the organic phase (i.e., not part of the capsule structure) is precluded. The result is clean cross-linking with high reproducibility and excellent structural integrity enabled by the use of these amphiphilic metathesis catalysts.
More specifically, representative of various other embodiments, the compounds and methods of this invention can be directed toward quantum dots functionalized with cyclic olefin ligands and interfacial cross-linking by ring-opening metathesis polymerization, at room temperature. With reference to examples 4-8 below, norbornene-functionalized CdSe/ZnS core/shell nanoparticles were prepared, found to assemble at an oil-water interface, and utilized for ligand cross-linking.
Application of ring-opening metathesis polymerization was first attempted using Grubb's Generation II catalyst, a representative catalyst of the prior art. Results showed that cross-linking was complicated by the presence of norbornene-functionalized nanoparticles in the continuous toluene phase. The hydrophobic nature of the catalyst led to ring-opening chemistry not specific to the interface, but occurring throughout the interface and the continuous phase to give inter-capsule cross-linked nanoparticles throughout the continuous phase, connected to, and extending outward from, the capsules.
Interfacial cross-linking was improved dramatically by use of an amphiphilic metathesis catalyst compound in this invention, capable of function in both the water phase and at the interface. For instance and without limitation, cross-linking of the nanoparticle assemblies using catalyst 4 (Scheme 2) was performed by mixing an aqueous solution of the catalyst with a toluene solution of norbornene-functionalized CdSe/ZnS core/shell nanoparticles, followed by shaking the mixture vigorously until a cloudy dispersion was obtained. Capsules obtained through this process were allowed to settle in the toluene phase, then collected.
Variation of cross-linking conditions, especially catalyst concentration, revealed differences in capsule morphology. It was found by comparison of fluorescence confocal micrographs that the use of lower catalyst quantities (e.g., 25 as compared to 5 and 1 mg/ml) gave capsules of generally spherical morphology with few defects. Evidence for successful interfacial cross-linking was obtained by visualization of the capsules upon removal of the interface, by washing out the oil and water phases with a single solvent such as methanol. Fluorescence confocal microscopy showed removal of the interface does not disrupt nanoparticle assembly, as is common with uncross-linked assemblies. Rather, droplet structure is maintained, and folds and ridges are observed upon collapse and crumbling of the cross-linked encapsulated layer. (See, FIGS. 3A and 3B.)
Notwithstanding the beneficial results realized with the aforementioned embodiments, the separation of the PEGylated catalysts from excess PEG ligand can be non-trivial. An alternative method, overcoming such concerns, is the synthesis of PEGylated pyridines by the copper-catalyzed azide-alkyne cycloaddition (“click”) reaction. The resulting ligand compounds can be used to prepare corresponding catalysts, for use as previously described.
With reference to examples 9-14 and FIGS. 4-5, the series of alkyne-substituted pyridines (purchased from Aldrich) shown in Scheme 3 (examples 10a-e) was converted to PEGylated versions 2a-e by click cycloaddition with azide-terminated PEG, using CuSO4 and sodium ascorbate in 1:1 ethanol:water. The click reactions were monitored by thin layer chromatography, as well as infrared spectroscopy by monitoring the azide signal at 2100 cm−1, and the alkyne signals at 3200 cm−1. PEGylated products 2a-e were purified by column chromatography on silica gel. In the 1H NMR spectra of CDCl3 solutions of 2a-e, the triazole proton is seen at  ̃8.1 ppm, and a triplet for the methylene group attached to the triazole at  ̃4.6 ppm. Triazole signals in the 13C NMR spectra appear at  ̃144 and 123 ppm. Of the compounds shown in Scheme 3, 2c-e containing n  ̃7 are soluble in water.
As shown in Scheme 4 (examples 1a-e), triazole-coupled PEGylated pyridines of type 2 were used to functionalize the Grubbs'-type ruthenium benzylidene catalyst. To a dichloromethane solution of the pyridine-functionalized ruthenium catalyst (prepared from the tricyclohexylphosphine-functionalized version purchased from Aldrich) was added the PEG-pyridine ligand (two equivalents of PEG-pyridine per ruthenium), and the desired conversion to 3 was achieved by repeated dissolution and application of vacuum to remove pyridine. The PEGylated ruthenium benzylidene products of type 3 were purified by flash chromatography over silica gel, eluting first with dichloromethane, then dichloromethane-methanol mixtures. The meta- and para-substituted versions proved more straightforward to isolate and characterize than the ortho-substituted 3a. Compounds of type 3 (examples 11a-e) are green waxy solids, with good solubility in dichloromethane. Compounds 3d and 3e, containing PEG chains of average molecular weight 350 g/mole, are also soluble in water (>50 mg/mL), due to the significant PEG character provided by the ligands. In the example of para-substituted 3e (Scheme 4), the 1H NMR spectrum recorded in CDCl3 shows the benzylidene proton resonance at 19.2 ppm, while the 13C NMR spectrum, also in CDCl3, shows the carbene carbon at 317 ppm. Electrospray ionization (ESI) mass spectral analysis of 3e (not shown) supports a structure containing two PEG-pyridine ligands associated with the catalyst, with the expected breadth of signals (centered at  ̃1,513 g/mole) characteristic of the ligand. A weaker set of signals centered at  ̃1,045 g/mole represents the catalyst with one PEG-pyridine ligand, which could be a minor product of the ligand exchange procedure, or the result of ligand dissociation during the ESI measurement. Integration of the 1H NMR spectrum of 3e gave a 1:58 ratio of benzylidene-to-PEG methylene protons, further supporting the depicted structure.
The amphiphilic nature of PEG allows catalysts with n  ̃7 to be used in both organic solvents and water. With reference to FIG. 4, using para-substituted 3e, ROMP of oxanorbornene dimethylester 4 in dichloromethane proved very effective, giving fast initiation and, within minutes, polymer products of type 5, in the  ̃10-60 kDa range, with exceptionally low polydispersity indices (PDI, or Mw/Mn, of 1.1 or less) characteristic of Grubbs' Generation III-type (i.e., 3-bromopyridine substituted) ROMP catalysts. The gel permeation chromatography traces of three such polymers, run in THF and calibrated against polystyrene standards (and thus providing only estimates of polymer molecular weight) are shown in FIG. 4.
PEGylated catalyst 3e (example 11e) was evaluated for its ability to perform ROMP in aqueous solution with the PEGylated oxanorbornene monomer 6 under a variety of conditions (FIG. 5, examples 12-16 and Table 1). At room temperature and pH  ̃1.5, complete conversion of 6 was achieved in less than 2 hours, as judged by 1H NMR spectroscopy recorded on aliquots removed from the reaction mixture. The PEGylated polyolefins shown as 7 (FIG. 5) were obtained with considerable molecular weight (>40,000 g/mole, as estimated by GPC in DMF using poly(methyl methacrylate) standards), and polydipsersity indices (PDIs) under 2. Attempted ROMP of 6 at pH 4 and 7 led to a significantly lower conversion ( ̃20-40%) and molecular weight, and multi-modal GPC traces. This pH-dependent behavior can be rationalized as possibly stemming from dissociation of equilibrium-protonated pyridine from the metal center, which facilitates productive metathesis. Thus, ROMP in acidic aqueous solution proceeds more effectively than under neutral conditions. That the catalysts reported here lead to any metathesis at pH 7 is distinct from prior work on ether-linked PEG-pyridine functionalized ROMP catalysts. Previously, no monomer conversion at neutral pH was seen, presumably due in part to the higher basicity of the 4-ethereal pyridines relative to pyridine itself, excluding the ligand dissociation needed to initiate ROMP. In catalysts of type 3, no substantial electronic substituent effect is imparted on the pyridine. Nonetheless, observations that ROMP with catalysts of type 3 proceed most effectively in the presence of Bronstead acid may hamper its use in conjunction with acid-sensitive monomers. Thus, the addition of copper salts to the ROMP polymerization mixtures was explored (example 14), under the presumption that competitive coordination of the pyridine ligands to copper would promote productive metathesis. When CuSO4 or CuBr2 was added to aqueous solutions of 6 with catalyst 3e at pH 7, nearly 70% monomer conversion (as judged by 1H NMR spectroscopy) was achieved, and PEGylated poly(oxanorbornene) 7 was produced with average GPC-estimated molecular weights over 50,000 g/mole, and PDI values in the 1.3-1.5 range. FIG. 5 compares GPC traces of polymer 7, prepared under conditions that demonstrate the beneficial presence of H+ and copper salts in the reaction mixture. The ability to perform aqueous ROMP at neutral pH, combined with the very simple synthesis of the water solubilizing PEGylated ligands, is seen as advantageous for future work in aqueous ROMP, as well as potentially other metathesis chemistries for the synthesis of small molecules (i.e., ring-closing metathesis and cross-metathesis).







TABLE 1







ROMP of 6 using catalyst 3e.















Monomer:Catalyst
Monomer
Molecular weight (g/mole)


Entry
pH
Additive
ratio
conversion
by GPC in DMF















1
1.5
None
10
Quantitative
Mn 31,500; Mw 41,000; PDI 1.3


2
1.5
None
17
Quantitative
Mn 63,800; Mw 120,000; PDI 1.9


3
1.5
None
34
Quantitative
Mn 94,000; Mw 141,000; PDI 1.5


4
4
None
20
40%
Mn 2,400; Mw 3,700; PDI 1.5


5
7
None
20
23%
Mn 12,000; Mw 21,800; PDI 1.8


6
7
CuSO4
20
70%
Mn 54,000; Mw 82,000; PDI 1.5


7
7
CuBr2
20
70%
Mn 54,000; Mw 75,000; PDI 1.4









While PEGylated ROMP catalysts proved effective in aqueous environments, other substituents to the pyridine ring can also be considered, as discussed above and in accordance with various broader aspects of this invention. Consistent therewith, phosphorylcholine (PC) groups were also employed for the preparation of PC-azide 8. In synthetic polymer chemistry, PC pendent groups have been exploited effectively in methacrylic polymers to provide water solubility and biocompatibility. As shown in Scheme 5 and examples 15-17, reaction of 6-azido-hexanol with 2-chloro-1,3,2-dioxaphospholane-2-oxide (COP) is followed by ring-opening with trimethylamine to give 8. Click cycloaddition of 8 with 4-alkynylpyridine gives PC-pyridine 9, which is then used for functionalization of the ruthenium benzylidene catalyst in similar fashion to the PEG case described above. PC-pyridine catalyst 10 was obtained in good yield as a green, hygroscopic powder that dissolves readily in water, dichloromethane, chloroform, and methanol (example 18). Characterization of 10 by electrospray ionization (ESI) mass spectroscopy revealed a peak corresponding to 1414.4 g/mole, in accord with the catalyst functionalized with two equivalents of PC-pyridine ligand 9; the benzylidene proton in the 1H NMR spectrum of CDCl3 solutions of 9 was seen at 19.2 ppm.
ROMP with PC-pyridine catalyst 10 in aqueous media was carried out in similar fashion as for PEG-pyridine catalyst 3e, by addition of catalyst to an aqueous solution of the aforementioned PEGylated oxanorbornene 6 (example 19). The polymerizations were run for 1-2 hours, and the increase in molecular weight was monitored by aqueous GPC. The results of these experiments are summarized in Table 2. With monomer 6, PC catalyst 10 gives quantitative monomer conversion in experiments performed at 20:1 and 50:1 monomer-to-catalyst ratios. Interestingly, this high conversion is observed in both neutral and acidic (pH 1.5) media, giving molecular weights comparable to those targeted, and PDI values of 2 or less.







TABLE 2







Polymerization results obtained for ROMP of 6 using catalyst 10.















Monomer:Catalyst
Monomer
Molecular weight (g/mole)


Entry
pH
Additive
ratio
conversion
by GPC in H2O





1
7.0
None
50:1
Quantitative
Mn 9,800; Mw 16,000; PDI 1.7


2
1.5
None
50:1
Quantitative
Mn 11,100; Mw 18,700; PDI 1.7


3
7.0
CuSO4
50:1
Quantitative
Mn 17,800; Mw 28,200; PDI 1.6


4
7.0
None
20:1
Quantitative
Mn 8,400; Mw 13,800; PDI 1.6









As relates to certain other embodiments, PC-pyridine catalyst 10 and variations thereof are capable of liposome formation in aqueous media. Such bi-layer structures can also be prepared in combination with one or more liposome-forming zwitterionic compounds known in the art, such as but not limited to 1,2-dilauryl-sn-gylcero-3-phosphocholine (DLPC). Without limitation, representative liposomes can be formed with a 3:1 ratio of DLPC:PC-catalyst. Regardless, such assemblies can provide an approach for incorporation of reactive and/or catalytic function into a liposome structure, for subsequent use or application.
As discussed and illustrated by representative examples, below, benzylidene catalysts can be made amphiphilic and/or hydrophilic by PEG- and PC-substitution of the pyridine ligands that coordinate to the metal center. This approach is a convenient synthetic alternative to the procedure that integrates PEG into the N-heterocyclic carbene component of the catalyst structure. Such catalysts are convenient to prepare and effective for enabling various synthetic chemistries including but not limited to ROMP reactions.
EXAMPLES OF THE INVENTION
The following non-limiting examples and data illustrate various aspects and features relating to the catalyst compounds and/or methods of the present invention, including use thereof to cross-link nanoparticulate ligand components, as are available through the synthetic methodologies described herein. In comparison with the prior art, the present catalysts and related methods provide results and data which are surprising, unexpected and contrary thereto. While the utility of this invention is illustrated through the use of several catalyst compounds, pyridinyl ligands and associated polymeric components, it will be understood by those skilled in the art that comparable results are obtainable with various other catalyst compounds, pyridinyl moieties and associated polymeric components, as are commensurate with the scope of this invention.
Materials
With regard to examples 1-8, 4-hydroxypyridine (95%, Aldrich) was passed through a plug of neutral alumina (80/20 CHCl3/MeOH eluent), precipitated into diethyl ether, filtered, and dried in vacuo. Furan (Aldrich) was purified by vacuum distillation over calcium hydride. Tetraethylene glycol (99%) was purchased from Alfa-Aesar and purified by fractional distillation. Tetrahydrofuran (THF) was distilled from sodium benzophenone ketyl. Dichloromethane was washed with concentrated sulfuric acid, dried over magnesium sulfate, and distilled over calcium hydride. Triphenylphosphine (99%), diisopropyl azodicarboxylate (95%), maleic anhydride (99%), maleimide (99%), ethyl vinyl ether (99%), diethylene glycol vinyl ether (98%), and Grubbs' Generation II Catalyst tricyclohexylphosphine[1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidine]ruthenium (IV) dichloride were purchased from Aldrich and used as received.
With regard to examples 9-19, N,N-diisopropylethylamine (DIPEA, 99%), 6-bromo-1-hexanol (97%), sodium azide (99.5%), trimethylamine (99+%), bromotris(triphenylphosphine)copper(I) (98%), 2-ethynylpyridine (98%), 3-ethynylpyridine (98%) and 4-ethynylpyridine hydrochloride (97%) were purchased from Sigma Aldrich. Copper(II) sulfate pentahydrate (99.6%, Fischer Scientific) and sodium ascorbate (Source Naturals), were used as received. Ethylene chlorophosphate (98%) was purchased from Sigma Aldrich and purified by distillation. Triethylamine, acetonitrile, and methylene chloride were all distilled over CaH2 before use. THF was dried and distilled over sodium/benzophenone ketyl.
Instrumentation
With regard to examples 1-8, nuclear magnetic resonance (NMR) spectroscopy was performed on a Brüker Avance 400 spectrometer (referenced to CDCl3): 1H at 400 MHz and 13C at 100 MHz. Molecular weights and polydispersity indices (PDIs) for polymer 5 were estimated by gel permeation chromatography (GPC) in THF (1.0 mL/min) against linear polystyrene standards, using a Knauer HPLC Pump (K-501), Refractive Index detector (K-2301), and three Polymer Laboratories (PL) Mixed D columns (5 μm, 300 mm×7.5 mm). GPC analysis of polymer 7 was performed in dimethylformamide (DMF) (1.0 mL/min) with LiBr (0.05 μM) at 50° C., using a PL GPC 50 system equipped with two PL Resipore® columns (3 μm, 300 mm×7.5 mm) and referenced against linear poly(methyl methacrylate) standards. HPLC analysis was performed using a Waters Alliance 2695 multi-solvent delivery system equipped with a Waters 2996 photodiode array detector and a Waters XTerra® column (C8, 5 μm, 4.6 mm×150 mm). Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was performed on a PerkinElmer Spectrum One spectrometer equipped with a Universal Diamond ATR sampling accessory.
With regard to examples 9-19, Nuclear magnetic resonance (NMR) spectroscopy was performed on Brüker Avance 400 and Bruker-Spectrospin 300 (referenced to CDCl3) machines. Molecular weights and polydispersity indices (PDIs) were estimated by gel permeation chromatography (GPC) in THF at 1.0 mL/min against linear polystyrene standards (Knauer pump K-501, refractive index detector K-2301, and three Polymer Laboratories Mixed D columns (5 μm, 300 mm×7.5 mm), or in dimethylformamide (DMF) at 1.0 L/min with LiBr (0.05 M) using a PL GPC 50 system equipped with two PL Resipore® columns (3 μm, 300 mm×7.5 mm) and referenced against poly(methyl methacrylate) standards.
Example 1a
Representative synthesis of PEG-pyridine ligand (compound 2 in Scheme 1, n=2). In a dry, round-bottom flask, 4-hydroxypyridine (3.00 g, 31.5 mmol), triphenylphosphine (8.7 g, 33 mmol), and triethylene glycol (14.2 g, 94.6 mmol) were combined and diluted in 100 mL dry THF. The flask containing this mixture was cooled in an ice-water bath (ca. 0° C.), and diisopropylazodicarboxylate (6.40 mL, 33.1 mmol) was injected. After 30 minutes, the ice bath was removed and the mixture was stirred under an atmosphere of nitrogen for 12 hours at room temperature. The mixture was concentrated and dissolved in ether. The product was extracted three times with 1 M HCl(aq). The combined aqueous fractions were treated with aqueous NaOH solution until a pH of 12 was reached. The product was then extracted with chloroform, and the combined organic fractions were dried over MgSO4 and concentrated by rotary evaporation. This crude product was purified by column chromatography over silica gel using chloroform-methanol mixtures to afford 2.9 g of pure 2 (41% yield): 1H NMR (CDCl3) δ 8.26 (d, 2H), 6.70 (d, 2H), 4.04 (m, 3H), 3.73 (m, 2H), 3.58 (br m, 8H); 13C NMR (CDCl3) δ 164.8, 150.6, 110.3, 72.6, 70.7, 70.2, 69.2, 69.1, 67.1, 61.2; ATR-FTIR 3246, 3036, 2870, 1639, 1591, 1568, 1502, 1454, 1422, 1352, 1284, 1211, 1119, 1051, 1000, 991, 929, 887, 817, 730, 699 cm−1.




Example 1b
With reference to Scheme 1, compound 1 is prepared in an analogous manner from 3-hydroxypyridine. Without limitation, both compounds 1 and 2 can vary by chain length (e.g., n can be from 2 to about 10 or greater), and/or terminal moiety (e.g., amino, alkyl, etc.). See more specifically, examples 1c-1f below.
Example 1c
Synthesis of triethylene glycol substituted pyridine (2-{2-[2-(Pyridin-4-yloxy)-ethoxy]-ethoxy}-ethanol). To a dry, round-bottom flask was added 4-hydroxypyridine (5.00 g, 52.6 mmol), triphenylphosphine (20.68 g, 78.9 mmol), triethylene glycol (23.7 g, 157.8 mmol), and dry THF (125 mL). The mixture was stirred under N2(g) at 0° C., and diisopropyl azodicarboxylate (10.69 mL, 55.2 mmol) was added by addition funnel over 30 minutes. This mixture was stirred for 30 minutes, then the ice bath was removed, and the mixture was stirred under N2(g) for 12 hours at room temperature. The mixture was then concentrated, dissolved in chloroform, and extracted with 1 M HCl(aq). The combined aqueous fractions were treated with a 30 wt % NaOH solution until a pH of 12 was reached. The product was extracted three times with chloroform, and the combined organic fractions were dried over MgSO4 and concentrated. The product was purified first by silica gel chromatography (9:1 CHCl3:MeOH). Next, the product was dissolved in water and passed through Amberlite®IR-120H ion exchange resin (1 M KOH). The product was extracted three times with CHCl3, the organic fractions combined, dried over MgSO4, and concentrated to a colorless oil (24% yield): 1H NMR (CDCl3) δ 8.37 (d, 2H), 6.78 (d, 2H), 4.13 (t, 2H), 3.83 (t, 2H), 3.55-3.71 (br m, 8H), 3.08 (br s, 1H); HPLC (acetonitrile, 0.1% trifluoroacetic acid) retention time, 2.121 min.
Example 1d
Synthesis of Tetraethylene Glycol Substituted Pyridine 1-(2-(2-{2-[2-(Pyridin-4-yloxy)-ethoxy]-ethoxy}-ethoxy)-ethanol). To a dry, round-bottomed flask were added 4-hydroxypyridine (3.00 g, 31.6 mmol), triphenylphosphine (9.10 g, 34.7 mmol), tetraethylene glycol (36.8 g, 189 mmol), and dry THF (125 mL). The mixture was stirred under N2(g) at 0° C. (ice-water bath), and diisopropyl azodicarboxylate (6.80 mL, 34.7 mmol) was added by syringe over a 10-min period. The mixture was stirred for 30 min, the ice bath was removed, and the reaction was stirred under nitrogen for 12 h at room temperature. The reaction mixture was then concentrated, dissolved in chloroform, and extracted three times with 1 M HCl(aq). The combined aqueous fractions were treated with a 30 wt % NaOH solution until a pH of 12 was reached. The product was extracted three times with chloroform, and the combined organic fractions were dried over MgSO4 and concentrated. Excess tetraethylene glycol was removed by vacuum distillation, and the residue was purified by column chromatography over silica gel to yield 3.4 g of a colorless oil (40% yield): 1H NMR (CDCl3) δ8.38 (d, 2H), 6.80 (d, 2H), 4.14 (t, 2H), 3.83 (t, 2H), 3.55-3.70 (br m, 12H), 3.08 (br s, 1H); 13C NMR (CDCl3) δ 164.8, 150.6, 110.3, 72.6, 70.7, 70.2, 69.2, 69.1, 67.1, 61.2; ATR-FTIR 3246, 3036, 2870, 1639, 1591, 1568, 1502, 1454, 1422, 1352, 1284, 1211, 1119, 1051, 1000, 991, 929, 887, 817, 730, 699 cmm−1; HPLC (7:3 H2O/aceto-nitrile (0.1% trifluoroacetic acid)) retention time, 1.62 min.
Example 1e
Synthesis of hexaethylene glycol substituted pyridine (2-{2-[2-(2-{2-[2-(Pyridin-4-yloxy)-ethoxy]-ethoxy}-ethoxy)-ethoxy]-ethoxy}-ethanol). To a dry, round-bottom flask was added 4-hydroxypyridine (2.32 g, 24.4 mmol), triphenylphosphine (9.61 g, 36.6 mmol), hexaethylene glycol (8.27 g, 29.3 mmol), and dry THF (125 mL). The mixture was stirred under N2(g) at 0° C. (ice-water bath), and diisopropyl azodicarboxylate (4.96 mL, 25.6 mmol) was added via an addition funnel over a 30 minute period. The mixture was stirred for 30 minutes, the ice bath was removed, and the reaction was allowed to stir under nitrogen for 48 hrs at room temperature. The reaction mixture was then concentrated, dissolved in chloroform, and extracted three times with 1 M HCl(aq). The combined aqueous fractions were treated with a 30 weight percent NaOH solution until a pH of 12 was reached. The product was extracted three times with chloroform, and the combined organic fractions were dried over MgSO4 and concentrated. The product was purified by silica gel chromatography (9:1 CHCl3:MeOH), then dissolved in water and passed through Amberlite® IR-120H ion exchange resin (1 M KOH). The product was extracted three times with CHCl3, the organic fractions combined, dried over MgSO4, and concentrated to a colorless oil: 1H NMR (CDCl3) δ 8.42 (d, 2H), 6.82 (d, 2H), 4.17 (t, 2H), 3.88 (t, 2H), 3.60-3.75 (br m, 20H), 2.70 (br s, 1H).
Example 1f
Synthesis of PEG 550 monomethyl ether-substituted pyridine. To a dry, round-bottom flask was added 4-hydroxypyridine (4.98 g, 52.4 mmol), triphenylphosphine (20.60 g, 78.5 mmol), PEG-550 monomethyl ether (28.8 g, 52.4 mmol), and dry THF (125 mL). The mixture was stirred under N2(g) at 0° C. (ice-water bath), and diisopropyl azodicarboxylate (10.65 mL, 55.0 mmol) was added via an addition funnel over a 30 minute period. The mixture was stirred for 30 minutes, the ice bath was removed, and the reaction was allowed to stir under nitrogen for 12 hours at room temperature. The reaction mixture was then concentrated, dissolved in chloroform, and extracted three times with 1 M HCl(aq). The combined aqueous fractions were treated with a 30 weight percent NaOH solution until a pH of 12 was reached. The product was extracted three times with chloroform, the organic fractions were combined, dried over MgSO4, and concentrated. The crude mixture was purified by silica gel chromatography a colorless oil: 1H NMR (CDCl3) δ 7.34 (d, 2H), 6.30 (d, 2H), 3.89 (t, 2H), 3.72 (t, 2H), 3.47-3.60 (br m, 40.5H), 2.68 (br s, 1H).
Example 2a
Representative synthesis of PEG-substituted ruthenium benzylidene catalyst (compound 4 in Scheme 2, n=2). Tricyclohexylphosphine[1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidine]ruthenium (IV) dichloride 3 (50 mg, 0.060 mmol) and PEG-pyridine 2 (320 mg, 0.60 mmol) were combined and diluted in 0.5 mL of dry dichloromethane. The mixture was stirred under nitrogen for 30 minutes. Dichloromethane was removed under vacuum, and the residue was dissolved in methanol. The solid precipitate was filtered leaving a clear, dark green solution. This solution was concentrated and dissolved in water. The aqueous solution was centrifuged for approximately 10 minutes to give a clear, dark green supernatant that was isolated and used directly for metathesis polymerization chemistry.




Catalyst 4 (n≧3) is amphiphilic due to the poly(ethylene glycol) chains. It forms optically clear homogeneous solutions in water, polar protic solvents (e.g., methanol, ethanol, isopropanol, etc.), polar aprotic solvents (e.g., dimethylformamide, dimethylsulfoxide, acetonitrile, etc.), and a variety of organic other organic solvents (e.g., acetone, dichloromethane, chloroform, tetrahydrofuran, diethyl ether, toluene, etc). Catalyst 4 is not soluble in hydrocarbon solvents such as pentane, hexane, octane, etc.

Example 2b
Various other catalyst compounds of this invention can be prepared as provided in Example 2a from other such pentavalent Group VIII transition metal (e.g., ruthenium or osmium) complexes known in the art and/or substituted pyridine ligand components, in accordance with this invention. Pentavalent Group VIII complexes useful in preparation of the catalysts of this invention are commercially available from Materia, Inc. or as described in U.S. Pat. No. 6,613,910, the entirety of which is incorporated herein by reference.
Example 2c
Synthesis of Tetraethylene Glycol Substituted Ruthenium Benzylidene Catalyst. With reference to Scheme 2, a solution of compound 3 (50.0 mg, 58.9 μmol) and PEG-pyridine ligand 2, n=3, (0.16 g, 0.59 mmol) in dry dichloromethane (0.3 mL) was stirred under nitrogen for 1 h. Dichloromethane was removed in vacuo, and the remaining green oil was diluted with water to precipitate tricyclohexylphosphine. This aqueous solution was subjected to centrifugation for 5 min to give a clear, dark green, aqueous solution that was removed by a pipette. The green aqueous catalyst solution was concentrated under vacuum (Kügelrohr) to afford a viscous green oil composed of a mixture of 2 and 4. This oil could be diluted in either organic solvents or water for use in ROMP.
1H NMR (CDCl3) δ19.20 (s, catalyst, benzylidene), 8.38 (d, PEG-pyridine ligand), 7.83 (d, catalyst), 7.71 (br s, catalyst), 7.65 (d, catalyst), 7.45 (m, catalyst), 7.33 (m, catalyst), 7.20 (m, catalyst), 7.05 (m, catalyst), 6.94 (t, catalyst), 6.93 (s, catalyst), 6.80 (d, PEG-pyridine ligand), 6.76 (m, catalyst), 6.21 (br s, catalyst), 4.14 (t, PEG-pyridine ligand), 3.83 (t, PEG-pyridine ligand), 3.55-3.70 (br m, PEG-pyridine ligand), 3.18 (m, catalyst), 2.93 (m, catalyst), 2.57, (s, catalyst), 2.15-2.4 (br m, catalyst); 31P NMR-no signals, indicative of absence of tricyclohexylphosphine.
Example 2d
Alternatively, catalyst compounds of this invention can be prepared from various hexavalent Group VIII transition metal (e.g., ruthenium or osmium) complexes of the type described in U.S. Pat. No. 6,759,537, the entirety of which is incorporated herein by reference. See, e.g., examples 2e and 2f, below, also illustrating catalyst preparation substantially absent excess substituted pyridine ligand.
Example 2e
Synthesis of triethylene glycol substituted ruthenium catalyst. To a dry, two-neck round bottom flask was added (IMesH2)(C5H5N)2(Cl)2Ru=CHPh (0.1041 g, 0.143 mmol), triethylene glycol substituted pyridine (0.065 g, 0.286 mmol), and dry dichloromethane (0.2 mL). The mixture was stirred for thirty minutes and the solvent and pyridine ligand were removed in vacuo. Dry dichloromethane (0.2 mL) was added again, stirred for fifteen minutes, and removed in vacuo. This process was repeated six times, at which point a dark green, amorphous solid was obtained. The catalyst was used without further purification. 1H NMR (CDCl3) δ 19.14 (s, catalyst, benzylidene), 8.44 (d, PEG-pyridine ligand), 7.66 (d, catalyst), 7.60 (d, catalyst), 7.45 (m, catalyst), 7.19 (m, catalyst), 7.16 (m, catalyst), 7.05-7.10 (br m, catalyst), 6.97 (m, catalyst) 6.89 (d, PEG-pyridine ligand), 6.76 (m, catalyst), 6.76 (br s, catalyst), 6.51 (d, catalyst) 4.14 (t, PEG-pyridine ligand), 3.89 (t, PEG-pyridine ligand), 3.55-3.70 (br m, PEG-pyridine ligand), 2.97 (m, catalyst), 2.57, (s, catalyst), 2.2-2.44 (br m, catalyst), 2.17 (s, catalyst)




Example 2f
Synthesis of PEG 550 monomethyl ether substituted ruthenium catalyst. To a dry, two-neck round bottom flask was added (IMesH2)(C5H5N)2(Cl)2Ru=CHPh (0.1667 g, 0.229 mmol), polyethylene glycol 550 monomethyl ether-substituted pyridine (0.2719 g, 0.458 mmol), and dry dichloromethane (0.2 mL). The mixture was stirred for thirty minutes and the solvent and pyridine were removed in vacuo. Dichloromethane (0.2 mL) was added again, stirred for fifteen minutes, and removed in vacuo. This process was repeated six times, at which point a dark green, amorphous solid was obtained. The catalyst was used without further purification. 1H NMR (CDCl3) δ 19.17 (s, catalyst, benzylidene), 8.62 (br s, catalyst), 7.81 (br s, catalyst), 7.61 (d, catalyst), 7.47 (t, catalyst), 7.38 (d, PEG-pyridine ligand), 7.06 (t, catalyst), 6.93-7.00 (br m, catalyst), 6.74 (s, catalyst) 6.36 (d, PEG-pyridine ligand), 4.19 (br m, catalyst), 4.03 (br m, catalyst), 3.93 (t, PEG-pyridine ligand), 3.75 (t, PEG-pyridine ligand), 3.53-3.65 (br m, PEG-pyridine ligand), 3.36 (s, catalyst), 2.63 (s, catalyst), 2.22-2.42 (br m, catalyst), 2.1 (br s, catalyst)




Example 3
Examples of metathesis chemistry using amphiphilic ruthenium benzylidene catalyst 4. Examples 3a and 3b schematically show polymerization chemistry that can be performed in neutral water using the PEG-substituted ruthenium benzylidene catalysts of this invention. Examples 3c and 3d schematically show small molecule chemistry that can be performed in water with these catalysts, for example cross-metathesis (example 3c) and ring-opening cross-metathesis (example 3d). These important organic transformations are, as a result of this invention, now feasible in neutral water with use of highly active heterocyclic carbene-substituted ruthenium (osmium) benzylidene-type ROMP catalysts. Examples 3e-3 g describe, more specifically, use of the amphiphilic catalyst compounds of this invention, as illustrated through the polymerization of representative bicyclic alkenes. (See, FIGS. 1 and 2.)
Example 3a
Ring opening metathesis polymerization of PEG-substituted cyclooctene derivatives in water, where the PEG chain is attached to the cyclooctene derivative by an ether, amide, ester or other linkage.




Example 3b
Ring opening metathesis polymerization of oxanorbornene derivative in water




Example 3c
Cross-metathesis reaction in water




Example 3d
Ring opening cross-metathesis reaction in water




Example 3e
Synthesis of Tetraethylene Glycol Substituted Oxanorbornene 6-(4-(2-{2-[2-(2-Hydroxy-ethoxy)-ethoxy]-ethoxy}-ethyl)-10-oxa-4-aza-tricyclo [5.2.1.02,6]dec-8-ene-3,5-dione). To a dry round-bottomed flask were added the oxanorborne imide, 10-oxa-4-aza-tricyclo[5.2.1.02,6] dec-8-ene-3,5-dione, (3.00 g, 18.2 mmol), triphenylphosphine (5.50 g, 20.9 mmol), tetraethylene glycol (17.6 g, 90.8 mmol), and dry THF (150 mL). (The dione was prepared according to the literature: Kwart et al., JACS, 1952, 74, 3094-3097.) The mixture was stirred under N2(g) at 0° C. (ice-water bath), and diisopropyl azo-dicarboxylate (4.10 mL, 20.9 mmol) was added by syringe over a 10-min period. The mixture was stirred for 30 min. The ice bath was then removed, and the mixture stirred for 12 h at room temperature. The mixture was then concentrated, dissolved in ether, and extracted three times with water. The aqueous fractions were combined, and the product was then extracted from the aqueous phase with chloroform. The chloroform solution was dried over MgSO4 and concentrated, and the product was purified by column chromatography on silica gel using hexane/ethyl acetate mixtures to yield 3.8 g (61% yield) of a viscous, colorless oil.
1H NMR (CDCl3) δ6.48 (s, 2H), 5.23 (s, 2H), 3.55-3.70 (br m, 18H), 2.84 (s, 2H); 13C NMR (CDCl3) δ 176.4, 136.7, 81.0, 72.6, 70.7, 70.6, 70.5, 70.2, 67.3, 61.8, 47.6, 38.3; ATR-FTIR 3458, 2896, 1772, 1694, 1429, 1398, 1336, 1287, 1193, 1096, 1067, 1020, 916, 877, 853, 825, 813, 721, 710 cm−1; HPLC (7:3 H2O/acetonitrile (0.1% trifluoroacetic acid)) retention time, 1.99 min.
Example 3f
Ring-Opening Metathesis Polymerization in Dichloromethane. With reference to FIG. 1, exo,exo-5,6-Bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene (0.2 g, 0.9 mmol) was stirred in dry dichloromethane (1.9 mL) at room temperature under N2(g). A 0.03 M solution (0.64 mL) of catalyst compound 4 (Scheme 2, n=3) in dichloromethane was added rapidly by syringe. The mixture was stirred for 30 min, and ethyl vinyl ether (0.5 mL) was added. Precipitation into cold methanol gave a white solid that was filtered and dried in vacuo to afford 0.17 g (85% yield) of the corresponding polymer.
1H NMR (CHCl3) δ5.89 (m, 1H), 5.62 (m, 2H), 5.05 (br m, 2H), 4.71 (br m, 1H), 3.68 (br m, 6H), 3.08 (m, 2H); GPC (in THF vs. linear polystyrene standards) Mn=65,900 g/mol, Mw=71,400 g/mol, PDI=1.08.
Example 3g
Ring-Opening Metathesis Polymerization in Water. With reference to FIG. 2 a 0.015 M solution (1.6 mL) of catalyst compound 4 (Scheme 2, n=3) in acidified water (HCl, pH 1.5) was added to 1.3 mL acidified water (HCl, pH 1.5) in a reaction tube, and the mixture was stirred at room temperature under nitrogen. A 0.60 M stock solution (1.0 mL) of tetraethylene glycol substituted oxanorbornene in acidified water (HCl, pH 1.0) was injected rapidly into the catalyst solution, and the mixture was stirred for 30 min. Diethylene glycol vinyl ether was added, and the mixture was then concentrated, dissolved in a minimal amount of CHCl3, and precipitated into cold hexane. The hexane was decanted and the polymer residue dried under vacuum to afford 0.16 g (80% yield) of the corresponding polymer as a tacky solid.
1H NMR (CHCl3) δ6.08 (br s, 1H), 5.78 (br m, 1H), 5.05 (br m, 1H), 4.49 (br m, 1H), 3.55-3.70 (br m, 18H), 2.84 (br s, 2H); GPC (DMF with LiBr (0.05 M) vs. linear poly(methyl methacrylate) standards) Mn=67,000 g/mol, Mw=90,700 g/mol, PDI=1.35.
Example 4
With reference to examples 5-8, compound 6 can be prepared as shown below, then used with a catalyst compound of this invention en route to interfacial assembly of a nanoparticulate composite comprising cross-linked ligand components.




General. Selenium (99.999%) and tri-n-octylphosphine (tech. grade) were purchased from Alfa Aesar. Hexylphosphonic acid (HPA) was purchased from Organometallics, Inc. Cadmium oxide, 5-norbornene-2-carboxylic acid, dicyclohexylcarbidiimide, hexadecylamine, hydrazine acetate and all other reagents were purchased from Aldrich. Tetrahydrofuran and toluene was purified by conventional distillation over sodium/benzophenone and methylene chloride was dried over calcium hydride. 1H, 13C, and 31P NMR spectra were recorded on a Bruker-Spectrospin 300. Transmission electron microscopy (TEM) was performed on a JEOL JEM-3010. TEM grids were purchased from Ted Pella, Inc. and consisted of 3-4 nm amorphous carbon film supported on a 400-mesh copper grid. Confocal microscopy was performed on a Leica TCS SP2 LSCM with an oil-emersion objective and Ar-laser excitation (excitation: 488 nm, detection: 590 nm).
Example 5
Preparation of compound 5. 5-norbornene-2-carboxylic acid (1.00 g, 7.20 mmol), 11-thioacetate undecanol (2.14 g, 8.70 mmol), dicyclohexylcarbodiimde (1.79 g, 8.70 mmol), and 4-(dimethylamino)pyridine (0.53 g, 4.40 mmol) were dissolved in CH2Cl2 (20 mL). The reaction was stirred at room temperature under an inert atmosphere for 1 hr. The reaction mixture was filtered and the solvent was removed under reduced pressure to give a viscous liquid. The product was purified by column chromatography eluting with CHCl3:hexane mixtures to yield 1 (1.93, 89%). 1H NMR (300 MHz, CDCl3) δ 6.20-5.91 (m, 2H), 4.04 (m, 2H), 3.21 (br s, 1H), 2.91 (m, 4H), 2.32 (s, 3H), 1.94-1.2 (m, 24H) ppm; 13C NMR (75 MHz, CDCl3) δ 196.0, 174.8, 138.0, 132.3, 64.5, 64.3, 55.7, 49.6, 46.6, 46.3, 45.7, 43.3, 43.2, 42.5, 41.6, 34.9, 30.6, 30.3, 29.5, 29.4, 29.3 ppm.
Example 6
Preparation of compound 6. Compound 5 (1.0 g, 2.7 mmol) was dissolved in DMF (15 mL) and stirred at room temperature under an inert atmosphere. Hydrazine acetate (0.75 g, 8.1 mmol) was added to the solution and allowed to react for 20 min. The reaction mixture was filtered and the solvent was removed under reduced pressure to yield (0.68 g, 97%). 1H NMR (300 MHz, CDCl3) δ 6.20-5.91 (m, 2H), 4.02 (m, 2H), 3.21 (br s, 1H), 2.89 m, 4H), 2.50 t, 2H), 2.30 (br, 1H), 1.63-1.26 (m, 20H) ppm; 13C NMR (75 MHz, CDCl3) δ 174.8, 138.0, 132.3, 64.3, 46.6, 46.3, 45.7, 43.3, 43.1, 42.5, 41.6, 34.0, 29.4, 29.1, 29.0, 28.6, 28.3, 25.9, 24.6 ppm.
Example 7
Preparation of 6-functionalized CdSe/ZnS nanoparticles. TOPO-covered CdSe/ZnS nanoparticles were prepared as described in the literature. Chen, Y. F.; Ji, T. H.; Rosenzweig, Z. Nano Letters 2003, 3, 581. The particles were dissolved in pyridine and refluxed overnight under an inert atmosphere. The pyridine was partially removed under reduced pressure to give a viscous solution. The nanoparticles were precipitated by the addition of hexane and centrifuged. The supernate was discarded, and the precipitate (ca. 20 mg CdSe nanoparticles) was stirred as a suspension in freshly distilled, dry THF. Compound 6 (ca. 150 mg) was added, and the suspension was stirred for several hours at 50° C. The THF was partially removed by distillation, and the remaining solution was precipitated with anhydrous methanol and centrifuged. The supernate was again discarded, and the 6-covered nanoparticles were dissolved in freshly distilled toluene (7 mL). Other nanoparticulate substrates, either commercially-available or as known in the art, can be used, accordingly or with various other coupled alkenes, with comparable effect.
Example 8
General procedure for the preparation of cross-linked nanoparticle composites. 300 μL of 6-functionalized CdSe/ZnS nanoparticles (ca. 2 mg/1 mL) in toluene and 25 μL of ethyl vinyl ether were added to an eppendorf tube. 25 μL aqueous solution of catalyst 5 (1 mg/1 mL) was added to the nanoparticle solution and shaken vigorously. The nanoparticle capsules were allowed to settle to the bottom of the solution and the excess nanoparticle solution was removed and fresh toluene was added.
TEM was performed by transferring the cross-linked nanoparticle capsules to TEM grids and allowing the capsules to dry. A low magnification TEM image, shown in FIG. 3A, demonstrates that the spherical nature of the capsule was maintained following drying, an observation consistent with successful cross-linking. Moreover, the close-packed liquid-like nature of the nanoparticles, while expected from prior studies, is confirmed by the higher-magnification TEM image of FIG. 3B.
Example 9
Synthesis of PEG-350 monomethyl ether azide 1b. With reference to Scheme 3, PEG-350 monomethyl ether (9.0 g, 2.6 mmol) and triethylamine (0.50 mL, 2.9 mmol) were stirred in THF (40 mL) in an ice bath. To this was added methanesulfonyl chloride (4.5 g, 4.0 mmol) dropwise. The reaction mixture was allowed to warm to room temperature, then stirred overnight. The solvent was removed by rotary evaporation, and the residue was dissolved in EtOH (95%, 50 mL). Sodium azide (2.6 g, 4.0 mmol) was added, and the mixture was heated to reflux overnight. The solvent was removed by rotary evaporation, and the crude product was dissolved in ether and washed three times with brine. The organic layer was dried over MgSO4, concentrated by rotary evaporation, and the residue purified by column chromatography on silica gel (eluting with 5% methanol in dichloromethane) to afford the product (3.5 g, 35% yield) as a colorless oil: 1H NMR (400 MHz, CDCl3): δ (ppm) 3.50-3.70 (m, 28H), 3.35 (s, 3H, CH2—N3) ppm; 13C NMR (100 MHz, CDCl3): δ (ppm) 71.8, 70.5, 69.9, 58.9, 50.5 ppm.
Synthesis of Triazole-Coupled PEG-Pyridine Ligand (TPEGPy) Ligand Compounds 2a-2e




Example 10a
TPEGPy 2a: Copper (II) sulfate (7.2 mg, 0.03 mmol) and sodium ascorbate (56 mg, 0.28 mmol) were added to a dispersion of 2-ethynylpyridine (300 mg, 2.90 mmol) and 1a (500 mg, 2.6 mmol) in 1:1 ethanol-water (12 mL). The mixture was stirred at room temperature for 20 hours, then most of the solvent was removed by evaporation. The mixture was extracted with dichloromethane (3×30 mL), and the dichloromethane layers were combined and washed with brine, then dried over anhydrous MgSO4. Purification by column chromatography (eluting with 80% acetone in hexanes) provided the desired compound (380 mg, 50% yield) as light yellow oil. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.51 (d, J=5.6 Hz, 1H), 8.25 (s, 1H), 8.08 (d, J=8.0 Hz, 1H), 7.69 (t, J=8.0 Hz, 1H), 7.14 (t, J=5.8 Hz, 1H), 4.54 (t, J=4.8 Hz, 2H), 3.85 (t, J=4.8 Hz, 2H), 3.50-3.59 (m, 6H), 3.41-3.47 (m, 2H), 3.26 (s, 3H) ppm; 13C NMR (100 MHz, CDCl3): δ (ppm) 150.4, 149.3, 148.2, 136.7, 123.1, 122.6, 120.0, 71.8, 70.5, 70.4, 69.3, 58.9, 50.3 ppm. FAB-MS: Calcd. 292.1 g/mol. found 293.2 g/mol [M+H].
Example 10b
TPEGPy 2b was prepared in similar fashion, using 1a (500 mg, 2.60 mmol), 3-ethynylpyridine (300 mg, 2.90 mmol), copper (II) sulfate (7.2 mg, 0.03 mmol) and sodium ascorbate (56 mg, 0.28 mmol). Purification by column chromatography (eluting with 60% acetone in hexanes) gave the desired compound (440 mg, 58% yield) as light yellow oil. 1H NMR (300 MHz, CDCl3): δ (ppm) 9.03 (br, 1H), 8.57 (br, 1H), 8.22 (d, J=7.5 Hz, 1H), 8.12 (s, 1H), 7.36 (t, J=7.5 Hz, 1H), 4.60 (t, J=4.7 Hz, 2H), 3.91 (t, J=4.7 Hz, 2H), 3.57-3.69 (m, 6H), 3.48-3.54 (m, 2H), 3.33 (s, 3H); 13C δ (ppm) 148.9, 146.9, 144.5, 132.8, 126.9, 123.7, 121.4, 71.8, 70.4, 69.3, 58.9, 50.3 ppm.
Example 10c
TPEGPy 2c was prepared in similar fashion, using 1b (1.0 g, 2.7 mmol), 2-ethynylpyridine (300 mg, 2.90 mmol), copper (II) sulfate (7.2 mg, 0.028 mmol) and sodium ascorbate (56 mg, 0.28 mmol). Purification by column chromatography (eluting with acetone) gave the desired compound (515 mg, 43% yield) as yellow oil. 1H NMR (300 MHz, CDCl3): δ (ppm) 8.58 (br, 1H), 8.31 (s, 1H), 8.16 (d, J=10.4 Hz, 1H), 7.75 (t, J=7.2 Hz, 1H), 7.22 (t, J=7.2 Hz, 1H), 4.61 (t, J=6.4 Hz, 2H), 3.92 (t, J=6.4 Hz, 2H), 3.59-3.67 (m, 22H), 3.50-3.55 (m, 2H), 3.37 (s, 3H); 13C NMR (100 MHz, CDCl3): δ (ppm) 150.4, 149.3, 148.1, 136.7, 120.0, 71.8, 70.5, 70.4, 69.3, 58.9, 50.3. FAB-MS: calcd 468.2 g/mol. found 469.3 g/mol [M+H] for n=7, 513.3 g/mol [M+H] for n=8, and 557.3 g/mol [M+H] for n=9.
Example 10d
TPEGPy 2d was prepared essentially in similar fashion, using compound 1b (1.0 g, 2.7 mmol), 3-ethynylpyridine (300 mg, 2.90 mmol), copper (II) sulfate (7.2 mg, 0.028 mmol) and sodium ascorbate (56 mg, 0.28 mmol). Purification by column chromatography (eluting with acetone) gave the desired compound (603 mg, 48% yield) as yellow oil. 1H NMR (300 MHz, CDCl3): δ(ppm)=9.05 (br, 1H), 8.60 (br, 1H), 8.23 (d, J=7.8 Hz, 1H), 8.15 (s, 1H), 7.39 (br, 1H), 4.64 (t, J=4.8 Hz, 2H), 3.93 (t, J=4.8 Hz, 2H), 3.45-3.69 (m, 24H), 3.38 (s, 3H); 13C NMR (100 MHz, CDCl3): δ (ppm)=148.9, 147.0, 144.6, 132.8, 127.2, 123.7, 121.5, 71.8, 70.4, 69.3, 58.9, 50.4. FAB-MS: calcd. 468.2 g/mol. found 469.3 g/mol [M+H] for n=7, 513.3 g/mol [M+H] for n=8, 557.3 g/mol [M−H] n=9.
Example 10e
TPEGPy 2e: To a stirred solution of triethylamine (292 mg, 2.90 mmol) and 4-ethynylpyridine hydrochloride (403 mg, 2.90 mmol) in 1:1 ethanol-water (20 mL) was added copper (II) sulfate (7.2 mg, 0.03 mmol) and sodium ascorbate (56 mg, 0.28 mmol). The mixture was stirred at room temperature for 20 hours, then most of the solvent was removed by evaporation. The residue was extracted with dichloromethane (3×30 mL), and the dichloromethane layers were combined and washed with brine, then dried over anhydrous MgSO4, filtered, and purified by column chromatography (eluting with acetone) to give the desired compound (795 mg, 60% yield) as light yellow oil. 1H NMR (300 MHz, CDCl3): δ (ppm) 8.40-8.90 (br, 2H), 8.20 (s, 2H), 7.54-7.97 (br, 2H), 4.60 (t, J=4.9 Hz, 2H), 3.90 (t, J=4.9 Hz, 2H), 3.41-3.66 (m, 24H), 3.37 (s, 3H); 13C NMR (100 MHz, CDCl3): δ (ppm) 149.7, 144.4, 137.8, 122.5, 119.6, 71.3, 69.9, 68.7, 59.4, 49.9. FAB-MS: calculated 468.2 g/mol. found 469.3 g/mol [M+H] for n=7, 513.3 g/mol [M+H] for n=8, and 557.3 g/mol [M+H] for n=9.
Synthesis of TPEGPy-Substituted Ruthenium Catalyst Compounds 3a-3e




Example 11a
Catalyst Compound 3a: With reference to schemes 3-4, to a solution of Grubbs' pyridine-based complex (0.36 g, 0.50 mmol) in dry dichloromethane (2 mL) was added a solution of 2a (0.29 g, 1.0 mmol) in dry dichloromethane (1 mL). The reaction mixture was subjected to three freeze-pump-thaw cycles, and stirred under nitrogen atmosphere for 15 minutes at room temperature. The solvent was removed by vacuum, and dry dichloromethane (2 mL) was added. The reaction mixture was subjected to three freeze-pump-thaw cycles, and this evaporation/redissolution cycling was repeated three times. Following the final evaporation, the residue was purified by flash column chromatography using 2-5% methanol in dichloromethane under nitrogen pressure to give a viscous green liquid (250 mg). 1H NMR (400 MHz, CDCl3): δ (ppm) 18.4 (s), 17.8-18.1 (m), 8.4-9.1 (m), 8.2 (br s), 6.0-7.8 (m), 4.2-4.7 (m), 2.9-3.9 (m), 1.5-2.4 (m).
Example 11b
Catalyst Compound 3b was prepared in similar fashion, using Grubbs' pyridine-based catalyst (0.36 g, 0.50 mmol) and 2b (0.29 g, 1.0 mmol). Purification by flash column chromatography (under nitrogen pressure, eluting with 2-5% methanol in dichloromethane) gave the 3b (288 mg, 25%) as a green viscous oil. 1H NMR (300 MHz, CDCl3): δ (ppm)=19.2 (s, 1H), 9.0 (br, 2H), 8.6 (br, 2H), 8.0-8.3 (m, 4H), 7.7 (d, J=5.0 Hz, 4H), 7.5 (t, J=8.2 Hz, 1H), 7.3-7.4 (m, 2H), 7.0-7.1 (m, 3H), 6.8 (br, 1H), 4.6 (br, 4H, 4.1 (br, 4H), 3.9 (br 4H), 3.6-3.8 (m, 12H), 3.5-3.6 (m, 4H), 3.4 (s, 6H), 2.6 (s, 6H), 2.31 (s, 6H), 2.27 (br, 6H).
Example 11c
Catalyst Compound 3c was prepared in similar fashion, using Grubbs' pyridine-based complex (0.36 g, 0.50 mmol) and 2c (0.47 g, 1.0 mmol). Column chromatography (under nitrogen pressure, eluting with 5-7% methanol in dichloromethane) provided a green viscous oil (200 mg): 1H NMR δ (ppm) 18.10 (s), 17.92 (s) 8.59 (s), 8.32 (s), 8.04-8.23 (m), 7.61-7.82 (m), 7.09-7.35 (m), 6.18-7.04 (m), 4.49-5.11 (m), 3.11-4.00 (m), 2.44-2.74 (m), 1.71-2.38 ppm.
Example 11d
Catalyst Compound 3d was prepared in similar fashion, using Grubbs' pyridine-based complex (0.36 g, 0.50 mmol) and 2d (0.47 g, 1.0 mmol). Column chromatography (under nitrogen pressure, eluting with 5-7% methanol in dichloromethane) gave 3d (495 mg, 66%) as a green viscous oil. 1H NMR (300 MHz, CDCl3): δ (ppm) 19.22 (s, 1H), 9.07 (br, 2H), 8.61 (br, 2H), 8.08-8.23 (m, 4H), 7.83-8.03 (br, 2H), 7.70 (d, J=7.1 Hz, 2H), 7.41 (t, J=7.3 Hz, 1H), 7.28-7.33 (m, 2H), 6.99-7.06 (m, 2H), 6.69-6.89 (m, 2H), 4.62 (br, 4H), 4.06 (br, 4H), 3.93 (br, 4H), 3.55-3.68 (m, 56H, 3.50-3.54 (m, 6H), 3.36 (s, 6H), 2.63 (br, 6H), 2.11-2.34 (m, 12H); 13C NMR (100 MHz, CDCl3): δ (ppm) 317.6 (m, Ru=CHPh), 216.9 (RuC(N)2), 152.5, 149.9, 149.1, 147.3, 144.4, 137.8, 137.5, 131.9, 130.4, 129.0, 127.4, 126.5, 123.2, 121.4, 71.8, 70.4, 70.3, 69.4, 58.5, 54.1, 51.7, 50.3, 22.6, 18.2-21.3, 15.2 ppm.
Example 11e
Catalyst Compound 3e was prepared in similar fashion, using Grubbs' pyridine-based complex (0.36 g, 0.50 mmol) and 2e (0.47 g, 1.0 mmol). Column chromatography (under nitrogen pressure, eluting with 5-7% methanol in dichloromethane) gave the desired compound 3e (375 mg, 50%) as a green viscous oil. 1H NMR (300 MHz, CDCl3): δ (ppm)=19.19 (s, 1H), 8.72 (br, 2H), 8.18 (s, 1H), 8.02 (s, 1H), 7.91 (br, 2H), 7.58-7.72 (m, 4H), 7.42 (t, J=7.8 Hz, 1H), 7.21 (br, 2H), 7.04 (t, J=7.8 Hz, 2H), 6.91 (br, 2H, 6.73 (s, 2H), 4.56 (br, 4H), 4.06 (br, 4H), 3.87 (br, 4H), 3.45-3.66 (m, 48H), 3.36 (s, 6H), 2.63 (br, 6H), 2.27 (s, 12H); 13C NMR (75 MHz, CDC13): δ (ppm)=316.7 (m, Ru=CHPh), 217.2 (RuC(N)2), 152.0, 217.2, 152.0, 151.8, 150.2, 144.7, 143.9, 137.5, 130.5, 129.1, 123.2, 122.8, 119.4, 118.8, 71.7, 70.3, 69.1, 58.8, 53.7, 51.5, 50.3, 29.5, 20.9, 18.2-20.0 (m). Electrospray ionization mass spectrometry (not shown) reflects molecular weight distribution centered at 1513.3 (n=7) g/mole.
Example 12
Procedure for ROMP of 4 in dichloromethane using catalyst compound 3e (Table 1). To a stirred solution of exo,exo-5.6-Bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene1 (4) (212 mg, 1.00 mmol) in dry dichloromethane (2 mL) was added a 0.03 M solution (0.65 mL) of 3e in dichloromethane. (See, Kwart, H.; Burchuk, I. J. Am. Chem. Soc. 1952, 74, 3094-3097.) The mixture was stirred for 30 minutes, and ethyl vinyl ether (0.5 mL) was added. Precipitation in cold methanol gave a white solid, which was collected and dried in vacuo to afford polymer 5 (170 mg, 80%). GPC (in THF vs. linear polystyrene standards): Mn57,000 g/mol, Mw 84,000, PDI 1.05.
Example 13
Procedure for ROMP of 6 in acidic water (Table 1, entry 3). To a solution of catalyst 3e (35 mg) under nitrogen atmosphere in degassed water (0.5 mL) was added a degassed acidic solution (1.0 mL, pH=1.5) of oxanorbornene 6 (80 mg). The mixture was stirred for 30 minutes, and diethylene glycol vinyl ether was added. The mixture was concentrated, dissolved in minimal amount of CHCl3, and precipitated into cold hexanes. The solvent was decanted and the polymer residue dried under vacuum to afford 56 mg (70% yield) of polymer. GPC (in THF vs. linear polystyrene standards) Mn 31,500, Mw 41,000, PDI 1.3.
Example 14
Example procedure for ROMP of 6 in water using copper additive (Table 1). To a solution of catalyst 3e (26 mg, 0.018 mmol) under nitrogen atmosphere in degassed water (1 mL) was added 0.5 mL of a degassed solution of 6 (120 mg, 0.35 mmol) and copper sulfate (4.3 mg, 0.018 mmol). The mixture was stirred for 2 hours, and diethylene glycol vinyl ether was added. The mixture was concentrated, dissolved in minimal CHCl3, and precipitated into cold hexanes. The solvent was decanted, and polymer residue was dried under vacuum to afford 60 mg (50% yield) of polymer. GPC (in THF vs. linear polystyrene standards): Mn 54,000; Mw 82,000, PDI 1.5.




Example 15
Synthesis of 6-azido-1-hexanol. A solution of 6-bromo-1-hexanol (3.6 g, 20 mmol) and sodium azide (2.6 g, 40 mmol) in 95% ethanol (50 mL) was heated with stirring to reflux for 12 hours. The mixture was filtered, and the filtrate concentrated by rotary evaporation. The residue was dissolved in ether (250 mL) and washed three times with water. The ether layer was dried over anhydrous MgSO4, and concentrated by rotary evaporation to give the desired product as a colorless liquid in 88% yield: 1H NMR (CDCl3, 400 MHz): δ (CHCl3 7.26 ppm) 3.65-3.62 (t, J=6.52 Hz, 2H), 3.28-3.24 (t, J=6.88 Hz, 2H), 1.60 (m, 4H), 1.40 (m, 4H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 62.7, 51.3, 32.5, 28.8, 26.5, 25.3.
Example 16
Synthesis of 1-phosphorylcholine-6-azidohexane (8). In a dry roundbottom flask equipped with nitrogen inlet and addition funnel was stirred a solution of 1-hydroxyl-6-azidohexane (3.2 g, 23 mmol), triethylamine (3.5 mL) and THF (40 mL). The solution was cooled to −20° C., and stirred for 15 minutes. A solution of COP (3.6 g, 25 mmol) in THF (10 mL) was added by addition funnel over 30 minutes. The mixture was stirred for 1 hour at −20° C., then allowed to warm to room temperature. Residual solids were removed by filtration through Celite, under a flow of nitrogen. The solution was concentrated and dried under vacuum to give a viscous yellow liquid. This was dissolved in dry acetonitrile (60 mL) and transferred to a glass pressure vessel. The solution was cooled to −20° C., and trimethylamine (10 mL) was added. The vessel was heated to 70° C. for 15 hours. Finally, the solution was cooled to −20° C. to produce a white solid which was collected by filtration and dried under vacuum for a yield of 30%: 1H NMR (CDCl3, 400 MHz): 6 (CHCl3=7.26 ppm) 4.25 (br, 2H), 3.82-3.77 (m, 4H), 3.40 (s, 9H), 3.26-3.21 (t, J=6.9 Hz, 2H) 1.58-1.54 (m, 4H), 1.37-1.32 (m, 4H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 66.2, 65.2, 59.2, 54.3, 51.3, 30.8, 28.8, 26.5, 25.4; 31P NMR (CDCl3, 162 MHz): δ-0.3 ppm. FAB-MS: Calcd 308.161 g/mol. found 309.171 g/mol [M+H].
Example 17
Synthesis of Triazole-coupled PC-pyridine (TPCPy) Ligand compound 9. To a dry roundbottom flask equipped with nitrogen inlet and septum was added 4-ethynylpyridine hydrochloride (0.23 g, 1.6 mmol), PC-azide 8 (0.50 g, 1.6 mmol), and dry dichloromethane (15 mL). N,N-diisopropylethylamine (0.57 mL) was added, and the solution was stirred until 4-ethynylpyridine hydrochloride dissolved. Bromotris(triphenylphosphine)copper (I) (0.15 g, 0.16 mmol) was then added, and the mixture was stirred at room temperature for 16 hours. The product was extracted from into water. The water layer was passed through a plug of Celite, then concentrated under vacuum to give the product as an orange viscous liquid in 86% yield: 1H NMR (CDCl3, 400 MHz): δ (CHCl3=7.26 ppm) 7.75 (s, br, 1H), 7.65-7.59 (m, 2H), 7.44-7.42 (m, 2H), 4.28 (br, 2H), 3.91-3.80 (m, 4H), 3.41 (s, 9H), 3.25-3.20 (m, 2H), 1.55-1.37 (m, 8H); 13C NMR (CD3OD, 100 MHz): δ (ppm) 135.0, 133.4, 133.2, 129.9, 129.8, 66.1, 65.3, 53.4, 50.2, 42.4, 17.4, 15.9, 11.8; 31P NMR (CDCl3, 162 MHz): δ-1.5 ppm. ESI-MS: calculated 411.2 g/mol, actual 412.2 g/mol [M+H].
Example 18
Synthesis of phosphorylcholine-substituted ruthenium benzylidene catalyst 10. To a dry roundbottom flask equipped with a septum was added the pyridine complex of Grubbs' second generation catalyst (0.29 g, 0.40 mmol) in dry dichloromethane (1 mL). A solution of 9 (0.33 g, 0.80 mmol) in dry dichloromethane (1 mL) was added, and the mixture was stirred for 10 minutes. The solvent was removed under vacuum, and dichloromethane (1 mL) was added. This solution was stirred for 10 minutes, and the solvent removed by vacuum. This dissolution/evaporation procedure was repeated three times, and finally solvent was removed, and the desired catalyst obtained as a green solid in 84% yield: 1H NMR (CDCl3, 400 MHz): δ (CHCl3=7.26 ppm) 19.17 (s, 1H), 8.62-8.59 (s, 2H), 7.82 (br, 2H), 7.68-7.61 (m, 4H) 7.55-7.53 (m, 1H) 7.50-7.46 (m, 2H), 7.16-7.06 (m, 4H), 6.98 (br, 2H), 6.84 (br, 2H), 4.20-4.18 (br, 2H), 4.07-4.04 (br, 2H), 3.71-3.65 (m, 4H), 3.43 (s, 4H), 3.13-3.05 (m, 4H), 2.83 (6H), 2.50-2.29 (m, 12H), 1.73 (s, 10H), 1.57-1.52 (m, 6H), 1.45-1.43 (d, 6H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 312.0, 219.10, 151.88, 151.05, 139.73, 138.61, 134.89, 134.60, 133.45, 133.31, 131.79, 129.95, 129.80, 129.67, 129.28, 128.55, 123.60, 123.27, 66.50, 65.32, 53.44, 51.74, 50.57, 43.70, 21.62, 20.93, 20.32, 18.51, 17.27, 11.98; 31P NMR (CDCl3, 162 MHz): δ-1.2 ppm. ESI-MS: calcd. 1390.7 g/mol. found 1413.4 g/mol [M+Na]+.
Example 19
Example ROMP of oxanorbornene 6. To a 20 mL vial equipped with a septum was added a solution of oxanorbornene 6 (0.10 g, 0.29 mmol) in water (0.5 mL), followed by a solution of PC-catalyst 9 (8.2 mg, 0.0058 mmol) in water (0.5 mL). The reaction was stirred under nitrogen atmosphere and monitored by GPC. The mixture was quenched with di(ethylene glycol) vinyl ether (0.10 mL), and the solvent removed under vacuum. The residue was dissolved in minimal CHCl3, and precipitation in cold hexane gave the desired polymer 7: 1H NMR (CDCl3, 400 MHz): δ (CHCl3=7.26 ppm) 6.06 (br, s, 1H), 5.77 (s, br, 1H), 4.99 (s, br, 1H), 4.46 (s, br, 1H), 3.98-3.58 (m, br, m, 18H) 3.33 (br, s, 2H); GPC (NaNO3/NaN3 solution in H2O, linear polyethylene oxide standards) Mn 9,800 g/mol, Mw 16,200 g/mol, PDI 1.7.
While several principles relating to this invention have been described in connection with specific embodiments, it should be understood clearly that these descriptions are added only by way of example and are not intended to limit, in any way, the scope of this invention. For instance, as metathesis reactions become increasingly useful in drug synthesis, water soluble catalyst compounds of this invention will find increasing use in the reaction of polar compounds, thereby reducing risk of contamination by organic solvents. More generally, the utility of such catalyst compounds and aqueous and/or polar media, can provide access to functional amphiphilic and/or water soluble polymers not otherwise attainable through conventional polymerization techniques. As such, the present invention represents a divergent class of Group VIII catalyst compounds and their extension to chemistries and products not available through the prior art.

## Claims

1. A Group VIII transition metal compound of a formula




wherein M is a metal selected from a Group VIII transition metal; X1 and X2 are independently selected from anionic ligand components; L1-L3 are independently selected from neutral electron donor ligand components, providing one of said L1-L3 components is an N-heterocyclic carbene component and the other said L1-L3 components are independently selected from substituted pyridinyl ligand components, said substituent comprising at least one of an alkoxy moiety and an alkoxycarbonyl moiety; and R1-R2 are independently selected from hydrogen, alkyl, substituted alkyl, cyclic alkyl, substituted cyclic alkyl, alkenyl, substituted alkenyl, cyclic alkenyl, substituted cyclic alkenyl, phenyl and substituted phenyl moieties.

2. The compound of claim 1 wherein at least one of said pyridinyl ligand components comprises a polyalkoxy substituent.

3. The compound of claim 2 wherein said substituent comprises (OCH2 CH2)n, and n ranges from about 2 to about 100.

4. The compound of claim 1 wherein M is selected from Ru and Os.

5. The compound of claim 4 wherein R1 is hydrogen and R2 is phenyl.

6. A metathesis catalyst compound of a formula




wherein X1 and X2 are independently selected from anionic ligand components; L1-L3 are independently selected from neutral electron donor ligand components, providing one of said L1-L3 components is an N-heterocyclic carbene component and the other said L1-L3 components are independently selected from substituted pyridinyl ligand components, said substituent comprising at least one of an alkoxy moiety and an alkoxycarbonyl moiety; and R1-R2 are independently selected from hydrogen, alkyl, substituted alkyl, cyclic alkyl, substituted cyclic alkyl, alkenyl, substituted alkenyl, cyclic alkenyl, substituted cyclic alkenyl, phenyl and substituted phenyl moieties.

7. The compound of claim 6 wherein at least one of said pyridinyl ligand components comprises a polyalkoxy substituent.

8. The compound of claim 7 wherein said substituent comprises (OCH2 CH2)n, and n ranges from about 2 to about 100.

9. The compound of claim 6 wherein said carbene ligand component comprises a 4,5-dihydroimidazolylidene moiety.

10. The compound of claim 9 wherein R1 is hydrogen and R2 is phenyl.

11. The compound of claim 6 wherein a said substituent is coupled to said pyridinyl ligand with a triazole moiety.

12. The compound of claim 6 wherein at least one of said pyridinyl ligand component substituents comprises a phosphorylcholine moiety.

13. A reaction system comprising an compound of claim 6 and at least one alkene compound.

14. The system of claim 13 comprising two acyclic alkene compounds, said system for a cross-metathesis reaction.

15. The system of claim 14 comprising a cyclic alkene compound and an acyclic alkene compound, said system for a ring-opening cross-metathesis reaction.

16. The system of claim 13 comprising a cyclic alkene compound, said system for a ring-opening metathesis polymerization reaction.

17. The system of claim 16 wherein said alkene compound is coupled to a substrate.

18. The system of claim 17 wherein said substrate is a nanodimensioned particulate.

19. The system of claim 17 wherein said alkene compound is cross-linked with another said alkene compound coupled to said substrate.

20. The system of claim 19 wherein said nanodimensional particulate comprises a semiconductive, luminescent material.

21. A method of using an N-heterocyclic carbene ruthenium benzylidene catalyst for a ring-opening metathesis reaction in an aqueous medium, said method comprising:
providing a cyclic alkene compound; and
contacting said alkene compound and a catalyst compound of claim 6, said catalyst compound wherein R2 is phenyl, said contact for a time sufficient for reaction of said alkene compound, at least one of said alkene and said catalyst compounds in an aqueous medium.

22. The method of claim 19 wherein at least one of said pyridinyl component substituent comprises at least one of an alkoxy moiety and a phosphorylcholine moiety.

23. The method of claim 21 wherein said alkene component is coupled to a substrate component.

24. The method of claim 23 wherein said coupled components are provided in a substantially hydrophobic medium, said catalyst compound in an aqueous medium, said contact for a time sufficient to cross-link said alkene compound.