Electronically strongly coupled 1,4-divinylphenylenebridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(P

An electronically strongly coupled 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties, its synthesis, and its use as a catalyst in organic processes.

BACKGROUND

The present disclosure relates to a compound that is an electronically strongly coupled 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(PiPr3)2 moieties with 2-mercaptopyridine co-ligands, its synthesis, and its use as a catalyst for organic compounds.

2. Description of the Related Art

Since the reporting of ruthenium hydrido complexes of the type {[HRu(CO)Cl(PR3)2](R=Ph, Me, cyclohexyl, iPr)} in the 1960s, considerable interest has been focused on the pivotal catalytic activates of such chemical families towards selective hydrogenation of terminal olefins and alkynes, the coupling of terminal alkynes with carboxylic acid-derived compounds, the dehydrogenation of alcohol to ketones, dialdehydes to lactones, and in particular on regio- and stereospecific insertion of the ruthenium-hydride bond into a terminal —C≡CH bond of the alkyne substrates to form the ruthenium-alkenyl type-families.

More recently, interest in (multi)ruthenium-alkenyl type-complexes has been intensively scrutinized in terms of redox chemistry, electronic coupling, electro switchable poly-electrochromic near infrared (NIR) dyes, tri-, tetra-, and hexametal-organic macrocycles and antiproliferative effects in tumor cell lines.

As these complexes have attracted widespread interest, divinylarylene-bridged diruthenium complexes of the general type [{Ru(CO)(Cl)(PiPr3)2}2(μ-CH═CH—Ar—CH═CH—)]{Ar=bridging n-conjugated arylene linker} have been investigated and revealed to exhibit two consecutive, chemically and electrochemically, well-behaved, reversible one-electron oxidations at well-accessible potentials. The half-wave redox splitting, ΔE1/2=E1/2+/2+−E1/20/+, between their two individual redox one-electron oxidations waves depends on the π-conjugated arylene linker “bridge” and can be ranged to be well-separated (strongly coupled) as in the case of five-membered 2,5-N-arylpyrroles- or -furanes- or -thiophenes heterocycles arylene linkers; moderately coupled as in 4,4′-biphenylenes, 2,2′-bipyridines, and many others arylene linkers; or weakly coupled as in the case of the enforced π-stacking of the two phenyl rings in para-[2.2]- or ortho-[2.1]-cyclophanes linkers.

Cross-coupling reactions play the most effective role in the development of the chemical industrial processes. Homogeneous catalysts of transition metal complexes are of great interest for synthesizing fine-chemical/specialty chemical/medical and pharmaceutical products for their high activity and modified chemo-, stereo- and regio-selectivity advantages within the widely used cross coupling reaction of C—C, C—O, C—N and C—S bonding. The most recent chemical transformation consumes high energy for selective productivity.

Azoarylenes and its similar related derivatives were intensively investigated and attracted enormous interest due to their straightforward derivative synthesis step through classical homo-oxidative cross-coupling of aryl diazonium salts using Cu-catalyzed Sandmeyer-style reaction. Moreover, these chromophores usually show a strong π→π* transition in the UV-Vis regime which can be predictively tuned by introducing substituents on the aryl rings.

SUMMARY

The electrochemical electronic coupling, polyelectrochromic behavior, and spectro(electro)scopic features of bis(ruthenium-alkenyl) moieties incorporated into an azoarylene bridge linker have been investigated as described herein. Accordingly, the present subject matter relates to a novel electronically strongly coupled 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties with the general formula [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)]. This six-coordinated, octahedaral, bis(ruthenium-alkenyl) type-complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4) was classically prepared in high yields by substitution of the chloro ligands of the precursor complex [{Ru(CO)Cl(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] with the corresponding deprotonated 2-mercaptopyridine in a CH2Cl2/MeOH solvent mixture according to a routine protocol in a stoichiometric ratio of 1:2.

The complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] may be routinely characterized in a neutral state by classical IR, UV/Vis and NMR spectroscopy techniques, and in two different reachable oxidized states by IR, UV/Vis/NIR spectro-electrochemistry along with electrochemical techniques. The complex[{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] undergoes two consecutive, chemically and electrochemically, well-behaved, reversible one-electron oxidations at well-accessible potentials with a half-wave redox splitting of ΔE1/2=315 mV referring to strong electronic coupling “communication” between the two bis(ruthenium-alkenyl) moieties. The results on the complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] show dominant contributions of the π-conjugated divinylphenylene bridge to the two redox processes and an even delocalization of the electron hole and spin density over the entire π-conjugated divinylphenylene diruthenium backbone with only minor involvement of the peripherally attached κ2[N,S]— donor ligands. The complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] also shows strong polyelectrochromic behavior with at least three distinct states with remarkable activity as homogeneous catalyst for applicable chemical manufactories of organic compounds syntheses.

In an embodiment, the present subject matter relates to an electronically strongly coupled 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties having the formula I:

In another embodiment, the present subject matter relates to a compound that is a yellow solid.

In a further embodiment, the present subject matter relates to a metallic complex that may act as a catalyst.

In one more embodiment, the present subject matter relates to a method of making the 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties, the method comprising: stirring 2-mercaptopyridine and K2CO3 in a solvent of CH2Cl2 and MeOH to obtain a first reaction mixture; adding the first reaction mixture to a solution of a complex [{Ru(CO)Cl(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] in CH2Cl2 to obtain a second reaction mixture; stirring the second reaction mixture for at least about 1 hour to obtain a precipitate; removing the solvent under reduced pressure to obtain a precipitate; washing the precipitate; drying the precipitate; and obtaining the 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Definitions

It will be understood by those skilled in the art with respect to any chemical group containing one or more substituents that such groups are not intended to introduce any substitution or substitution patterns that are sterically impractical and/or physically non-feasible.

The present subject matter relates to an electronically strongly coupled novel 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties with the general formula [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)].

This six-coordinated, octahedral, 18-VEs type-complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] has been successfully prepared in high yields by substitution of the chloro ligands of the precursor complex [{Ru(CO)Cl(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] with the corresponding deprotonated 2-mercaptopyridine in a CH2Cl2/MeOH solvent mixture. The complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] was routinely characterized in the neutral state by classical IR, UV/Vis and NMR spectroscopy techniques, and in its two different reachable oxidized states by IR, UV/Vis/NIR spectroelectrochemistry along with electrochemical techniques. The 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties may function as a catalyst in organic processes.

The product can be acquired in exceptional yields (average about 89%) by substitution of the chloro ligands of the precursor complex [{Ru(CO)Cl(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] with the corresponding deprotonated 2-mercaptopyridine in a CH2Cl2/MeOH solvent mixture. The reaction components could be purified by some non-chromatographic techniques. The product can be analyzed using spectral data; IR, NMR & elemental analysis. The prepared compound can be used as a catalyst for organic processes.

In an embodiment, the present subject matter relates to an electronically strongly coupled 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties having the formula I:

In certain embodiments, the 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties can be obtained as a yellow solid.

In another embodiment, the present subject matter relates to a catalyst for organic reactions and processes.

In one more embodiment, the present subject matter relates to a method of making the 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties, the method comprising: stirring 2-mercaptopryidine and K2CO3 in a solvent of CH2Cl2 and MeOH to obtain a first reaction mixture; adding the first reaction mixture to a solution of a complex [{Ru(CO)Cl(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] in CH2Cl2 to obtain a second reaction mixture; stirring the second reaction mixture for at least about 1 hour to obtain a precipitate; removing the solvent under reduced pressure to retrieve the precipitate; washing the precipitate; drying the precipitate; and obtaining the 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2.

The present production methods can be further seen by referring to the following Scheme 1:

In an embodiment of the present production methods, the precipitate can be yellow.

In another embodiment of the present production methods, the precipitate can be washed with n-hexane and MeOH.

In a further embodiment of the present production methods, the precipitate can be dried in a vacuum.

In another embodiment of the present production methods, washing the precipitate may remove unreacted starting materials and formed KCl.

In a further embodiment of the present production methods, the 2-mercaptopyridine and K2CO3 may be added in equimolar amounts.

In another embodiment of the present production methods, the 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 can be obtained as a yellow solid.

In an additional embodiment of the present production methods, the 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 can be obtained in an about 89% yield.

The following examples relate to various methods of manufacturing the specific compounds and application of the same, as described herein. All compound numbers expressed herein are with reference to the synthetic pathway figures shown above.

EXAMPLES

Preparation of 1,4-Divinylphenylene-Bridged Diruthenium Complex Bearing Two Ru(CO)(2-Mercaptopyridine)(PiPr3)2

0.8 mmol of 2-mercaptopyridine and equimolar amounts of K2CO3 (111 mg, 0.8 mmol, 2.2 eq.) were stirred at room temperature in a solvent mixture of 7 mL of CH2Cl2 and 7 mL of MeOH for 15 minutes. This solution was slowly added via cannula to a solution of 395 mg (0.36 mmol, 1 eq.) of the complex [{Ru(CO)Cl(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] in 7 mL of CH2Cl2. After complete addition, stirring was continued for one further hour at room temperature to give a deep yellow solution. The solvents were removed under reduced pressure and the yellow precipitate was washed twice with 10 mL of n-hexane and 10 mL of MeOH each to remove unreacted starting material and the formed KCl. The resulting residue was then dried in vacuum. 0.8 mmol, 2.2 eq. of 2-mercaptopyridine yielded 425 mg (0.32 mmol, 89%) of complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)].

Characterization of the prepared compound was determined using 1H NMR and 31P-NMR. The elemental analysis can be seen as follows.

NMR Characterization

NMR Characterization

To investigate the electrochemical electronic coupling, polyelectrochroic behavior, catalytic activity and spectro(electro)scopic features of bis(ruthenium-alkenyl) moieties incorporated into 1,4-divinylphenylene-bridge linker terminated with deprotonated, 2-mercaptopyridine as monoanionic, chelating, bidentate co-ligands. We have successfully prepared a novel [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] as depicted in Scheme 1 previously illustrated.

This six-coordinated, octahedaral, bis(ruthenium-alkenyl) type-complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] was classically prepared by in high yields by substitution of the chloro ligands of the precursor complex [{Ru(CO)Cl(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] with the corresponding deprotonated 2-mercaptopyridine in a CH2Cl2/MeOH solvent mixture according to a routine protocol in a stoichiometric ratio of 1:2. Upon addition of the solution of the deprotonated chelate 2-mercaptopyridine, the reaction solution color changed promptly from red to deep yellow with the concomitant precipitation of KCl. [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] was routinely characterized in their neutral state by conventional IR, UV/Vis and NMR spectroscopy and analytical techniques, and in its two different reachable oxidized states by IR, UV/Vis/NIR spectroelectrochemistry.

Our results indicate that the mercaptopyridine-olate complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] exists as three isomers with a ratio of about 94:4:2 that differ with respect to the orientation of the N and S donors relative to the CO and vinyl ligands in the equatorial coordination plane as depicted in Scheme 2.

31P-NMR spectrum of the complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)], and other ruthenium-alkenyl of similar family, showed a sharp singlet resonance at 6=30.05 ppm, confirming that the four PiPr3 ligands are chemically equivalent in which two of them are trans-disposed at each {Ru} end-groups.

1H-NMR spectrum shows classical doublet at δ 8.48 ppm and doublet of triplet at δ 6.40 ppm of the four equivalent vinylic protons Ru—CH═(H1) and Ru—CH═CH (H2) with a large coupling constant 3JH-H of about 13.3 Hz, respectively. This high coupling constant confirms a trans-geometry at the two vinylic double bonds.

The redox behavior of 1,4-divinylphenylene-bridged diruthenium complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] was initially scrutinized by cyclic voltammetry (CV) and square-wave voltammetry (SWV) techniques to probe the electrochemical properties and the extend of the electronic interaction (coupling) between the two ruthenium vinyl moieties. The experiments were performed in CH2Cl2/n-NBu4+PF6− (0.1 M) as the supporting electrolyte. The CV and SWV of the complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] in n-NBu4+PF6− recorded at a sweep rate of 0.1 V/s at r.t. versus the CP2Fe0/+ reference couple. Complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] undergoes two consecutive, chemically and electrochemically, well-behaved, reversible one-electron oxidations at well-accessible potentials. The half-wave redox splitting, ΔE1/2=E1/2+/2+−E1/20/+, between their two individual redox one-electron ΔE1/2=310 mV referring to strong electronic coupling “communication” between the two bis(ruthenium-alkenyl) moieties.

IR spectroelectrochemistry (SEC) is a quantitative and an informative tool used in this study to get a crucial insight into the ruthenium- versus divinylphenylene bridge-based character of the individual redox processes. This can be fulfilled via investigating the changes in the energies and the band patterns for the degree of metal dπ/π*(CO) backbonding upon accessible sequential oxidations, since those remarkable tokens are considered as an indicative measure of altering the electron density at the two ruthenium-vinyl moieties. Complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] in its neutral state, shows classical intense vibrational bands at around 2900, 1880, 1550 cm−1 assigned to the C—H(aryl, alkyl), Ru(C≡O), and C═C(vinyl, aryl) stretches, respectively. This low energy of the v (CO) stretch band reflects, however, the high electron density at the two ruthenium-alkenyl moieties. First and second oxidations of complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] cleanly converted the neutral from to its corresponding mono- and di-cation in a stepwise fashion as indicated by distinct sets of isosbestic points. As a general scenario in stepwise fashion oxidation to the first radical cations of complex [{(Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] led to replace the neutral Ru(CO) band at 1886 cm−1 into a high a blue shift band at 1913 cm−1 with a weak shoulder at 1927 cm−1. As the oxidation proceeded to the di-cation, the two CO bands of mixed-valent (MV) complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)]+ are again blued-shifted and merged into a single band at 1961 cm−1. This typical observation pattern confirms a strongly coupled Class III system of Robin-Day classification of MV states.

Likewise all five-coordinated bis(ruthenium-alkenyl) complexes of the type {Ru}-arylene-{Ru}({Ru}═{Ru(CO)Cl(PiPr3)2(CH═CH)}), complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)], features a main intense absorption UV-band at 340 nm which attributed to π→π* transitions within the extended metal-organic divinylarylene bridge chromophore. Electrochemical oxidation was achieved by applying appropriate positive potentials to the complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] in NBu4+PF6−/CH2Cl2 in the UV/Vis/NIR regimes. Upon the first oxidation, the intensity of the UV-band of the neutral complex collapsed with the concomitant of growth of new intense band at the border of Vis/NIR region at 650 nm and strong NIR band between 1200 to 1600 nm. The NIR band is assigned to a π→π* transition within an open-shell, extended π-system. As the oxidation proceeded to the di-cation [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)]2+, both bands of [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)]+ have disappeared and growth of new band in visible region at 700 nm. Thus complex [{Ru(CO)(2-mercaptopyridine)(PiPr3)2}2(μ-CH═CH—C6H4—CH═CH-1,4)] shows strong electrochromic behavior with at least three distinct states, as each individual oxidations are accompanied by the growth of intense absorption bands in the near infrared (NIR) and/or the visible (Vis) regime of electromagnetic radiation

It is to be understood that the 1,4-divinylphenylene-bridged diruthenium complex bearing two Ru(CO)(2-mercaptopyridine)(PiPr3)2 moieties, compositions containing the same, and methods of using and producing the same are not limited to the specific embodiments described above, but encompasses any and all embodiments within the scope of the generic language of the following claims enabled by the embodiments described herein, or otherwise shown in the drawings or described above in terms sufficient to enable one of ordinary skill in the art to make and use the claimed subject matter.