bluuebunny/crossref_metadata_2025 huggingface dataset:
Oligophosphane Ligands, XLI. Oxidative Additions of Transition Metal–Hydrogen Bonds: Reactions of CpM(CO)3H (M = Mo, W) with [tBuP(CH2CH2CH2PPh2)2]M′Cl(M′ = Rh, Ir)
Authors: Dahlenburg Lutz , Halsch Eva , Moll Matthias , Höck Niels
Published: July 2007

Treatment of (PP2)IrCl[PP2 = tBuP(CH2CH2CH2PPh2)2] with an equimolar quantity of CpM(CO)3H (M = Mo, W) or with HCl in THF resulted in smooth protonation of the d8 substrate producing [(PP2)Ir(H)Cl]X {X– = [CpMo(CO)3]– (1), [CpW(CO)3]– (2), Cl– (3)}. Combination of (PP2)IrCl and CpM(CO)3H in a 2:1 stoichiometry gave (PP2)Ir(H)Cl2 (7) together with [(PP2)IrCO]‐[Mo(CO)3Cp] (8) or [(PP2)IrCO][W(CO)3Cp] (9). The rhodium analogues (PP2)Rh(H)Cl2 (4), [(PP2)RhCO][Mo(CO)3Cp] (5), and [(PP2)RhCO][W(CO)3Cp] (6) were obtained similarly from (PP2)RhCl and CpM(CO)3H. Structural assignments for [(PP2)Ir(H)Cl]+ and (PP2)M′(H)Cl2 (M′ = Rh, Ir) as diastereomers in which the hydrido ligand and the tBu substituent on the central phosphorus atom are located on the same side or on opposite sides of the PP2 reference plane of the meridionally bound tBuP(CH2CH2CH2PPh2)2 ligand are made on the basis of (i) correlations with known structures and reactivities of similar [(RP(CH2CH2CH2PR′2)2M′(H)Cl]+ cations and (ii) an X‐ray structure determination of 4. The crystal structure analysis of a [(PP2)RhCO]+ salt, closely related to 5/6 and 8/9, [(PP2)Rh(CO)][OCO2H] (10), demonstrates that in the solid state the four‐coordinate [(PP2)RhCO]+ cation and its counterion exist as essentially charge‐neutralized Rh ⃛O‐contacted ion pairs, two of which are linked by OH ⃛O bridges to centrosymmetric dimers. Ion pairing was also observed by IR spectroscopy for THF solutions of metalates 5/6 and 8/9.
New β‐Amino Alcohols as Chiral Ligands for the Catalytic Enantioselective Reduction of Prochiral Ketones and the Nucleophilic Addition of Diethylzinc to Benzaldehyde
Authors: Peper Viola , Martens Jürgen
Published: July 2007

New optically active β‐amino alcohols, derived from various acyclic and cyclic amino acids with alkyl groups on the carbinol carbon atom, were used in the enantioselective reduction of prochiral ketones. The attachment of alkyl groups to the nitrogen atom of the catalyst (R)‐1b was shown to influence favorably the enantioselectivity of the addition of diethylzinc to benzaldehyde. In both cases the resulting secondary alcohols were obtained in moderate to high optical yields.
Synthese und Kristallstrukturen der Amido‐Komplexe [Na(12‐Krone‐4)2][M{N(SiMe3)2}3] mit M = Mn, Fe und Co
Authors: Putzer Markus A. , Neumüller Bernhard , Dehnicke Kurt , Magull Jörg
Published: July 2007

Syntheses and Crystal Structures of the Amido Complexes [Na(12‐Crown‐4)2][M{N(SiMe3)2}3] with M = Mn, Fe, and Co

The ionic amido complexes [Na(12‐crown‐4)2][M[N‐(SiMe3)2}3] with M = Mn (1), Fe (2) and Co (3) were prepared by the reaction of M[N(SiMe3)2]2 (M = Mn, Co) and Fe[N‐(SiMe3)2]3, respectively, with sodium bis(trimethylsilyl)amide in toluene solution in the presence of 12‐crown‐4. 1–3 were characterized by IR spectroscopy and by crystal structure determinations. The complexes consist of cations [Na(12‐crown‐4)2]+ with a sandwich‐like structure and anions [M{N(SiMe3)2}3]– in which the metal atoms are planarly coordinate by the three nitrogen atoms of the bis(trimethylsilyl)amido groups.
Silyl Triflates – Valuable Synthetic Materials in Organosilicon Chemistry
Authors: Uhlig Wolfram
Published: July 2007

The highly reactive silyl triflates R4–nSi(OSO2CF3)n are valuable materials in organosilicon chemistry. Numerous new triflate derivatives of mono‐, oligo‐, and polysilanes were prepared by stepwise substitution of trifluoromethylsulfonyl groups for phenyl groups or other leaving groups. Conversions of silyl triflates with nucleophiles proceed regioselectively and, in most cases, quantitatively at low temperatures with short reaction times. Therefore, silyl triflates are suitable reagents for the synthesis and functionalization of linear and cyclic oligosilanes. Novel polycarbosilanes, polysilylalkynes, and polysilylphenylenes, which show a regular alternating arrangement of silylene groups and organic units, were prepared from α,ω‐bis[(trifluoromethylsulfonyloxy)silyl]‐substituted compounds and dinucleophiles. Branched polysilanes and polysilynes were obtained by reductive coupling of polymeric silyl triflates with potassium‐graphite.
Structural and Electrochemical Comparison of NiII in an N2S2 Plane with Two, One and No Axial Ligands: Isolation and Characterization of a Five‐Coordinate Nickel(II) Complex
Authors: Buonomo Rizalia M. , Reibenspies Joseph H. , Darensbourg Marcetta Y.
Published: July 2007

Addition of two equivalents of benzyl bromide to [N,N′‐bis(2‐mercaptoethyl)‐1,5‐diazacyclooctane]nickel(II) (Ni‐1) produced the green dibenzyl dithioether complex [Ni‐1‐Bzl2Br2] structurally characterized by X‐ray crystallography as a six‐coordinate octahedral complex in a monoclinic crystal system and the P21/c space group. Benzylation of the methyl thioether/thiolate [(Ni‐1‐Me)+I– yielded the mixed benzyl/methyl dithioether [(Ni‐1‐BzlMe)Br]I, structurally characterized by X‐ray crystallography as a five‐coordinate square pyramidal nickel(II) complex with a Ni–Br distance of 2.451 Å. The complex crystallizes in the orthorhombic Cmca space group. The latter is the first nickel(II) pentacoordinate complex isolated for the N,N′‐bis(2‐mercaptoethyl)‐1,5‐diazacyclooctane (daco) ligand. Structural comparison of these two complexes with the square‐planar dimethyl compound [Ni‐1‐Me2]I2 found an expansion of the N2S2 plane upon addition of axial ligands. The five‐coordinate nickel complex showed a displacement of the Ni ion from the N2S2 plane by 0.43 Å toward the axial bromide ligand, a common observation of pentacoordinate complexes of this ligand with metals such as Zn and Fe. Electrochemical studies as well as the X‐ray crystal structures for complex [Ni‐1‐Bzl2Br2] and [(Ni‐1‐BzlMe)Br]I are presented and discussed in detail.
Cyclobutadiene Complexes, XII. Alkynyl‐Substituted Tricarbonyl(cyclobutadiene)iron Complexes: Stille Coupling of Iodocyclobutadiene Complexes with Stannylalkynes
Authors: Bunz Uwe H. F. , Wiegelmann‐Kreiter Jutta E. C.
Published: July 2007

The synthesis of mono‐, di‐, tri‐ and tetraalkynylated tricarbonyl(cyclobutadiene)iron complexes is accomplished by a repetitive metalation/iodination/coupling sequence. Application of this sequence leads to the synthesis of oligomeric cyclobutadiene complexes with various topologies, inter alia to the synthesis of a perethynylated dimer 24. Alternatively a one‐step coupling procedure (Stille‐Farina) has been used to synthesize tetraalkynylated tricarbonyl(cyclobutadiene)‐irons 26.
Silver(I) Sandwich Complexes of Oxa‐Crowned Derivatives of Dithiomaleonitrile
Authors: Drexler Hans‐Joachim , Reinke Helmut , Holdt Hans‐Jürgen
Published: July 2007

The coordination chemistry of the four oxa‐crowned derivatives of dithiomaleonitrile mn‐12S2O2, mn‐15S2O3, mn‐18S2O4, and mn‐21S2O5 as well as of the acyclic bis(methylthio)maleonitrile mn‐S2 with AgI was investigated by X ray structural and spectroscopic methods. The 2:1 complexes (ligand/AgI) [Ag(mn‐12S2O2)2]PF6, [1]PF6, [Ag(mn‐15S2O3)2]PF6, [2]PF6, and [Ag(mn‐S2)2]PF6, [6]PF6, and the 1:1 complexes [Ag(mn‐15S2O3)]ClO4, [3]ClO4, [Ag(mn‐18S2O4)]PF6, [4]PF6, and [Ag(mn‐21S2O5)]PF6 [5]PF6, were obtained with AgPF6 or AgClO4 in MeOH. The stoichiometry of the macrocyclic AgI complexes and the coordination mode of mn‐S2On+1 coronands (n = 1–4) is determined by the length of the macrocyclic oligoethylene chain. – The mn‐crown dithioethers mn‐12S2O2 and mn‐15S2O3 form with AgPF6 the new sandwich complexes [Ag(mn‐12S2O2)2]PF6, [1]PF6, and [Ag(mn‐15S2O3)2]PF6, [2]PF6. [1]PF6 crystallises in the triclinic space group P1. In the centrosymmetric cation [1]+ each mn‐12S2O2 ligand is coordinated to the AgI centre in an endo manner via both S atoms and one O atom. The distance of the second O atom of mn‐12S2O2 to AgI is somewhat longer than a normal Ag–Oether bond. The overall environment around AgI in [1]+ is that of a distorted cubic S4O4 set of donors. [2]PF6 crystallises in the monoclinic space group C2/c. In the centrosymmetric cation [2]+ silver(I) is planar‐coordinated by the four S atoms of both mn‐15S2O3 molecules. The six O atoms of both mn‐15S2O3 ligands show only long‐range interactions to the AgI ion. They surround AgI almost vertically to the planar S4 set of donors in a crown‐like manner. – The crystal structures of the 1:1 complexes [Ag(mn‐18S2O4)]PF6, [4]PF6, and [Ag(mn‐21S2O5)]PF6, [5]PF6, consist of linear chain polymers. [5]PF6 forms an N‐bridged chain polymer of endocyclic [Ag(mn‐21S2O5)]+ units with S1O4NNitrile coordination at the AgI centre. In the 2:1 complex [Ag(mn‐S2)2]PF6, [6]PF6, each mn‐S2 acts as a monodentate NNitrile donor. – 13C‐NMR studies in nitromethane solution confirm that the AgI ions in the complexes of the mn‐crown dithioethers remain coordinated. However, the AgI ion in complex of mn‐S2 is decoordinated.
(Di‐tertbutylmethylsilyl)amide – a Building Block for Azasilacyclobutane Synthesis
Authors: Ruwisch Lutz , Klingebiel Uwe , Rudolph Stefanie , Herbst‐Irmer Regine , Noltemeyer Mathias
Published: July 2007

Di‐tert‐butylmethylsilylamide reacts with n‐BuLi to give the tetrameric lithium di‐tert‐butylmethylsilylamide 1. Reactions of lithium (di‐tert‐butylmethylsilyl)amide 1 with SiF4 give the mono‐ (2), bis‐ (3), tris‐ (4), and tetrakis‐ (5) ‐[(di‐tert‐butylmethylsilyl)amino]silanes. Lithiated 3 reacts with Me3SiCl to form (di‐tert‐butylmethylsilyl‐trimethylsilyl)amino‐(di‐tert‐butylmethylsilyl)amino‐difluorosilane (6); the 1,3‐diaza‐2,4‐disilacyclobutane 7 is obtained by LiF elimination. The lithium derivative of 6 (compound 8) crystallizes with formation of a (SiFNLi) four‐membered ring system. The 19F‐NMR spectrum proves that the Li–F bond fluctuates in solution. Reactions of 1 with (Me3Si)2C(SiF3)2 afford different products (9, 10) by controlling the reaction sequence. An excess of 1 reacts to give a four‐membered CSi2N ring system, the 1‐(di‐tert‐butylmethylsilyl)‐2,4‐bis‐[(di‐tert‐butylmethylsilyl)‐amino]‐2,4‐difluoro‐3‐bis(trimethylsilyl)‐1‐aza‐2,4‐disila‐cyclobutane (9), disubstitution with formation of bis[(di‐tert‐butylmethylsilyl)aminodifluorosilyl]bis(trimethylsilyl)methane (10) occurs in a molar ratio of 2:1. The cyclodisilazane 11 is obtained from dilithiated 10 in an intramolecular interconversion reaction. The crystal structures of 1, 8, 9, and 11 are reported.
Metall‐π‐Komplexe von Benzolderivaten, 50. Arylborane als Sandwichliganden: Darstellung von [(iPrO)2B(η6‐Ph)]2M und [Mes2B(η6‐Ph)]2M (M = V, Cr). Redoxeigenschaften und EPR Untersuchung M(d5)‐konfigurierter Neutralkomplexe sowie Bor‐zentrierter Radikalanionen
Authors: Elschenbroich Christoph , Kühlkamp Peter , Koch Jürgen , Behrendt Andreas
Published: July 2007

Metal π Complexes of Benzene Derivatives, 50. – Arylboranes as Sandwich Ligands: Preparation of [(iPrO)2B(η6‐Ph)]2M and [Mes2B(η6‐Ph)]2M (M = V, Cr). Redox Properties and EPR Study of M(d5) Neutral Complexes and Boron‐Centered Radical Anions

Bis(η6‐arene)metal complexes bearing peripheral boryl substituents have been prepared by means of metal‐atom ligand‐vapor cocondensation leading to [(iPrO)2B‐η6‐C6H5]2Cr (7) and [(iPrO)2B‐η6‐C6H5]2V (8) as well as by lithiation and subsequent reaction with Mes2BF with formation of [Mes2B‐η6‐C6H5]2Cr (11) and [Mes2B‐η6‐C6H5]2V (12). According to the NMR spectra, rotation about the η‐C–BR2 bonds in 7 and 11 is free at 25°C, restrictions setting in at –85°C. The neutral radicals 8• and 12• have been studied by EPR spectroscopy: despite of the profound difference in the electron‐accepting properties of the groups (iPrO)2B‐ and Mes2B, the hyperfine coupling constants a(51V) differ by 5% only; the extent of perturbation of the electronic structure manifests itself more clearly in the g tensor, which is tetragonal for 8 but orthorhombic for 12, the degeneracy of the LUMO's e1g being raised in the latter. Cyclovoltammetry on 11 exhibits reversible oxidation as well as reduction processes. Reduction which, according to EPR, is ligand‐centered, occurs in two steps which are separated by the redox splitting ΔE1/2 = 570 mV. This value, which is a measure of electronic communication between the two Mes2B groups, lies between those of 1,4‐bis(dimesitylboryl)benzene (δE1/2 = 690 mV) and 4,4′‐bis(dimesitylboryl)biphenyl (ΔE1/2 = 270 mV). The EPR spectrum of the radical anion 11−• reveals hyperfine coupling to one boron nucleus of a magnitude very similar to that of the free ligand radical anion Mes2BC6H. Therefore, reduction of 11 is ligand‐centered, and an intramolecular electron exchange between the boron centers is slow on the EPR time scale. As inferred from the observation of the hyperfine interactions a(53Cr) and a(1H), oxidation of 11 is metal‐centered; relative to parent bis(η6‐benzene)chromium (9), the two Mes2B groups cause an anodic shift of 290 mV for the couple 11+/0. The radical cations 11+• are prone to protodeborylation, in this aspect resembling the respective silyl derivatives.
Stepwise Insertion of Alkylisocyanides into the Metal‐Alkyne Bond of Half‐Sandwich Type Rhodium Complexes: Synthesis and Structural Characterization of Metallacyclobutenes and Metallacyclopentenes
Authors: Werner Helmut , Heinemann Anja , Windmüller Bettina , Steinert Paul
Published: July 2007

The cyclopentadienyl complexes [C5H5Rh(RCCR′)(SbiPr3)] (5–8), which were prepared from trans‐[RhCl‐(RCCR′)(SbiPr3)2] (1–4) and NaC5H5 and which contain a labile Rh–SbiPr3 bond, reacted with CO and CNR″ (R″ = Me, tBu) to give the carbonyl and isocyanide derivatives [C5H5Rh(RCCR′)(CO)] (9–11) and [C5H5Rh(RCCR′)‐(CNR″)] (12–16), respectively. On treatment of 12 (R = R′ = Ph; R″ = Me) with SbiPr3, the metallacyclobutene complex [C5H5Rh{κ2(C,C}‐C( = NMe)CPh=CPh}(SbiPr3)] (17) was formed; it reacts with excess CNMe or CNtBu to yield the metallacyclopentenes [C5H5Rh{κ2(C,C)‐C(NMe)CPhCPhC‐(NR)}(CNR)] (18, 19). Similar compounds 20–23 containing a five‐membered RhC4 metallacycle were prepared either from [C5H5Rh(RCCR′)(SbiPr3)] (7, 8) or [C5H5Rh‐(PhCCPh)(CNtBu)] (14) and excess isocyanide. The crystal and molecular structures of 17 and 18 (R = Me) have been determined.
Semiconductor‐Catalysed Photoaddition: γ,δ‐Unsaturated Amines from Cyclopentene and Schiff Bases
Authors: Schindler Wolfram , Knoch Falk , Kisch Horst
Published: July 2007

Irradiation of methanolic cadmium sulfide suspensions in the presence of Schiff bases and cyclopentene opens an easy access to new γ,δ‐unsaturated amines. Their formation can be described as a kind of paired photoelectrolysis induced by the photogenerated electron‐hole pair trapped at reactive surface sites of CdS. At the reductive site the imine is converted to an α‐aminobenzyl radical by a proton‐coupled electron transfer, while at the oxidative site cyclopentene is transformed to the cyclopentenyl radical through deprotonation of the intermediate radical cation. C–C coupling of these radicals affords the addition products. Competitive dimerisation of the radicals produces hydrodimers of the imines and dehydrodimers of the olefin, as demonstrated in the case of 1‐phenylcyclohexene. Using optical active imines, we found no significant diastereoselectivity. In the absence of an olefin the alcoholic solvent was added to the imine. The molecular structure of one hydrodimer was resolved by X‐ray analysis. When CdS/Pt was used as photocatalyst, hydrolysis products of the imine were formed, suggesting involvement of an intermediate OH radical.
Synthesis, Spectroscopic Characterization, and Crystal Structure Determination of Cationic [(Cyclopentadienyl)dicarbonyliron](alkynyl)‐aminocarbene Complexes
Authors: Rück‐Braun Karola , Kühn Jörg , Schollmeyer Dieter
Published: July 2007

(Alkynoyl)iron complexes 1, Cp(CO)2Fe(OCCCR) (R = CH3, Ph, SiMe3), were synthesized by applying a mixed anhydride procedure and transformed into the cationic methoxycarbene complexes 2, [Cp(CO)2 Fe(C(OMe)CCR)+]‐[PF6–]. Primary amines H2NR′ react with the methoxycarbene complexes to furnish exclusively cationic aminocarbene complexes 3, [Cp(CO)2 Fe(C(NHR′)CCR)+][PF6–], or (2‐methoxyvinyl)aminocarbene complexes 5. The spectroscopic properties of the new complexes are discussed. The (alkynyl)‐aminocarbene complexes 3e and 3f were characterized by X‐ray crystal structure analysis.
Preparation, Properties, and Reactions of Metal‐Containing Heterocycles, XCV. Transition‐Metal‐Mediated Cyclocotrimerization of Selenophosphinites with Activated Alkynes
Authors: Lindner Ekkehard , Bosch Elke , Fawzi Riad , Steimann Manfred , Mayer Hermann A. , Gierling Karlheinz
Published: July 2007

Selenophosphinito complexes (OC)4Mn(η2‐Se\documentclass{article}\usepackage{amsmath}\pagestyle{empty}\begin{document}$ \dddot - $\end{document}PR21) (2a, b) [R1 = cyc‐Hex (a), tBu (b)] are formed by the reaction of BrMn(CO)5 with the phosphane selenides R21HPSe (1a, b) in the presence of the auxiliary base Et(iPr)2N. According to an X‐ray structural analysis, 2a crystallizes in the space group \documentclass{article}\pagestyle{empty}\begin{document}$ P\bar 1 $\end{document} with Z = 2. The dimeric complex [(OC)4Mn(μ‐Se\documentclass{article}\usepackage{amsmath}\pagestyle{empty}\begin{document}$ \dddot - $\end{document}PMe2)]2 (4c) is not obtained in a straightforward way. Compound 4c is only obtained via the intermediate Br(OC)4Mn–Se\documentclass{article}\usepackage{amsmath}\pagestyle{empty}\begin{document}$ \dddot - $\end{document}P(H)Me2 (3c) by HBr elimination with nBuLi. Complex 3c is formed by replacement of carbon monoxide in BrMn(CO)5 by Me2HPSe (1c). A dissociative equilibrium between [(OC)4 Mn(μ‐Se\documentclass{article}\usepackage{amsmath}\pagestyle{empty}\begin{document}$ \dddot - $\end{document}PMe2)]2 (4c) and the monomeric species (OC)4Mn(\documentclass{article}\usepackage{amsmath}\pagestyle{empty}\begin{document}$ \dddot - $\end{document}2‐Se\documentclass{article}\usepackage{amsmath}\pagestyle{empty}\begin{document}$ \dddot - $\end{document}PMe2) was not observed. The cyclocotrimerization of the >P\documentclass{article}\usepackage{amsmath}\pagestyle{empty}\begin{document}$ \dddot - $\end{document}Se function with the activated alkynes ZCCZ [Z = CO2R2; R2 = Me (d), Et (e), iPr (f), cyc‐Hex (g)] was successful only in the case of the cyclohexyl derivative 2a to give the selenaphosphamanganabicycloheptadienes 5d – g. An X‐ray structural analysis proved that 5d crystallizes in the space group \documentclass{article}\pagestyle{empty}\begin{document}$ P\bar 1 $\end{document} with Z = 2. Under CO pressure 5d was degraded to the selenophene 6.
A YBa2 Cluster Based on Simple Ligands (OtBu)
Authors: Borup Björn , Streib William E. , Caulton Kenneth G.
Published: July 2007

Reaction of a 1:2 mixture of Y[N(SiMe3)2]3 and Ba[N(SiMe3)2]2 with tBuOH (8 mol equivalents) in Et2O at 25°C yields YBa2(OtBu)7(tBuOH), which has a triangular structure with two μ3‐OtBu and three μ2‐OtBu ligands, one terminal OtBu on Y and on one Ba, and one terminal tBuOH on the second Ba. All metals are thus five‐coordinate. The crystal structure is comprised of chains of triangles of triangles held together by hydrogen bonds from tBuOH of one YBa2 unit to the terminal OtBu on Ba of the next YBa2 unit. This serves as support for the idea that, in certain cases, the heterometallic alkoxide product from alcoholysis of a mixture of two metal complexes can faithfully duplicate the global solution metal stoichiometry.
Self‐Assembly of Substituted 6‐Hydroxy‐trans‐3‐hexenoic Acids – Formation of Extended Ribbon‐Like Structures by Hydrogen Bonds
Authors: Strauch Hans Christian , Erker Gerhard , Fröuhlich Roland
Published: July 2007

The substituted 6‐hydroxy‐trans‐3‐hexenoic acids 2a and 2b are prepared by an organometallic template reaction involving a sequence of CC coupling reactions between a CO2 equivalent, butadiene, and 3‐cyclopenten‐1‐one or 3,4‐diphenyl‐3‐cyclopenten‐1‐one, respectively. In the crystal 2a assembles to form an infinite ribbon‐type structure, exhibiting an alternating array of 12 and 18 atom‐containing loops. The former are each constructed by an alternating CO2H/OH/CO2H/OH sequence, originating from four different monomeric units, that are linked together by means of hydrogen bonds. Two complementary ribbons of 2a are connected by van der Waals interactions to form staples that constitute the microscopic building blocks of the true (2a)n structure in the crystal. Stacks of cyclopentene π bonds are oriented inside the columnar structure of 2a. Acid 2b also forms a related ribbon‐like assembly in the solid state. Here the bulky 3,4‐diphenylcyclopentadienylidene moieties are oriented laterally at the ribbons, and van‐der‐Waals interactions with adjacent ribbons construct a three‐dimensional hydroxyhexenoic acid network.
Syntheses, Structures, and Reactivity of 1‐Phosphanylnaphth‐2‐ols
Authors: Heinicke Joachim , Kadyrov Renat , Kindermann Markus K. , Kloss Matthias , Fischer Axel , Jones Peter G.
Published: July 2007

P‐tertiary or amino‐substituted 1‐phosphanylnaphth‐2‐yl silyl ethers 3 are synthesized by stepwise reaction of lithium 1‐lithio‐2‐naphtholate 1 with chlorophosphanes and ClSiMe3. The free phosphanylnaphthols 4 are prepared by alcoholysis. As established by characteristic coupling constants and X‐ray structural analyses (of 3c, 4c), 3 exhibit in solution and in the solid state a cis‐bisecting conformation, whereas 4 prefers the opposite trans‐bisecting arrangement, allowing easy protonation and formation of chelate complexes. Substitution reactions of phosphanylnaphtholates 2 with Ph2PCl and formation of chelate complexes LNi‐η5‐Cp and L2Pd are described. Attempts to prepare secondary and primary phosphanylnaphthols failed because of facile cleavage of the P–C(naphthyl) bond in PH‐substituted 1‐phosphanylnaphth‐2‐ols.
Control of the SO2 Coordination Mode at the (Monochelate)rhodium Complex ClRh(P∼O) with the Hemilabile Ligand Cy2PCH2CH2OCH3
Authors: Lindner Ekkehard , Keppeler Berthold , Fawzi Riad , Steimann Manfred
Published: July 2007

The SO2 coordination mode at the rhodium complex [ClRh(P∼O)()] (1) [  η2(O,P)‐chelated Cy2PCH2CH2OCH3 ligand; P∼O  1(P)‐coordinated] is controlled by the hemilabile ligand Cy2PCH2CH2OCH3 and shows a dependence on the polarity of the solvent. In polar organic solvents (e.g. acetone) the addition of sulfur dioxide results in the formation of a trigonal‐pyramidal oriented SO2 group in [ClRh(η1‐SO2)(P∼O)()] (2a). However, in nonpolar media (e.g. n‐hexane) a trigonal‐coplanar geometry of the SO2 unit in [ClRh(η1‐SO2)(P∼O)2] (2b) is favored.
Übergangsmetall‐Stannyl Komplexe, 10[1]. Molybdocen‐ und Wolframocen‐Derivate mit zwei unterschiedlichen Liganden der 4. Hauptgruppe
Authors: Seebald Steffen , Möller Frank , Schubert Ulrich , Kickelbick Guido
Published: July 2007

Transition‐Metal Stannyl Complexes, 10 – Molybdocen and Wolframocen Derivatives with Two Different Main‐Group‐4 Ligands

Reactions of Li[Cp2MSnPh3] (M  Mo, W) with CH3I, BuBr, PhCH2Br, PhC(O)Cl or Br(CH2)nBr (n  4,5) yield Cp2M(R)SnPh3 [R  CH3, Bu, CH2Ph, C(O)Ph, (CH2)nBr], while tBuBr or CH3C(O)Cl give the hydrido complexes Cp2M(H)SnPh3. A silyl stannyl complex is only obtained from Li[Cp2WSnPh3] and Me3SiOSO2CF3, but not with Me3SiCl or from the anionic Mo complex. In contrast, the reactions of chlorostannanes provide the bis(stannyl) complexes Cp2M(SnR′3)SnPh3 or Cp2M(SnR′2Cl)SnPh3. R/Cl exchange at the tin atom is observed when an excess of the chlorostannane is used. Upon reaction of Li[Cp2MSnPh3] with Ph3PbCl only Cp2M(PbPh3)SnPh3 is formed, while a mixture of Cp2M(PbMe3)SnPh3 and Cp2M(PbMe2Cl)SnPh3 is obtained with Me3PbCl due to redistribution reactions. The structures of Cp2W(SnPh3)C(O)Ph, Cp2W(SnPh3)SntBu2Cl and Cp2W(SnPh3)PbMe2Cl were determined by X‐ray structure analyses.
Hydride Fluxionality in Transiton Metal Complexes: An Approach to the Understanding of Mechanistic Features and Structural Diversities
Authors: Gusev Dmitry G. , Berke Heinz
Published: July 2007

The mechanisms of intramolecular dynamics in transition metal hydride complexes are surveyed in this review. The NMR data for a number of fluxional hydrides are interpreted in terms of principal and secondary topological changes of the coordinated ligands. The principal ligand motions can be further categorized as being of migratory (M) and replacement (R) type. Discussion of these ligand motions is followed by analysis of more complex rearrangements of hydride systems, in which both types are operative in multiple exchange processes. The attempted systematic approach appears to be a useful general mechanistic concept for the understanding of the fluxional behavior of hydride complexes.
Azidopentazole is Probably the Lowest‐Energy N8 Species – A Theoretical Study
Authors: Nguyen Minh Tho , Ha Tae‐Kyu
Published: July 2007

Ab initio molecular orbital calculations at the quadratic configuration interaction [QCISD(T)/6‐31G(d)] and coupled‐cluster theory [CCSD(T)/DZP] levels based on MP2/6‐31G(d) optimized geometries show that azidopentazole is likely to be the global minimum of the N8 isomers lying 13 and 18 kcal/mol below the acyclic diazidyldiimide and the cyclic pentalene analogue, respectively. Azidopentazole is characterized by a significant energy barrier to ring closure and is expected to be stable with respect to cycloreversion and thus constitutes the most realistic N8 target for a synthetic preparation.
Activation of Bis(trimethylsilyl) Peroxide and tert‐Butyl Hydroperoxide with Oxo and Peroxo Complexes of Vanadium, Molybdenum, and Tungsten for the Sulfoxidation of Thianthrene 5‐Oxide
Authors: Adam Waldemar , Golsch Dieter , Sundermeyer Jörg , Wahl Günter
Published: July 2007

Bis(trimethylsilyl) peroxide (BTSP) and tert‐butyl hydroperoxide (tBuOOH) were activated by various oxo and peroxo complexes of molybdenum, tungsten, and vanadium as catalysts for the sulfoxidation of thianthrene 5‐oxide (SSO). A screening of a number of phosphane oxide and amine oxide ligands revealed that BTSP was most efficiently activated by the [MoO5(OPtBu3)] complex. The best results for tBuOOH as oxygen source were achieved with the vanadates [VO(OR)3] (R = tBu, iPr). Comparative selectivity and rate data for the stoichiometric and catalytic sulfoxidations of SSO mediated by the MoO5L complex (L = OPtBu3, OPnOct3, ONnBu3, ONnOct3) suggest that the bisperoxo metal complex is the active oxygen transfer species.
The First Triisopropylstibane Ruthenium(II) and Ruthenium(0) Complexes Including the X‐ray Crystal Structure of [Ru(η3‐C3H5)2(SbiPr3)2]
Authors: Werner Helmut , Gr ünwald Claus , Laubender Matthias , Gevert Olaf
Published: July 2007

The hydridoruthenium(II) complexes [RuHCl(H2)(SbiPr3)3] (2) and [RuH2(H2(SbiPr3)3] (3), containing dihydrogen as ligand, were prepared from [RuCl2(C8H12)]n (1) as the starting material. Compound 3 reacts with CO by displacement of H2 to yield [RuH2(CO)(SbiPr3)3] (4) and with C2H4 to give both [RuH2(C2H4)2(SbiPr3)2] (5) and [RuH2(C2H4)(SbiPr3)3] (6), the latter as the more stable and isolable product. Treatment of 3 with propene leads to the formation of [Ru(η3‐C3H5)2] (7) while the reaction of 3 with butadiene affords the pentacoordinated ruthenium(0) compound [Ru(η4‐C4H6)2(SbiPr3)] (8). The molecular structure of the bis‐(allyl) complex 7 was determined by X‐ray crystallography.
Electrophilic Substitution at the NB9 and NB11closo‐Skeletons
Authors: Lomme Petra , Roth Martin , Englert Ulli , Paetzold Peter
Published: July 2007

The aza‐closo‐boranes ArNB9H9 (1, Ar = p‐ClC6H4) and MeNB11H11 (2) were brominated, iodinated, or methylated under Friedel‐Crafts conditions to give ArNB9H4Br5 (3), ArNB9H7I2 (4), ArNB9H4Me5 (7), MeNB11H10Br (5), MeNB11H10I (6), and MeNB11H5Me6 (9), respectively. The upper boron belt adjacent to nitrogen is not involved in the substitution reactions with 1 and 2. The antipodal position and the lower belt are attacked by electrophiles in the case of 1; the antipodal position is the preferred one in the case of 2. By prolongated action of triflic acid on the methylated species 7 and 9, one methyl group is replaced by the triflate group to give ArNB9H4Me4(OTrf) (8) and MeNB11H5Me5‐(OTrf) (10) with this group in the positions 6 and 12, respectively. The NMR data indicate the cluster symmetries Cs (4, 8), C4v (3, 7), and C5v (5, 6, 9, 10). Crystal structure investigations of 5 (space group Cc) and 10 (space group C2/c) showed that the molecular dimensions of the NB11 skeleton are comparable to those of closo, ‐(PhCH2)NB11H11.
Crystal Structure of a Representative Mixed Adduct of Trimethylaluminium and a Lithium Amide and a Theoretical MO Study on Model Systems
Authors: Armstrong David R. , Craig Fiona J. , Kennedy Alan R. , Mulvey Robert E.
Published: July 2007

Reaction of the simple alane adduct [Me3Al · HN(CH2Ph)2] (2) with the lithium amide [(PhCH2)2NLi] leads to the formation of the mixed adduct [Me3Al · (PhCH2)2NLi · HN(CH2Ph)2] (1). The crystal structures of 1 and 2 are reported. Exhibiting a four‐membered, mixed‐metal, mixedanion ring‐core, the structure of 1 is unusual in containing a monomeric lithium dibenzylamide fragment. Such fragments generally convert to aza‐allyl derivatives, so its existence here can be attributed to the stabilising effect of the attached Me3Al ligand. Crystalline 2 adopts the classical, distorted‐tetrahedral arrangement of simple monomeric alane adducts. Ab initio MO calculations on model systems show that mixed adduct formation from Me3Al and Me2NLi is exothermic, while further reaction to give Me2AlNMe2 and MeLi (i.e., complete transmetallation) is endothermic.
Structural Chemistry of Alkali Metal Phenylhyrazides
Authors: Gemünd Birgit , Nöth Heinrich , Sachdev Hermann , Schmidt Martin
Published: July 2007

The crystal and molecular structures of a series of N‐phenyl‐substituted lithium hydrazides were determined in order to investigate possible Li···Ph π interactions. These are pronounced when there are no donor molecules present to solvate the Li centers. An η6‐Li···Ph interaction is particularly distinct in tetrameric (Me3Si)2N–N(Ph)Li but also in trimeric Ph2N–N(SiMe3)Li Deprotonation of N,N′ ‐diphenylhydrazine with butyllithium in ether resulted in the formation of Ph(Li)N–N(Ph)Li · 2 LiNPh2 · 2 OEt2 with phenyl group migration and N–N bond cleavage by a redox process. An increase of the size of the cations, as shown for Ph(Me3‐Si)N–N(Ph)Na · NH3 and the caesium salt (Me3‐Si)2N–N(Ph)Cs · nTHF, results in increased coordination of the metal ion to the phenyl group. The caesium compound forms a three‐dimensional network. Channels along the c axis are partially filled with THF molecules.
Sulfenato, Thiosulfinato, and Thiosulfonato Transition Metal Complexes
Authors: Weigand Wolfgang , Wünsch Ralf
Published: July 2007

The synthesis and coordination chemistry of sulfenic, thiosulfinic, and thiosulfonic acid anions are reviewed. Different approaches, which yield the platinum(II) and ruthenium(II) complexes containing the anionic sulfur(0), sulfur(II), and sulfur(IV) oxid ligands, are described. The oxidative addition of thiosulfinates or N‐sulfinyl phthalimides to platinum(0) complexes L2Pt(C2H4) [L = PPh3, 1/2 PPh2CH2CH2PPh2, 1/2 (R,R)‐(–)‐DIOP, 1/2 (C5H4PPh2)Fe(C5H4PPh2) leads to sulfenato complexes; those of N‐thiosulfinyl phthalimidies or trisulfid 1‐oxides afford the thiosulfinato complexes. Moreover, the reactions of CpRu(PPh3)(L)(SH) (L = CO, PPh3) with N‐sulfinyl phthalimides forming the thiosulfinato moiety, are reported. The spectroscopic, structural and chemical properties of these complexes are discussed.
Optically Active Titanium Complexes Containing Linked Amido‐cyclopentadienyl Ligands: Their Use as Asymmetric Hydrogenation Catalysts
Authors: Okuda Jun , Verch Sabine , Spaniol Thomas P. , Stürmer Rainer
Published: July 2007

Optically active titanium complexes of the formula Ti(η5:η1−C5R4SiMe2NCHMePh)Cl2 (R = H, Me), containing the cyclopentadienyl ligand linked to a chiral 1‐phenylethylamido moiety, were synthesized and characterized in both enantiomerically pure forms. A single‐crystal X‐ray structural analysis of (S)()Ti(η5:η1−C5H4SiMe2NCHMePh)Cl2 shows a conformation in which the phenyl group is turned away from the metal center. NOE measurements suggest that a related structure is retained in solution. Upon activation with n‐butyllithium, these complexes show hydrogenation activity toward imines with slight enantioselectivity.
The Mechanism of the Double Bond Cleavage in the Titanium Zeolite‐catalyzed Oxidation of α‐Methylstyrene by Hydrogen Peroxide: the β‐Hydroperoxy Alcohol as Intermediate
Authors: Adam Waldemar , Corma Avelino , Martínez Agustín , Renz Michael
Published: July 2007

It is unequivocally shown that acetophenone, an oxidation product in the titanium zeolite‐catalyzed oxidation of α‐methylstyrene, derives from 2‐hydroperoxy‐2‐phenyl‐1‐propanol as intermediate, which was detected and isolated in this reaction for the first time.
Synthesis, Structure and Reactions of the Homoleptic Alkyne Nickel(0) Complex (Alkyne)4Ni3 (Alkyne: 2‐methyl‐4‐trimethylsilyl‐3‐butyn‐2‐ol)
Authors: Klettke Thomas , Walther Dirk , Schmidt Andreas , Görls Helmar , Imhof Wolfgang , Günther Wolfgang
Published: July 2007

Treatment of (cdt)Ni (cdt: cyclododeca‐1,5,9‐triene) with 2 equivalents of 2‐methyl‐4‐trimethylsilyl‐3‐butyn‐2‐ol leads to the selective formation of the homoleptic complex (alkyne)4Ni3 (compound 3), which can be isolated in excellent yields. The solid‐state structure of 3 exhibits three Ni centers, forming a bent Ni3 chain connected by two bridging alkynes. The other two alkynes are terminally coordinated. Additionally, the trimeric units are stabilized by three intramolecular hydrogen bonds. Two intermolecular hydrogen bonds connect the trimeric units to form a polymer rope. According to the 13C‐ and 1H‐NMR spectra in THF the structure of the complex 3 in solution is very similar to that in the solid state. The reaction of 3 with some alkynediols and with 2,5,5‐trimethylhex‐3‐yn‐2‐ol affords compounds of the type (alkyne)2Ni. Cot (cot: 1,3,5,7‐cyclooctatetraene) converts 3 into [(cot)Ni]2, which in turn reacts with 2,5‐dimethylhex‐3‐yne‐2,5‐diol to form the dimeric complex (alkyne)2Ni2(cot) 6. X‐ray analysis of 6 reveals a very symmetrical structure in which cot connects both Ni(0) centers at opposite sides of the ring system.
Hydride Addition to Coordinated S2CPR3 Ligands in Mononuclear Mn and Re Complexes: Phosphane‐dithioformate Adducts as Five‐electron Bridging Ligands
Authors: Barrado Georgina , Miguel Daniel , Miguel Jesús A. , Riera Víctor , Soláns Xavier
Published: July 2007

The cationic tetracarbonyl complex cis‐[Mn(CO)4‐(S2CPCy3)]+ undergoes addition of hydride ion to the central carbon of the S2CPR3 ligand to afford, after spontaneous dimerization with loss of CO, the dimer [Mn2(CO)6{μ‐S2C(H)PCy3}2] (5a), which was characterized by analytical and spectroscopic methods as well as by X‐ray diffraction. In the molecule of 5a each S2C(H)PCy3− ligand is coordinated to one manganese in an η2‐S,S′ chelate fashion, and one sulfur of each ligand serves as a bridge to bind the other manganese atom, thus forming a distorted Mn2S2 square. This appears to be a very stable arrangement. Compound 5a can be more easily prepared by treating the perchlorato complex [Mn(CO)3(S2CPCy3)(OClO3)] (2a) with NaBH4. This procedure is general and can be used for the preparation of several derivatives containing either manganese or rhenium [M2(CO)6{μ‐S2C(H)PR3}2] 5a–d. The reaction of cationic tricarbonyl complexes [M(CO)3(S2CPR3)(PPh3)]PF6 (M = Mn, Re) with NaBH4 produced the same dimers 5a or 5c by displacement of the PPh3 ligand. Treatment of the dimer 5a with excess PEt3 or P(OMe)3 leads to the cleavage of the bridges and loss of one CO and the PR3 group from the S2C(H)PR3 unit to afford ultimately the dithioformate complexes [Mn(CO)2(S2CH)(L)2] [L = PEt3, P(OMe)3].
P/O Ligand Systems: Synthesis, Reactivity, and Structure of Tertiary o‐Phosphanylphenol Derivatives
Authors: Heinicke Joachim , Kadyrov Renat , Kindermann Markus K. , Koesling Manuela , Jones Peter G.
Published: July 2007

Reactions of C,O‐dilithium reagents 1 (M = M′ = Li) or C,O‐lithium‐sodium reagents 1 (M = Li, M′ = Na) with chlorophosphanes afford C,O‐disubstitution products 2 or phosphanylphenolates 3 which are treated subsequently with ClSiMe3 to give 4‐methyl‐ and bulky 4,6‐di‐tert‐butyl substituted o‐phosphanylphenol silyl ethers 4. These were applied for the preparation of the corresponding o‐phosphanylphenols 5, mainly P‐asymmetric derivatives. Limitations and side reactions by use of 1 in the above synthesis are discussed. Acid‐base properties, pH‐dependent solubility in water/hexane, and substitution reactions at oxygen and phosphorus of selected representatives of 5 are reported. An example for the separation of enantiomers by esterification with (1S)‐()‐camphanic acid chloride is given. IR studies revealed intramolecular PHO bonds and 2J(PC) the preferred trans arrangement of the phenoxy group in solution. In the solid state, inter‐ and intramolecular PHO bonds were detected by X‐ray structure analysis. The trans arrangement of the phenoxy group is preserved. Because of steric hindrance, the O substituents are tilted towards the phosphorus atom and thus induce large through‐space coupling constants. The PSn distance of 336.9 pm in the bulky substituted OSnMe3 moiety 8h is however too large for the formation of genuine intramolecular coordination. The versatility of o‐hydroxyarylphosphanes and objectives of further studies are shown by preliminary results on complex formation and applications of these phosphanes in catalysis.
Crystal Structure, Solid‐state Polymerization, and Ionic Conductivity of Alkali Salts of Unsaturated Carboxylic Acids, 4. Investigations on Lithium Sorbate
Authors: Schlitter Stephan M. , Beck Horst P.
Published: July 2007

The structure of lithium sorbate (C6H7LiO2) was determined by single‐crystal X‐ray diffraction. It may be divided into organic and inorganic layers. The ionic part of the structure consists of a two‐dimensional network of corner‐ and edge‐sharing lithium oxotetrahedra, a structural pattern already known from other lithium carboxylates. Irradiation of the substance with X‐rays or its thermal treatment results in the formation of a polymer exhibiting ionic conductivity at higher temperatures. Due to the rather large distances between potentially reactive atoms the polymerization results in a structural breakdown. Nevertheless, during the solid‐state polymerization preferred orientations of building units are partially preserved. The probable course of the polymerization and the structure of the resulting polymer are discussed.
Synthesis, Structure and Conformation of cis‐ and trans‐(μ‐1,6‐Dimethylheptalene)bis(tricarbonyliron)
Authors: Grimm Felix W. , Hafner Klaus , Lindner Hans J.
Published: July 2007

The reaction of 1,6‐dimethylheptalene (2) with Fe2(CO)9 affords two binuclear iron complexes 4a and 4b, each bearing two tricarbonyliron moieties, in trans and cis orientation, respectively. The reaction leads additionally to the formation of the monocomplexed compound 3. NMR studies indicate that the heptalene moiety of the new compounds is a π‐bond isomer of 2, and this is clearly attributable to steric factors. Single‐crystal X‐ray structure analyses of the metal complexes 4a and 4b confirm that the Fe(CO)3 fragments adopt trans and cis geometries, respectively, with respect to the plane of the carbocycle. The ring systems of the two isomers adopt different conformations in the solid state. In the case of 4a, a hitherto unknown chair‐like conformation is determined, whereas in complex 4b the ring system shows a twisted double boat conformation.
Metallkomplexe mit biologisch wichtigen Liganden, LXXXIX. Oxidative Addition von elektrophilen α‐Aminosäurederivaten an Platin(II)‐ und Cobalt(I)‐Komplexe: α‐Übergangsmetallierte Aminosäuren
Authors: Kayser Bernd , Nöth Heirnrich , Schmidt Martin , Steglich Wolfgang , Beck Wolfgang
Published: July 2007

Metal Complexes of Biologically Important Ligands, LXXXIX

Part LXXXVIII: Ref.[1].

.
— Oxidative Addition of Electrophilic Derivatives of α‐Amino Acids to Platinum(II) and Cobalt(I) Complexes: α‐Transition‐Metallated Amino Acids

Herrn Professor Dr. Hans Georg von Schnering zum 65. Geburtstag gewidmet.

The addition of methyl α‐bromohippurate to PtMe2(bipy) gives the α‐metallated amino acid derivative (bipy)‐Me2(Br)PtC(H)(NHCOPh)(CO2Me) as a mixture of isomers 1a, b of which the trans adduct 1a was characterized by X‐ray diffraction. Methyl α‐bromohippurate and N‐Boc‐O‐tosylserine methyl ester are added to [Co(py)(DH)]− (DH = dimethylglyoxime, diphenylglyoxime) to give cobalt(III) complexes 2–5 with a cobalt‐carbon bond.
Zinkorganische Phosphaniminato‐Komplexe mit Heterocuban‐Struktur
Authors: Krieger Matthias , Gould Robert O. , Harms Klaus , Parsons Simon , Dehnicke Kurt
Published: July 2007

Organo‐Zinc Phosphaneiminato Complexes with Heterocubane Structure

The organo‐zinc heterocubanes [ZnR(NPMe3)]4 with R = CH3 (1) and n‐C4H9 (2) were prepared by the reaction of [ZnBr(NPMe3)]4 with MeLi and nBuLi, respectively, in hexane solution. In a similar reaction of nBuLi with [ZnI(NPMe3]4 the phosphaneiminato complex [Zn4I(nBu)4(NPMe3)3] (3) is formed. 1–3 were characterized by IR, NMR and MS spectroscopy, and by crystal‐structure determinations. 1 and 2 possess heterocubane structures in which the zinc atoms are linked via μ3‐N bridges of the phosphaneiminato groups, and all bond angles in the Zn4N4 core are close to 90°. A distorted heterocubane structure is observed for 3 with one of the NPMe3 moieties replaced by an iodine atom.
Generation and Synthetic Application of Metallated Methyl Isopropenyl Ether, A Substitute for Acetone Enolate
Authors: Taherirastgar Foroogh , Brandsma Lambert
Published: July 2007

Methyl isopropenyl ether (1) has been metallated at low temperature with a 1:1 molar mixture of n‐BuLi/t‐BuOK in THF‐hexane, and subsequently functionalized with a variety of electrophilic reagents. At temperatures higher than – 30°C, the metallated methyl isopropenyl ether (2) decomposes with formation of allene. When the suspension of 2 is allowed to warm up to room temperature in the presence of an additional equivalent of n‐BuLi, the intermediary allene is converted into 1‐propynyllithium (2c), which reacts with propylthiocyanate to give 1‐propylthio‐1‐propyne (4). Some of the functionalization products were subjected to acidic hydrolysis affording the expected methyl ketones.
A Structural Study of Selenobenzamides: Crystal Structures and Dynamic 13C NMR
Authors: Otten Pieter A. , Gorter Syb , Gen Arne Van Der
Published: July 2007

The solid‐state structures of (p‐bromoselenobenzoyl)morpholine (2a) and [p‐(dimethylamino)selenobenzoyl]morpholine (2b) were determined by X‐ray diffraction. Both molecules show a flat selenoamide group. The larger contribution of resonance stabilization by the aromatic ring carrying the p‐dimethylamino substituent is reflected by the smaller interplanar angle Θ between the aromatic ring and the selenoamide group [53.3(1)° vs. 81.1(1)°] and by the shorter length of the CSe bond [1.824(5) Å vs. 1.840(3) Å]. The Gibbs free energy of activation of C‐N bond rotation (ΔG≠rot) of five p‐substituted (selenobenzoyl)morpholines was determined by dynamic 13C NMR. The activation barriers were found to range from 61.6 kJ/mol (X = NNMe2) to 75.1 kJ/mol (X = H). The ΔG≠rot values of the corresponding (thiobenzoyl)morpholines were found to be from 3.2 kJ/mol (X = NMe2) to 5.0 kJ/mol (X = H) lower. In both cases, ΔG≠rot showed an excellent linear Hammett correlation with s̀+p.
Asymmetric Catalysis, 105. Stereoselective Hydrogenation of Folic Acid with Immobilized Optically Active Rhodium(I)/Diphosphane Catalysts
Authors: Brunner Henri , Bublak Petra , Helget Martina
Published: July 2007

For the hydrogenation of the CN bonds in the pyrazine ring of the vitamin folic acid (1) optically active rhodium(I)/diphosphane complexes immobilized on supports such as silica gel or Al2O3 were used. The reduction was carried out at 50 bar hydrogen pressure in an aqueous solution buffered to pH 7. Thus, 5,6,7,8‐tetrahydrofolic acid (2) was obtained which contains a new asymmetric center at C‐6 of the pterine system. Therefore, in combination with the (S) configuration of the natural L‐glutamic acid part of the molecule two diastereomers with (6S,S) and (6R,S) configuration arise. The relatively unstable tetrahydrofolic acid (2) was converted into its 5‐formyl derivative folinic acid (4) by treatment with methyl formate/formic acid in a 5:1 mixture of DMSO/pyridine. The Ca salt of folinic acid (4) is the widely used drug leucovorin. The diastereomers were separated by silica gel HPLC. To the column bovine serum albumine (BSA) is covalently bound. With optically active rhodium(I)/diphosphane catalysts, immobilized on silica gel supports, a diastereoselectivity of up to 90% could be achieved in the hydrogenation of folic acid (1).
Conformational Mobility and Preferences of Allyl‐Type Organometallic Intermediates: Dodec‐2‐enylpotassium
Authors: Franzini Livia , Moret Etienne , Schlosser Manfred
Published: July 2007

Alk‐2‐enylpotassium compounds having the endo conformation are synthetically very valuable precursors of (Z)‐olefinic derivatives substituted at the outward allylic position. They may be generated by „stereoconservative’︁ metalation of the readily available (Z)‐alk‐2‐enes by using the superbasic mixture of butyllithium and potassium tert‐butoxide or by metalation under similar conditions of stereorandom mixtures of alk‐2‐enes or alk‐1‐enes followed by torsional isomerization of the concomitantly formed exo conformers to the thermodynamically more stable endo species. The principal factors that dictate the rate and the extent of the endo/exo equilibration are the substrate geometry, the solvent, the temperature, the reagent stoichiometry, and catalysis.
Dimeric Silver(I) Complexes of Some Isothiazole‐Based Ligands
Authors: Konrad Matthias , Meyer Franc , Büchner Michael , Heinze Katja , Zsolnai Laszlo
Published: July 2007

A series of isothiazole‐based potential ligands bearing substituents with additional donor sites in the 5‐position of the heterocycle was synthesized [3‐Me‐5‐R‐C3HNS; R = CHN(CH2)2py (1), CHNCH2py (2), CH2N(CH2CH2NEt2)2 (4), (CH2)2SMe (5)]. Upon reaction with AgO3SCF3 they formed complexes [(1)AgOSO2CF3]2 (6), [(2)AgOSO2CF3]2 (7), [(4)Ag]2+2(O3SCF−3)2 (8) and [(5)AgOSO2CF3]2 (9), respectively. 6, 8 and 9 were shown by X‐ray structural analyses to consist of dimeric units L2Ag2+2, either discrete (8), coordinated by terminal CF3SO−3 units (6). In 8 and 9 the isothiazole moiety is bonded to the metal center via the ring‐N. The coordination potential of the isothiazole heterocycle is discussed.
A Specific Route to Enantiomerically Pure Asymmetric (η6‐Arene)(η4‐1,5‐cyclooctadiene)Ru(0) Complexes
Authors: Heinemann Frank , Klodwig Ens , Knoch Falk , Wündisch Marion , Zenneck Ulrich
Published: July 2007

Chiral or achiral (arene)(COD)Ru complexes can be made by replacing the η6‐ligands of (η4‐1,5‐COD)(η6‐1,3,5‐cyclooctatriene)Ru (1) or (η4‐1,5‐COD)(η6‐naphthalene)Ru (2) by a suitable arene. This well known reaction has been extended to mono‐ and dibromoarenes and we report a novel route to substituted (arene)(COD)Ru species, utilizing (bromoarene)‐(COD)Ru as starting materials. These facilitate a rapid bromine‐lithium exchange reaction with nBuLi at low temperatures and the lithiated species react readily with alkyl chloroformates as electrophiles. By using chiral electrophiles [alkyl = (‐)‐menthyl] enantiomerically pure or diastereomeric complexes containing CO2R* groups are formed, depending on the symmetry of the original complex. A diastereomeric 1:1 mixture was separated by recrystallization. All (arene)‐(COD)Ru complexes tested so far are useful as catalysts for the hydrogenation of simple alkenes at room temperature.