18178-59-1

Compounds having a vinyldimethylsilyl group at both terminals have been successfully cyclized by ruthenium hydride catalysts to give selectively disilacycles of various ring sizes via a metathetical reaction, i.e. ethene elimination from the two terminal vinyl groups, not involving metallocarbene-metallacyclobutane type intermediates.

Zinc complexes are described which find use in methods of selective hydrogenation of compounds which contain reducible double or triple bonds, such as the reduction of alkynes to alkenes. The zinc complexes have a general structure according to formula (I): (I) Methods of manufacturing such zinc complexes are also described.

Multidentate carbene ligands are valuable frameworks for the preparation of carbene complexes displaying higher nuclearity. In the present work, we report the synthesis of a series of mono- to tetra-[Rh(COD)I] complexes (3a- d) supported by mesoionic triazol-5-ylidenes. The general synthetic procedure involves the one step reaction of the appropriate triazolium (2a-d) salt in the presence of KHMDS and stoiquiometric amounts of the rhodium(I) precursor. Treatment of complexes 3a-d with an excess of carbon monoxide allows for the quantitative preparation of complexes 4a-d featuring a [Rh(CO)2I] fragment used for the detemination of the donor properties of the new triazolylidene ligands. All complexes have been fully characterized by means of 1H and 13C NMR spectroscopy, melting point, elemental analysis, and in the case of complex 3a, by X-ray crystallography. Comparison of the catalytic activity of the new rhodium complexes in C-C and C-Si bond forming processes demonstrate the enhanced performance of the tetranuclear species suggesting the possibility of strong cooperative effects in these multinuclear complexes.

1H NMR studies of reactions of titanocene [Cp?2Ti] (Cp? = η5-C5Me5) and its derivatives [Cp?(η5:η1-C5Me4CH2)TiMe] and [Cp?2Ti(η2-CH2CH2)] with excess dihydrogen at room temperature and pressures lower than 1 bar revealed the formation of dihydride [Cp?2TiH2] (1) and the concurrent liberation of either methane or ethane, depending on the organometallic reactant. The subsequent slow decay of 1 yielding [Cp?2TiH] (2) was mediated by titanocene formed in situ and controlled by hydrogen pressure. The crystalline products obtained by evaporating a hexane solution of fresh [Cp?2Ti] in the presence of hydrogen contained crystals having either two independent molecules of 1 in the asymmetric part of the unit cell or cocrystals consisting of 1 and [Cp?2Ti] in a 2:1 ratio. Hydrogenation of alkyne complexes [Cp?2Ti(η2-R1CCR2)] (R1 = R2 = Me or Et) performed at room temperature afforded alkanes R1CH2CH2R2, and after removing hydrogen, 2 was formed in quantitative yields. For alkyne complexes containing bulkier substituent(s) R1 = Me or Ph, R2 = SiMe3, and R1 = R2 = Ph or SiMe3, successful hydrogenation required the application of increased temperatures (70-80 °C) and prolonged reaction times, in particular for bis(trimethylsilyl)acetylene. Under these conditions, no transient 1 was detected during the formation of 2. The bulkier auxiliary ligands η5-C5Me4tBu and η5-C5Me4SiMe3 did not hinder the addition of dihydrogen to the corresponding titanocenes [(η5-C5Me4tBu)2Ti] and [(η5-C5Me4SiMe3)2Ti] yielding [(η5-C5Me4tBu)2TiH2] (3) and [(η5-C5Me4SiMe3)2TiH2] (4), respectively. In contrast to 1, the dihydride 4 did not decay with the formation of titanocene monohydride, but dissociated to titanocene upon dihydrogen removal. The monohydrides [(η5-C5Me4tBu)2TiH] (5) and [(η5-C5Me4SiMe3)2TiH] (6) were obtained by insertion of dihydrogen into the intramolecular titanium-methylene σ-bond in compounds [(η5-C5Me4tBu)(η5:η1-C5Me4CMe2CH2)Ti] and [(η5-C5Me4SiMe3)(η5:η1-C5Me4SiMe2CH2)Ti], respectively. The steric influence of the auxiliary ligands became clear from the nature of the products obtained by reacting 5 and 6 with butadiene. They appeared to be the exclusively σ-bonded η1-but-2-enyl titanocenes (7) and (8), instead of the common π-bonded derivatives formed for the sterically less congested titanocenes, including [Cp?2Ti(η3-(1-methylallyl))] (9). The molecular structure optimized by DFT for compound 1 acquired a distinctly lower total energy than the analogously optimized complex with a coordinated dihydrogen [Cp?2Ti(η2-H2)]. The stabilization energies of binding the hydride ligands to the bent titanocenes were estimated from counterpoise computations; they showed a decrease in the order 1 (-132.70 kJ mol-1), 3 (-121.11 kJ mol-1), and 4 (-112.35 kJ mol-1), in accordance with the more facile dihydrogen dissociation.

(E)-β-(Silyl)-α,β-unsaturated ketones have been efficiently synthesized via one-pot sequential ruthenium-catalyzed silylative homo-coupling of dimethylphenylvinylsilane or trimethylvinylsilane (Marciniec coupling) and rhodium-catalyzed selective desilylative acylation (Narasaka coupling) of (E)-1,2-bis(silyl)ethenes with acid anhydrides. Synthetic strategy relies on the selective mono-substitution of the bis(silyl)ethene intermediate.

Herein, the iron-catalyzed reduction of a variety of alkynes with silanes as a reductant has been examined. With a straightforward catalyst system composed of diiron nonacarbonyl and tributyl phosphane, excellent yields and chemoselectivities (>99 %) were obtained for the formation of the corresponding alkenes. After studying the reaction conditions, and the scope and limitations of the reaction, several attempts were undertaken to shed light on the reaction mechanism. Im Rahmen dieser Arbeit wird die Eisen-katalysierte Reduktion von Alkinen zu den entsprechenden Alkenen mit Hilfe von Silanen vorgestellt. Hierbei konnten exzellente Ausbeuten und Selektivitaeten (>99 %) durch die Modifikation des eingesetzten Eisenkatalysators mit Phosphanen beobachtet werden. Nach genauer Untersuchung verschiedenster Reaktionsparameter wurden die hervorragenden Eigenschaften des Katalysatorsystems in der Reduktion zahlreicher Alkine gezeigt. Zum besseren Verstaendnis der Reaktion wurden verschiedene mechanistische Experimente durchgefuehrt. Iron Made′m: In situ generated iron complexes catalyze the reduction of alkynes with silanes as a hydride source with excellent selectivity (>99 %). Copyright

Early metal gets the H: Under 1 atm of H2, the vanadium complex 1 (PFTB=perfluoro-tert-butoxide) catalytically semihydrogenates alkynes to Z alkenes. Synthetic and DFT studies, in combination with H2/D 2 and NMR experiments, indicate that H2 is activated by 1,2-addition to 1. Upon insertion of an alkyne into the V-H bond of A, the product alkene and 1 are generated by the 1,2-α-NH-elimination of the alkenyl ligand.

A new ruthenium complex-catalyzed O-silylation of silanols with vinylsilanes leading to siloxane bond formation with the evolution of ethylene is described. A maximum conversion of silanol is reached using an excess of vinylsilane to also yield the product of the homo-coupling of the latter. Under the optimum conditions, when vinylsilane with at least one ethoxy substituent is used, the reaction gives exclusively unsymmetrical siloxanes.

(Diiodomethyl)trimethylsilane (Me3SiCHI2, 1) is produced by treatment of iodoform with manganese in the presence of Me 3SiCl. Aldehydes are converted to (E)-1-trimethylsilyl-1-alkenes in a stereoselective manner with a geminal dichromium reagent generated from 1, manganese, Me3SiCl, and a catalytic amount of CrCl 3[thf]3 in THF. Similarly, (E)-1-alkenylboronic esters are prepared stereoselectively in good to excellent yields by treatment of aldehydes with a geminal dichromium reagent derived from Cl2CHB(OR) 2 [(OR)2 = OCMe2CMe2O] and LiI instead of 1.

The first cross-coupling reaction of thermally stable titanium(II)-alkyne complexes with aryl iodides in the presence of a catalytic amount of Ni(cod)2 is presented.

A catalytic amount of [RuCl(η5-C5H5)(PPh3)2] (1) (0.1 mol- percent) at 60 deg C stereoselectively decomposes α-diazo carbonyl compounds N2CHCOR [R=EtO, Me, Et, nPr, iPr, Ph, (CH2)10Me, and (CH2)14Me] affording quantitatively RCOCH=CHCOR carbene dimers [R=EtO (10), Me (11), Et (12), nPr (13), iPr (14), Ph (15), (CH2)10Me (16), and (CH2)14Me (17)]. The cis isomer is formed in 95-99 percent purity, depending on the R group. Under the same experimental conditions, N2CHCOR1 and N2CHCOR2 react in equimolar amounts to give mixtures of unsymmetrical cis-R1COCH=CHCOR2 (18-32), and symmetrical cis-R1COCH=CHCOR1 and cis-R2COCH=CHCOR2 alkenes. The unsymmetrical cis-alkenes 23-32 are formed in about 50 percent yield from the reaction between two α-diazo ketones. The yield of the cis-R1COCH=CHCOR2 compounds 18-22 increases to ca. 60 percent when a mixture of α-diazo ketone and N2CHCOOEt is catalytically decomposed. Higher conversions into the unsymmetrical products have been obtained by treating N2CHCOR and N2CHSiMe3, from which cis-RCOCH=CHSiMe3 derivatives 34-41 are formed in 83-91 percent yield. The catalytic decomposition of α,ω-bis(diazo) ketones N2CHCO(CH2)nCOCHN2 (n=4, 8, or 10) has also been investigated, and found to afford cyclic cis-alkenes arising from both intra- [n=4 (45), 8 (46), and 10 (47)] and intermolecular carbene-carbene coupling processes.

The reversible insertion of the vinylsilane molecule into the Ru-Si bond occurs in two different ways to give E-1,2-bis(silyl)ethene and 1,1-bis(silyl)ethene which, in combination with the previous experiments by Wakatsuki et al., provides convincing evidence for a non-metallacarbene mechanism of silylalkene disproportionation.

Self metathesis of vinyltrimethylsilane in the presence of an oxygenated benzene solution of RuCl2(PPh3)3 and RuH2(PPh3)4 follows an unusual course and yields two products, 1,2-bis(silyl)ethene (E) and 1,1-bis(silyl)ethene, with products of dimerization, namely 1,4-bis(silyl)butenes-2 (E + Z) and butenylsilanes as well as hexamethyldisiloxane.Gaseous ethylene and traces of ethane were also detected.It is proposed that vinylsilane is inserted into the Ru-Si bond (via ortho-metallation of the ruthenium triphenylphosphine complex) in competition with pathways involving metal-carbene species.Complexes of ruthenium containing no phenylphosphine give stereoselectively only the (E)-product of metathesis (even in the absence of oxygen and hydrosilane co-catalysts) accompanied by traces of the same by-products. Key words: Silicon; Ruthenium; Metathesis; Olefin

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