Silicon-carbon complexes

Organometallic Complexes with Silicon-Transition Metal or Silicon-Carbon-Transition Metal Bonds... 

ORGANOMETALLIC COMPLEXES WITH SILICON-CARBON-TRANSITION METAL BONDS... 

In addition to activation of sihcon bonds by fluoride ions as discussed in Section 2.4, silicon-silicon, silicon-carbon, silicon-hydrogen, and silicon-nitrogen bonds are activated by transition metal salts and transition metal complexes. Thus, hydrolysis of silicon-carbon bonds such as in phenyltrimethylsilane 81 can be induced by... 

Silenes with a wide range of structures have been synthesized over the years, from the simplest possible compound, H2Si=CH2, which has a transient existence, to species that contain four complex groups attached to the ends of the silicon-carbon double bond, e.g., (Me3Si)MesSi=C... 

The stable silene Me2Si=C(SiMe3(SiMe(r-Bu)2) was first reported as a stable complex with THF,34 and its crystal structure showed the length of the silicon-carbon double bond as 1.747 A. Subsequently, it was possible to remove the THF and isolate the uncomplexed silene, which had a noticeably shorter Si=C bond length of 1.702 A.29 Further investigation showed that stable complexes of this or closely related silenes with trimethyl- or ethyldimethylamine, pyridine, and fluoride ion were also readily formed and moderately stable.31141... 

Sakurai et al. have provided what is probably the most important mechanistic finding in the area of intermolecular additions of silenes in recent years, namely a detailed proposal for the mechanism of alcohol addition to the silicon-carbon double bond.68 A cyclic silene 116 was synthesized in the presence of various amounts of methanol and other alcohols, and varying proportions of methanol adducts 117 and 118 were obtained. It was concluded that the methanolysis involved two steps, the first being the association of the oxygen lone pairs with the sp 2-hybridized silicon atom of the silene. The second step, proton transfer, could occur in two ways. If the proton was transferred from the complexed methanol molecule (path a) its delivery would result in syn addition. However, if a second molecule of methanol participated (path b), it would deliver its proton... 

The silyl radicals formed in the initial scission appear to undergo further reactions, which may be complex. A possible secondary reaction is hydrogen transfer from an alpha carbon atom to give Si-H and a silicon carbon double bond (21)... 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

In 1982, Curtis and co-workers reported that Vaska s complex promotes the formation of phenylsiloxanes from the reaction of hydridosiloxanes and benzene in a catalytic, albeit low-yield, process.93 Catalytic arylsilane formation has also been reported by Tanaka and co-workers. Under photo-lytic conditions, RhCl(CO)(PMe3)2 catalyzes the C-H bond activation of arenes in reactions with hydrosilanes or disilanes, leading to the formation of new silicon-carbon bonds.94 More recently, C-H bond activation of arenes resulting in arylsilane formation has been observed in the... 

Pauling, in one of his last scientific contributions, pointed out that, based on the observed Si—C bond length, there is a covalent silicon-carbon (of the toluene) bonding in the triethylsilicenium-toluene complex 272. The bond number, n, is 0.35, according to equation 4,... 

No experimental evidence concerning compounds with silicon-carbon triple bonds is known, so that experimental efforts should be concentrated on the search for these fascinating species. 2-Silaallenes and 2-silaketenes, which also would contain a sp-hybridized silicon atom, could not be isolated up to now and remain a challenge of organosilicon chemistry (for 1-silaallene and for silylene-CO complexes cf Section VIII). 

Braunstein and coworkers have shown (vide supra) that in the bimetallic Fe—Pt complex (CO)3(SiR3)Fe(yU.-PPh2)Pt(PPh3)CO(Fe—Pt), a silyl migration occurred from the Fe to the Pt center (Scheme 17)102. Remarkably, the first example of a well-characterized insertion of a transition-metal fragment into a strained silicon-carbon bond of a silicon-bridged [l]ferrocenophane was recently reported by Sheridan, Lough and Manners. The... 

The reaction of methylenecyclopropanes with transition metal complexes is well known to promote a catalytic a-ir cycloaddition reaction with unsaturated compounds, in which a trimethylenemethane complex might exist71-76. Recently, much interest has been focused on the interaction of strained silicon-carbon bonds with transition metal complexes. In particular, the reaction of siliranes with acetylene in the presence of transition metal catalysts was extensively investigated by Seyferth s and Ishikawa s groups77-79. In the course of our studies on alkylidenesilirane, we found that palladium catalyzed reaction of Z-79 and E-79 with unsaturated compounds displayed ring expansion reaction modes that depend on the (Z) and (E) regiochemistry of 79 as well as the... 

The strained silicon-carbon bonds of silacyclobutanes are subject to activation by Pd and Pt complexes. This reactivity has been used for a catalytic carbon-carbon bond formation.294,295... 

A second possibility is that the ozone forms some kind of complex with the silane before attack on the hydrogen. From this complex, all hydrogens are equally accessible, and the decomposition is first order in complex. In the hope of observing such a complexation, the ultraviolet spectra of ozone/silane mixtures in carbon tetrachloride were examined (33). Although no spectral bands attributable to a silicon-ozone complex were found, it was observed that any silicon-containing species catalyzed the decomposition of ozone. That is, not only triethylsilane, but tri-ethylsilanol and tetramethylsilane as well, destroy ozone in carbon tetrachloride. This result indicates an association of the ozone with the silicon atom, regardless of the functionality of the silicon species (within the types examined) and completely independent of the silicon substrate s... 

Since silene is an unstable species, various transition metal-silene complexes coordinated by the silicon-carbon double bond have been reported. In 1970, Pannel reported the formation of silene by irradiation of an iron complex (Eq. 6) [8]. He obtained an iron-TMS complex that was apparently formed from silene and an iron-hydride complex generated from the starting iron complex by /3-hydrogen elimination [8]. Wrighton confirmed the existence of tungsten-and iron-silene complexes by examination of NMR spectra obtained at low temperature (Eqs. 7 and 8) [9]. 

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