Organosilicon compounds reaction with transition metals

The strained-ring compound 1,1-dimethyl-l-silacyclobutane (which may be regarded as an olefin of organosilicon chemistry) reacts with diiron nonacarbonyl in benzene at 6°-20°C as shown in Eq. (100) (89). (There is here some analogy with the reactions of transition metal complexes with strained hydrocarbons, which often produce valence tautomerization.) The... 

Organosilicon compounds are widely used in our daily life as oil, grease, rubbers, cosmetics, medicinal chemicals, etc. However, these compounds are not naturally occurring substances but artificially produced ones (for reviews of organosilicon chemistry, see [59-64]). Hydrosilylation reactions catalyzed by a transition-metal catalyst are one of the most powerful tools for the synthesis of organosilicon compounds. Reaction of an unsaturated C-C bond such as alkynes or alkenes with hydrosilane affords a vinyl- or alkylsilane, respectively (Scheme 16). 

Although for the catalytic transformations of organosilicon compounds only hydrosilylation is well known as industrially important process, in the last 20 years other reactions of silicon compounds catalyzed by transition metal complexes have been discovered and developed. They include double (bis)silylation of alkenes and alkynes, silylative coupling of alkenes and alkynes with vinylsi-lanes, dehydrocoupling of hydrosilanes, silylformylation and silylcarbonylation of unsaturated compounds, and dehydrogenative silylation of alkenes and alkynes with hydrosilanes. Only the latter, as related to hydrosilylation (and very often its side reaction), has been discussed here (13). 

Very few such compounds are known. Three general procedures can be used for their preparation (a) addition of the olefin to a transition metal compound (b) replacement of carbon monoxide in metal carbonyls and (c) migration of organosilicon groups from metal to ligand in some reactions of silylmetal compounds with acetylenes. 

Silicon compounds with coordination number larger than four are the object of many studies first with respect to their application as catalysts in organic and inorganic syntheses and second as starting materials for the preparation of a broad variety of organosilicon compounds [1]. Additionally, hypervalent silicon hydride compounds can successfully be used as model compounds to study, for instance, the mechanism of nucleophilic substitution reactions, which is of great interest since the silicon atom is able to easily extend its coordination number [1]. Moreover, hypervalent silanes are suitable as starting materials for the synthesis and stabilization of low-valent silanediyl transition metal complexes [2-5]. 

Transition-metal catalyzed metathesis of carbon-halogen bonds with Si-Si bonds provides useful access to organosilicon compounds. Most of the reaction may involve initial oxidative addition of the carbon-halogen bond onto the transition-metal followed by activation of the Si-Si bond to give (organosilyl)(orga-no)palladium(II) complex, which undergoes reductive elimination of the carbon-silicon bond. 

The chemistry of organosilicon compounds has expanded with the use of transition metals. Both catalytic processes (179) and the chemistry of silicon transition metal compounds (180) have been developed. Catalytic reactions of organosilanes and more recently, reactions of silyl-transition metal complexes have already found interesting applications in organic synthesis (80,181,182). 

A number of transition-metal-mediated reactions involving addition of an alkyne to an organosilicon compound may involve an alkyne insertion step (Section III.A and Section VI.E.4). One example, for which alternative mechanisms are possible, is shown in equation 80224. Nickel silyl derivatives (bipy)Ni(SiX3)2 (SiX3 = SiCl3, SiMeCl2) react with... 

Organosilicon compounds are largely produced by the hydrosilylation of unsaturated organic substrates [47]. Various transition metal catalysts have been used to obtain alkyl-SiR products from the reaction of H-SiRj with an alkene. Alkene insertion into an M-Si bond is recognized as a fairly common process which plays a key role in catalytic hydrosilylation processes. The reaction of 1,3-butadiene (3-6) with triethylsilane in the presence of [Cr(CO)g] under photochemical condition yields exclusively the ds-1,4-adduct, ds-l-(triethylsilyl)-2-butene (7) (Scheme 10.7) [48]. In all cases, 1-4 addition products form in major, however, in some cases 1-2 addition product (9) also forms in minor yield. Formation of product 12 can be rationalized in terms of double bond migration subsequent to the initial hydrosilylation (Scheme 10.7). 

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