Alkene hydrosilation catalysis

Ammonia N-donor Ligands Asymmetric Synthesis by Homogeneous Catalysis Decarbonylation Catalysis Hydride Complexes of the Transition Metals Hydroboration Catalysis Hydrogenation Isomerization of Alkenes Hydrosilation Catalysis P-donor Ligands Rhodium Organometallic Chemistry. 

Other substituent groups are usually introduced via Hydrosilation reactions. In this important reaction, Si-H bonds add across C=C or C=C bonds in 1,2 fashion to give products. Many transition metals and their complexes will catalyze hydrosilation, but the usual catalyst is platinum see Hydrosilation Catalysis). Thus CF3CH2CH2Si(Me)Cl2 is made by hydrosilation of 3,3,3-triflu oropropene with methyldichlorosilane (equation 12). n-Alkylmethyldichlorosilanes can be made similarly, by hydrosilation of 1-alkenes. Vinylmethyldichlorosilane maybe obtained in analogous fashion by hydrosilation of acetylene, as shown in equation (13). An alternate route to the same compound is hydrosilation of vinyl chloride, followed by dehydrochlorination (equations 14 and 15). 

Platinum(O) phosphine complexes undergo a variety of oxidative addition reactions with compounds containing Group 14 elements. These reactions are of widespread interest because similar processes are probably involved in the catalysis by platinum complexes of reactions such as the hydrosilation of alkenes and the disilylation of dienes and alkenes. 

The range of reactions which have been examined is wide (248) and includes hydrogenations (256), ammonia synthesis (257), polymerizations (257), and oxidations (258). Little activity has occurred in this area during the past few years. Recent reports of the effects of sonication on heterogeneous catalysis include the liquefaction of coal by hydrogenation with Cu/Zn (259), the hydrogenation of olefins by formic acid with Pd on carbon (260), and the hydrosilation of 1-alkenes by Pt on carbon (261). 

Transition metals have already established a prominent role in synthetic silicon chemistry [1 - 5]. This is well illustrated by the Direct Process, which is a copper-mediated combination of elemental silicon and methyl chloride to produce methylchlorosilanes, and primarily dimethyldichlorosilane. This process is practiced on a large, worldwide scale, and is the basis for the silicones industry [6]. Other transition metal-catalyzed reactions that have proven to be synthetically usefiil include hydrosilation [7], silane alcdiolysis [8], and additions of Si-Si bonds to alkenes [9]. However, transition metal catalysis still holds considerable promise for enabling the production of new silicon-based compounds and materials. For example, transition metal-based catalysts may promote the direct conversion of elemental silicon to organosilanes via reactions with organic compounds such as ethers. In addition, they may play a strong role in the future... 

The silicon hydrides do not spontaneously add to alkenes either. However, the hydrosilation, or hydrosilylation reaction, of olefins is of significant utility in the preparation of alkyl-subtituted silanes with the use of either radical or transition metal catalysis. The preferred metal catalysts for hydrosilation are platinum complexes. Chloro-platinic acid will catalyze hydrosilations with halosilanes, alkylarylhalosilanes, alkoxy-silanes, and siloxanes that in many cases are quantitative under ambient conditions. Yields and conversions are generally poorer for alkyl,- and arylsilanes. Many other coordination complexes have been found to catalyze the hydrosilation reaction, and these can provide certain advantages, particularly in regiochemistry. Some typical hydrosilation reactions are shown in Table... 

Unlike hydrosilation discussed in the preceding subsection, which requires catalysis in essentially all cases, hydrostannation can be observed typically at or above 50 °C under thermal conditions. Under such conditions, however, the reaction tends to be capricious and unpredictable. Thus, for example, the reaction of terminal alkynes with HSnMes, HSnBus, and other triorganylstannanes tends to produce mixtures of a-, cis-f -, and trans-j8-stannyl-substimted alkenes except for some special cases, such as those shown in Scheme 19.W7H49]... 

Photolysis of dinuclear complexes such as Co2(CO)g and Mn2(CO)io can in principle lead to 17 electron metal radicals which can participate in further catalysis with silanes. Such species might be anticipated to act in one of two ways. Abstraction of a hydrogen from a H-Si bond in a manner which might favor radical chain reaction catalysis of hydrosilation and might be attractive given the lower homolytic dissociation energy of Si-H bonds (relative to H-H). Alternatively, the highly labile 17 e species provide routes for active substitution of alkene substrates and or silanes into the coordination sphere. 

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