Catalyzed homogeneous hydrosilation

A Review of Recent Progress in Catalyzed Homogeneous Hydrosilation 5... 

The cluster [Co2Ni(//3-CMe)Cp(CO)6] has been used to catalyze the homogeneous hydroformylation of 1-pentene to hexanal and 2-methylpentanal. Hydro-formylation of styrene was achieved under mild conditions with moderate to high branched-to-normal selectivity. This cluster could be recovered in high yield (>90%) after catalysis. It also catalyzes the hydrosilation of acetophenone. ... 

The addition of Si-H bonds to organic unsaturations such as olefins, acetylenes, and ketones is known as the hydrosilation reaction. A majority of the hydrosilation reactions are catalyzed by soluble transition-metal complexes and are known as homogeneous hydrosilation reactions [43]. Catalytic hydrosilation reactions are known to be very complex reactions. However, a few generalizations have been drawn about the mechanism of such reactions (Figure 15.4). Homogeneous olefin hydrosilation are presumed to start with an obligatory oxidative addition of the Si-H bond in a cis fashion to the catalytic metal [44]. This process is followed... 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Despite its few binary compounds, the element gives rise to many complexes. Table 1 indicates the diversity of complexes formed. Several low oxidation state complexes of the element are important homogeneous catalysts, particularly in the oligomerization, isomerization. Hydrogenation, Hydro-formylation, Hydroboration, or Hydrosilation of alkenes. lodorhodium complexes catalyze the industrial-scale carbony-lation of methanol to acetic acid. 

Homogeneous photoinitiated hydrosilation of acetophenone has been catalyzed by... 

This fundamentally sound model of the catalytic cycle continues to be widely accepted, but its simplistic picture cannot explain some common observations and the formation of certain products in hydrosilations catalyzed by several transition metals other than platinum. The most difficult to explain and accommodate via the Chalk-Harrod mechanism are formation of vinylsilanes, highly-colored solutions often associated with gray-black metal precipitation, and frequently an induction period before the catalytic cycle kicks off in earnest. The deeper question of whether the catalysis occurs homogeneously or on the surface of colloidal metal has been an additional mystery that has shrouded the catalysis, especially in light of the fact that... 

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