Hydrosilylation photocatalytic

Nickel catalysts exhibit similar activity but are usually less selective than palladium 435-438 In addition to chlorosilanes, however, alkylsilanes also add in the presence of nickel catalysts. Nickel vapor showed an exceptionally high activity and selectivity in hydrosilylation.435 The photocatalytic hydrosilylation of 1,3-dienes with a chromium(O) complex occurs at room temperature to afford regioisomeric 1,4-adducts in quantitative yield.439... 

Of special significance are the catalytic properties of small metal clusters. At their surface such clusters have a large number of atoms with a low coordination number to which substrates bind. Catalytic reactions are being studied in hydrogenation, hydrosilylation, hydration, and the Heck reaction. Metal clusters are also of importance with regard to redox and electron transfer processes such as the photochemical decomposition of water (fuel cells) and photocatalytic hydrogenation. 

The proposed intermediacy of [Fe(CO)3], coupled with the high quantum efficiency observed with most mononuclear metal carbonyl complexes [54], inspired Schroeder and Wrighton to study photocatalytic olefin isomerization, hydrogenation and hydrosilylation reactions with Fe(CO)s [55], Irradiation of Fe(CO)s with near ultraviolet (Amax = 366nm) lightin the presence of excess 1-pentene furnished the thermodynamic mixture of cis and trons-2-pentene over the course of 2 h. From photolysis studies in neat olefin, it was estimated that each iron center produced... 

It is now accepted that alkene hydrosilylation catalyzed by several systems occur by the modified Chalk-Harrod medTanism. Wrighton s studies on tlie insertion of ethylene into the M-Si bond of (CO) CoSiMe3 led to die conclusion that this photocatalytic process occurs by the mechanism in Scheme 16.8. Conversion of the p-silylalkyl product of insertion to the free organosilane is thought to occur by a sequence of oxidative addition of silane... 

The catalytic uses of colloidal metals which will be described are found in a relatively small but important group of chemical reactions. These include hydrogenation, hydrosilylation, and hydration reactions of unsaturated organic molecules, as well as redox and other electron transfer processes such as the photochemical splitting of water and photocatalytic hydrogenations. 

The high catalytic activity of [Fe(CO)s] upon UV irradiation under mild temperature conditions (0-50° C) in the hydrosilylation of alkenes has been reported. The truly photocatalytic nature of the reactions is demonstrated by the quantum yields, which exceed unity, and by the strong influence of temperature on the photocatalysis. 

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