Photo-and Peroxide-Initiated Catalysis by Metal Complexes

Supported platinum, rhodium, and ruthenium complex catalysts have been used extensively in the reaction of trisubstituted silanes with acetylene in the gas phase, predominantly in a continuous-flow apparatus. Formation of a polymer layer on the surface after immobilization of the platinum complex has protected the catalyst against leaching in long-term hydrosilylation tests [91]. 

4 Photo- and Peroxide-Initiated Catalysis by Metal Complexes 

Photogenerated catalysts, which are defined as those obtained by light-induced generation of a ground-state catalyst from a catalytically inactive precursor, have become a topic of current interest in catalysis by transition metal complexes (cf. Section 3.2.9). Such methods have also been applied in hydrosilylation. 

Cr(CO)6 is active in the 1,4-hydrosilylation of 1,3-dienes to yield allylsilanes using a method of synthetic utility [1 ]. Wrighton and co-workers have reported the high catalytic activity of Fe(CO)s upon UV irradiation under mild temperature conditions (0-50 °C) in the hydrosilylation of alkenes [13]. Ru, Os, and Ir are effective photocatalysts of the hydrosilylation of acetone, whereas Fe3(CO)i2, Co2(CO)s, and Co4(CO)i2 are known to be efficient photoactivated catalysts in the hydrosilylation of olefins. It has been also demonstrated that Ru(CO)4PPh3 and Ru(CO)3(PPh3)2 complexes can serve as catalysts for the photochemical hydrosilylation of benzaldehyde [2]. 

Molecular oxygen has become a commonly used co-catalyst for inactive or weakly active transition metal complexes [1-5]. In addition, other oxidizing agents, mainly peroxides, have recently been used in active rhodium complexes in particular, but also in metal carbonyls, as catalysts for hydrosilylation. The catalytic activity of bis(triphenylphosphine)carbonylrhodium(I) in the hydrosilylation of C=C and C=0 bonds can be much increased by the addition of about a 50 % molar excess of tert-butyl hydroperoxide [100]. Chromium triad carbonyls M(CO)e, where M = Cr, Mo, W, have been tested to examine the effect of various organic peroxides on the hydrosilylation of 2,3-dimethyl-1,3-butadiene by triethyl-, triethoxy- and methyldiethoxysilanes [100]. The evidence for organic oxidant promotion of RhCl(cod)phosphine-catalyzed hydrosilylation of 1-hexene was demonstrated previously [101]. 

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