Cobalt(0) and Iron(0) Isocyanides as Catalysts for Alkene Hydrosilylation with Hydrosiloxanes

Iron and cobalt isocyanides, Fe(CNR)(5) (1) and CO2(CNR)(8) (2), where R = t-butyl (Bu-t), adamantyl (Ad), and mesityl (Mes), were prepared by reduction of FeBr(2 )or CoI2 in the presence of CNR by C8K or silica-Na. These complexes were subjected to catalytic hydrosilylation of alkenes with hydrosiloxanes, and the results are compared with those obtained by previously reported Fe(OPiv)(2)/CNAd or Co(OPiv)(2)/CNAd catalyst systems. Hydrosilylation of allylic ethers with 1,1,1,3,3-pentamethyldisiloxane (PMDS) catalyzed by 1 and the reaction of several alkenes with PMDS or 1,1,1,3,5,5,5-heptamethyltrisiloxane (MD'M) catalyzed by 2 exhibited greater catalytic activity than that observed for the Fe(OPiv)(2) or Co(OPiv)(2)/CNR catalyst system. Complexes 1 and 2 were effective for catalytic chemical modification of silicone fluids containing Si-H groups and for two-component silicone curing. In all cases, selectivity of the reaction in terms of formation of the desired product by hydrosilylation and of byproducts due to dehydrogenative silylation did not differ between the metal isocyanide complexes and the corresponding M(OPiv)2/CNR catalyst system. Catalytically active species generated from 1, 2, and the M(OPiv)(2)/CNR catalyst system were also investigated.