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 (tBu), adamantyl (Ad),
and mesityl (Mes), were prepared by reduction of FeBr2 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.