PHOTOCATALYTIC HYDROSILYLATION OF CONJUGATED DIENES WITH TRIETHYLSILANE IN THE PRESENCE CR(CO)(6)

Chromium carbonyl photocatalyzed hydrosilylation of 1,3-butadiene, tra ns-1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-butadiene, trans-2-methyl-1,3-pentadiene, and 1,3-cyclohexadiene with triethylsi lane yields the cis-1,4-adducts, 1-(triethylsilyl)-2-butene derivative s, as the main products which have been isolated by distillation or pr eparative GC and fully characterized by NMR spectroscopy. The proposed mechanism involves the initial conversion of Cr(CO)(6) into Cr(CO)(4) (eta(4)-1,3-diene) followed by a further photolytic CO substitution by triethylsilane forming a Cr(CO)(3)(H)(SiEt(3))(eta(4)-1,3-diene) inte rmediate. Experiments with D-SiEt(3) lead to the conclusion that rever sible addition of the hydride to the diene with formation of an eta(3) -enyl intermediate occurs prior to the irreversible silyl transfer to the organic moiety. The 1,4-hydrosilylation adduct is then replaced by new substrates to complete the catalytic cycle.