Photocatalytic hydrosilylation of conjugated dienes with triethylsilane in the presence Cr(CO)(6)

Chromium carbonyl photocatalyzed hydrosilylation of 1,3-butadiene, trans-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 triethylsilane yields the cis-1,4-adducts, 1-(triethylsilyl)-2-butene derivatives, as the main products which have been isolated by distillation or preparative 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) intermediate. Experiments with D-SiEt(3) lead to the conclusion that reversible 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.