A Mechanistic Investigation of the Carbon−Carbon Bond Cleavage of Aryl and Alkyl Cyanides Using a Cationic Rh(III) Silyl Complex

Cationic Rh(III) complex Cp(PMe(3))Rh(SiPh(3))(CH(2)Cl(2))BAr(4)' (1) activates the carbon-carbon bond of aryl and alkyl cyanides (R-CN, where R = Ph, (4-(CF(3))C(6)H(4)), (4-(OMe)C(6)H(4)), Me, (i)Pr, (t)Bu) to produce complexes of the general formula Cp*(PMe(3))Rh(R)(CNSiPh(3))BAr(4)'. With the exception of the (t)BuCN case, every reaction proceeds at room temperature (t(1/2) < 1 h for aryl cyanides, t(1/2) < 14 h for alkyl cyanides). A general mechanism is presented on the basis of (1) an X-ray crystal structure determination of an intermediate isolated from the reaction involving 4-methoxybenzonitrile and (2) kinetic studies performed on the C-C bond cleavage of para-substituted aryl cyanides. Initial formation of an eta(1)-nitrile species is observed, followed by conversion to an eta(2)-iminoacyl intermediate, which was observed to undergo migration of R (aryl or alkyl) to rhodium to form the product Cp*(PMe(3))Rh(R)(CNSiPh(3))BAr(4)'.