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*(PMe3)Rh(SiPh3)(CH2Cl2)]BAr4' (1) activates the carbon-carbon bond of aryl and alkyl cyanides (R-CN, where R = Ph, (4-(CF3)C6H4), (4-(OMOC6H4), Me, Pr-i, Bu-t) to produce complexes of the general formula [Cp*(PMe3)Rh(R)(CNSiPh3)]BAr4'. With the exception of the (BuCN)-Bu-t 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 n(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*(PMe3)Rh(R)(CNSiPh3)]BAr4'.