Mechanistic Studies of Si−CN and C−NC Bond Activation of Silylnitriles and Alkyl Isonitriles by Rhodium Porphyrin Radical: Novel Cyanide Transfer

The Si−CN and C−NC bonds of silylnitriles and alkyl isonitriles were activated by (tetramesitylporphyrinato)rhodium(II), Rh(tmp), to give rhodium porphyrin silyls or alkyls and rhodium porphyrin cyanide,
respectively. Pyridine and triphenylphosphine promoted the rates and yields of the reactions with
silylnitriles, but inhibited the rates and yields of the reactions with isonitriles. The reaction of Rh(tmp)
with Me3SiCN exhibited second-order kinetics (rate = kobs[Rh(tmp)][Me3SiCN]) at a sufficiently high
concentration of pyridine. The reaction with BuNC showed fourth-order kinetics, second-order in each
of the reactants; rate = kobs[Rh(tmp)]2[BuNC]2. A novel cyanide transfer rate-determining step was proposed
to account for the reaction mechanism.