C-CN Bond Activation of Benzonitrile with [Rh-1(dippe)]-

The complex [Rh(dippe)(mu-Cl)](2) (1) was reduced with potassium metal to produce the highly reactive Rh-1 species [Rh(dippe)(mu-K.THF)](2) (2). 2 was characterized by NMR spectroscopy (P-31, H-1) and IR spectroscopy after forming the derivative K[Rh(dippe)(CO)(2)] (2a). The C-CN bond of benzonitrile was cleaved by oxidative addition when it was reacted stoichiometrically with 2 to form the anionic Rh(I) complex K[Rh(dippe)(CN)(Ph)] (3). 3 has been characterized by NMR spectroscopy (P-31, H-1, C-13), and by the use of C-13-labeled benzonitrile. C-CN bond cleavage was also attempted by reacting benzonitrile with the zwitterionic complex [Rh(dippe)(eta(6)-Ph-BPh3)] (4). A product 5 was formed from reaction with 2 equiv of benzonitrile. Reaction with C-13-labeled benzonitrile has ruled out the possibility of C-CN cleavage in this species, and a C-H bond activation pathway is operative instead.