C–CN Bond Activation of Benzonitrile with [Rh–I(dippe)]−

The complex [Rh(dippe)(μ-Cl)]2 (1) was reduced with potassium metal to produce the highly reactive Rh–I species [Rh(dippe)(μ-K·THF)]2 (2). 2 was characterized by NMR spectroscopy (31P, 1H) 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 (31P, 1H, 13C), and by the use of 13C-labeled benzonitrile. C–CN bond cleavage was also attempted by reacting benzonitrile with the zwitterionic complex [Rh(dippe)(η6-Ph-BPh3)] (4). A product 5 was formed from reaction with 2 equiv of benzonitrile. Reaction with 13C-labeled benzonitrile has ruled out the possibility of C–CN cleavage in this species, and a C–H bond activation pathway is operative instead.