Metalloradical activations of aliphatic carbon-carbon bonds of nitriles: Scope and mechanism

The C(sp(3))-C(sp(3)) bonds of a series of alpha-alkylacetonitriles, 2-silylacetonitriles and 2-alkylbenzonitriles, have been activated by Rh(tmp) using Ph3P as the optimized promoter ligand at 130 degrees C. Selective aliphatic-aliphatic carbon-carbon bond activation (CCA) occurred for alpha-alkylacetonitriles and 2-alkylbenzonitriles without aromatic-aliphatic or aromatic-cyanide bond activation. Competitive activations of C-Si and C-C bonds were observed for 2-silylacetonitriles. The yields of Rh(tmp) alkyls were affected by bond energy and steric hindrance of the nitriles. Kinetic studies for the carbon-carbon bond activation (CCA) of (BuCN)-Bu-t at 130 degrees C revealed the rate law: rate = k'K-1[Rh(tmp)](m)[Ph3P](n) + k(3)K(2)(K-1[Ph3P])/(1 + K-1[Ph3P])[Rh(tmp)][(BuCN)-Bu-t]. The CCA is proposed to occur at the coordinated (BuCN)-Bu-t with Rh(tmp) in a 1:1 ratio in the transition state.