The reaction of linear nitriles with transition metal ions M⁺ (M = Fe, Co, Ni) in the gas phase. Does the back-bonding ability of the metal ions govern the geometry of the RCN/M⁺ complexes and what is the effect on the oxidative addition of internal CH bonds?

Experimental evidence is presented that RCN/M⁺ complexes (M = Co, Ni) exhibit practically identical reactivities upon collisional activation in the gas phase, while the analogous RCN/Fe⁺ systems are distinct. Insertion of the (complexed) transition metal ion M⁺ into internal CH bonds of linear alkyl nitriles commences for the RCN/Fe⁺ system with C(8) while, for the RCN/Co⁺ and RCN/Ni⁺ species, a trajectory is operative by which insertion occurs already at C(7). This behaviour can be explained by the different bonding situation of the RCN/Fe⁺ versus RCN/M⁺ (M = Co, Ni) systems. In the former, the deviation from the linear C-C-N-Fe⁺ alignment is less pronounced than in the C-C-N-M⁺ system (M = Co, Ni) with the consequence that CH bonds of the methylene chain closer to the functional group add oxidatively to the metal ion for M = Co, Ni. Some analogies with the recently described metal-silylene system are discussed.