Halide Abstraction Competes with Oxidative Addition in the Reactions of Aryl Halides with [Ni(PMe Ph ) ].

Density functional theory (DFT) calculations have been used to study the oxidative addition of aryl halides to complexes of the type [Ni(PMe Ph ) ], revealing the crucial role of an open-shell singlet transition state for halide abstraction. The formation of Ni versus Ni has been rationalised through the study of three different pathways: (i) halide abstraction by [Ni(PMe Ph ) ], via an open-shell singlet transition state; (ii) S 2-type oxidative addition to [Ni(PMe Ph ) ], followed by phosphine dissociation; and (iii) oxidative addition to [Ni(PMe Ph ) ]. For the overall reaction between [Ni(PMe ) ], PhCl, and PhI, a microkinetic model was used to show that our results are consistent with the experimentally observed ratios of Ni and Ni when the PEt complex is used. Importantly, [Ni(PMe Ph ) ] complexes often have little, if any, role in oxidative addition reactions because they are relatively high in energy. The behaviour of [Ni(PR ) ] complexes in catalysis is therefore likely to differ considerably from those based on diphosphine ligands in which two coordinate Ni complexes are the key species undergoing oxidative addition.