Iodomethane oxidatively substitutes trimethylphosphine in Ni(OC=O)(PMe3)3 (OC=O = 3-tert-butyl-5-methyl-2-oxobenzoyl (1) 3,5-di-tert-butyl-2-oxobenzoyl (2)) to afford the complexes mer-trans-Ni(Me)I(OC=O)(PMe3)2 (3 and 4, respectively). Both compounds undergo a regioselective C,C-coupling reaction in solution and in the crystal state, caused by thermal activation.