Abstract New cyclometalated platinum(II) complexes [PtMe(C^N)L], 1, in which C^N = deprotonated 2-phenylpyridine (ppy), benzo[ h]quinoline (bhq) or 2-( p-tolyl)pyridine (tpy) and L = PPh 3 or PMePh 2, were synthesized by the reaction of [PtMe(C^N)(SMe 2)] with 1 equiv of L. The reaction of complexes 1 with MeI gave the cyclometalated Pt(IV) complexes [PtMe 2I(C^N)L], 3. On the basis of kinetic studies, using Uv–visible spectroscopy, it was suggested that the latter oxidative addition reactions were proceeded by an S N2 mechanism. The rates of the reactions at different temperatures were measured and consistent with the proposed mechanism, large negative Δ S ‡ values were found for each reaction. Besides, rate of reactions (in CHCl 3) involving the PPh 3 complexes [PtMe(C^N)(PPh 3)], were almost 3–5 times slower than those involving the PMePh 2 complexes [PtMe(C^N)(PMePh 2)]. This was attributed to the electronic and steric effects of PPh 3 ligand as compared with that of PMePh 2 ligand which was further confirmed using density functional theory (DFT) calculations through finding approximate structures for the described complexes.