N-methylation versus oxidative addition using MeI in the reaction of organoplatinum( II) complexes containing pyrazine ligand

The new cyclometalated platinum(II) complexes [PtMe((CN)-N-boolean AND)(pyrazine)] [(CN)-N-boolean AND = benzo[h] quinolate (bhq), 1a; (CN)-N-boolean AND = 2-phenylpyridinate (ppy), 1c] have been prepared by the reaction of corresponding dimethylsulfide complexes with pyrazine. These complexes contain two potential nucleophilic centers, Pt(II) center and free N atom of pyrazine which can compete in the reaction with methyl iodide to give Pt(IV) oxidative addition or N-methylation products, respectively. To investigate which center is more reactive toward MeI, DFT calculations (based on the free energy barrier needed for N-methylation versus oxidative addition reactions) and experimental evidence is considered to predict and explain site selectivity. Both experimental and theoretical studies show that the oxidative addition of MeI to cyclometalated Pt(II) complexes occurs readily to give the Pt(IV) complexes. Theoretical results support remarkably the kinetic results obtained through UV-Vis spectroscopy which suggest an S(N)2 mechanism. (C) 2018 Elsevier B.V. All rights reserved.