C–H reductive elimination during the reaction of cycloplatinated(ii) complexes with pyridine-2-thione: kinetic follow up

Abstract

Substitution reactions of the labile SMe₂ ligand in the cycloplatinated(II) complexes [PtR(ppy)(SMe₂)], 1, in which ppy = 2-phenylpyridinate and R = Me, 1a, or p-MeC₆H₄, 1b, by pyridine-2-thione, C₅H₅SN, were studied. When each of the complexes 1 was treated with 1 equiv. C₅H₅SN, existing as a mixture of thiol (N⁁SH) and thione (HN⁁S) tautomers, a mixture containing the S-bound thiol complex [PtR(ppy)(η¹-S-S⁁NH)] (R = Me, 2a, or R = p-MeC₆H₄, 2b) and the dimeric complex [Pt(ppy)(N⁁S)]₂, 3 (having two bridging deprotonated pyridine-2-thione (N⁁S) ligands), was observed along with free R–H. This mixture finally led to pure complex 3 after 3 days. Pure samples of the complexes 2a and 3 were obtained from the abovementioned 2a+3 mixture by using flash chromatography on silica gel. Kinetics of the reactions were investigated by UV-vis spectroscopy (complexes 1 have a MLCT band in the visible region which was used to easily follow the reactions) and ¹H NMR spectroscopy. On the basis of the results, a mechanism was proposed for the related reactions.