Substitution reactions involving cyclometalated platinum(II) complexes: Kinetic investigations

Substitution reaction of the labile SMe2 ligand in the cyclometalated platinum(II) complexes of general formula [PtAr(ppy)(SMe2)], 1, in which ppy = deprotonated 2-phenylpyridyl and Ar = p-MeC6H4 or p-MeOC6H4, by several N or P donor reagents were studied; the N-donors, N, are pyridine (Py) and substituted pyridines, N = 4-MePy, Py, Py-d5, 2-MePy, 3-PhPy, 3,4-Me2Py, 4-tBuPy or 3-C(O)OMePy, and the P-donors, L, are phosphines or phosphites, L = P(OPh)3, P(O-iPr)3, PPh3, PPh2Me and L2 = Ph2PCH2PPh2, bis(diphenylphosphino)methane (dppm). The products were identified by multinuclear NMR studies as [PtAr(ppy)(N)], 2, or [PtAr(ppy)(L)], 3, respectively. Complexes 1 have a MLCT band in the visible region which was used to easily follow the kinetics of the ligand substitution reactions by UV–vis spectroscopy. Although the complexes 1 contain two cis Pt–C bonds, the substitution reactions followed a normal associative mechanism. The rates of reactions were depended on the concentration and the nature of the entering group. The ΔH‡/ΔS‡ compensation plot gave a straight line suggesting the operation of the same mechanism for all entering nucleophiles.