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.

Graphical abstractKinetics and mechanism of substitution reaction of the labile SMe2 ligand in the cyclometalated platinum(II) complexes of general formula [PtAr(ppy)(SMe2)] in which ppy = deprotonated 2-phenylpyridyl and Ar = p-MeC6H4 or p-MeOC6H4, by several N or P donor nucleophiles were studied.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We prepare new cyclometalated platinum(II) compounds. ► Addition of P or N donor ligands to Pt(II) complex proceed by SN2 mechanism. ► The rates of reactions depend on the concentration and the nature of the entering group.