High Selectivity in Csp2–Csp2 versus Csp3–O Reductive Elimination from Cycloplatinated(IV) Complexes

The cycloplatinated(IV) complexes trans-[Pt(p-MeC₆H₄)(C^∧N)(OAc)₂(H₂O)] (C^∧N = benzo[h]quinolate, bhq, 2a, and 2-phenylpyridinate, ppy, 2b) were prepared by reacting the corresponding [Pt(p-MeC₆H₄)(C^∧N)(SMe₂)] precursors with PhI(OAc)₂ through an oxidative addition (OA) reaction. Thermolysis of 2a at 65 °C generates cis-[Pt(κ¹N-10-(p-MeC₆H₄)-bhq)(OAc)₂(H₂O)], 3a, which is the product of a Csp²_Ar-Csp²_bhq reductive elimination (RE). The observed coupling reaction is significantly different from the previously reported analogous thermolysis of trans-[PtMe(C^∧N)(OAc)₂(H₂O)] (C^∧N = bhq, 2c, and ppy, 2d) that selectively releases Me-OAc (C-O RE). The density functional theory (DFT) calculations and experimental observations reveal that the Csp²_Ar-Csp²_bhq coupling reaction occurs through the dissociation of a coordinated water ligand. This in turn is followed by the concomitant bond forming and bond breaking process via a three-center ring transition state, in contrast to the Csp³_Me-OAc coupling, which had taken place by an outer sphere S_N2 type RE reaction in methyl complexes.