High Selectivity in Csp 2 -Csp 2 versus Csp 3 -O Reductive Elimination from Cycloplatinated(IV) Complexes.

The cycloplatinated(IV) complexes trans -[Pt( p -MeC 6 H 4 )(C ∧ N)(OAc) 2 (H 2 O)] (C ∧ N = benzo[h]quinolate, bhq, 2a , and 2-phenylpyridinate, ppy, 2b ) were prepared by reacting the corresponding [Pt( p -MeC 6 H 4 )(C ∧ N)(SMe 2 )] precursors with PhI(OAc) 2 through an oxidative addition (OA) reaction. Thermolysis of 2a at 65 °C generates cis -[Pt(κ 1 N-10-( p -MeC 6 H 4 )-bhq)(OAc) 2 (H 2 O)], 3a , which is the product of a Csp 2 Ar -Csp 2 bhq reductive elimination (RE). The observed coupling reaction is significantly different from the previously reported analogous thermolysis of trans -[PtMe(C ∧ N)(OAc) 2 (H 2 O)] (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 Csp 2 Ar -Csp 2 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 Csp 3 Me -OAc coupling, which had taken place by an outer sphere S N 2 type RE reaction in methyl complexes.