Mechanism of Me–Re Bond Addition to Platinum(II) and Dioxygen Activation by the Resulting Pt–Re Bimetallic Center

Abstract

Unusual cis-oxidative addition of methyltrioxorhenium (MTO) to [PtMe 2 (bpy)], (bpy = 2,2′-bipyridine) ( 1 ) is described. Addition of MTO to 1 first gives the Lewis acid–base adduct [(bpy)Me 2 Pt–Re(Me)(O) 3 ] ( 2 ) and subsequently affords the oxidative addition product [(bpy)Me 3 PtReO 3 ] ( 3 ). All complexes 1, MTO, 2, and 3 are in equilibrium in solution. The structure of 2 was confirmed by X-ray crystallography, and its dissociation constant in solution is 0.87 M. The structure of 3 was confirmed by extended X-ray absorption fine structure and X-ray absorption near-edge structure in tandem with one- and two-dimensional NMR spectroscopy augmented by deuterium and 13 C isotope-labeling studies. Kinetics of formation of compound 3 revealed saturation kinetics dependence on [MTO] and first-order in [Pt], complying with prior equilibrium formation of 2 with oxidative addition of Me–Re being the rate-determining step. Exposure of 3 to molecular oxygen or air resulted in the insertion of an oxygen atom into the platinum–rhenium bond forming [(bpy)Me 3 PtOReO 3 ] ( 4 ) as final product. Density functional theory analysis on oxygen insertion pathways leading to complex 4, merited on the basis of Russell oxidation pathway, revealed the involvement of rhenium peroxo species.