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

Unusual
cis-oxidative addition of methyltrioxorhenium (MTO) to [PtMe2(bpy)], (bpy = 2,2′-bipyridine) (1) is described.
Addition of MTO to 1 first gives the Lewis acid–base
adduct [(bpy)­Me2Pt–Re­(Me)­(O)3] (2) and subsequently affords the oxidative addition product
[(bpy)­Me3PtReO3] (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 13C 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)­Me3PtOReO3] (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.