Binuclear intermediates in oxidation reactions: [(Me3SiCC)Me2(bipy)Pt-PtMe2(bipy)]+ in the oxidation of PtMe2(bipy) (bipy = 2,2'-bipyridine) by IPh(CCSiMe3)(OTf) (OTf = triflate)

Abstract

A study of the reaction of dimethyl(2,2'-bipyridine)platinum(II)) with phenyl(trimethylsilylalkynyl)iodonium triflate at low temperature in acetone, leading to detection of the Pt-Pt bonded cation [Pt2Me4(CCSiMe3)(bipy)2]+, an intermediate in the oxidation of platinum(II) to platinum(IV). The cation is assessed as Pt(III)-Pt(III) = Pt(IV)-Pt(II), and at the second extreme may be regarded as a cationic alkynylplatinum(IV) centre [PtMe2(CCSiMe3)(bipy)]+ stabilised by PtMe2(bipy as a donor ligand. The Pt-Pt interaction in is not supported by bridging groups, unlike all previously reported organoplatinum dimers with (average) formal oxidation state +III for platinum. NMR data are consistent with a significant Pt(IV)-Pt(II) influence for octahedral and square pyramidal Pt, respectively. The detection and isolation of the cation provides a number of insights into the mechanism of oxidation reactions. Two pi-stacked PtMe2(bipy) units may be involved in the initial oxidation step to enhance the nucleophilic character of Pt(II). Dimeric species similar to the cation may be formed as, to date undetected, intermediates in other reactions, including for other ligands, d8 metal systems and oxidants.