A η2-triflate (OTf) intermediate in the solution dynamics of PtMe3(OTf)·TMEDA: the ‘windscreen-wiper process’ revisited‡

Abstract

The reaction of tetrameric [PtMe₃(OTf)]₄ (OTf = triflate = CF₃SO₃^–) with TMEDA (N,N,N′,N′-tetramethylethylenediamine) gave the monomeric compound PtMe₃(OTf)·TMEDA in quantitative yield. The non-planar TMEDA ligand contains two different sorts of methyl groups in PtMe₃(OTf)·TMEDA, and thus offers a second and independent set of NMR parameters in addition to the commonly used signals of the Me₃Pt unit. The additional information derived from these NMR data provides detailed insight into the mechanistic picture of chelating phenomena at Pt^IV. At low temperature the twisting of the ethylene bridge of the TMEDA ligand can be observed; at room temperature an intramolecular two-step ligand exchange takes place. Evidence for an equilibrium involving a TMEDA chelate as well as a η²-O₃SCF₃ chelate has been found. Dependent on the applied temperature, two types of ligand exchange motions can be distinguished by dynamic NMR spectroscopy because of their different activation parameters. These motions have been identified as the two essential steps in the so-called ‘windscreen-wiper process’ that has been invoked for exchange phenomena in Me₃Pt complexes previously. Moreover, the data indicate the crucial role of a η²-triflate in this process in PtMe₃(OTf)·TMEDA.