A dynamic nuclear magnetic resonance study of trimethylplatinum(IV) halide complexes of 1,1,2,2-tetrakis(methylthio)ethane. Part 1. Low-temperature solution properties, and X-ray crystal structure of [PtlMe3{(MeS)2CHCH(SMe)2}]

Abstract

Trimethylplatinum(IV) halides [(PtXMe₃)₄] react with equimolar amounts of the ligand (MeS)₂CHCH(SMe)₂(L) to give chelate complexes of type [PtXMe₃L] as major products and dinuclear complexes [(PtXMe₃)₂L] as minor components. The chelate complexes in CDCl₃ solution exist as cis and trans configurational isomers, with the trans predominating. At temperatures below ca.–30 °C, pyramidal inversion of the co-ordinated S atoms is slow on the ¹H and ¹⁹⁵Pt time-scales and six invertomer species (viz. trans/DL-1,2,3, and 4 and cis-1 /meso-1 and DL) have been detected, identified, and characterised by ¹H and ¹⁹⁵Pt n.m.r. spectroscopy. The pyramidal inversion rates and energies of the co-ordinated S atom pairs in all six invertomers have been quantitatively measured by a combination of ¹H bandshape analysis and ¹⁹⁵Pt two-dimensional EXSY experiments. The resulting ΔG^‡(298.15 K) values lie in the range 54–65 kJmol^–1 and are governed primarily by the orientation of the contiguous unco-ordinated S-methyl group. The X-ray crystal structure of [PtlMe₃{(MeS)₂CHCH(SMe)₂}] depicts the ligand with its co-ordinated S-methyls trans to each other and trans to their contiguous unco-ordinated S-methyls. This structure corresponds to the most populous CDCl₃solution invertomer (trans/DL-2).