SYNTHESES AND DYNAMIC NUCLEAR-MAGNETIC-RESONANCE STUDIES OF COMPLEXES OF TRIMETHYLPLATINUM(IV) IODIDE WITH DITELLUROETHER CHELATE LIGANDS

Trimethylplatinum(iv) iodide complexes with ditelluroether ligands, namely [PtIMe3(L-L)] [L-L = MeTe(CH2)3TeMe, PhTe(CH2)3TePh or o-C6H4(TeMe)2] have been isolated as pure solids. Pt-195-{H-1} and Te-125-{H-1} NMR studies show that ambient-temperature solutions of the complexes with aliphatic ligand backbones consist predominantly of DL isomers. The complex [PtIMe3{MeTe(CH2)3TeMe}] also exists in significant amounts of both meso forms. In contrast, the meso-1 form is present in only very low abundance in [PtIMe3{PhTe(CH2)3TePh}] and [PtIMe3{o-C6H4(TeMe)2}]. Pyramidal tellurium inversion interconverts these isomeric species and precise rates of this process were measured at near-ambient temperatures by Pt-195-{H-1} and Te-125-{H-1} NMR two-dimensional exchange spectroscopy experiments, or by H-1 one-dimensional NMR bandshape analysis at above-ambient temperatures in the case of [PtIMe3{o-C6H4(TeMe)2}]. Tellurium pyramidal inversion-energy barriers [DELTA-G-double-ended-dagar (298.15 K)] were in the range 70-84 kJ mol-1, reflecting the nature of the the substituent at Te and the ligand backbone. Comparison of the tellurium inversion energy in [PtIMe3{MeTe(CH2)3TeMe}] with data for Se and S in analogous complexes of chalcogen ligands establishes the trend in inversion energies, namely Te > Se > S, on a firm quantitative basis.