Syntheses and dynamic nuclear magnetic resonance studies of complexes of trimethylplatinum(IV) iodide with ditelluroether chelate ligands

Abstract

Trimethylplatinum(IV) iodide complexes with ditelluroether ligands, namely [PtlMe₃(L–L)][L–L = MeTe(CH₂)₃TeMe, PhTe(CH₂)₃TePh or o-C₆H₄(TeMe)₂] have been isolated as pure solids. ¹⁹⁵Pt-{¹H} and ¹²⁵Te-{¹H} NMR studies show that ambient-temperature solutions of the complexes with aliphatic ligand backbones consist predominantly of DL isomers. The complex [PtlMe₃{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 [PtlMe₃{PhTe(CH₂)₃TePh}] and [PtlMe₃{o-C₆H₄(TeMe)₂}]. Pyramidal tellurium inversion interconverts these isomeric species and precise rates of this process were measured at near-ambient temperatures by ¹⁹⁵Pt-{¹H} and ¹²⁵Te-{¹H} NMR two-dimensional exchange spectroscopy experiments, or by ¹H one-dimensional NMR bandshape analysis at above-ambient temperatures in the case of [PtlMe₃{o-C₆H₄(TeMe)₂}]. Tellurium pyramidal inversion-energy barriers [ΔG^‡(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 [PtlMe₃{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.