Cyclometallated platinum complexes with thienyl imines. X-ray crystal structure of [PtMe{3-(PhCH 2NCH)C 4H 2S}PPh 3

Abstract

The reaction of [Pt 2Me 4(μ-SMe 2) 2] with ligands 3-(Me 2NCH 2CH 2NCH)C 4H 3S ( 2a) and 3-(PhCH 2NCH)C 4H 3S ( 2b) produced cyclometallation at the α-position of the thiophene ring to give the platinum(II) complexes [PtMe{3-(Me 2NCH 2CH 2NCH)C 4H 2S}] ( 4a) and [PtMe{3-(PhCH 2NCH)C 4H 2S}SMe 2] ( 4b), containing [C,N,N′] or [C,N] ligands, respectively. The reaction of these compounds with triphenylphosphine produced [PtMe{3-(Me 2NCH 2CH 2NCH)C 4H 2S}PPh 3] ( 5a) and [PtMe{3-(PhCH 2NCH)C 4H 2S}PPh 3] ( 5b). Compound 5b was structurally characterized. Attempts to achieve the cyclometallation of the ligands 2-(Me 2NCH 2CH 2NCH)C 4H 3S ( 2c) and 2-(PhCH 2NCH)C 4H 3S ( 2d) were unsuccessful and only compounds [PtMe 2{2-(Me 2NCH 2CH 2NCH)C 4H 3S}] ( 3c) and [PtMe 2{2-(PhCH 2NCH)C 4H 3S}SMe 2] ( 3d), in which the imine behaves as a [N,N′] or [N]-donor ligand, respectively, could be obtained. The electrochemical properties of the compounds based on cyclic voltammetry or square-wave voltammetry were studied at various temperatures. Reversible one-electron reductions, assigned to ligand-centered processes, were observed at room temperature for 5b and at lower temperatures for 4a, 4b and 5a. The reversibility varies with the ligand trans to the thienyl moiety. The one-electron oxidations always occurred in an irreversible manner and were assigned to oxidation at the platinum center. Oxidative addition of methyl iodide to 4a yielded [PtMe 2I{3-(Me 2NCH 2CH 2NCH)C 4H 2S}] ( 6a), while the reactions of methyl iodide with 4b and 5b each gave mixtures of isomers, arising from oxidative addition with trans stereochemistry followed by isomerization of the resulting platinum(IV) compounds. The reaction of methyl iodide with compound 5a yielded a complex mixture of compounds.