Cyclometallated platinum complexes with thienyl imines.: X-ray crystal structure of [PtMe{3-(PhCH2NCH)C4H2S}PPh3]

The reaction of [Pt2Me4(mu-SMe2)(2)] with ligands 3-(Me2NCH2CH2NCH)C4H3S (2a) and 3-(PhCH2NCH)C4H3S (2b) produced cyclometallation at the alpha-position of the thiophene ring to give the platinum(II) complexes [PtMe{3-(Me2NCH2CH2NCH)C4H2S}] (4a) and [PtMe{3-(PhCH2NCH)C4H2S}SMe2] (4b), containing [C,N,N'] or [C,N] ligands, respectively. The reaction of these compounds with triphenylphosphine produced [PtMe{3-(Me2NCH2CH2NCH)C4H2S}PPh3] (5a) and [PtMe{3-(PhCH2NCH)C4H2S}PPh3] (5b). Compound 5b was structurally characterized. Attempts to achieve the cyclometallation of the ligands 2-(Me2NCH2CH2NCH)C4H3S (2c) and 2-(PhCH2NCH)C4H3S (2d) were unsuccessful and only compounds [PtMe2{2-(Me2NCH2CH2NCH)C4H3S}] (3c) and [PtMe2{2-(PhCH2NCH)C4H3S}SMe2] (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 [PtMe2I{3-(Me2NCH2CH2NCH)C4H2S}] (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. (C) 2000 Elsevier Science S.A. All rights reserved.