EFFECTS OF CHLORINE SUBSTITUENTS UPON THE FORMATION, REACTIVITY AND ELECTROCHEMICAL PROPERTIES OF PLATINUM(II) AND PLATINUM(IV) METALLACYCLES

The reactions of [Pt2Me4(mu-SMe2)(2)] (1) with chlorinated ligands Me2 NCH2CH2N=CHAr (Ar = C6Cl5 (2a); 2,3,6-C6H2Cl3 (2b); 2,3,5-C6H2Cl3 (2c) ; 2,4-C6H3Cl2 (2d); 3,5-C6H3Cl2 (2e) and 3-C6H4Cl (2f)) yield either c yclometallated [C,N,N'] platinum(IV) complexes [PtMe2Cl(Me2NCH2CH2N=CH R-C,N,N')], arising from C-Cl bond activation, or cyclometallated [C,N ,N'] platinum(II) complexes [PtMe(Me2NCH2CH2N=CHR-C,N,N')], arising fr om C-H bond activation, followed by methane elimination. These process es occur at room temperature except for the formation of compound [PtM e{Me2NCH2CH2N=CH(3,5-C6H2Cl2)}] (4e) which is produced in refluxing to luene, since at room temperature cyclometallation of ligand 2e is not achieved. Compound [PtMe2 {Me2NCH2CH2N=CH(3,5-C6H3Cl2)-N,N')}] (3e), a rising from coordination of the ligand to the platinum center, is obta ined at room temperature. The reactions of 1 with ligands PhCH2N=CHAr (Ar = 2,3,6-C6H2Cl3 (2g) and 2,3,5-C6H2Cl3 (2h)) produce cyclometallat ed [C,NJ platinum(IV) complexes. The reactivities of the platinum comp lexes towards phosphines and methyl iodide have been studied. All comp lexes have been characterized by NMR spectroscopy and the X-ray crysta l structure of [PtMe2Cl {Me2NCH2CH2N=CH(3,5-C6H2Cl2)-C,N,N'}] (4c) has been determined. The electrochemical properties of the compounds base d on cyclic voltammetry have also been studied. While the first reduct ion step is nearly reversible for cyclometallated platinum(II) compoun ds, coordination complex 3e and cyclometallated platinum(IV) compounds exhibit an irreversible reduction wave. In all cases oxidation occurs in an irreversible manner. The processes involved and the influence o f the chlorine substituents are discussed. (C) 1998 Elsevier Science S .A. All rights reserved.