Preparation of Dimethyl and Chloro/Methyl Complexes of Platinum(II) Supported byα-Diimine Ligands: Trends in the Ease of Oxidation to Platinum(IV)

Abstract

α-Diimine ligands react with the platinum(II) alkyl complexes [(Me2S)PtMe2]2 and (Me2S)2PtClMe to form (RDABR′)PtMe2 and (RDABR′)PtClMe (RDABR′=RN=CR′−CR′=NR; R=2,6-Me2Ph, 2,6-(CHMe2)2Ph, 3,5-Me2Ph, 3,5-(CF3)2Ph, C6H11; R′=Me, H). The oxidation of these complexes with Cl2, I2, N-chlorosuccinimide, [PtCl6]2− and (TMEDA)PtMe2I2 has been investigated. Attempts to determine the oxidation potentials of the PtII complexes electrochemically yielded only irreversible one-electron oxidations. However, a qualitative ordering of increasing difficulty of oxidation has been determined for the series (RDABR′)PtMe2<(RDABR′)PtClMe<(RDABR′)PtCl2≪(RDABR′)PtMe(solvent)]+. The oxidation proceeds via a two-electron inner-sphere electron transfer from a bridged binuclear intermediate. The oxidation of (RDABR′)PtMe2 by (TMEDA)PtMe2I2 exhibits characteristic third-order kinetics, first-order each in [PtII], [PtIV] and [I−]. Oxidation by a one-electron process in MeCN solution results in a rapid subsequent disproportionation to PtIIMe and PtIVMe3 cations with MeCN occupying the fourth or sixth coordination sites. Single-crystal X-ray structure determinations for [(2,6-Me2PhDABMe)PtMe3(MeCN)]+[PtCl6]0.5(MeCN) and [(CyDABH)PtMe3(MeCN)]+[PtCl6]0.5(MeCN) are reported.