Preparation of dimethyl and chloro/methyl complexes of platinum(II) supported by alpha-diimine ligands: Trends in the ease of oxidation to platinum(IV)

alpha -Diimine ligands react with the platinum(II) alkyl complexes [(Me2S)P tMe2](2) and (Me2S)(2)PtClMe to form (RDAB(R)')PtMe2 and (RDAB(R)')PtClMe ( RDAB(R)=RN=CR'-CR'=NR; R=2,6-Me2Ph, 2,6-(CHMe2)(2)Ph, 3,5-Me2Ph, 3,5-(CF3)( 2)Ph, C6H11; R'= Me, H). The oxidation of these complexes with Cl-2, I-2, N -chlorosuccinimide, [PtCl6](2-) and (TMEDA)PtMe2I2 has been investigated. A ttempts to determine the oxidation potentials of the Pt-II complexes electr ochemically yielded only irreversible one-electron oxidations. However, a q ualitative ordering of increasing difficulty of oxidation has been determin ed for the series (RDAB(R))PtMe2 < (RDAB(R)')PtClMe < RDAB(R))PtCl2 much le ss than (RDAB(R)')PtMe(solvent)](+). The oxidation proceeds via a two-elect ron inner-sphere electron transfer from a bridged binuclear intermediate. T he oxidation of (RDAB(R)')PtMe2 by (TMEDA)PtMe2I2 exhibits characteristic t hird-order kinetics, first-order each in [Pt-II], [Pt-IV] and [I-]. Oxidati on by a one-electron process in MeCN solution results in a rapid subsequent disproportionation to (PtMe)-Me-II and (PtMe3)-Me-IV cations with MeCN occ upying the fourth or sixth coordination sites. Single-crystal X-ray structu re determinations for [(2,6-Me(2)PhDAB(Me))PtMe3(MeCN)](+) [PtCl6](0.5)(MeC N) and [(CyDAB(H))PtMe3(MeCN)] (+)[PtCl6](0.5)(MeCN) are reported.