Reactions with nucleophiles and cathodic electrochemical behaviour of some neutral and cationic diamino-, dioxy-, and aminooxycarbene complexes of palladium(II) and platinum(II)

Article abstract of DOI:10.1016/0022-328X(92)83290-X

The bis-diaminocarbene complexes cis- (M = Pt or Pd) react with one mole of the diphosphine cis-Ph2PCH=CHPPh2 (diphoe) in tetrahydrofuran at room temperature or in 1,2-dichloroethane at reflux for 8h to form cationic derivatives cis-<(diphoe)M (M = Pt, 1; Pd, 2) with chloride displacement.The cationic hydridocarbene complex trans-<(PPh3)2Pt(H) reacts with one mole of diphoe in CH2Cl2 at room temperature to cleave the ring of the dioxycarbene, generate CO2 and C2H4, and form the cationic complex <(diphoe)Pt(H)(PPh3)>.The reaction of trans-<(PPh3)2Pt(H) with Cl^- ions in CH2Cl2 gives the ring-opened alkoxycarbonyl complex trans-<(PPh3)2Pt(H)>, trans-<(PPh3)2Pt(H)(Cl)>, ClCH2CH2OH and Pt⁰ species.The cathodic behaviour of the diaminocarbene complexes cis-(L)> (L = PPh3, R = C6H4OMe-p or ^tBu; L = CN^tBu, R = ^tBu; L = PPhMe2, R = C6H4CH2Cl-o), as well as of the aminooxy- and dioxy-carbene compounds trans-<(PPh3)2Pt(X) (X = Cl or Br) and trans-<(PPh3)2Pt(H), has been studied by cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in aprotic media.They exhibit an irreversible reduction wave (E^red_p in the range -1.50 to -2.0 V vs.SCE), corresponding to two-electron and single-electron cathodic processes for the dichloro-complexes and the other species, respectively.Evidence for the fromation of low-coordingation number zerovalent palladium species is presented, and, in the case of the electrochemical reduction of the dioxycarbenehydrido-complex, quantitative fragmentation of the cyclic carbene to CO2 and ethylene and liberation of dihydrogen were proved by gas chromatography.