REACTIONS WITH NUCLEOPHILES AND CATODIC ELECTROCHEMICAL-BEHAVIOR OF SOME NEUTRAL AND CATIONIC DIAMINOOXYCARBENE, DIOXYOXYCARBENE AND AMINOOXYCARBENE COMPLEXES OF PALLADIUM(II) AND PLATINUM(II)

The bis-diaminocarbene complexes cis-[Cl2M{CN(C6H4-p-OMe)CH2CH2NH}2] (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 8 h to form cationic derivatives cis-[(diphoe)M{CN(C6H4-p-OMe)CH2CH2NH}2]Cl (M = Pt, 1; Pd, 2) with chloride displacement. The cationic hydridocarbene complex trans-[(PPh3)2Pt(H){COCHCH2O}][BF4] 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)][BF4]. The reaction of trans-[(PPh3)2-Pt(H){COCH2CH2O}][BF4] with Cl- ions in CH2Cl2 gives the ring-opened alkoxycarbonyl complex trans-[(PPh3)2Pt(H){C(O)OCH2CH2C}], trans-[(PPh3)2Pt(H)(Cl)], ClCH2CH2OH and Pt0 species. The cathodic behaviour of the diaminocarbene complexes cis-[Cl2Pd{CN(R)CH2CH2NH}(L)] (L = PPh3, R = C6H4OMe-p or (t)Bu; L = CNtBu, R = (t)Bu; L = PPhMe2, R = C6H4CH2Cl-o), as well as of the aminooxy- and dioxy-carbene compounds trans-[(PPh3)2Pt(X)(COCH2CH2NCH2CH=CH2)][BF4] (X = Cl or Br) and trans-[(PPh3)2Pt(H)(COCH2CH2O)][BF4], has been studied by cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in aprotic media. They exhibit an irreversible reduction wave (E(p)red 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 formation of low-coordination 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.