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

Abstract

The bis-diaminocarbene complexes cis-[Cl 2M{ CN(C 6H 4- p-OMe)CH 2N H} 2] (M  Pt or Pd) react with one mole of the diphosphine cis-Ph 2PCHCHPPh 2 (diphoe) in tetrahydrofuran at room temperature or in 1,2-dichloroethane at reflux for 8 h to form cationic derivatives cis-[(diphoe)M{ CN(C 6H 4- p-OMe)CH 2CH 2N H} 2]Cl 2 (M  Pt, 1; Pd, 2) with chloride displacement. The cationic hydridocarbene complex trans-[(PPh 3) 2Pt(H){ COCH 2CH 2O }][BF 4] reacts with one mole of diphoe in CH 2Cl 2 at room temperature to cleave the ring of the dioxycarbene, generate CO 2 and C 2H 4, and form the cationic complex [(diphoe)Pt(H)(PPh 3)][BF 4]. The reaction of trans-[(PPh 3) 2-Pt(H){ COCH 2CH 2O }][BF 4] with Cl − ions in CH 2Cl 2 gives the ring-opened alkoxycarbonyl complex trans-[(PPh 3) 2Pt(H){C(O)OCH 2CH 2C}], trans-[(PPh 3) 2Pt(H)(Cl)], ClCH 2CH 2OH and Pt 0 species. The cathodic behaviour of the diaminocarbene complexes cis-[Cl 2Pd{ CN(R)CH 2CH 2N H}](L)] (L  PPh 3, R  C 6H 4OMe- p or tBu; L  CN tBU, R  tBu; L  PPhMe 2, R  C 6H 4CH 2Cl- o), as well as of the aminooxy- and dioxy-carbene compounds trans-[(PPh 3) 2Pt(X)( COCH 2CH 2N CH 2CHCH 2)][BF 4] (X  Cl or Br) and trans-[(PPh 3) 2Pt(H)( COCH 2CH 2O )][BF 4], 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 CO 2 and ethylene and liberation of dihydrogen were proved by gas chromatography.