Synthesis of Dipositive Molybdenum(II) and Tungsten(II) cArbonyl Cations by eLectrochemically Generated Internal Addition Reactions

Alan M. Bond, Ray Colton, Katherine McGregor

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Electrochemical oxidation of M(CO)31-L-L)(η2-L-L) (M = Mo, W; L-L = various ditertiary phosphines and a mixed phosphine/arsine) in acetone (0.1 M Et4NC1O4) or in dichloromethane (0.1 M Bu4NC1O4) solution under carbon monoxide at a platinum electrode yields isolable [M(CO)32-L,-L)2]2+ cations by the electrochemically generated internal addition reaction M(CO)31-L-L)(η2-L-L) → [M(CO)32-L-L)2]2+ + 2e-. Electrochemical synthesis therefore provides at present the only route to novel dipositive carbonyl cations in the special case where a pendent phosphorus (or arsenic) atom is available to provide the additional donor ligand required to achieve an 18-electron configuration. Chemical oxidations do not give the same products because of nucleophilic attack by solvent, the anion of the oxidant, or adventitious impurities on the dipositive cation. The [M(CO)32-L-L)2]2+ cations decompose very slowly under carbon monoxide and much more rapidly under nitrogen to give first the 16-electron trans-[M(CO)22-L-L)2]2+ species (or weakly solvated species), which then undergo nucleophilic attack by the electrochemical supporting electrolyte NBu4ClO4 to generate [M(CO)22-L-L)2(ClO4)]+: [M(CO)32-L-L)2]2+ → trans-[M(CO)22-L-L)2]2+ → [M(CO)22-L-L)2(ClO4)]+. The product of the oxidation of Mo(CO)3(η1-dpm)(η2-dpm)2 (dpm = Ph2PCH2PPh2) by AgClO4 has been isolated and shown to be Mo(η2-dpm)2(ClO4)2, but its structure is not known.

Original languageEnglish
Pages (from-to)1227-1230
Number of pages4
Issue number4
Publication statusPublished - 1990
Externally publishedYes

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