Details

Autor(en) / Beteiligte

• VISCO, STEVEN JOSEPH

Titel

ELECTROCHEMISTRY OF ACETYLENE-BRIDGED DICOBALT HEXACARBONYLS AND RELATED SYSTEMS

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

1982

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• The techniques of DC polarography and cyclic voltammetry have been employed to investigate the complex redox behavior of the X(,2)Co(,2)(CO)(,6) system {X(,2) = PhC(,2)Ph, ('t)BuC(,2)('t)Bu, As(,2)}, and the related Co(,2)(CO)(,8) complex. The acetylene and diarsenic-bridged complexes of this type undergo electrochemically reversible one-electron reductions to the radical anions at potentials ranging from -0.6 V to -1.1 V vs. Ag/AgCl in acetone. With the exception of the diarsenic complex, these radical anions are quite unstable at room temperature and decompose rapidly into a variety of mono-cobalt species including Co(CO)(,4)('-) and RC(,2)R'Co(CO)(,3) {R,R' = Ph,('t)Bu}. Cyclic voltammograms of the RC(,2)R'Co(,2)(CO)(,6) complexes were obtained over a large temperature range, from which the radical anion lifetimes and activation parameters for radical anion decay were calculated. In the presence of CO, the radical anions decay almost solely via an(' )ECE mechanism to yield Co(CO)(,4)('-) and RC(,2)R'Co(CO)(,3)('-). In the presence of phosphines, phosphites, arsines, and stibines, the radical anions undergo a series of complicated reactions which can be analyzed in terms of EC(' )and(' )ECE mechanisms. Major products include Co(CO)(,4)('-), Co(CO)(,3)('-), RC(,2)R'Co(CO(,2))L, and RC(,2)R'Co(,2)(CO)(,5)L {L = PPh(,3), P('n)Bu(,3), PEt(,3), P(OMe)(,3), P(OPh)(,3), AsPh(,3), SbPh(,3)}. The electrochemistry of the diarsenic compound is much cleaner and does not appear to involve fragmentation to monocobalt species. Detailed studies of the redox behavior of the Lewis base derivatives, RC(,2)R'Co(,2)(CO)(,5)L {L = PPh(,3), P(OMe)(,3)}, are also presented. The derivatives undergo one-electron reductions to the radical anions, but rapidly fragment to monocobalt species. The complex redox chemistry described in this study can be understood in terms of intermediate radical anions produced by metal-metal bond rupture to yield a coordinatively unsaturated metal center. The electron-induced nucleophilic substitution mechanism discovered in this study appears to be quite general, and should prove to be an important synthetic tool in the future. The electrochemistry of Co(,2)(CO)(,8) was explored using cyclic voltammetry at a Pt electrode. It appears that Co(,2)(CO)(,8) undergoes an initial one-electron transfer to form the radical anion Co(,2)(CO)(,8)('-). This radical anion is extremely unstable and rapidly fragments to yield Co(CO)(,4)('-) and Co(CO)(,4)('(.)), or in the presence of PPh(,3) fragments to yield Co(CO)(,4)('-), and Co(CO)(,3)PPh(,3). The radical fragments are immediately reduced, resulting in a net two-electron transfer via an(' )ECE mechanism.