PHOTOELECTROCHEMICAL DEHALOGENATION - BIS(CYCLOPENTA-DIENYL)-VANADIUMDICHLORIDE AND MOLYBDENUM DICHLORIDE

The electrochemistry of [M(cp)2Cl2] (M = Mo or V, cp = eta-C5H5) has b een investigated in the presence of light of wavelengths between 300 a nd 400 nm. For both compounds appreciable photocurrents were found to flow at potentials more positive than those required for their oxidati on. It is shown that these result from the absorption of light by the cation formed by the one-electron oxidation of [M(cp)2Cl2] and that th ey are mechanistically described by a photo-e.c.e (electrochemical-che mical-electrochemical) process [equations (i)-(iii)]. The chemical nat ure of the photoinduced reaction is discussed. Additionally, in the e. step [M(cp)2Cl2]- e- --> [M(cp)2Cl2]+ (i) c. step [M(cp)2Cl2]+ + MeCN + hv --> Cl. + [M(cp)2Cl(MeCN)]+ (ii) e. step [M(cp)2Cl(MeCN)]+ - e- --> [M(cp)2Cl(MeCN)]2+ (iii) case of [V(cp)2Cl2], a parallel c.e. proc ess also occurs as a result of the photofragmentation of the parent mo lecule [equations (iv) and (v)]. The kinetics and mechanism of this re action are reported. c. step [V(cp)2Cl2]+ hv --> [V(cp)2Cl] + 1/2Cl2 ( iv) e. step [V(CP)2Cl]- e- --> [V(cp)2Cl]+ (v)