New homoleptic organometallic derivatives of vanadium(III) and vanadium(IV):: Synthesis, characterization, and study of their electrochemical behaviour

The arylation of [VCl3(thf)(3)] with LiRCl, where R-Cl, is a polychlorinated phenyl group [C6Cl5, 2,4,6-trichlorophenyl(tcp), or 2,6-dichlorophenyl (dcp)] gives four-coordinate, homoleptic organovanadium(iii) derivatives with the formula [Li(thf)(4)]-[V-III(R-Cl)(4)] (R-Cl=C6Cl5 (1), tcp (2), dcp (3)). The anion [V-III(C6Cl5)(4)](-) has an almost tetrahedral geometry, as observed in the solid-state structure of [NBu4][V(C6Cl5)(4)](-) (1') (X-ray diffraction). Compounds 1-3 are electrochemically related to the neutral organovanadium(iv) species [V-IV(R-Cl)(4)] (R-Cl=C6Cl5 (4), tcp (5). dcp (6)). The redox potentials of the V-IV/V-III semisystems in CH2Cl2 decrease with decreasing chlorination of the phenyl ring (Et2O= 0.84 (4/1), 0.42 (5/2), 0.25 V (6/3)). All the [V-IV(R-Cl)(4)] derivatives involved in these redox couples could also be prepared and isolated by chemical methods. The arylation of [VCl3(thf)(3)] with LiC6F5 also gives a homoleptic organovanadium(iii) compound, but with a different stoichiometry: [NBu4](2)[V-III(C6F5)(5)] (7). In this five-coordinate species, the C6F5 groups define a trigonal bipyramidal environment for the vanadium atom (X-ray diffraction). EPR spectra for the new organovanadium compounds 1-6 are also given and analysed in terms of an elongated tetrahedral structure with C-2r local symmetry. It is suggested that the R-Cl groups exert a protective effect towards the vanadium centre.