PROTON-MEDIATED AND CARBONYL-MEDIATED ELECTRON-TRANSFER PROCESSES FROM THE HEXACARBONYLVANADATE(-1) ANION

Hexacarbonylvanadate( - I) derivatives of several heterocyclic nitrogen bases, BH+[V(CO),]-, have been synthesized. The deep red volatile pyridinium derivative [C,H,NH]+[V(CO),]-, was studied by X-ray diffraction methods and found to be tetragonal, space group 14,/amd, with a 10.384(3), c 12.373(3) A and Z= 4. Solution of the structure by the heavy-atom method followed by full-matrix leastsquares refinement gave the final residuals (R = 0.0450 and R, = 0.0442) for 180 unique observed reflections. Coordination about the vanadium atom, which lies at a site of local 42rn symmetry, is octahedral due to two independent carbonyl groups. The pyridine moiety is disordered. The major feature of the molecular structure is the interaction of the nitrogen proton with the carbonyl oxygens of [V(CO),]- in the equatorial plane of the octahedron. The structural features are regarded as evidence in favour of the carbyne-type of structure for the C,HO,V precursor of V(CO), (C,HO,V + l/2 H, + V(CO),). Several substitution and redox processes involving the protonated nitrogen base derivatives have been observed, namely: (a) nitrogen base exchange; (b) dihydrogen evolution upon treatment with sodium metal; (c) electron-transfer from [V(CO),]- to the nitrogen-bonded proton, with dihydrogen evolution; (d) electron-transfer from [V(CO),]- to the cation with carbon-carbon coupling in the case of the acridinium derivative. All the compounds reported are deeply coloured (the quinolinium derivative is black), suggesting the existence of a multicentre CO-mediated charge transfer from vanadium to the nitrogen base.