(C5H5)CO-INDUCED HEAD-HEAD COUPLING OF DIMETHYLFULVENE - FORMATION, MOLECULAR-STRUCTURE AND ELECTROCHEMISTRY OF ,1,2,2-TETRAMETHYL-1,2-ETHANEDIYL)BIS(COBALTOCENE)

Head-head coupling of a dimethylfulvene ligand occures in the reaction of 6,6-dimethylpentafulvene (1a) with [(C5H5)Co(C2H4)(2)] (7) to give (1,1,2,2-tetramethyl-1, 2-ethanediyl)bis(cobaltocene) (8a). In contra st, the mononuclear eta(4)- fulvene complexes 3b, c are obtained from 6-ethyl-6-methyl(1b) and 6,6-diethylfulvene (1c) and 7. The crystal st ructures of 8a and the corresponding bis(ferrocene) 9a have been deter mined. The electrochemical behaviour of 8a and 9a shows 8a(+), 8a(-), and 9a(+) to be localised mixed-valence species. Molecular mechanics c alculations have been performed on the title complex and related deriv atives.