New trisubstituted cyclopentadienyl ligands: synthesis, characterisation and catalytic properties of mono and dinuclear cobalt, rhodium, iron and ruthenium complexes

The synthesis of a set of dialkyl 4-alkoxycarbonylcyclopenta-1,3-diene-l,2-diacetates (1a-e) is described. Their coordinating abilities as anions have been investigated in relation to the formation of new sandwich, half-sandwich and dinuclear complexes and their structural features. We report here the preparation and characterisation of some complexes such as a mononuclear half-sandwich cobalt(1,5-COD) complex which has shown to be a very efficient catalyst for the cyclocotrimerisation reaction of alkynes and nitriles to pyridines. Half-sandwich rhodiumdicarbonyl complexes containing trisubstituted cyclopentadienyl ligands with ester chains of different length have been employed successfully as catalysts for hydroformylation of styrene. Finally ligands la-e have been used for the synthesis of ferrocenes and dinuclear carbonyl complexes of iron and ruthenium. The structures of the complexes 1,5-cycloctadiene[1 -methoxycarbonyl-3,4-di(methoxycarbonylmethylene)cyclopentadienyl]cobalt [Co(MDMCp)COD] (9), dicarbonyl[1-methoxycarbonyl-3,4-di(methoxycarbonylmethylene)cyclopentadienyl] rhodium [Rh(MD MCp)(CO)(2)] (2a) and of a new ferrocene complex [Fe(MDMCp)(2)] (15a) have been determined by X-ray diffraction methods.