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-1,2-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 1a–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(MDMCp)(CO)2] (2a) and of a new ferrocene complex [Fe(MDMCp)2] (15a) have been determined by X-ray diffraction methods.