www.elsevier.nl/locate/jorganchem Journal of Organometallic Chemistry 619 (2001) 179 – 193 New trisubstituted cyclopentadienyl ligands: synthesis, characterisation and catalytic properties of mono and dinuclear cobalt, rhodium, iron and ruthenium complexes Mirco Costa a, *, Enrico Dalcanale a , Francisco Santos Dias b , Claudia Graiff c , Antonio Tiripicchio c , Lorenzo Bigliardi a a Dipartimento di Chimica Organica e Industriale, Uniersita ` degli Studi di Parma, Parco Area delle Scienze 17A, 43100 Parma, Italy b Departamento de Quı ´mica Orga ˆnica e Inorga ˆnica, Uniersidade Federal do Ceara ` , C.P. 12200, CEP 60455 -760, Fortaleza, CE, Brazil c Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Centro di Studio per la Strutturistica Diffrattometrica del C.N.R., Parco Area delle Scienze 17A, 43100 Parma, Italy Received 3 August 2000; accepted 18 August 2000 Abstract 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. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Substituted cyclopentadiene; Cyclopentadienyl complexes: cobalt, rhodium, iron, ruthenium; Alkyne cyclisation; Hydroformylation 1. Introduction Derivatives of cyclopentadiene form one of the most important and versatile classes of ligands in the metal- lorganic chemistry. In their substituted or unsubstituted form they are able to stabilise metals in both high or low oxidation states through  1 –  5 bonding modes [1]. The functionalisation of the cyclopentadienyl ring can alter significantly the steric and electronic properties of the corresponding complexes [2]. In the last few years, significant efforts have been devoted to work out smooth synthetic procedures for the preparation of new multiple functionalised cy- clopentadienyl ligands and their sandwich and half- sandwich metal complexes [2 – 4]. Several synthetic strategies are available for the syn- thesis of substituted mono- and di- 5 -cyclopentadienyl metal complexes. Two main experimental approaches can be distinguished: the former is based on the direct use of suitable substituted cyclopentadienyl rings which are caused to react with transition metal complexes according to the procedure for the synthesis of sand- wich and half-sandwich complexes [5]; the latter is based on the introduction of substituents in the ring after preparation of a cyclopentadienyl metal complex. This includes metallation reactions and electrophilic aromatic substitution reactions [6]. Recently we developed a new multistep procedure to prepare a cyclopentadiene derivative substituted by one * Corresponding author. Fax: +39-0521-905472. E-mail address: costa@unipr.it (M. Costa). 0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0022-328X(00)00652-5