Syntheses, structures and comparative electrochemical study of p-acetylene complexes of cobalt M.J. Macazaga a , M.L. Marcos b , C. Moreno a , F. Benito-Lopez a , J. Gomez-Gonza ´lez a , J. Gonza ´lez-Velasco b , R.M. Medina a, * a Departamento de Quı ´mica Inorga ´ nica, Facultad de Ciencias, Universidad Auto ´ noma de Madrid, Francisco Tomas y Valiente No. 7, 28049 Madrid, Spain b Departamento de Quı ´mica, Facultad de Ciencias, Universidad Auto ´ noma de Madrid, Francisco Tomas y Valiente No. 7, 28049 Madrid, Spain Received 10 June 2005; received in revised form 14 July 2005; accepted 15 July 2005 Available online 29 September 2005 Abstract The preparation and characterization of the complexes [Co 2 (CO) 4 (l-dppm)] 2 (l-g 2 -Me 3 SiC 2 (CBC) 2 C 2 H) (2), [Co 2 (CO) 4 (l- dppm)] 2 (l-g 2 -HC 2 (CBC) 2 C 2 H) (3), Co 2 (CO) 4 (l-dmpm)(l-g 2 -Me 3 SiC 2 CBCSiMe 3 )(4), Co 2 (CO) 4 (l-dmpm)(l-g 2 -Me 3 SiC 2 CBCH) (5), [Co 2 (CO) 4 (l-dmpm)] 2 (l-g 2 -Me 3 SiC 2 (CBC) 2 C 2 SiMe 3 )(6) and [Co 2 (CO) 4 (l-dmpm)] 2 (l-g 2 -HC 2 (CBC) 2 C 2 H) (7) are described. A comparative electrochemical study of all these complexes and the related [Co 2 (CO) 4 (l-dppm)] 2 (l-g 2 -Me 3 SiC 2 (CBC) 2 C 2 SiMe 3 ) (1), Co 2 (CO) 4 (l-dppm)(l-g 2 -Me 3 SiC 2 CBCH) and Co 2 (CO) 4 (l-dppm)(l-g 2 -HC 2 CBCH) is presented by means of the cyclic and square-wave voltammetry techniques. Crystals of 2 and 3 suitable for single-crystal X-ray diffraction were grown and the molecular structures of these compounds are discussed. Ó 2005 Elsevier B.V. All rights reserved. Keywords: p-Acetylene; Cobalt carbonyl complexes; Electrochemistry 1. Introduction Carbon rich organometallic containing polyynes and acetylenic arrays continue to garner attention and in- creased research interest. Polyynediyl bridging ligands have been shown to be specially efficient in allowing the passage of electronic effects between redox active cen- tres [1] and this raises possibilities for the generation of wire-like polyynyl materials with electronic properties tuned by both the end-capping and p-bound metal frag- ments [1c,2]. Interactions between identical mononuclear or cluster-based redox active groups bridged by ynyl and polyynyl spacers have been studied extensively [3], and it has been concluded that the strong electronic communi- cation in these systems is a result of efficient mixing be- tween filled metal fragment and polyyne-based orbitals. The redox chemistry of Co 2 -alkyne is well known and communication between these redox centres has been demonstrated for several systems [4]. We have previously reported the electrochemical behaviour of the complex, synthesized by Diederich [5], [Co 2 (CO) 4 (l-dppm)] 2 (l-g 2 -Me 3 SiC 2 (CBC) 2 C 2 SiMe 3 ) (1), showing the existence of electronic communication [1h]. Here, in order to evaluate the influence of the car- bon chain end groups and the influence of a more basic and less steric demanding phosphine ligand on the cobalt atoms, we report the electrochemical study of the complexes [Co 2 (CO) 4 (l-L-L)] 2 (l-g 2 -RC 2 (CBC) 2 C 2 R 0 ) (L–L = dppm, R = H, R 0 = SiMe 3 , 2, R, R 0 = H, 3; L– L = dmpm, R, R 0 = SiMe 3 , 6) together with that of the individual components, [Co 2 (CO) 4 (l-dmpm)](l-g 2 -Me 3 - SiC 2 CBCR) (R = SiMe 3 , 4, R = H, 5). The results are 0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2005.07.065 * Corresponding author. Tel.: +34 91 4974838; fax: +34 91 4974833. E-mail address: rosam.medina@uam.es (R.M. Medina). Journal of Organometallic Chemistry 691 (2006) 138–149 www.elsevier.com/locate/jorganchem