Amido-bridged dinuclear rhodium(I) complexes by deprotonation of mononuclear rhodium(I) amine complexes Bas de Bruin, Theo P.J. Peters, Nicolaas N.F.A. Suos, Rene ´ de Gelder, Jan M.M. Smits, Anton W. Gal * Department of Inorganic Chemistry, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands Received 1 March 2002; accepted 3 May 2002 Dedicated to Professor Karl Wieghardt Abstract The preparation of a series of new amido bridged binuclear complexes [(N à /N à /N)Rh I 2 (cod) 2 ] (cod /Z ,Z -1,5-cyclooctadiene), [(N à /N à /N)Rh I 2 (hed) 2 ] (hed /1,5-hexadiene) and [(N à /N à /N)Rh I 2 (CO) 4 ] is reported. These complexes contain chelating imidazole à / amido Ã/imidazole, pyridine à /amido à /pyridine and pyridine Ã/amido Ã/pyrrolate ligands (N à /N à /N). The cod complexes have been prepared through deprotonation of their mononuclear amine precursors [(N à /HN à /N)Rh I (cod)] in the presence of [Rh I (cod)]  . Reaction of the binuclear complexes [(N à /N à /N)Rh I 2 (cod) 2 ] with CO results in the complexes [(N à /N à /N)Rh I 2 (CO) 4 ]. For N à /N à /N Ä/ chelating imidazole à /amido Ã/imidazole ligand, the X-ray structures of [(N à /N à /N)Rh I 2 (cod) 2 ], [(N à /N à /N)Rh I 2 (CO) 4 ], and their mononuclear amine precursor [(N Ã/HN à /N)Rh I (cod)] are reported. Electrochemical oxidation of the complexes is related to the relative donor strength of the N-ligands. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Rhodium; Binuclear complexes; N-ligands; Olefin complexes; Carbonyl complexes 1. Introduction Cooperation between two metal centra in binuclear substrate binding and activation plays an important role in several enzymatic processes (e.g. hemerytrin, hemo- cyanine and Cu à /Ni superoxide dismutase catalysed transformations) [1]. In homogeneous catalysis however, examples of binuclear cooperation are scarce. Stanley and coworkers reported increased reactivity and regio- selectivity in hydroformylation, using a binuclear rho- dium catalyst [2]. Hydroformylation at one rhodium center was proposed to proceed via hydrogen transfer from a second rhodium center, which is facilitated in a dinuclear species. Another example of binuclear coop- eration in homogeneous catalysis is shown by Karlin et al. [3]. A binuclear copper complex proved to be an efficient catalyst for the hydrolysis of DMF, while an analogous mononuclear derivative showed no activity [3]. It was suggested that the hydrolysis reaction at one center is facilitated by coordination of DMF to the other center. Wieghardt and coworkers recently re- ported catalytic formation of 1,2-glycols upon catalytic oxidation of alcohols by air. The mechanism of this reaction obviously involves radical coupling of two ketyl radicals, which was proposed to be facilitated by the dinuclear nature of the copper catalyst [4]. Inspired by these examples we have prepared bi- nuclear rhodium complexes of chelating imidazole à / amido à /imidazole, pyridine à /amido à /pyridine and pyridine à /amido à /pyrrolate ligands from mononuclear rhodium precursors. 2. Results and discussion Recently we have reported the cationic, mononuclear five-coordinate complex [1]X (X / Cl  , PF 6  ), and its oxygenation by O 2 and H 2 O 2 [5]. This mononuclear * Corresponding author. Tel.:  /31-24-365 2185; fax:  /31-24-355 3450 E-mail address: gal@sci.kun.nl (A.W. Gal). Inorganica Chimica Acta 337 (2002) 154  /162 www.elsevier.com/locate/ica 0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0020-1693(02)01030-7