An Organometallic Methodology Affording Dinuclear Copper(I) Complexes Euro Solari, Mario Latronico, † Philippe Blech, and Carlo Floriani* Institut de Chimie Mine ´rale et Analytique, BCH, Universite ´ de Lausanne, CH-1015 Lausanne, Switzerland Angiola Chiesi-Villa and Corrado Rizzoli Dipartimento di Chimica, Universita ` di Parma, I-43100 Parma, Italy ReceiVed January 24, 1996 Introduction Synthetic access to the very important class of copper(I) coordination compounds is based on the metathesis reaction between copper halides and the salt of the corresponding ligand. 1-3 Such reactions must be carried out in coordinating polar solvents, which is usually why copper(I) disproportionates to copper(II) and copper metal. An additional problem, mainly when we are dealing with a polynucleating polyprotic ligand, can be the difficulty in obtaining the ligand as the alkali metal salt and in managing the nuclearity of the resulting compound. Thus we felt the necessity for a different metalating methodology in the case of copper(I) complexes, which should avoid the use of any salt and halide derivative, that is, the direct reaction of a copper(I) source with the protic form of the ligand in an innocent solvent. This method employing [Cu 5 Mes 5 ] 4 [Mes ) 2,4,6-Me 3 C 6 H 2 ] as starting material has been efficiently used in organometallic chemistry by van Koten and co-workers. 5 We wish to illustrate the effectiveness of such a method in the synthesis of dinuclear copper(I) complexes, 6,7 which are par- ticularly attractive, and, among others, in the field of dioxygen activation. 6,7 In order to emphasize the relevance of this synthetic approach, we used molecules which are usually mononucleating ligands but are potential binucleating ligands, such as the tetradentate Schiff bases, which can force two copper(I) ions into an interesting close geometrical proximity. These ligands, used under conventional conditions, induce the disproportionation of copper(I). 2 We report here the reaction of the homoleptic copper(I)-aryl [Cu 5 Mes 5 ] compound, which is available on a large scale, 4 with acacenH 2 [N,N′-ethylenebis- (acetylacetone imine)], salophenH 2 [N,N′-o-phenylenebis(sali- cylaldimine)], and o-phthalic acid, leading to a variety of dinuclear copper(I) complexes. Results and Discussion The metalation of tetradentate Schiff bases, such as acacenH 2 [N,N′-ethylenebis(acetylacetone imine)] and salophenH 2 [N,N′- o-phenylenebis(salicylaldimine)], in their protic forms was carried out by mixing either toluene or THF solutions of [Cu 5 - Mes 5 ], 1 (Mes ) 2,4,6-Me 3 C 6 H 2 ), and the ligand in the presence of a copper(I)-stabilizing agent such as CO, PPh 3 , RNC. 2 The metalation of acacenH 2 and salophenH 2 is reported in Scheme 1. The trans arrangement of the halves of such ligands, which normally act as tetradentate binders for a single metal ion, is based on the X-ray-determined solid state structure of 4. We should comment, however, that we are referring to the solid state, while in solution the cis arrangement may also be possible and the two metal centers may be accessible in the appropriate disposition for dinuclear reactivity. In the case of complex 2, the reaction was also carried out in a carbon monoxide atmosphere. Although CO loss from the solid is facile, it rebinds under such conditions. The CO stretching vibration for 2 is very high (2071 cm -1 ), 8 in agreement with the electrophilic nature of the d 10 metal which is unable to π-back-donate. Compound 3 shows the same spectroscopic characteristics as 2, with a very high stretching vibration of the CtNR group at 2166 cm -1 , though in the latter case there is no reversibile binding of Bu t NC, as in the case of carbon monoxide. 8 On the † Present address: D.I.F.A., Universita ` della Basilicata, I-85100 Potenza, Italy. (1) (a) Copper Coordination Chemistry: Biochemistry and Inorganic PerspectiVes; Karlin, K. D., Zubieta, J., Eds.; Adenine: Guilderland, NY, 1983. (b) Biological and Inorganic Copper Chemistry; Karlin, K. D., Zubieta, J., Eds.; Adenine: Guilderland, NY, 1986. (2) Hataway, B. In ComprehensiVe Coordination Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: Oxford, U.K., 1987; Vol. 5, p 533. (3) Jardine, F. H. AdV. Inorg. Chem. Radiochem. 1975, 17, 115. (4) Meyer, E. M.; Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Organometallics 1989, 8, 1067. (5) (a) Aalten, H. L.; van Koten, G.; Goubitz, K.; Stam, C. H. J. Chem. 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Copper(I)-Carbon Monoxide Chemistry: Recent Advances and Perspectives. In Ref 1a, pp 311-330. Scheme 1 4526 Inorg. Chem. 1996, 35, 4526-4528 S0020-1669(96)00072-9 CCC: $12.00 © 1996 American Chemical Society