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Trinuclear iridium and rhodium complexes: the solution to a puzzle involving the multiple coordination possibilities of 1,8-naphthyridine-2-one ligands |
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| Authors: | B Eva Villaroya Luis A Oro Fernando J Lahoz Andrew J Edwards Miguel A Ciriano Pablo J Alonso Antonio Tiripicchio Marisa Titipicchio Camellini |
| Institution: | a Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-C.S.I.C., E-50009, Zaragoza, Spain b Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-C.S.I.C., E-50009, Zaragoza, Spain c Dipartimento di Chimica Generale ed Inorganica, Chimic analitica, Chimica Fisica, Centro di Studio per la Strutturistica Diffrattometrica del CNR, Universitá di Parma, Viale delle Scienze 78, I-43100, Parma, Italy |
| Abstract: | The multiple coordination possibilities of 1,8-naphthyridine-2-one (HOnapy) and 5,7-dimethyl-1,8-napthyridine-2-one (HOMe2napy) ligands allow the synthesis of a variety of tri- di- and mononuclear complexes, showing fluxional behaviour and frequent exchange of the coordinated ML2 fragments. Thus, reactions of M2(μ-OMe)2(cod)2] (cod = 1,5-cyclooctadiene) with HOnapy and HOMe2napy yield the compounds of the general formula M(μ-OR2napy) (cod)]n (M = Ir, R = Me (1a, 1b, H (2); M = Rh, R = Me (3a, 3b). They crystallise as inconvertible yellow (a) and purple/orange (b) forms and also show a puzzling behaviour in solution. X-ray diffraction studies on both forms (3a, 3b) and spectroscopic data reveal that the yellow forms are mononuclear complexes whilst the dark-coloured crystals contain dinuclear complexes. In solution, the nuclearity of the complexes depends on the solvent. In addition both types of complexes are fluxional. The mixed-ligand complexes M2(μ-OMe2napy)2(CO)2(cod)] M = Ir (5), Rh (6) have been isolated and characterised; they are found to be intermediates in the synthesis of the trinuclear complexes M3(μ3-OMe2napy)2(CO)2(cod)2]+ M = Rh (8), Ir (9). Reactions of IrCl(CO)2(NH2-p-tolyl] with the complexes Rh(μ-OR2napy)(diolefin)]n followed by addition of a poor donor anion is a general one-pot synthesis for the hetertrinuclear complexes Rh2Ir(μ3-OR2napy)2(CO)2(diolefin)2]+ (R=Me, DIOLEFIN = cod (10), tetrafluorobenzo-barrelene (tfbb) (11), 2,5-norbornadiene (nbd) (12); R=H, DIOLEFIN=cod (13)). This synthesis follows a stepwise mechanism from the mononuclear to the trinuclear complexes in which mixed-ligand heterodinuclear complexes are involved as intermediates of the type (diolefin)Rh(μ-OMe2napy)2Ir(CO)2]. Heteronuclear complexes which possess the core RhIr2]3+, such as RhIr2(μ3-OR2napy)2(CO)2(cod)2]BF4 (R=Me (14), H (15)), result from the reaction of 1 or 2 with Rh(CO)2Sx]+ (S = solvent). The trinuclear complexes undergo two chemically reversible one-electron oxidation processes. The chemical oxidation of 10, 14 and 9 with silver salts gives the mixed-valence trinuclear radicals Rh2Ir(μ3-OMe2napy)2(CO)2(cod)2]2+ (16), RhIr2(μ3-OMe2napy)2(CO)2(cod)2]2+ (17) and Ir3(μ3-OMe2napy)2(CO)2(cod)2]2+ (18), which have been isolated as the perchlorate and tetrafluoroborate salts. The EPR spectrum of 16 indicates that the unpaired electron is essentially in an orbital delocalised on the metals. The molecular structures of the complexes 3a, 3b, 6, 10b and 16a are described. Crystals of 3a are triclinic, P-1, with a = 9.7393(2), b = 14.0148(4), c = 16.0607(4) Å, α = 88.122(3), β = 83.924(3), γ = 87.038(3)°, Z = 4; 3b crystallises in the Pna2i orthorhhombic space group, with a = 16.7541(3), B = 11.7500(8), c = 17.7508(7) Å, Z = 4; complex 6 is packed in the monoclinic space group P2i/c, a = 9.6371(1), b = 11.8054(4), c = 27.2010(9) Å, β = 90.556(4)°, Z = 4; crystals of 10b are monoclinic, P21/n, with a = 17.546(7), b = 13.232(6), c = 17.437(8) Å, β = 106.18(1)°, Z = 4; crystals of 16a are triclinic, P-1, with a = 10.318(4), b = 12.562(6), C = 19.308(8) Å, α = 92.12(8), β = 97.65(9), γ = 90.68(5)°, Z = 2. The five different structures show the coordination versatility of the OMe2napy molecule as ligand, which behaves as a N,N′-chelating (3a), bidentate N,O-donor (3b, 6), or as a tridentate N,N′,O-donor bridging ligand (10b, 16a). |
| Keywords: | Crystal structures Rhodium complexes Iridium complexes Mixed-ligand complexes Paramagnetic complexes Trinuclear complexes |
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