Stepwise Construction of Polynuclear Complexes of Rhodium and Iridium Assisted by Benzimidazole-2-thiol. NMR and X-ray Diffraction Studies

• Published in: Inorganic chemistry 1996-07, Vol.35 (15), p.4360-4368
• Main Authors: Tejel, Cristina, Villarroya, B. Eva, Ciriano, Miguel A, Oro, Luis A, Lanfranchi, Maurizio, Tiripicchio, Antonio, Tiripicchio-Camellini, Marisa
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic960046m

Reactions of [M2(μ-Cl)2(cod)2] (cod = 1,5-cyclooctadiene, M = Rh, Ir) with benzimidazole-2-thiol (H2Bzimt) afford the mononuclear complexes [MCl(H2Bzimt)(cod)] (M = Rh (1), Ir (2)) for which a S-coordination of the ligand is proposed based on their spectroscopic data. The dinuclear complexes [M2(μ-HBzimt)2(cod)2] (M = Rh (3), Ir (4)) are isolated from the reaction of [M(acac)(cod)] and benzimidazole-2-thiol. They contain the monodeprotonated ligand (HBzimt-) bridging the two metals in a μ2-(1κN,2κS) coordination mode and in a relative cis,cis-HT arrangement. Complexes 3 and 4 react with the appropriate species [M(cod)(Me2CO)2]+ to afford the trinuclear cationic aggregates [M3(μ-HBzimt)2(cod)3]+ (M = Rh (5), Ir (6)) and with the [M‘2(μ-OMe)2(cod)2] compounds to give the homo- and heterotetranuclear complexes [MM‘(μ-Bzimt)(cod)2]2 (M = M‘ = Rh (7), Ir (8); M = Ir, M‘ = Rh (9)) containing the dideprotonated ligand (Bzimt2-). The trinuclear neutral complexes [M3(μ-Bzimt)(μ-HBzimt)(cod)3] are intermediates detected in the synthesis of the tetranuclear complexes. Protonation of 9 with HBF4 gives the unsymmetrical complex [Ir2Rh(μ-HBzimt)2(cod)3]BF4 (10). This reaction involves the protonation of the bridging ligands followed by the removal of one “Rh(cod)” moiety to give a single isomer. The molecular structure of [Rh2(μ-Bzimt)(cod)2]2 (7) has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P21/n, a = 20.173(5) Å, b = 42.076(8) Å, c = 10.983(3) Å, β = 93.32(2)°, Z = 8, 7145 reflections, R = 0.0622, and R w = 0.0779. The complete assignment of the resonances of the 1H NMR spectra of the complexes 3, 4, and 7−9 was carried out by selective decoupling, NOE, and H,H-COSY experiments. The differences in the chemical shifts of the olefinic protons are discussed on the basis of steric and magnetic anisotropy effects.