Metal Basicity of Dirhodium and Diiridium Complexes Induced by Isocyanide Ligands. Model for the Oxidative-Addition Reaction of Methyl Iodide with Dinuclear Complexes

Abstract

Reactions of [{Rh(μ-Pz)(CNBut)2}2] (1) and the new compounds [{M(μ-L)(CNBut)2}2] (M = Rh, L = SBut; M = Ir, L = pyrazolate (Pz)) with MeI give [{Rh(μ-Pz)(Me)(CNBut)2}2(μ-I)]I (2), [{Rh(μ-SBut)(Me)(CNBut)2}2(μ-I)]I, and [{Ir(μ-Pz)(Me)(CNBut)2}2(μ-I)]I, respectively. The oxidative-addition reactions that occur at each metal center are stereoselective. No differences in reactivity associated with the nature of the metals are observed due to the strong metal basicity induced by the isocyanide ligands. However, the influence of the nature of the metals is evident in the reactions of the mixed-ligand complexes [(cod)M(μ-Pz)2M(CNBut)2] (M = Rh, Ir; cod = 1,5-cyclooctadiene) with MeI to give the mixed-valence Rh(I)−Rh(III) complex [(cod)Rh(μ-Pz)2Rh(Me)(I)(CNBut)2] and the Ir(III) complex [(cod)(Me)Ir(μ-Pz)2(μ-I)Ir(Me)(CNBut)2]I, respectively. The former exists as a mixture of two conformers interconverting through a boat−boat inversion of the six-membered “Rh(Pz)2Rh” ring. The related Rh(I)−Rh(III) isocyanide complex [(CNBut)2Rh(μ-Pz)2Rh(Me)(I)(CNBut)2], which could not be isolated because it rearranges to complexes 1 and 2, reacts with MeI instantaneously and quantitatively to give 2. The nucleophilic character of the metals in 1 is shown by the reaction with MeCF3SO3 to give [{Rh(μ-Pz)(Me)(CNBut)2}2(μ-CF3SO3)]CF3SO3 with stereochemistry identical to that of 2. The structures of the complexes [{Rh(μ-Pz)(Me)(CNBut)2}2(μ-X)]CF3SO3 (X = I, CF3SO3), have been determined by X-ray diffraction and show discrete dimethyl dinuclear cationic complexes triply bridged by two pyrazolate groups and an iodo or monodentate triflate ligand.