Oxidative-Addition of Organic Monochloro Derivatives to Dinuclear Iridium Complexes: The Detection of Tautomeric Equilibria and Their Implications on the Reactivity

Abstract

Reactions of MeCOCH2Cl, MeCO2CH2Cl, and (−)-methyl(S)-2-chloropropionate with [{Ir(μ-Pz)(CNBut)2}2] (Pz = pyrazolate, 1) gave the metal−metal bonded diiridium(II) complexes [(CNBut)2(Cl)Ir(μ-Pz)2Ir(η1-CH2R)(CNBut)2] (R = COMe (2), CO2Me (3)) and the two enantiomers of [(CNBut)2(Cl)Ir(μ-Pz)2Ir(η1-CH(Me)CO2Me)(CNBut)2] (4). Similar reactions of 1 with equimolar amounts of benzyl chloride and allyl chloride rendered [(CNBut)2(Cl)Ir(μ-Pz)2Ir(η1-CH2R)(CNBut)2] ((R = Ph (5), CHCH2 (7)), which were found to be the metal−metal bonded complexes in the solid state, but in equilibrium with the mixed-valence Ir(I)−Ir(III) complexes [(CNBut)2Ir(μ-Pz)2Ir(Cl)(η1-CH2R)(CNBut)2] in solution. Replacement of chloride by iodide in 5 affords only the diiridium(II) complex [(CNBut)2(I)Ir(μ-Pz)2Ir(η1-CH2Ph)(CNBut)2] (6). Complexes 5 and 7 reacted further with a second molar equivalent of chloro derivative to render dialkyldiiridium(III) complexes [{Ir(μ-Pz)(η1-CH2R)(CNBut)2}2(μ-Cl)]Cl, ((R = Ph (8), CHCH2 (10a)), while those showing a single static species in solution (2−4 and 6) were inactive. The reaction of 7 with allyl chloride gave also the isomer [(CNBut)2(Cl)Ir(η1,η2-CH2CHCH2)(μ-Pz)2Ir(η1-allyl)(CNBut)2]Cl (10b), in which one allyl group bridges the two iridium atoms in an unsymmetrical fashion. This complex isomerizes into the thermodynamic product [{Ir(μ-Pz)(η1-allyl)(CNBut)2}2(μ-Cl)]Cl, an stereoisomer of 10a. The structures of 10b and 5 were solved by single-crystal X-ray diffraction methods.