Formation and reactivity of an (alkene)peroxoiridium(iii) intermediate supported by an amidinato ligand

Abstract

An Ir^I complex of an acetamidinato ligand was synthesized by reaction of N,N′-diphenylacetamidine, PhNC(Me)NHPh, with either MeLi and [{Ir(cod)}₂(μ-Cl)₂] or [{Ir(cod)}₂(μ-OMe)₂] and was characterized by X-ray crystallography as a mononuclear complex, [Ir{PhNC(Me)NPh}(cod)] (1; where cod = 1,5-cyclooctadiene). Reaction of 1 with CO afforded a dinuclear carbonyl complex, [{Ir(CO)₂}₂{μ-PhNC(Me)NPh-κN:κN′}₂] (2), as indicated by EI mass spectrometry and solution- and solid-state IR spectroscopy [ν_CO (n-pentane) = 2067, 2034 and 1992 cm⁻¹]. Activation of O₂ by 1 in solution at 20 °C was irreversible and produced an (alkene)peroxoiridium(III) intermediate, [Ir{PhNC(Me)NPh}(cod)(O₂)] (3), which was characterized by one- and two-dimensional NMR techniques and IR spectroscopy (for 3, ν_OO = 860 cm⁻¹; for 3–¹⁸O₂, ν_OO = 807 cm⁻¹). Complex 3 oxidized PPh₃ to OPPh₃, and its decay in the absence of added substrates followed by reaction with cod yielded 4-cycloocten-1-one and a minor amount of 1. In comparison with the results for the previously reported guanidinato complex [Ir{PhNC(NMe₂)NPh}(cod)(O₂)] (4), the formation of 3 and its reaction with PPh₃ are significantly faster, indicating considerable ligand effects in these reactions.