Regioselective Ortho-Functionalization of Phenols Promoted by the “Cp*Ir” Unit in [Cp*Ir(oxo-η5-cyclohexadienyl)][BF4] Complexes

Abstract

A series of alkylated phenols (phenol, 3,5-dimethylphenol and 3,4-dimethylphenol) were complexed by the [Cp*Ir(solvent)3][BF4]2 (1) unit prepared in situ; subsequent treatment with NEt3 produced the (oxo-η5-cyclohexadienyl)iridium complexes [Cp*Ir(η5-C6H3R2O)][BF4] [R = H (2); R = Me (3, 4)]. The X-ray molecular structure of 3 was determined. These (oxo-η5-cyclohexadienyl)iridium derivatives react with NaOMe in methanol to give the novel iridium cyclohexadienone complexes [Cp*Ir{η4-C6H3R2O(OMe)}] [R = H (5); R = Me (6, 7)] in 75−90% yield with nucleophilic attack occurring exclusively at the ortho-position relative to the CO function. Addition of HBF4·Me2O to these iridium cyclohexadienone complexes 5−7 affords the starting material (oxo-η5-cyclohexadienyl)iridium derivatives 2−4 with MeOH. Further exposure to HBF4·Me2O produces the corresponding phenolic compounds [Cp*Ir(η6-C6H3R2OH)][BF4]2 (8−10); these chemical reactions are accompanied with hapticity changes η4 → η5 → η6 of the coordinated π-hydrocarb...