Heterolytic Benzene C−H Activation by a Cyclometalated Iridium(III) Dihydroxo Pyridyl Complex: Synthesis, Hydrogen−Deuterium Exchange, and Density Functional Study

We report the synthesis of the pincer-cyclometalated (NNC t-Bu)Ir(III) dihydroxo pyridyl complex 6, which catalyzes hydrogen−deuterium (H/D) exchange between water and benzene in the presence of base (TOF = ∼6 × 10−3 s−1 at 190 °C). Experimental and density functional theory (B3LYP) studies suggest that H/D exchange occurs through loss of pyridine followed by benzene coordination and C−H bond activation by a heterolytic substitution mechanism to give a phenyl aquo complex, which may dimerize. Exchange of H2O for D2O followed by the microscopic reverse of CH activation leads to deuterium incorporation into benzene. Synthesis of the μ-hydroxo phenyl dinuclear complex [(NNC t-Bu)Ir(Ph)(μ-OH)]2 (9) also catalyzes H/D exchange with a turnover frequency (TOF = ∼7 × 10−3 s−1 at 190 °C) similar to that for 6.