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 ^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 x 1O ^-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 H ₂O for D ₂O 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 x 1O ^-3 s ^-1 at 190 °C) similar to that for 6.