Hydroboration of carbon dioxide with catecholand pinacolborane using an Ir- CNP* pincer complex. Water influence on the catalytic activity

Iridium complexes based on deprotonated lutidine-derived CNP* pincers 2a/2b selectively catalyzed the hydroboration of CO2 under mild conditions (1-2 bar CO2, 30 degrees C) to methoxyborane using HBcat (TOF up to 56 h(-1)) and to the formate level with HBpin (TOF up to 1245 h(-1)). Interestingly, an intriguing, positive water effect on the reaction rates has been observed. NMR spectroscopy and ESI-MS analysis of the hydroboration reactions have shown the formation of ligand-protonated [Ir(CNP)(CO)(BR2)H][B(R-2)(2)] (R-2 = catecholate, pinacolate) derivatives under catalytic conditions. Control experiments, however, have demonstrated that these derivatives are not catalytically competent species in the hydroboration of CO2.