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

Abstract

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 °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(R₂)₂] (R₂ = catecholate, pinacolate) derivatives under catalytic conditions. Control experiments, however, have demonstrated that these derivatives are not catalytically competent species in the hydroboration of CO₂.