Switchable hydrogenation with a betaine-derived bifunctional Ir–NHC catalyst

A bifunctional iridium catalyst based on the ‘uracil–abnormal NHC’ hybrid ligand platform was developed for switchable hydrogenation of quinoxalines. Control studies suggested heterolytic H₂ activation via a metal–ligand bifunctional operation to generate Ir–H and an adjacent protic O–H group for facile H⁺/H⁻ transfer to quinoxaline. The presence of a base blocked the most essential H⁺-transfer step thus switching off the catalysis, while an acid stimulus reversed the action to switch on the reaction again.