CO2 Conversion to formates catalyzed by iridium(III) catalysts precursors with proton responsive OH and NH electron-rich tetrazole ligands

Abstract

Recent efforts in addressing the environmental problems have involved using CO2 as a cheap and nontoxic C1 source. Iridium catalysts with bidentate ligands are excellent catalysts for CO2, especially if these complexes possess proton-responsive OH or NH groups. Here-in we report the synthesis of novel Ir half-sandwich complexes with N^N bidentate tetrazolyl ligands. Serendipitous deprotection of methoxy groups resulted in N^N bidentate ligands bearing OH groups. The complexes were evaluated for CO2 hydrogenation, for which the roles of steric bulk or the presence of electronic effects influence their catalytic activity in CO2 hydrogenation. The complexes are highly active for CO2 hydrogenations with around 4.3 mmol of formate produced. The presence of proton responsive groups on the catalysts was found to steer the mechanistic cycle away from using a bridged Ir-H-Ir intermediate before forming catalytically active species. In addition, these catalysts were found to hydrogenate CO2 in the presence of bicarbonate ions selectively.