Hydroboration of CO2 catalyzed by heteroscorpionate zwitterionic zinc and magnesium hydride complexes†
Abstract
The heteroscorpionate zinc hydride complex LZnH 2, (L = (MePz)2CP(Ph)2NPh, MePz = 3,5-dimethylpyrazolyl), its formate complex 3, and magnesium hydride complex LMgH 5 with the same ligand were synthesized and detected for the catalytic hydroboration reaction of CO2. With BH3·SMe2 as the reductant, zinc-based hydride complex 2 and formate complex 3 show a similar capability of hydroboration of CO2, featuring excellent reactivity and selectivity. The conversion of BH3·SMe2 reached 84%, the highest TON of 252 compared to other zinc catalysts was achieved at room temperature and borate ester products at reduction levels of CH3OH were obtained. Magnesium-based hydride complex 5 showed inferior activity for the hydroboration reduction of CO2.