Metal‐Free Reduction of CO 2 to Methanol Using Boranes at Ambient Conditions Promoted by Boron‐Appended N‐Heterocyclic Nitrenium Catalysts
Rahul Mondal, Reetu Rani Mondal, K. GeetharaniABSTRACT
The chemical reduction of carbon dioxide (CO 2 ) into value‐added C1 building blocks, particularly under sustainable, metal‐free conditions, remains a profound challenge in modern catalysis. Herein, we report robust boron‐tethered N‐heterocyclic nitrenium (NHN) catalysts for the reduction of CO 2 under ambient conditions to produce methoxide‐level products. The developed protocol works under room temperature and 1 bar CO 2 pressure, with a low catalyst loading. The borane reductant governs the selectivity of the hydroboration reaction. Employing catecholborane (HBcat) or borane dimethylsulfide complex (BH 3 ·SMe 2 ) drives rapid, selective, complete reduction to methoxide‐level products. In contrast, the use of 9‐borabicyclo[3.3.1]nonane (9‐BBN) under identical conditions yields a mixture of acetal‐level (CH 2 (OBBN) 2 ) and methoxyborane (MeOBBN) species, while pinacolborane (HBpin) exhibits lower reactivity, generating a distribution across all three reduction states. Overall, the catalytic platform exhibits excellent turnover numbers (TON). This work establishes a sustainable, metal‐free methodology for tunable reduction of CO 2 to methanol equivalents, highlighting the versatility of main‐group catalysis.