Every reaction Detail Matters: An in silico driven Step-by-Step Guide to understand the B2O3-Catalyzed CO2 to cyclic carbonates conversion

Abstract

The catalytic conversion of carbon dioxide (CO₂) to cyclic organic carbonates (COCs) via cycloaddition with epoxides offers a dual benefit of reducing CO₂ emissions while producing valuable chemical products. In this detailed in silico study, we employ density functional theory (DFT) to meticulously investigate the mechanisms underlying the B₂O₃/n-NBu₄Br-catalyzed cycloaddition of CO₂ and epoxides, following a step-by-step approach according to the reaction details. We provide a comprehensive comparison of the non-catalyzed, n-NBu₄Br alone, and B₂O₃/n-NBu₄Br-catalyzed pathways, emphasizing two distinct active sites within the B₂O₃ framework: Site 1 (six-membered boroxol ring) and Site 2 (open chain configuration). Our computational analysis highlights that the Site 1-catalyzed reaction pathway is more favorable, featuring a lower overall energy barrier of 26.8 kcal/mol, compared to 32.5 kcal/mol for the Site 2-catalyzed pathway. Detailed intrinsic bond orbital (IBO), natural adaptive orbital (NAdO) and distortion-interaction analysis (DIA) reveal significant differences in bonding properties and energy interactions, elucidating why Site 1 exhibits superior catalytic activity over Site 2. These findings are corroborated by experimental observations, which indicate that ball milling B₂O₃ increases defect sites, thereby enhancing exposure of active sites Site 1 and improving catalytic performance. This study provides an in-depth understanding of how the intrinsic properties of boron active sites influence the catalytic efficiency of B₂O₃, offering valuable insights for the design and optimization of metal-free catalysts for CO₂ conversion.