Comparison of the Efficiency of B–O and B–C Bond Formation Pathways in Borane-Catalyzed Carbene Transfer Reactions Using α-Diazocarbonyl Precursors: A Combined Density Functional Theory and Machine Learning Study
Year: 2024
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide Lewis acidic boranes, especially tris(pentafluorophenyl)borane [B(C 6 F 5 ) 3 ], have emerged as metal-free catalysts for carbene transfer reactions of α-diazocarbonyl compounds in a variety of functionalization reactions. The established mechanism for how borane facilitates carbene generation for these compounds in the scientific community is based on the formation of a B–O (C═O) intermediate ( path O ). Herein, we report an extensive DFT study that challenges the notion of a ubiquitous path O, revealing that B–C(═N═N) bond formation ( path C ) for certain diazocarbonyl substrates proves to be the preferred pathway. This study elucidates, through the introduction of 22 various substituents on each side of the α-diazocarbonyl backbone, how the electron-donating and -withdrawing properties of substituents influence the competition between these B–O and B–C pathways. To elucidate the impact of the electronic features of diazo substrates on the competition between the O and C pathways in the studied dataset, we employed a machine learning approach based on the Random Forest model. This analysis revealed that substrates with higher electron density on the diazo-attached carbon, lower electron density on the carbonyl carbon, and more stable HOMO orbitals tend to proceed via path C . Furthermore, this study not only demonstrates that borane efficiency in facilitating N 2 release is greatly affected by the nature of substituents on both sides of the α-diazocarbonyl functionality but also shows that for some substrates, borane is incapable of catalyzing the release of molecular nitrogen.
Source: ACS Catalysis
Authors: Kaveh Farshadfar, Kari Laasonen
Institution: Aalto University
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,500
OpenAlex ID: W4402806899