Conformational and Substituent Effects on The Rehybridization of Boron in β‐Substituted Ethylboranes. Issue 6 (29th April 2021)

• Record Type: Journal Article
• Authors: Martins, Francisco A.; Freitas, Matheus P.
• Is Part Of: Asian journal of organic chemistry. Volume 10:Issue 6(2021)
• Page Start: 1486
• Page End: 1491
• Publication Date: 2021-04-29
• Subjects: organoboron compounds -- conformational analysis -- electron delocalization -- quantum-chemical calculations; Chemistry, Organic -- Periodicals; Organic compounds -- Synthesis -- Periodicals; 547.005
• DOI: 10.1002/ajoc.202100167
• Languages: English
• ISSNs: 2193-5807

Abstract

Abstract: The chemistry of boron‐containing molecules pervades the study of biomolecules, new materials, organic synthesis, and beyond. In addition, the stereochemistry and rehybridization capability of boron in molecules influence the reactivity and selectivity of reactions. Therefore, conformational analysis and the study of substituent effects on the modulation of the sp 2 – sp 3 character of boron in β‐substituted ethylboranes may be valuable for the rational design of compounds in which the empty p B orbital plays a central role in the reaction intermediate. Accordingly, we have quantum‐chemically studied the orbital interactions and bonding properties that govern the conformational behavior and boron hybridization in β‐substituted ethylboranes (substituents, X=H, CH3, F, Cl, NH2, PH2, OH, and SH). Conformations with an anti arrangement along the B−C−C−X path are generally preferred over syn and/or gauche conformations, while a B−H bond tends to eclipse with the C−C bond rather than with a less sterically hindered C−H bond. However, the s character of boron relative to the C−B bond strongly decreases in the syn conformation, where X can participate as an electron donor to the empty p B orbital. Indeed, such interaction makes the syn conformation of 2‐aminoethylborane the single stable conformer in the gas phase. Abstract : That's rehybridizable ! While alkane chains adopt staggered conformations, some β‐substituted ethylboranes may prefer to assume an eclipsed form or even close the ring, due to a strong electron donation from the substituent to the empty p B orbital. This interaction causes a significant sp 2 – sp 3 rehybridization in the boron, which can be useful to modulate the stability of reaction intermediates, important in e. g . boronate synthesis.