Mapping the Electronic Structure and the Reactivity Trends for Stabilized alpha-Boryl Carbanions

Identifier:  imarina:9225155

Handle: https://hdl.handle.net/20.500.11797/imarina9225155

Authors:  Maza, Ricardo J; Fernandez, Elena; Carbo, Jorge J

Abstract:
The chemistry of stabilized alpha-boryl carbanions shows remarkable diversity, and can enable many different synthetic routes towards efficient C-C bond formation. The electron-deficient, trivalent boron center stabilizes the carbanion facilitating its generation and tuning its reactivity. Here, the electronic structure and the reactivity trends of a large dataset of alpha-boryl carbanions are described. DFT-derived parameters were used to capture their electronic and steric properties, computational reactivity towards model substrates, and crystallographic analysis within the Cambridge Structural Dataset. This study maps the reactivity space by systematically varying the nature of the boryl moiety, the substituents of the carbanionic center, the number of alpha-boryl motifs, and the metal counterion. In general, the free carbanionic intermediates are described as borata-alkene species with C-B pi interactions polarized towards the carbon. Furthermore, it was possible to classify the alpha-boryl alkylidene metal precursors into three classes directly related to their reactivity: 1) nucleophilic borata-alkene salts with alkali and alkaline earth metals, 2) nucleophilic eta(2)-(C-B) borata-alkene complexes with early transition metals, Cu and Ag, and 3) alpha-boryl alkyl complexes with late transition metals. This trend map aids selection of the appropriate reactive synthon depending on the reactivity sought.