Completing the series of boron-nucleophilic cyanoborates : boryl anions of type NHC–B(CN)₂⁻

Titelangaben

Böser, Richard ; Haufe, Lisa C. ; Freytag, Matthias ; Jones, Peter G. ; Hörner, Gerald ; Frank, René:
Completing the series of boron-nucleophilic cyanoborates : boryl anions of type NHC–B(CN)₂⁻.
In: Chemical Science. Bd. 8 (2017) Heft 9 . - S. 6274-6280.
ISSN 2041-6539
DOI: https://doi.org/10.1039/C7SC02238G

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Abstract

Since the first seminal report of boron-centred nucleophiles, the area of boryl anions has developed only sporadically and requires further systematisation. The boryl anions of type NHC–B(CN)2− (NHC = N-heterocyclic carbene) described herein complete a consistent series with the known anions cAAC–B(CN)2− [cAAC = cyclic(alkyl)(amino)carbene] and B(CN)32−. A novel approach towards NHC-stabilised cyanoboranes based on alkylthio-cyano exchange at boron is presented, and in contrast to other methods affords the products in better purity and yield. Reduction of suitable NHC–dicyanoboranes gave two unprecedented examples of NHC–B(CN)2− boryl anions. The latter were shown to react as boron-centred nucleophiles with facile formation of B–E bonds, where E = C, Si, Sn, P, Au. Bonding analysis by DFT calculations suggests a systematic variation of the energy of the boron-centred HOMO depending on the carbene, which in turn can control the nucleophilic character.