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

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)₃^2-. 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.

SUBMITTER: Boser R 

PROVIDER: S-EPMC5628389 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature