Nucleophilic addition and substitution at coordinatively saturated boron by facile 1,2-hydrogen shuttling onto a carbene donorElectronic supplementary information (ESI) available: General experimental details, characterization data for all reported compounds and details of the DFT calculations. CCDC 1563216-1563221. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc03193a

The reaction of [(cAAC Me )BH 3 ] (cAAC Me = 1-(2,6- i Pr 2 C 6 H 3 )-3,3,5,5-tetramethylpyrrolidin-2-ylidene) with a range of organolithium compounds led to the exclusive formation of the corresponding (dihydro)organoborates, Li + [(cAAC Me H)BH 2 R] − (R = sp 3 -, sp 2 -, or sp-hybridised organic...

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Main Authors: Auerhammer, Dominic, Arrowsmith, Merle, Braunschweig, Holger, Dewhurst, Rian D, Jiménez-Halla, J. Oscar C, Kupfer, Thomas
Format: Article
Language:English
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Summary:The reaction of [(cAAC Me )BH 3 ] (cAAC Me = 1-(2,6- i Pr 2 C 6 H 3 )-3,3,5,5-tetramethylpyrrolidin-2-ylidene) with a range of organolithium compounds led to the exclusive formation of the corresponding (dihydro)organoborates, Li + [(cAAC Me H)BH 2 R] − (R = sp 3 -, sp 2 -, or sp-hybridised organic substituent), by migration of one boron-bound hydrogen atom to the adjacent carbene carbon of the cAAC ligand. A subsequent deprotonation/salt metathesis reaction with Me 3 SiCl or spontaneous LiH elimination yielded the neutral cAAC-supported mono(organo)boranes, [(cAAC Me )BH 2 R]. Similarly the reaction of [(cAAC Me )BH 3 ] with a neutral donor base L resulted in adduct formation by shuttling one boron-bound hydrogen to the cAAC ligand, to generate [(cAAC Me H)BH 2 L], either irreversibly (L = cAAC Me ) or reversibly (L = pyridine). Variable-temperature NMR data and DFT calculations on [(cAAC Me H)BH 2 (cAAC Me )] show that the hydrogen on the former carbene carbon atom exchanges rapidly with the boron-bound hydrides. Anionic organic sp 3 -, sp 2 - and sp-nucleophiles as well as neutral Lewis bases were shown to add to a coordinatively saturated cyclic (alkyl)(amino)carbene (cAAC) supported borane thanks to reversible transfer of a hydrogen atom from boron to the adjacent Lewis acidic cAAC carbene carbon atom.
ISSN:2041-6520
2041-6539
DOI:10.1039/c7sc03193a