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- Title
The Hydride-Ion Affinity of Borenium Cations and Their Propensity to Activate H<sub>2</sub> in Frustrated Lewis Pairs.
- Authors
Clark, Ewan R.; Del Grosso, Alessandro; Ingleson, Michael J.
- Abstract
A range of frustrated Lewis pairs (FLPs) containing borenium cations have been synthesised. The catechol (Cat)-ligated borenium cation [CatB(P tBu3)]+ has a lower hydride-ion affinity (HIA) than B(C6F5)3. This resulted in H2 activation being energetically unfavourable in a FLP with the strong base P tBu3. However, ligand disproportionation of CatBH(P tBu3) at 100 °C enabled trapping of H2 activation products. DFT calculations at the M06-2X/6-311G(d,p)/PCM (CH2Cl2) level revealed that replacing catechol with chlorides significantly increases the chloride-ion affinity (CIA) and HIA. Dichloro-borenium cations, [Cl2B(amine)]+, were calculated to have considerably greater HIA than B(C6F5)3. Control reactions confirmed that the HIA calculations can be used to successfully predict hydride-transfer reactivity between borenium cations and neutral boranes. The borenium cations [Y(Cl)B(2,6-lutidine)]+ (Y=Cl or Ph) form FLPs with P(mesityl)3 that undergo slow deprotonation of an ortho-methyl of lutidine at 20 °C to form the four-membered boracycles [(CH2{NC5H3Me})B(Cl)Y] and [HPMes3]+. When equimolar [Y(Cl)B(2,6-lutidine)]+/P(mesityl)3 was heated under H2 (4 atm), heterolytic cleavage of dihydrogen was competitive with boracycle formation.
- Publication
Chemistry - A European Journal, 2013, Vol 19, Issue 7, p2462
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201203318