Reactivity of a Frustrated Lewis Pair and Small‐Molecule Activation by an Isolable Arduengo CarbeneB{3,5‐(CF₃)₂C₆H₃}₃ Complex

Abstract

Tris[3,5-bis(trifluoromethyl)phenyl]borane reacts with the sterically demanding Arduengo carbenes 1,3-di-tert-butylimidazolin-2-ylidene and 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene to form isolable normal adducts. In the case of 1,3-di-tert-butylimidazolin-2-ylidene, the adduct exhibits dynamic behaviour in solution and frustrated-Lewis-pair (FLP) reactivity. Fast cleavage of dihydrogen and THF, the C-H activation of phenylacetylene, and carbon dioxide fixation were achieved by using solutions of this adduct in benzene. This adduct is stable at room temperature in the absence of suitable substrates; however, thermal rearrangement into an abnormal carbene-borane adduct can be observed. In contrast, the 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene adduct exhibits no evidence of FLP reactivity or of dissociation in solution. DFT calculations confirmed the experimental behaviour and stability of these carbene-borane adducts.

Non-conventional Lewis Acids and Bases in Frustrated Lewis Pair Chemistry

“…It is important to note that the N-heterocyclic carbenes (NHCs) do not undergo analogous reactivity, presumably the result of the diminished acceptor capacity. In simultaneous studies, our group [68] [70].…”

“…The reaction of this FLP (27) with phenylacetylene at room temperature resulted in two distinct products in a 3:1 ratio, a phosphonium alkynylaluminate (28) formed by the deprotonation of the alkyne by the phosphine and a second product formed by the addition of the FLP across the alkyne (29). This reaction can be pushed to give exclusively 29 by gently heating the reaction to 70 C. This geminal FLP was also shown to activate CO 2 , resulting in the formation of a 5-membered heterocycle (30). The addition of CO 2 was found to be reversible at 135 C, which is in contrast to the P/B intramolecular systems which rapidly lose CO 2 [60].…”

Metal-free electrocatalytic hydrogen oxidation using frustrated Lewis pairs and carbon-based Lewis acids

“…We have recently examined the possibility of using tris[3,5-bis(trifluoromethyl)phenyl]borane (BArF 18 ) as the Lewis acidic component of an electrochemical–FLP system 45. The activation of H 2 by BArF 18 -containing FLPs is rapid and favours the formation of the bridging hydride, [(μ-H) (BArF 18 ) 2 ] – 46,47. However, the oxidation potential of [(μ-H) (BArF 18 ) 2 ] – is too positive to be useful for electrochemical–FLP applications ( ca.…”

Experimental Insights into the Structure and Reactivity of Frustrated Lewis Pairs

“…No such chemical exchange was observed in the case of 10, confirming that such an adduct is stronger than the previous one, likely due to the lower bulkiness of the isopropyl substituent. [42] …”