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In a publication just designated as 'hot paper' in Angewandte Chemie, HIMS researchers shed new light on the mechanism of reactions involving frustrated Lewis pairs (FLPs). They demonstrate that within FLP chemistry, both polar and radical pathways can be accessed. Their paper, which was also highlighted in ChemistryViews, describes how the latter generally proceeds via Lewis acid coordination to the substrate prior to radical formation.

Figure from the paper
Change in electron affinity when B(C6F5)3 coordinates and the resulting LUMO for two different B(C6F5)3-coordinated substrates. Image: HIMS / Angewandte Chemie.

Abstract:

Frustrated Lewis pairs (FLPs) are well known for their ability to activate small molecules. Recent reports of radical formation within such systems indicate single‐electron transfer (SET) could play an important role in their chemistry. Herein, we investigate radical formation upon reacting FLP systems with dihydrogen, triphenyltin hydride, or tetrachloro‐1,4‐benzoquinone (TCQ) both experimentally and computationally to determine the nature of the single‐electron transfer (SET) events; that is, being direct SET to B(C6F5)3 or not. The reactions of H2 and Ph3SnH with archetypal P/B FLP systems do not proceed via a radical mechanism. In contrast, reaction with TCQ proceeds via SET, which is only feasible by Lewis acid coordination to the substrate. Furthermore, SET from the Lewis base to the Lewis acid–substrate adduct may be prevalent in other reported examples of radical FLP chemistry, which provides important design principles for radical main‐group chemistry.

Paper:

Flip Holtrop, Andy Jupp, Bastiaan Kooij, Klaas van Leest, Bas de Bruin, Chris Slootweg: Single‐electron Transfer in Frustrated Lewis Pair Chemistry, Angew. Chem. Int. Ed. 2020. DOI: 10.1002/anie.202009717

ChemistryViews highlight: Frustrated Lewis Pair Radical Chemistry