Geometrically Constrained Organoboron Species as Lewis Superacids and Organic Superbases
Weiwei Lv, Yuyang Dai, Rui Guo, Yuanting Su, David A. Ruiz, Liu Leo Liu, Chen‐Ho Tung, Lingbing Kong
Abstract
Abstract This report unveils an advancement in the formation of a Lewis superacid (LSA) and an organic superbase by the geometrical deformation of an organoboron species towards a T‐shaped geometry. The boron dication [ 2 ] 2+ supported by an amido diphosphine pincer ligand features both a large fluoride ion affinity (FIA>SbF 5 ) and hydride ion affinity (HIA>B(C 6 F 5 ) 3 ), which qualifies it as both a hard and soft LSA. The unusual Lewis acidic properties of [ 2 ] 2+ are further showcased by its ability to abstract hydride and fluoride from Et 3 SiH and AgSbF 6 respectively, and effectively catalyze the hydrodefluorination, defluorination/arylation, as well as reduction of carbonyl compounds. One and two‐electron reduction of [ 2 ] 2+ affords stable boron radical cation [ 2 ]⋅ + and borylene 2 , respectively. The former species has an extremely high spin density of 0.798 e at the boron atom, whereas the latter compound has been demonstrated to be a strong organic base (calcd. p K BH + (MeCN)=47.4) by both theoretical and experimental assessment. Overall, these results demonstrate the strong ability of geometric constraining to empower the central boron atom.