Reactions of a BICAAC with hydroboranes: propensity for Lewis adduct formation and carbene insertion into the B–H bond

Abstract

The reactivity of a bicyclic (alkyl)(amino)carbene (BICAAC) towards different boranes has been examined in the present work. The reactions with boranes BX₃·SMe₂ (X = H, Cl, Br), BF₃·OEt₂ and BCl₃ yield Lewis adducts [BICAAC·BH₃] (1), [BICAAC·BHCl₂] (2), [BICAAC·BH₂Cl] (3), [BICAAC·BF₃] (4), [BICAAC·BCl₃] (5) and [BICAAC·BBr₃] (6) respectively, whereas more hydridic boranes, 9-borabicyclo[3.3.1]nonane (9-BBN) and catecholborane (HBcat), enable the insertion of the carbene carbon into the B–H bond to form [BICAAC(H)-(9-BBN)] (7) and [BICAAC(H)-Bcat] (8). These complexes are the first examples of BICAAC–boron compounds and have been characterized using IR, multinuclear NMR spectroscopy, HRMS spectrometry and single crystal X-ray diffraction. Computational analyses were also performed to gain insight into the mechanism of B–H bond activation and adduct formation. Furthermore, the reactions of the BICAAC with boranes have been compared with the known reactions of CAACs and NHCs.