Synthesis, Characterization, and Density Functional Theory Studies of Three-Dimensional Inorganic Analogues of 9,10-Diboraanthracene-A New Class of Lewis Superacids.

Abstract

The three-dimensional inorganic analogues of 9,10-diboraanthracene, B2X2(C2B10H10)2 (X = Cl, 1; X = Br, 2), were attained by salt elimination of Li2C2B10H10 and trihaloboranes. The methyl- and phenyl-substituted compounds B2Me2(C2B10H10)2 (3) and B2Ph2(C2B10H10)2 (4) were obtained by treating 1 or 2 with the corresponding Grignard reagents. These compounds were fully characterized by NMR, cyclic voltammetry (CV), IR, and single-crystal X-ray diffraction analyses. Experimental (CV and Gutmann-Beckett method) and computational (fluoride ion affinity, hydride ion affinity and LUMO energy) results suggest that the order of Lewis acidity is 2 > 1 > 4 > 3 > SbF5. Treatment of 1 or 2 with HSiEt3 gave a rare neutral borane-silane adduct, (Et3SiH)2B2H2(C2B10H10)2 (5). The equilibrium of 5 in solution was thoroughly investigated by spectroscopy and quantum calculations.