Reversible Photothermal Isomerization of Carborane-Fused Azaborole to Borirane: Synthesis and Reactivity of Carbene-Stabilized Carborane-Fused Borirane

A fully reversible photothermal isomerization between carborane-fused trigonal-planar azaborole (dark-purple) and tetrahedral borirane (pale-yellow) has been observed, leading to the isolation and structural characterization of the first example of carborane-fused borirane. DFT calculations indicate that the azaborole is thermodynamically more stable than the borirane by 11.2 kcalmol(-1), and the energy barrier for the thermal conversion from azaborole to borirane is 35.5 kcalmol(-1). The reactivity studies show that the B-C(cage) bond in borirane can be broken in the reaction with CuCl, HCl, or elemental sulfur.