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 kcal mol−1, and the energy barrier for the thermal conversion from azaborole to borirane is 35.5 kcal mol−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.