Tris(ortho-carboranyl)borane: An Isolable, Halogen-Free, Lewis Superacid

The synthesis of tris(ortho-carboranyl)borane (BoCb(3)), a single site neutral Lewis superacid, in one pot from commercially available materials is achieved. The high fluoride ion affinity (FIA) confirms its classification as a Lewis superacid and the Gutmann-Beckett method as well as adducts with Lewis bases indicate stronger Lewis acidity over the widely used fluorinated aryl boranes. The electron withdrawing effect of ortho-carborane and lack of pi-delocalization of the LUMO rationalize the unusually high Lewis acidity. Catalytic studies indicate that BoCb(3) is a superior catalyst for promoting C-F bond functionalization reactions than tris(pentafluorophenyl)borane [B(C6F5)(3)].

Automated summary

The synthesis of a single site neutral Lewis superacid, tris(ortho-carboranyl)borane (BoCb(3)), was achieved in one pot from commercially available materials. It was confirmed to be a Lewis superacid due to its high fluoride ion affinity (FIA), and exhibited stronger Lewis acidity compared to widely used fluorinated aryl boranes, as evidenced by the Gutmann-Beckett method and adducts with Lewis bases. The unusually high Lewis acidity can be rationalized by the electron-withdrawing effect of ortho-carborane and lack of pi-delocalization of the LUMO. Catalytic studies demonstrated that BoCb(3) is a superior catalyst for promoting C-F bond functionalization reactions compared to tris(pentafluorophenyl)borane [B(C6F5)(3)].