An Unsymmetrical, Cyclic Diborene Based on a Chelating CAAC Ligand and its Small-Molecule Activation and Rearrangement Chemistry

A one-pot synthesis of a CAAC-stabilized, unsymmetrical, cyclic diborene was achieved via consecutive two-electron reduction steps from an adduct of CAAC and B2Br4(SMe2)(2). Theoretical studies revealed that this diborene has a considerably smaller HOMO-LUMO gap than those of reported NHC- and phosphine-supported diborenes. Complexation of the diborene with [AuCl(PCy3)] afforded two diborene-Au-I pi complexes, while reaction with DurBH(2), P-4 and a terminal acetylene led to the cleavage of B-H, P-P, and C-C pi bonds, respectively. Thermal rearrangement of the diborene gave an electron-rich cyclic alkylideneborane, which readily coordinated to Ag-I via its B=C double bond.

Automated summary

A one-pot synthesis of a CAAC-stabilized, unsymmetrical, cyclic diborene was achieved through consecutive two-electron reduction steps, resulting in a diborene with a smaller HOMO-LUMO gap. Complexation with [AuCl(PCy3)] led to two diborene-Au-I pi complexes, while reactions with different reagents led to cleavage of various bonds, and thermal rearrangement gave rise to an electron-rich cyclic alkylideneborane that easily coordinated to Ag-I.