Bicyclic (Alkyl)(Amino)Imine-Anchored Diphosphine and Its Radical Cation

We report the synthesis of a new carbene-based imino ligand, [(BICAAC)N^-], derived from the highly amphiphilic bicyclic (alkyl)(amino)carbene (BICAAC) through a classical Staudinger reaction. (BICAAC)NH exhibits a high proton affinity (263.0 kcal/mol), indicating strong basicity. Subsequently, a series of phosphines was synthesized from [(BICAAC)N^-], and their structures were characterized by single-crystal X-ray diffraction and multinuclear NMR spectroscopy. Reduction of (BICAAC)N-P(Br)-Tipp (Tipp = 2,4,6-triisopropylphenyl) with KC₈ afforded a diphosphine compound featuring a P-P single bond, which remained stable in solution even at elevated temperatures. Single-electron oxidation of this diphosphine yielded a persistent radical cation (6^•+), as confirmed by EPR spectroscopy and DFT studies. DFT analysis reveals that the unpaired electron in 6^•+ is delocalized over the two BICAAC-imino frameworks and the P-P bond.