Unveiling Borane Complexes With N, O Chelation: Synthesis, Reactivity, and Theoretical Studies

We synthesized a series of 2‐aminotropone (N, O)‐based borane complexes ( 2a – 2c ) in a five‐membered scaffold that exhibits strong fluorescence in solution. The photoluminescence lifetimes of these complexes, measured in dichloromethane, range from 3.40 to 3.91 ns. Correspondingly, fluorescence quantum yields of boranes ( 2a ‐ 2c ) range from 10% to 15%, indicating the quantum yields and fluorescence decay times have minimal impact of the substituents present on the nitrogen atom. Treatment of these borane complexes with trimethylsilyl trifluoromethanesulfonate (TMS‐OTf) results in the formation of mixtures of borenium (three coordinated) and boronium (four coordinated) cations in solution. In contrast, reacting 2‐aminotropones with BBr 3 at room temperature selectively afforded boronium cations ( 4a – 4c ). All these neutral and cationic complexes were fully characterized using multinuclear NMR spectroscopy and single‐crystal x‐ray diffraction analysis. Furthermore, Density Functional Theory (DFT) studies were performed to analyze the electronic properties of both neutral and cationic boron species.