Unveiling Borane Complexes with N, O Chelation: Synthesis, Reactivity, and Photophysical Properties

We synthesized a series of 2-aminotropone-based borane complexes (2a–2c) that exhibit strong fluorescence in solution. The photoluminescence lifetimes of these complexes, measured in dichloromethane, range from 3.40 to 3.91 ns, with the substituents on the nitrogen atom influencing their photophysical properties. Treatment of these borane complexes with trimethylsilyl trifluoromethanesulfonate (TMS-OTf) results in the formation of mixtures of borenium and boronium cations in solution. In contrast, reacting 2-aminotropone with BBr₃ at room temperature selectively affords boronium cations (4a–4c). These cations were fully characterized using multinuclear NMR spectroscopy and single-crystal X-ray diffraction analysis.