T-Shaped Stannyliumylidene Ion: Synthesis, Reactivity, and Redox Catalysis

We report the synthesis and characterization of a T-shaped, 8-electron stannyliumylidene ion bearing a rigid acridane-based pincer ligand. This cationic Sn(II) complex exhibits pronounced ambiphilic reactivity, participating in electrophilic, nucleophilic, and σ-bond activation reactions. All derived compounds were characterized by nuclear magnetic resonance spectroscopy, single crystal x-ray diffraction analysis, and high-resolution mass spectrometry. Density functional theory calculations reveal the coexistence of a lone pair of electrons and a vacant 5p-orbital at the tin center, which rationalizes the experimentally observed dual reactivity. Remarkably, the transition metal-like electronic structure enables this organotin(II) species to act as an efficient catalyst for transfer hydrogenation of azoarenes and imines using NH₃BH₃ as hydrogen source. Combined experimental and computational mechanistic studies reveal a distinct catalytic platform based on Sn(II)/Sn(IV) redox cycle at a single tin(II) center. This work demonstrates the first Sn(II)/Sn(IV) catalyzed reduction of unsaturated bonds, offering a paradigm for mimicking transition metal reactivity through rationally designed main group systems in mediating diverse chemical transformations.