A Tsinghua research team has developed neutral monovalent antimony analogs of “zero-valent carbon” compounds

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Recently, the research group led by Associate Professor Zhang Shaoguang from the Department of Chemistry at Tsinghua University made significant progress in the field of synergistic activation of small molecules by \"transition metals–main-group elements\". In this work, neutral bidentate monovalent antimony compounds were synthesized and characterized; for the first time, their electron-donating ability as ligands was quantitatively determined. Their applications in bimetallic coordination chemistry, C–O/C–F bond activation, and light-driven radical-based redox catalysis were demonstrated, providing molecular structure design strategies for the development of redox catalysts based on main-group elements. Simulating main-group element catalytic systems of transition metals is an advanced fundamental research area. Monovalent antimony compounds, due to their two pairs of lone electrons, serve as analogs of \"zero-valent carbon\" compounds. However, not only is it difficult to synthesize such compounds, but their redox properties, acidity and basicity, as well as their ability to coordinate with transition metals, remain unresolved questions in the academic community regarding their similarities to analogs of lighter elements. Multiple research teams, both domestic and international, have reported cationic bidentate Sb(I) species, but their positive charge nature limits their potential as strong electron donors, preventing them from binding to two electrophilic metal centers simultaneously. The research group led by Zhang Shaoguang proposed a ligand design strategy based on the \"charge effect + electron effect\". By taking advantage of the monanionic properties of borane dicarbene (BCB), they synthesized electrically neutral bidentate monovalent antimony compounds, and confirmed their structures through single-crystal X-ray diffraction and nuclear magnetic resonance spectroscopy. Density functional theory calculations (DFT), intrinsic bond orbital (IBO) localization analysis, and electron local function (ELF) results indicate that the antimony center in Sb(I) possesses two pairs of orthogonal unpaired 5s/5p lone electrons. The experimental study determined that the Tolman electron parameter of the Sb(I) center is approximately 2040 cm⁻¹. This value is lower than that of traditional trialkylphosphines and aziridines, suggesting for the first time that the electron-donating ability of Sb(I) is comparable to that of strong electron-donating ligands such as \"zero-valent carbon\" analogs. Sb(I) can efficiently form dinuclear Pd coordination compounds, and computational chemistry analyses such as ETS-NOCV and QTAIM confirm the existence of 5s/5p dual coordination. Sb(I), acting as a Lewis base, facilitates the activation of C–F bonds at the para positions of aromatic rings in B(C6F5)3, as well as C–O bonds in THF; this represents the first time that an antimony compound has been used as a Lewis base to participate in the activation of bond pairs involving hindered Lewis acids. Furthermore, Sb(I) catalyzes 1,2-iodoperfluoralkylation of olefins with perfluorohexyl iodide under 365 nm light irradiation. The research team isolated the key oxidation addition intermediate; by combining ultraviolet spectroscopy, computational chemistry to determine the bond energy of the Sb–CF bond, and radical capture experiments, they proposed that under 365 nm light irradiation, Sb–C homolysis occurs to generate perfluoroalkyl radicals. The Sb(I) complexes developed in this study integrate multiple functions, including strong electron donation, bimetallic coordination, FLP-type chemical bond activation, and photo-driven radical-catalyzed coupling reactions. The research findings, titled “Charge-neutral and strongly donating antimony(I) complexes: bimetalation, bond activation, and catalysis,” were published online in Chemistry on February 17. Zhou Jinyang, a doctoral student in the Department of Chemistry at Tsinghua University in the class of 2023, is the first author of the paper, while Zhang Shaoguang, an associate professor in the same department, is the corresponding author. The research was funded by the **Major Research Program Training Project of the National Natural Science Foundation, Tsinghua University’s Dushi Special Fund, the China Postdoctoral Foundation’s Recruitment Program, and other sources.