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<p>Ground-state <i>σ</i><sup>0</sup><i>π</i><sup>2</sup> carbenes are among the least explored and least understood classes of low-valent carbon. Known examples of isolable <i>σ</i><sup>0</sup><i>π</i><sup>2</sup> carbenes remain largely limited to cationic compounds. Here we report the synthesis of a neutral <i>σ</i><sup>0</sup><i>π</i><sup>2</sup> carbene, namely a rhodadiphosphinocarbene featuring a planar RhP<sub>2</sub>C ring. In sharp contrast to small-molecule activation by conventional <i>σ</i><sup>2</sup><i>π</i><sup>0</sup> carbenes, which typically proceeds via nucleophilicity-driven, <i>π</i>-face, non-least-motion trajectories mandated by orbital-symmetry constraints, this neutral <i>σ</i><sup>0</sup><i>π</i><sup>2</sup> carbene cleaves H<sub>2</sub> under ambient conditions via a <i>σ</i>-face pathway. Computations reveal an electrophilicity-driven early transition state characterized by minimal reorganization of the carbene framework and a concerted yet asynchronous H–H scission to form two C–H bonds. These findings show that a stable carbene can enable small-molecule activation through a <i>σ</i>-face pathway and deepen our understanding of electronic structure–reactivity correlations in low-valent carbon chemistry.</p><p></p>

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A neutral σ0π2 carbene enabling hydrogen activation via a σ-face pathway

  • 期刊论文

  • 发表日期：

    2026年5月11日

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  • Fei Fan,
  • Haoxiang Nong,
  • Miaomiao Zhou,
  • Liu Leo Liu

摘要

Ground-state σ0π2 carbenes are among the least explored and least understood classes of low-valent carbon. Known examples of isolable σ0π2 carbenes remain largely limited to cationic compounds. Here we report the synthesis of a neutral σ0π2 carbene, namely a rhodadiphosphinocarbene featuring a planar RhP2C ring. In sharp contrast to small-molecule activation by conventional σ2π0 carbenes, which typically proceeds via nucleophilicity-driven, π-face, non-least-motion trajectories mandated by orbital-symmetry constraints, this neutral σ0π2 carbene cleaves H2 under ambient conditions via a σ-face pathway. Computations reveal an electrophilicity-driven early transition state characterized by minimal reorganization of the carbene framework and a concerted yet asynchronous H–H scission to form two C–H bonds. These findings show that a stable carbene can enable small-molecule activation through a σ-face pathway and deepen our understanding of electronic structure–reactivity correlations in low-valent carbon chemistry.