A stable rhodium-coordinated carbene with a σ<sup>0</sup>π<sup>2</sup> electronic configuration.
basic_science · Level V
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- Also identified by DOI 10.1126/science.adk6533.
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Abstract
Isolable singlet carbenes have universally adopted a σ<sup>2</sup>π<sup>0</sup> electronic state, making them σ-donors and π-acceptors. We present a rhodium-coordinated, cationic cyclic diphosphinocarbene with a σ<sup>0</sup>π<sup>2</sup> ground state configuration. Nuclear magnetic resonance spectroscopy studies show a carbene carbon chemical shift below -30.0 parts per million. X-ray crystallography reveals a planar RhP<sub>2</sub>C configuration. Quantum chemical calculations rationalize how σ-electron delocalization/donation and π-electron negative hyperconjugation together stabilize the formally vacant σ orbital and the filled π orbital at the carbene center. In contrast to traditional carbene counterparts this carbene can undergo synthetic transformations with both a Lewis base and a silver salt, producing a Lewis acid/base adduct and a silver π-complex, respectively. Exhibiting ambiphilic reactivity, it can also form a ketenimine through reaction with an isocyanide.