A stable rhodium-coordinated carbene with a ⁰² electronic configuration

Isolable singlet carbenes have universally adopted a sigma(2)pi(0) electronic state, making them sigma-donors and pi-acceptors. We present a rhodium-coordinated, cationic cyclic diphosphinocarbene with a sigma(0)pi(2) 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 RhP2C configuration. Quantum chemical calculations rationalize how sigma-electron delocalization/donation and pi-electron negative hyperconjugation together stabilize the formally vacant sigma orbital and the filled pi 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 pi-complex, respectively. Exhibiting ambiphilic reactivity, it can also form a ketenimine through reaction with an isocyanide.