aNHC-Stabilized Low-Valent Phosphorus Compound: Exploring Dual Catalytic Activity via Nucleophilicity and P(I)/P(III) Redox Reactivity

In this work, we present the synthesis and detailed characterization of a low-valent phosphorus compound, mesoionic N-heterocyclic phosphinidene (mNHP, <b>2</b>), stabilized by an abnormal N-heterocyclic carbene (aNHC). Natural resonance theory analysis and the formation of a bis-borane adduct (confirmed by a single-crystal X-ray diffraction study) revealed that the phosphorus center in mNHP has access to two lone pairs of electrons, as expected for a P(I) species. Beyond its structural characterization, we also investigated both the nucleophilic and redox reactivity of mNHP. Its interactions with CO₂ and CS₂ demonstrated its nucleophilic capabilities, while its reaction with a C(Ar)-F bond highlighted its redox behavior through oxidative addition at the P(I) center, transforming it into a P(III) species. These dual reactivities were subsequently integrated into catalytic cycles, positioning mNHP as an effective low-valent, metal-free catalyst for the formylation of thiols using CO₂ via nucleophilicity and hydrodefluorination of aryl fluoride compounds via the P(I)/P(III) redox cycle. Various spectroscopic investigations, including X-ray photoelectron spectroscopy (XPS), trapping of intermediates, and detailed DFT studies, helped us to understand the dual reactivity of this low-valent phosphorus compound.