Ph₃PC - A Monosubstituted C(0) Atom in Its Triplet State.

Area of Science:

• Organometallic Chemistry
• Radical Chemistry
• Spectroscopy

Background:

• Divalent carbon compounds are typically excited to high-energy states.
• Understanding the electronic configuration of carbon centers is crucial in chemistry.

Purpose of the Study:

• To introduce and characterize a novel class of carbon-centered diradicals.
• To investigate the electronic structure and stability of phosphine-stabilized carbon diradicals.

Main Methods:

• Photochemical generation from a diazophosphorus ylide precursor (Ph3PCN2).
• Characterization using Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) spectroscopy.
• Computational analysis using multireference electronic structure calculations.

Main Results:

• Successful generation and characterization of the Ph3P→C diradical.
• Experimental confirmation of a triplet ground state with a long lifetime (approx. 10 min at 127 K).
• Low zero-field splitting parameter D=0.543 cm⁻¹ and negligible rhombicity (|E|/D=0.002).
• Computational prediction of a significant singlet-triplet gap (>20 kcal/mol).

Conclusions:

• The novel Ph3P→C diradical possesses a stable triplet ground state.
• This stability arises from the direct involvement of carbon in its natural 3P state, unlike other divalent carbon compounds.
• This discovery expands the understanding of carbene reactivity and electronic structures.