Ph3PC – a monosubstituted C(0) atom in its triplet state
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Date
2025-01-27
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Abstract
This study introduces a novel class of carbon-centered diradicals: a monosubstituted C atom stabilized by a phosphine. The diradical Ph3P→C was photochemically generated from a diazophosphorus ylide precursor (Ph3PCN2) and characterized by EPR and isotope-sensitive ENDOR spectroscopy at low temperatures. Ph3P→C features an axial zero-field splitting parameter D=0.543 cm−1 with a vanishingly small rhombicity |E|/D=0.002. Time- and temperature-dependent measurements confirm a triplet ground state with a lifetime of approximately 10 min at 127 K in toluene-d8. Multireference electronic structure calculations predict a clear triplet ground state with a singlet-triplet gap greater than 20 kcal/mol. In contrast to divalent C(0) compounds, such as Ph3P→C←PPh3, in which carbon needs excitation into a highly-excited closed-shell 2s02p4 configuration, Ph3P→C can be explained by direct involvement of carbon in its natural 3P state arising from the 2s22p2 configuration.
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reactive intermediates, carbon, EPR spectroscopy, diradicals, carbones