Efficient CO₂ Activation Mediated by Triplet Pnictinidenes

The present investigation delineates the mechanistic landscape governing the [1 + 2] cycloaddition of CO₂ with triplet monomeric pnictinidenes ([G15-Rea]³; G15 = Group 15 element) and identifies the principal energetic factors controlling their periodic reactivity. The computed potential-energy profiles support a stepwise mechanism in which cycloaddition is initiated on the triplet potential-energy surface through [G15-TS]³, followed by a singlet-triplet surface-crossing event at [G15-T/S] and subsequent relaxation to the singlet heterocyclic products [G15-Prod]¹. ASM analysis reveals that the activation barriers are governed primarily by the deformation penalty associated with CO₂, whereas deformation of the pnictinidene and interfragment interaction contribute comparatively little to the overall barrier. The systematic increase in this deformation penalty with increasing G15 atomic radius provides a direct energetic basis for the progressive attenuation of reactivity from the lighter to the heavier pnictinidenes. Taken together, these findings establish a deformation-controlled origin for the periodic reactivity trend and provide a qualitative theoretical framework for assessing the feasibility and mechanistic implications of the proposed experimental observations.