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.