Theoretical Study of the Activation Reaction of a Zr/P-Based Frustrated Lewis Pair with Carbon Dioxide.

The combination reactions of carbon dioxide with a Zr/P-based frustrated Lewis pair (FLP) were computationally explored within the density functional theory framework [B3LYP-D3(BJ)/def2-TZVP]. Results showed that these reactions are exothermic, associated with relatively low activation barriers, and proceed concertedly involving Zr-O and P-C chemical bond formations. Theoretical analysis revealed that the shorter the Zr···P bond length of the Zr/P-based FLP, the shorter the stretching O-C bond length of CO upon reaction, the larger the ∠OCO bending angle of CO, the smaller the deformation energy of CO, the lower the barrier height, and the greater the reactivity between the Zr/P-based FLP and CO. According to the energy decomposition analysis-natural orbitals for chemical valence, the bonding natures of their associated transition states are determined by the singlet-singlet interaction (donor-acceptor interaction), not the triplet-triplet interaction (electron-sharing interaction). Moreover, the bonding characteristics between Zr/P-based FLPs and CO are established predominantly by the lone pair orbital(P) → the empty p-π* orbital (CO) interaction, not the empty d-orbital(Zr) ← the filled p-π orbital (CO) interaction. With the use of the activation strain model, theoretical examinations showed that the reactivity trend of such combination reactions is mainly attributed to the deformation energies of the deformed reactants. The relationship between deformed geometrical structures and related activation energies is in good agreement with Hammond's postulate.