| Summary: | As a desired feedstock for sustainable energy source and for chemical synthesis, the capture and utilization of CO<sub>2</sub> have attracted chemists’ continuous efforts. The homogeneous CO<sub>2</sub> insertion into a nickel hydride complex to generate formate provides insight into the role of hydrogen as an active hydride form in the hydrogenation of CO<sub>2</sub>, which serves as a practicable approach for CO<sub>2</sub> utilization. To parameterize the activities and to model the structure–activity relationship in the CO<sub>2</sub> insertion into nickel hydride, the comprehensive mechanism of CO<sub>2</sub> insertion into a series of square planar transition metal hydride (TM–H, TM = Ni, Pd, and Co) complexes was investigated using density functional theory (DFT) computations. The stepwise pathway with the TM-(H)-formate intermediate for the CO<sub>2</sub> insertion into all seven square planar transition metal hydride (TM–H) complexes was observed. The overall rate-determining step (RDS) was the nucleophilic attraction of the terminal O atom on the Ni center in Ni-(H)-formate to form Ni-(O)-(<i>exo</i>)formate. The charge of the Ni atom in the axially vacant [Ni]<sup>+</sup> complex was demonstrated as the dominant factor in CO<sub>2</sub> insertion, which had an excellent linear correction (R<sup>2</sup> = 0.967) with the Gibbs barrier (ΔG<sup>‡</sup>) of the RDS. The parameterized activities and modeled structure–activity relationship provided here light the way to the design of a more efficient Ni–H complex in the capture and utilization of CO<sub>2</sub>.
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