Insights into the Capture of CO₂ by Nickel Hydride Complexes

Abstract

As a desired feedstock for sustainable energy source and for chemical synthesis, the capture and utilization of CO2 have attracted chemists’ continuous efforts. The homogeneous CO2 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 CO2, which serves as a practicable approach for CO2 utilization. To parameterize the activities and to model the structure–activity relationship in the CO2 insertion into nickel hydride, the comprehensive mechanism of CO2 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 CO2 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)-(exo)formate. The charge of the Ni atom in the axially vacant [Ni]+ complex was demonstrated as the dominant factor in CO2 insertion, which had an excellent linear correction (R2 = 0.967) with the Gibbs barrier (ΔG‡) 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 CO2.

Keywords

• nickel hydride
• CO₂ insertion
• catalyst design
• DFT