Control in the Rate-Determining Step Provides a Promising Strategy To Develop New Catalysts for CO₂ Hydrogenation: A Local Pair Natural Orbital Coupled Cluster Theory Study

Abstract

The development of efficient catalysts with base metals for CO2 hydrogenation has always been a major thrust of interest. A series of experimental and theoretical work has revealed that the catalytic cycle typically involves two key steps, namely, base-promoted heterolytic H2 splitting and hydride transfer to CO2, either of which can be the rate-determining step (RDS) of the entire reaction. To explore the determining factor for the nature of RDS, we present herein a comparative mechanistic investigation on CO2 hydrogenation mediated by [M(H)(η(2)-H2)(PP3(Ph))](n+) (M = Fe(II), Ru(II), and Co(III); PP3(Ph) = tris(2-(diphenylphosphino)phenyl)phosphine) type complexes. In order to construct reliable free energy profiles, we used highly correlated wave function based ab initio methods of the coupled cluster type alongside the standard density functional theory. Our calculations demonstrate that the hydricity of the metal-hydride intermediate generated by H2 splitting dictates the nature of the RDS for the Fe(II) and Co(III) systems, while the RDS for the Ru(II) catalyst appears to be ambiguous. CO2 hydrogenation catalyzed by the Fe(II) complex that possesses moderate hydricity traverses an H2-splitting RDS, whereas the RDS for the high-hydricity Co(III) species is found to be the hydride transfer. Thus, our findings suggest that hydricity can be used as a practical guide in future catalyst design. Enhancing the electron-accepting ability of low-hydricity catalysts is likely to improve their catalytic performance, while increasing the electron-donating ability of high-hydricity complexes may speed up CO2 conversion. Moreover, we also established the active roles of base NEt3 in directing the heterolytic H2 splitting and assisting product release through the formation of an acid-base complex.

Redox‐Induced Oxidative C−C Bond Cleavage of 2,2′‐Pyridil in Diruthenium Complexes

“…The connectivity of each TS was validated through a relaxed potential‐energy surface scan for the corresponding reaction coordinate, and was found to be the highest‐energy point that connected the relevant reactant and product. The zero‐point vibrational energies, thermal corrections were obtained from the harmonic frequency calculations at the M06L level of theory …”

Hydrogenative Carbon Dioxide Reduction Catalyzed by Mononuclear Ruthenium Polypyridyl Complexes: Discerning between Electronic and Steric Effects

“…7,13 One promising chemical strategy is the selective reduction of CO2 with hydrogen gas to formic acid. 7,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] The reverse reaction, that is, the transformation of formic acid/formate ion into CO2 and H2 gases is thermodynamically favored, and thus formic acid has been recognized as a hydrogen storage material with high atom-efficiency when suitable catalysts are used.…”

Carbon/Silicon Exchange at the Apex of Diphos‐ and Triphos‐Derived Ligands – More Than Just a Substitute?

“…The influence of C/Si exchange can easily be highlighted by a series of Fe, Ni, and Co complexes comprising the E(PR 2 ) 3 moiety (E = C, Si; R = phenyl, isopropyl; compounds 14 – 16 , Figure ) for the activation of N 2 and the hydrogenation of CO 2 . These differences are, however, expected to be due to a direct interaction between the metal center and the C or Si atom.…”

“…N 2 activation on Fe complexes and Co‐based hydrogenation catalyst for CO 2 comprising the E(PR 2 ) 3 (R = phenyl, isopropyl) moiety …”