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Title: Rationalizing the Reactivity of Bimetallic Molecular Catalysts for CO 2 Hydrogenation

Abstract

In this study, we have recently reported the heterobimetallic nickel–gallium complex, NiGaL (where L represents the tris(phosphinoamido)amine ligand, [N( o-(NCH 2P i-Pr 2) C 6H 4) 3] 3–), which is the most active Ni-based molecular catalyst for CO 2 hydrogenation to date. Understanding the reaction mechanism of this catalytic system and identifying the factors that govern its catalytic activity are important in order to design even more efficient base–metal catalysts. Here, we present a computational study of possible reaction pathways for CO 2 hydrogenation catalyzed by NiGaL. The most favorable predicted pathway for formate production agrees well with key experimental observations and is defined by four elementary steps: (1) H 2 binding to the Ni center, (2) deprotonation of the H 2 adduct, (3) hydride transfer to CO 2 to form a formate adduct, and (4) formate release to regenerate NiGaL. The overall catalytic process has two main time periods: an induction period, during which the deprotonation of the H 2 adduct by exogenous base is predicted to be rate-limiting, followed by a subsequent period where the produced formate assists in deprotonation by acting as a proton shuttle between the H 2 adduct and exogenous base. The barrier for Hmore » 2 adduct deprotonation is governed predominantly by the steric hindrance associated with the exogenous base and is found to be dramatically lowered by formate assistance. Once sufficient formate has been generated, the catalysis enters the steady-state period, during which hydride transfer to CO 2 is predicted to become rate-limiting once sufficient formate has been generated and the reaction rate remains constant until the base is nearly consumed. For hydride transfer to CO 2, the free energy of activation was found to depend linearly on the thermodynamic hydricity for a series of bimetallic HM 1M 2L– complexes, providing a simple and efficient strategy for screening other bimetallic catalysts. Furthermore, the relative binding energies of H 2 and formate were analyzed to predict the ability of the bimetallics to facilitate the catalytic turnover. The predicted trends and structure–activity relationships arising from these computational calculations can be further utilized for the rational design of more efficient catalysts for CO 2 hydrogenation and other hydride transfer processes for which reactive M–H species are generated in the presence of a Lewis base.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [1];  [2]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [1]
  1. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemistry and Minnesota Supercomputing Inst. and Chemical Theory Center
  2. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemistry
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Energy Frontier Research Center for Inorganometallic Catalyst Design (ICDC); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1545631
Grant/Contract Number:  
SC0012702
Resource Type:
Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 8; Journal Issue: 6; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; bimetallic complexes; H2 deprotonation; CO2 hydrogenation; basicity; steric hindrance; hydricity

Citation Formats

Ye, Jingyun, Cammarota, Ryan C., Xie, Jing, Vollmer, Matthew V., Truhlar, Donald G., Cramer, Christopher J., Lu, Connie C., and Gagliardi, Laura. Rationalizing the Reactivity of Bimetallic Molecular Catalysts for CO2 Hydrogenation. United States: N. p., 2018. Web. doi:10.1021/acscatal.8b00803.
Ye, Jingyun, Cammarota, Ryan C., Xie, Jing, Vollmer, Matthew V., Truhlar, Donald G., Cramer, Christopher J., Lu, Connie C., & Gagliardi, Laura. Rationalizing the Reactivity of Bimetallic Molecular Catalysts for CO2 Hydrogenation. United States. doi:10.1021/acscatal.8b00803.
Ye, Jingyun, Cammarota, Ryan C., Xie, Jing, Vollmer, Matthew V., Truhlar, Donald G., Cramer, Christopher J., Lu, Connie C., and Gagliardi, Laura. Fri . "Rationalizing the Reactivity of Bimetallic Molecular Catalysts for CO2 Hydrogenation". United States. doi:10.1021/acscatal.8b00803. https://www.osti.gov/servlets/purl/1545631.
@article{osti_1545631,
title = {Rationalizing the Reactivity of Bimetallic Molecular Catalysts for CO2 Hydrogenation},
author = {Ye, Jingyun and Cammarota, Ryan C. and Xie, Jing and Vollmer, Matthew V. and Truhlar, Donald G. and Cramer, Christopher J. and Lu, Connie C. and Gagliardi, Laura},
abstractNote = {In this study, we have recently reported the heterobimetallic nickel–gallium complex, NiGaL (where L represents the tris(phosphinoamido)amine ligand, [N(o-(NCH2Pi-Pr2) C6H4)3]3–), which is the most active Ni-based molecular catalyst for CO2 hydrogenation to date. Understanding the reaction mechanism of this catalytic system and identifying the factors that govern its catalytic activity are important in order to design even more efficient base–metal catalysts. Here, we present a computational study of possible reaction pathways for CO2 hydrogenation catalyzed by NiGaL. The most favorable predicted pathway for formate production agrees well with key experimental observations and is defined by four elementary steps: (1) H2 binding to the Ni center, (2) deprotonation of the H2 adduct, (3) hydride transfer to CO2 to form a formate adduct, and (4) formate release to regenerate NiGaL. The overall catalytic process has two main time periods: an induction period, during which the deprotonation of the H2 adduct by exogenous base is predicted to be rate-limiting, followed by a subsequent period where the produced formate assists in deprotonation by acting as a proton shuttle between the H2 adduct and exogenous base. The barrier for H2 adduct deprotonation is governed predominantly by the steric hindrance associated with the exogenous base and is found to be dramatically lowered by formate assistance. Once sufficient formate has been generated, the catalysis enters the steady-state period, during which hydride transfer to CO2 is predicted to become rate-limiting once sufficient formate has been generated and the reaction rate remains constant until the base is nearly consumed. For hydride transfer to CO2, the free energy of activation was found to depend linearly on the thermodynamic hydricity for a series of bimetallic HM1M2L– complexes, providing a simple and efficient strategy for screening other bimetallic catalysts. Furthermore, the relative binding energies of H2 and formate were analyzed to predict the ability of the bimetallics to facilitate the catalytic turnover. The predicted trends and structure–activity relationships arising from these computational calculations can be further utilized for the rational design of more efficient catalysts for CO2 hydrogenation and other hydride transfer processes for which reactive M–H species are generated in the presence of a Lewis base.},
doi = {10.1021/acscatal.8b00803},
journal = {ACS Catalysis},
number = 6,
volume = 8,
place = {United States},
year = {2018},
month = {4}
}

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