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Title: Acceleration of CO 2 insertion into metal hydrides: ligand, Lewis acid, and solvent effects on reaction kinetics

Abstract

The insertion of CO 2 into metal hydrides and the microscopic reverse decarboxylation of metal formates are important elementary steps in catalytic cycles for both CO 2 hydrogenation to formic acid and methanol as well as formic acid and methanol dehydrogenation. Here, we use rapid mixing stopped-flow techniques to study the kinetics and mechanism of CO 2 insertion into transition metal hydrides. The investigation finds that the most effective method to accelerate the rate of CO 2 insertion into a metal hydride can be dependent on the nature of the rate-determining transition state (TS). We demonstrate that for an innersphere CO 2 insertion reaction, which is proposed to have a direct interaction between CO 2 and the metal in the rate-determining TS, the rate of insertion increases as the ancillary ligand becomes more electron rich or less sterically bulky. There is, however, no rate enhancement from Lewis acids (LA). In comparison, we establish that for an outersphere CO 2 insertion, proposed to proceed with no interaction between CO 2 and the metal in the rate-determining TS, there is a dramatic LA effect. Furthermore, for both inner- and outersphere reactions, we show that there is a small solvent effect on themore » rate of CO 2 insertion. Solvents that have higher acceptor numbers generally lead to faster CO 2 insertion. Our results provide an experimental method to determine the pathway for CO 2 insertion and offer guidance for rate enhancement in CO 2 reduction catalysis.« less

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [1]; ORCiD logo [1]
  1. Yale Univ., New Haven, CT (United States). Dept. of Chemistry
  2. Univ. of Missouri, Columbia, MO (United States). Dept. of Chemistry
Publication Date:
Research Org.:
Yale Univ., New Haven, CT (United States); Univ. of Missouri, Columbia, MO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); National Inst. of Health (NIH) (United States)
OSTI Identifier:
1460464
Alternate Identifier(s):
OSTI ID: 1505499
Grant/Contract Number:  
SC0001059; SC0018222; CHE-1150826; GM050422
Resource Type:
Journal Article: Published Article
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 9; Journal Issue: 32; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Heimann, Jessica E., Bernskoetter, Wesley H., Hazari, Nilay, and Mayer, James M.. Acceleration of CO2 insertion into metal hydrides: ligand, Lewis acid, and solvent effects on reaction kinetics. United States: N. p., 2018. Web. doi:10.1039/c8sc02535e.
Heimann, Jessica E., Bernskoetter, Wesley H., Hazari, Nilay, & Mayer, James M.. Acceleration of CO2 insertion into metal hydrides: ligand, Lewis acid, and solvent effects on reaction kinetics. United States. doi:10.1039/c8sc02535e.
Heimann, Jessica E., Bernskoetter, Wesley H., Hazari, Nilay, and Mayer, James M.. Fri . "Acceleration of CO2 insertion into metal hydrides: ligand, Lewis acid, and solvent effects on reaction kinetics". United States. doi:10.1039/c8sc02535e.
@article{osti_1460464,
title = {Acceleration of CO2 insertion into metal hydrides: ligand, Lewis acid, and solvent effects on reaction kinetics},
author = {Heimann, Jessica E. and Bernskoetter, Wesley H. and Hazari, Nilay and Mayer, James M.},
abstractNote = {The insertion of CO2 into metal hydrides and the microscopic reverse decarboxylation of metal formates are important elementary steps in catalytic cycles for both CO2 hydrogenation to formic acid and methanol as well as formic acid and methanol dehydrogenation. Here, we use rapid mixing stopped-flow techniques to study the kinetics and mechanism of CO2 insertion into transition metal hydrides. The investigation finds that the most effective method to accelerate the rate of CO2 insertion into a metal hydride can be dependent on the nature of the rate-determining transition state (TS). We demonstrate that for an innersphere CO2 insertion reaction, which is proposed to have a direct interaction between CO2 and the metal in the rate-determining TS, the rate of insertion increases as the ancillary ligand becomes more electron rich or less sterically bulky. There is, however, no rate enhancement from Lewis acids (LA). In comparison, we establish that for an outersphere CO2 insertion, proposed to proceed with no interaction between CO2 and the metal in the rate-determining TS, there is a dramatic LA effect. Furthermore, for both inner- and outersphere reactions, we show that there is a small solvent effect on the rate of CO2 insertion. Solvents that have higher acceptor numbers generally lead to faster CO2 insertion. Our results provide an experimental method to determine the pathway for CO2 insertion and offer guidance for rate enhancement in CO2 reduction catalysis.},
doi = {10.1039/c8sc02535e},
journal = {Chemical Science},
issn = {2041-6520},
number = 32,
volume = 9,
place = {United States},
year = {2018},
month = {7}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1039/c8sc02535e

Citation Metrics:
Cited by: 4 works
Citation information provided by
Web of Science

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Works referenced in this record:

Reversible hydrogen storage using CO2 and a proton-switchable iridium catalyst in aqueous media under mild temperatures and pressures
journal, March 2012

  • Hull, Jonathan F.; Himeda, Yuichiro; Wang, Wan-Hui
  • Nature Chemistry, Vol. 4, Issue 5, p. 383-388
  • DOI: 10.1038/nchem.1295