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Towards a rational design of ruthenium CO2 hydrogenation catalysts by Ab initio metadynamics


Urakawa, A; Iannuzzi, M; Hutter, J; Baiker, A (2007). Towards a rational design of ruthenium CO2 hydrogenation catalysts by Ab initio metadynamics. Chemistry - A European Journal, 13(24):6828-6840.

Abstract

Complete reaction pathways relevant to CO2 hydrogenation by using a homogeneous ruthenium dihydride catalyst ({[}Ru(dmpe)(2)H-2], drape = Me2PCH2CH2PMe2) have been investigated by ab initio metadynamics. This approach has allowed reaction intermediates to be identified and free-energy profiles to be calculated, which provide new insights into the experimentally observed reaction pathway. Our simulations indicate that CO2 insertion, which leads to the formation of formate complexes, proceeds by a concerted insertion mechanism. It is a rapid and direct process with a relative-low activation barrier, which is in agreement with experimental observations. Subsequent H, insertion into the formate-Ru complex, which leads to the formation of formic acid, instead occurs via an intermediate {[}Ru(eta(2)-H-2)] complex in which the molecular hydrogen coordinates to the ruthenium center and interacts weakly with the formate group. This step has been identified as the rate-limiting step. The reaction completes by hydrogen transfer from the {[}Ru(eta(2)-H-2)] complex to the formate oxygen atom, which forms a dihydrogen-bonded Ru-H center dot center dot center dot HO(CHO) complex. The activation energy for the H, insertion step is lower for the trans isomer than for the cis isomer. A simple measure of the catalytic activity was proposed based on the structure of the transition state of the identified rate-limiting step. From this measure, the relationship between catalysts with different ligands and their experimental catalytic activities can be explained.

Complete reaction pathways relevant to CO2 hydrogenation by using a homogeneous ruthenium dihydride catalyst ({[}Ru(dmpe)(2)H-2], drape = Me2PCH2CH2PMe2) have been investigated by ab initio metadynamics. This approach has allowed reaction intermediates to be identified and free-energy profiles to be calculated, which provide new insights into the experimentally observed reaction pathway. Our simulations indicate that CO2 insertion, which leads to the formation of formate complexes, proceeds by a concerted insertion mechanism. It is a rapid and direct process with a relative-low activation barrier, which is in agreement with experimental observations. Subsequent H, insertion into the formate-Ru complex, which leads to the formation of formic acid, instead occurs via an intermediate {[}Ru(eta(2)-H-2)] complex in which the molecular hydrogen coordinates to the ruthenium center and interacts weakly with the formate group. This step has been identified as the rate-limiting step. The reaction completes by hydrogen transfer from the {[}Ru(eta(2)-H-2)] complex to the formate oxygen atom, which forms a dihydrogen-bonded Ru-H center dot center dot center dot HO(CHO) complex. The activation energy for the H, insertion step is lower for the trans isomer than for the cis isomer. A simple measure of the catalytic activity was proposed based on the structure of the transition state of the identified rate-limiting step. From this measure, the relationship between catalysts with different ligands and their experimental catalytic activities can be explained.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2007
Deposited On:22 Mar 2009 19:52
Last Modified:05 Apr 2016 12:26
Publisher:Wiley-Blackwell
ISSN:0947-6539
Additional Information:Published in Chemistry - A European Journal
Publisher DOI:10.1002/chem.200700254
PubMed ID:17566132
Permanent URL: http://doi.org/10.5167/uzh-3161

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