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The mechanism for catalytic hydrosilylation by bis(imino)pyridine iron olefin complexes supported by broken symmetry density functional theory

Lam, Yan Choi and Nielsen, Robert J. and Goddard, William A., III and Dash, Aswini K. (2017) The mechanism for catalytic hydrosilylation by bis(imino)pyridine iron olefin complexes supported by broken symmetry density functional theory. Dalton Transactions, 46 (37). pp. 12507-12515. ISSN 1477-9226. https://resolver.caltech.edu/CaltechAUTHORS:20170913-095452729

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Abstract

Density functional theory (DFT, B3LYP-D3 with implicit solvation in toluene) was used to investigate the mechanisms of olefin hydrosilylation catalyzed by PDI(Fe) (bis(imino)pyridine iron) complexes, where PDI = 2,6-(ArN CMe)_2(C_5H_3N) with Ar = 2,6-R_2-C_6H_3. We find that the rate-determining step for hydrosilylation is hydride migration from Et3SiH onto the Fe-bound olefin to form (PDI)Fe(alkyl)(SiEt_3). This differs from the mechanism for the Pt Karstedt catalyst in that there is no prior Si–H oxidative addition onto the Fe center. (PDI)Fe(alkyl)(SiEt_3) then undergoes C–Si reductive elimination to form (PDI)Fe, which coordinates an olefin ligand to regenerate the resting state (PDI)Fe(olefin). In agreement with experimental observations, we found that anti-Markovnikov hydride migration has a 5.1 kcal mol−1 lower activation enthalpy than Markovnikov migration. This system has an unusual anti-ferromagnetic coupling between high spin electrons on the Fe center and the unpaired spin in the pi system of the non-innocent redox-active PDI ligand. To describe this with DFT, we used the “broken-symmetry” approach to establish the ground electronic and spin state of intermediates and transition states over the proposed catalytic cycles.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1039/c7dt02300fDOIArticle
http://pubs.rsc.org/en/Content/ArticleLanding/2017/DT/C7DT02300FPublisherArticle
http://www.rsc.org/suppdata/c7/dt/c7dt02300f/c7dt02300f1.pdfPublisherSupplementary Information
ORCID:
AuthorORCID
Lam, Yan Choi0000-0001-7809-4471
Nielsen, Robert J.0000-0002-7962-0186
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2017 The Royal Society of Chemistry. The article was received on 25 Jun 2017, accepted on 04 Sep 2017 and first published on 05 Sep 2017. Dr Robert J. Nielsen and Prof. William A. Goddard III, gratefully acknowledge financial support from The Dow Chemical Company. Dr Yan Choi Lam was supported by the National Science Foundation (NSF) through the Centers for Chemical Innovation (CCI): Solar Fuels grant CHE-1305124. There are no conflicts of interest to declare.
Group:CCI Solar Fuels
Funders:
Funding AgencyGrant Number
Dow Chemical CompanyUNSPECIFIED
NSFCHE-1305124
Issue or Number:37
Record Number:CaltechAUTHORS:20170913-095452729
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170913-095452729
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81403
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:13 Sep 2017 22:43
Last Modified:03 Oct 2019 18:42

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