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Use of Ligand Steric Properties to Control the Thermodynamics and Kinetics of Oxidative Addition and Reductive Elimination with Pincer-Ligated Rh Complexes

Gu, Shunyan and Nielsen, Robert J. and Taylor, Kathleen H. and Fortman, George C. and Chen, Junqi and Dickie, Diane A. and Goddard, William A., III and Gunnoe, T. Brent (2020) Use of Ligand Steric Properties to Control the Thermodynamics and Kinetics of Oxidative Addition and Reductive Elimination with Pincer-Ligated Rh Complexes. Organometallics, 39 (10). pp. 1917-1933. ISSN 0276-7333. https://resolver.caltech.edu/CaltechAUTHORS:20200504-141304060

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Abstract

Oxidative addition and reductive elimination reactions are central steps in many catalytic processes, and controlling the energetics of reaction intermediates is key to enabling efficient catalysis. A series of oxidative addition and reductive elimination reactions using (RPNP)RhX complexes (R = tert-butyl, isopropyl, mesityl, phenyl; X = Cl, I) was studied to deduce the effect of the size of the phosphine substituents. Using (^RPNP)RhCl as the starting material, oxidative addition of MeI was observed to produce (^RPNP)Rh(Me)(I)Cl, which was followed by reductive elimination of MeCl to form (^RPNP)RhI. The thermodynamics and kinetics vary with the identity of the substituent R on phosphorus of the PNP ligand. The presence of large steric bulk (e.g., R = tert-butyl, mesityl) on the phosphine favors Rh(I) in comparison to the presence of two smaller substituents (e.g., R = isopropyl, phenyl). An Eyring plot for the oxidative addition of MeI to (^(tBu)PNP)RhCl in THF-d₈ is consistent with a polar two-step reaction pathway, and the formation of [(^(tBu)PNP)Rh(Me)I]I is also consistent with this mechanism. DFT calculations show that the steric bulk affects the reaction energies of addition reactions which generate six-coordinate complexes by tens of kcal mol⁻¹. The ligand steric bulk is calculated to have a reduced effect (a few kcal mol⁻¹) on S_N2 addition barriers, which only require access to one side of the square plane.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/acs.organomet.0c00122DOIArticle
ORCID:
AuthorORCID
Nielsen, Robert J.0000-0002-7962-0186
Dickie, Diane A.0000-0003-0939-3309
Goddard, William A., III0000-0003-0097-5716
Gunnoe, T. Brent0000-0001-5714-3887
Additional Information:© 2020 American Chemical Society. Received: February 19, 2020; Published: May 4, 2020. The Gunnoe group acknowledges support from the U.S. National Science Foundation (1800173). The Goddard group acknowledges support from the NSF (CBET-1805022). The authors declare no competing financial interest. Accession Codes: CCDC 1948889−1948897 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Funders:
Funding AgencyGrant Number
NSFCHE-1800173
NSFCBET-1805022
Other Numbering System:
Other Numbering System NameOther Numbering System ID
WAG1379
Issue or Number:10
Record Number:CaltechAUTHORS:20200504-141304060
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200504-141304060
Official Citation:Use of Ligand Steric Properties to Control the Thermodynamics and Kinetics of Oxidative Addition and Reductive Elimination with Pincer-Ligated Rh Complexes. Shunyan Gu, Robert J. Nielsen, Kathleen H. Taylor, George C. Fortman, Junqi Chen, Diane A. Dickie, William A. Goddard, and T. Brent Gunnoe. Organometallics 2020 39 (10), 1917-1933; DOI: 10.1021/acs.organomet.0c00122
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102983
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:04 May 2020 21:29
Last Modified:11 Jul 2020 09:58

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