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Title: Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Re-ductive Elimination Leads to Formation of Multimetallic Clusters

Abstract

A rhodium-catalyzed method for the hydrogenation of N-heteroarenes is described. A diverse array of unsubstituted N-heteroarenes including pyridine, pyrrole and pyrazine, traditionally challenging substrates for hydrogenation, were successfully hydrogenated using the organometallic precatalysts, (η5-C5Me5)Rh(N-C)H (N-C = 2-phenylpyridinyl (ppy) or benzo[h]quinolinyl (bq)). In addi-tion, the hydrogenation of polyaromatic N-heteroarenes exhibited uncommon chemoselectivity. Studies into catalyst activation revealed that photochemical or thermal activation of (η5-C5Me5)Rh(bq)H induced C(sp2)–H reductive elimination and generated the bimetallic complex, [(η5-C5Me5)Rh(µ2,η2-bq)Rh(η5-C5Me5)H]. In the presence of H2 both of the (η5-C5Me5)Rh(N-C)H precursors and [(η5-C5Me5)Rh(µ2,η2-bq)Rh(η5-C5Me5)H] converted to a pentametallic rhodium hydride cluster, (η5-C5Me5)4Rh5H7, the structure of which was established by NMR spectroscopy, X-ray and neutron diffraction. Kinetic studies on pyridine hydrogenation were conducted with each of the isolated rhodium complexes to identify catalytically relevant species. The data are most consistent with hydrogenation catalysis prompted by an unobserved multimetallic cluster with formation of (η5-C5Me5)4Rh5H7 serving as a deactivation pathway.

Authors:
 [1];  [1];  [1];  [2];  [1]
  1. Princeton Univ., NJ (United States). Dept. of Chemistry
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division, Neutron Sciences Directorate
Publication Date:
Research Org.:
Princeton Univ., NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1569484
Grant/Contract Number:  
SC0006498
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Name: Journal of the American Chemical Society; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Kim, Sangmin, Loose, Florian, Bezdek, Máté J., Wang, Xiaoping, and Chirik, Paul J. Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Re-ductive Elimination Leads to Formation of Multimetallic Clusters. United States: N. p., 2019. Web. doi:10.1021/jacs.9b09540.
Kim, Sangmin, Loose, Florian, Bezdek, Máté J., Wang, Xiaoping, & Chirik, Paul J. Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Re-ductive Elimination Leads to Formation of Multimetallic Clusters. United States. doi:10.1021/jacs.9b09540.
Kim, Sangmin, Loose, Florian, Bezdek, Máté J., Wang, Xiaoping, and Chirik, Paul J. Mon . "Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Re-ductive Elimination Leads to Formation of Multimetallic Clusters". United States. doi:10.1021/jacs.9b09540.
@article{osti_1569484,
title = {Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Re-ductive Elimination Leads to Formation of Multimetallic Clusters},
author = {Kim, Sangmin and Loose, Florian and Bezdek, Máté J. and Wang, Xiaoping and Chirik, Paul J.},
abstractNote = {A rhodium-catalyzed method for the hydrogenation of N-heteroarenes is described. A diverse array of unsubstituted N-heteroarenes including pyridine, pyrrole and pyrazine, traditionally challenging substrates for hydrogenation, were successfully hydrogenated using the organometallic precatalysts, (η5-C5Me5)Rh(N-C)H (N-C = 2-phenylpyridinyl (ppy) or benzo[h]quinolinyl (bq)). In addi-tion, the hydrogenation of polyaromatic N-heteroarenes exhibited uncommon chemoselectivity. Studies into catalyst activation revealed that photochemical or thermal activation of (η5-C5Me5)Rh(bq)H induced C(sp2)–H reductive elimination and generated the bimetallic complex, [(η5-C5Me5)Rh(µ2,η2-bq)Rh(η5-C5Me5)H]. In the presence of H2 both of the (η5-C5Me5)Rh(N-C)H precursors and [(η5-C5Me5)Rh(µ2,η2-bq)Rh(η5-C5Me5)H] converted to a pentametallic rhodium hydride cluster, (η5-C5Me5)4Rh5H7, the structure of which was established by NMR spectroscopy, X-ray and neutron diffraction. Kinetic studies on pyridine hydrogenation were conducted with each of the isolated rhodium complexes to identify catalytically relevant species. The data are most consistent with hydrogenation catalysis prompted by an unobserved multimetallic cluster with formation of (η5-C5Me5)4Rh5H7 serving as a deactivation pathway.},
doi = {10.1021/jacs.9b09540},
journal = {Journal of the American Chemical Society},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {10}
}

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This content will become publicly available on October 7, 2020
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