Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Reductive Elimination Leads to Formation of Multimetallic Clusters

Sangmin Kim; Florian Loose; Máté J. Bezdek; Xiaoping Wang; Paul J. Chirik

doi:10.1021/jacs.9b09540

Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Reductive Elimination Leads to Formation of Multimetallic Clusters

Sangmin Kim, Florian Loose, Máté J. Bezdek, Xiaoping Wang, Paul J. Chirik

Single Crystal Diffraction

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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 addition, 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 diffraction, 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.

Original language	English
Pages (from-to)	17900-17908
Number of pages	9
Journal	Journal of the American Chemical Society
Volume	141
Issue number	44
DOIs	https://doi.org/10.1021/jacs.9b09540
State	Published - Nov 6 2019

Funding

This research was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Catalysis Science program, under Award DE-SC0006498. Single-crystal neutron diffraction performed on TOPAZ used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory, under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. S.K. thanks Samsung Scholarship for financial support. F.L. acknowledges financial support from a DFG research fellowship (LO 2377/1-1). M.J.B. thanks the Natural Sciences and Engineering Research Council of Canada for a predoctoral fellowship (PSG-D) and Princeton University for a Porter Ogden Jacobus Honorific Fellowship. S.K. and P.J.C. acknowledge István Pelczer and Kenith Conover at Princeton University for measurement of T (min). The authors acknowledge the use of Princeton’s Imaging and Analysis Center (IAC), which is partially supported by the Princeton Center for Complex Materials (PCCM), a National Science Foundation (NSF) Materials Research Science and Engineering Center (MRSEC; DMR-1420541). S.K. thanks Taeho Son and C. Rose Kennedy for plotting kinetic data and Hongyu Zhong for the ORTEP. 1

Funders	Funder number
Catalysis Science Program	DE-SC0006498
Samsung Scholarship
National Science Foundation
U.S. Department of Energy
Office of Science
Basic Energy Sciences
Oak Ridge National Laboratory	DE-AC05-00OR22725
Princeton University
Materials Research Science and Engineering Center, Harvard University	DMR-1420541
Princeton Center for Complex Materials
Natural Sciences and Engineering Research Council of Canada
Deutsche Forschungsgemeinschaft	LO 2377/1-1

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title = "Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Reductive 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 addition, 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 diffraction, 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.",

author = "Sangmin Kim and Florian Loose and Bezdek, {M{\'a}t{\'e} J.} and Xiaoping Wang and Chirik, {Paul J.}",

note = "Publisher Copyright: {\textcopyright} 2019 American Chemical Society.",

year = "2019",

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doi = "10.1021/jacs.9b09540",

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T2 - Reductive Elimination Leads to Formation of Multimetallic Clusters

AU - Kim, Sangmin

AU - Loose, Florian

AU - Bezdek, Máté J.

AU - Wang, Xiaoping

AU - Chirik, Paul J.

PY - 2019/11/6

Y1 - 2019/11/6

N2 - 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 addition, 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 diffraction, 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.

AB - 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 addition, 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 diffraction, 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.

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JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 44

ER -

Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Reductive Elimination Leads to Formation of Multimetallic Clusters

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