Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 141, Issue 44, Pages 17900-17908Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.9b09540
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Funding
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Catalysis Science program [DE-SC0006498]
- DOE Office of Science User Facility [DE-ACOS-000R22725]
- Samsung Scholarship
- DFG [LO 2377/1-1]
- Natural Sciences and Engineering Research Council of Canada
- Princeton University
- Princeton Center for Complex Materials (PCCM), a National Science Foundation (NSF) Materials Research Science and Engineering Center (MRSEC) [DMR-1420541]
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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 pre-catalysts, [(eta(5)-CsMes)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 [(eta(5)-C5Me5)Rh(bq)H] induced C(sp(2))-H reductive elimination and generated the bimetallic complex, [(eta(5)-C5Me5)Rh(mu(2),eta(2)-bq)Rh(eta(5)-C5Me5)H]. In the presence of H-2, both of the [(eta(5)-(CMe5)-Me-5)Rh(N-C)H] precursors and [(eta(5)-C5Me5)Rh(mu(2),eta(2)-bq)Rh(eta(5)-C5Me5)H] converted to a pentametallic rhodium hydride cluster, [(eta(5)-C5Me5)(4)Rh5H7], 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 [(eta(5)-C5Me5)(4)Rh5H7] serving as a deactivation pathway.
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