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.
|Number of pages||9|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 2019 Nov 6|
Bibliographical noteFunding Information:
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
© 2019 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry