Selective hydroamination of terminal alkynes with primary aryl amines is catalyzed by an unprecedented well-defined silica-supported tantalum complex [(≡Si-O-)Ta(η1σ-NEtMe)2(=NtBu)]. A molecular-level characterization of the surface organometallic Ta species was done with the help of characterization tech-niques including as in situ infrared, in situ elemental microanal-ysis, 1H and 13C solid-state NMR (including double and triple quanta sequence), and X-ray absorption spectroscopies. These were complemented by the state-of-the-art DNP-SENS 15N characterization. Several catalytic intermediates have been isolated in particular the 4-membered metallacycle ring inter-mediate resulting from the anti Markovnikov addition of the alkyne to the surface tantalum imido. The mechanism proposed was based on the isolation of all intermediates. A DFT calcula-tion has confirmed all the elementary steps and intermediates that were fully characterized.
KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The research was supported by the King Abdullah University of Science and Technology (KAUST). The authors acknowledge EdyAbou-Hamad, Abdul-Hamid Emwas, and Andrei Gurinov for their assistance for NMR measurements. The work at the University of California was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (DE-FG02-04ER15513). We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities and thank Antonio Aguilar for assistance in using beamline BM30B.