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Real-Time Detection of Intermediates in Rhodium-Catalyzed Hydrogenation of Alkynes and Alkenes by Dissolution DNP

Boeg, Peter Andreas, Duus, Jens Øllgaard, Ardenkjær-Larsen, Jan Henrik, Karlsson, Magnus, Mossin, Susanne
Journal of physical chemistry 2019 v.123 no.15 pp. 9949-9956
alkenes, alkynes, butanes, carbon, catalysts, hydrogen, hydrogenation, isotope labeling, models, nuclear magnetic resonance spectroscopy, perchlorates, physical chemistry, reaction mechanisms, rhodium, signal-to-noise ratio, stable isotopes
The hydrogenation of alkynes and alkenes using Shrock–Osborn catalysts was followed in situ with dissolution dynamic nuclear polarization (dDNP) NMR. Natural abundance and ¹³C-labeled dimethyl acetylenedicarboxylate was hyperpolarized prior to hydrogenation using (1,4-bis{diphenylphosphino}butane)(2,5-norbornadiene) rhodium(I) perchlorate, [Rh(NBD)(DPPB)]ClO₄. The increased signal-to-noise ratio of dDNP compared to conventional ¹³C NMR allowed real-time detection of substrates and products as well as the modeling of the hydrogenation kinetics. The build-up of an intermediate was observed during interruption in hydrogen flow, substantiating the current view of the reaction mechanism. Selective inversion of the carbonyl NMR signal of the substrate was applied to demonstrate unequivocally that the new peak appearing in the spectrum originates from a reaction intermediate. The scope of the dDNP method for following reaction dynamics in real time was further demonstrated by substrate competition experiments.