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In situ PHIP‐NMR studies during the stereoselective hydrogenation of sorbic acid with a [Cp * Ru] + catalyst
Author(s) -
Niessen Heiko G.,
Schleyer Dana,
Wiemann Sabine,
Bargon Joachim,
Steines Stephan,
DriessenHoelscher Birgit
Publication year - 2000
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/1097-458x(200009)38:9<747::aid-mrc715>3.0.co;2-2
Subject(s) - chemistry , sorbic acid , catalysis , stereoselectivity , nuclear magnetic resonance spectroscopy , nmr spectra database , proton nmr , in situ , stereochemistry , organic chemistry , medicinal chemistry , spectral line , physics , astronomy
We report mechanistic studies on the homogeneously catalyzed stereoselective hydrogenation of sorbic acid ( trans,trans ‐2,4‐hexadienoic acid) using the catalyst [Cp * Ru(η 4 ‐CH 3 CHCHCHCHCO 2 H)][CF 3 SO 3 ]. The application of para‐hydrogen induced polarization (PHIP) NMR spectroscopy was found very useful for this investigation, since it allows us to investigate the hydrogenation mechanism of the reaction in situ , i.e. without disturbing the reaction for product analysis, e.g. via gas chromatography. Additionally, the reaction takes place under initial kinetic conditions without any product inhibition. These in situ PHIP‐NMR investigations proved the exclusive formation of cis ‐3‐hexenoic acid as the primary hydrogenation product via a 1,4‐addition of the dihydrogen to the sorbic acid's diene system. Any other mechanism for the formation of cis ‐3‐hexenoic acid can be excluded. trans ‐3‐Hexenoic acid is formed by a subsequent rearrangement reaction of the cis product, and all other reduced products are only obtained if the reaction is continued until total conversion of the starting material sorbic acid is reached. The conclusions are supported by simulated PHIP‐NMR spectra. Copyright © 2000 John Wiley & Sons, Ltd.