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Issue 21, 2010
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X-Ray absorption in homogeneous catalysis research: the iron-catalyzed Michael addition reaction by XAS, RIXS and multi-dimensional spectroscopy

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Abstract

A survey over X-ray absorption methods in homogeneous catalysis research is given with the example of the iron-catalyzed Michael addition reaction. A thorough investigation of the catalytic cycle was possible by combination of conventional X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) and multi-dimensional spectroscopy. The catalytically active compound formed in the first step of the Michael reaction of methyl vinyl ketone with 2-oxocyclopentanecarboxylate (1) could be elucidated in situ by RIXS spectroscopy, and the reduced catalytic activity of FeCl3·6H2O (2) compared to Fe(ClO4)3·9H2O (3) could be further explained by the formation of a [FeIIICl4]3[FeIII(1-H)2(H2O)2+][H+]2 complex. Chloride was identified as catalyst poison with a combined XAS-UV/vis study, which revealed that Cl binds quantitatively to the available iron centers that are deactivated by formation of [FeCl4]. Operando studies in the course of the reaction of methyl vinyl ketone with 1 by combined XAS-Raman spectroscopy allowed the exclusion of changes in the oxidation state and the octahedral geometry at the iron site; a reaction order of two with respect to methyl vinyl ketone and a rate constant of k = 1.413 min−2 were determined by analysis of the C[double bond, length as m-dash]C and C[double bond, length as m-dash]O vibration band. Finally, a dedicated experimental set-up for three-dimensional spectroscopic studies (XAS, UV/vis and Raman) of homogeneous catalytic reactions under laboratory conditions, which emerged from the discussed investigations, is presented.

Graphical abstract: X-Ray absorption in homogeneous catalysis research: the iron-catalyzed Michael addition reaction by XAS, RIXS and multi-dimensional spectroscopy

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Article information


Submitted
15 Dec 2009
Accepted
18 Feb 2010
First published
20 Apr 2010

Phys. Chem. Chem. Phys., 2010,12, 5575-5584
Article type
Paper

X-Ray absorption in homogeneous catalysis research: the iron-catalyzed Michael addition reaction by XAS, RIXS and multi-dimensional spectroscopy

M. Bauer and C. Gastl, Phys. Chem. Chem. Phys., 2010, 12, 5575
DOI: 10.1039/B926385C

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