Ligand Tethering by Ion-Exchange for the Immobilization of Homogeneous Catalysts
C. Salinas-Martinez de Lecea,
M. C. Roman-Martinez.
A Rh phosphine complex, derived from the Wilkinson’s catalyst, has been immobilized by ion-exchange on the
ammonium form of a Al-MCM-41 sample. Ammonium ions have been exchanged by cholamine ions, which act as an
amine ligand, and then the Wilkinson’s catalyst has been immobilized by substitution of a phosphine ligand by the
anchored amine. This is a novel immobilization procedure, as a ligand, instead of the whole complex, is tethered to the
support by ion exchange. The obtained hybrid catalyst has been characterized by Elemental Analysis, DRIFTS and XPS.
The quantitative exchange of ammonium by cholamine and coordination of Rh to amines has been observed. Most of the
anchored Rh is considered to be coordinated to the ligand tethered to the support and a small proportion seems to be
interacting with the protonated ligand or with the support surface. The catalyst has been tested in the hydrogenation of
cyclohexene and in the hydroformylation of 1-octene. In the first case the catalyst is active and reusable, while a strong
Rh leaching takes place in the second one.
Keywords: Immobilization, ion-exchange, hybrid catalysts, Al-MCM-41, Rh complex, BET, Soxhlet, NMR, FTIR, MCT, DRIFTS, rhodium, silanol groups, XPS analysis, chelating ligand
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