Rhodium-silica, catalysts, structure

A detailed study of the chemical structure of mesoporous silica catalysts containing rhodium ligands and nanoparticles was carried out by multidimensional solid-state NMR techniques. 

Additionally, ion-exchanged structures can be tied to SiC>2 as in [(EtO)3Si(CH2)3PBu3]+. It is also possible to synthesize a complex such as (Ph3P)2R2P-4(CH2)x Si(OR)3RhCl which, upon hydrogenolysis, yields a silica-supported rhodium catalyst. 

An aminated silica (13) was treated wiA HjPtCls and RhCl(PPh3)3 to give the aminated silica-supported platinum (13-Pt) and rhodium (13-Rh) catalysts, respectively. The metal content in the immobilized catalysts was 0.05 wt% for Pt and 0.35-0.49 wt% for Rh depending on the structure of amine moiety. The hydrosilyiation of 1-alkenes, allyl chloride, and allyl chloroacetate by HSiCl3 and HSifOEtj) was studied 13-Rh (NR2 = morpholino) retains its high catalytic activity even after nine times of use. ... 

Dimerization of ethylene. Rhodium(IlI) chloride supported on silica gel is an active heterogeneous catalyst for dimerization of ethylene to 1-butene and then to 2-butene the transfcis ratio is 2.9. The active catalyst may have the structure depicted in (1). ... 

Vazquez-Zavala, A., Fuentes, S., Pedraza, F. (1994). The Influence of Sulfidation on the Crystalline Structure of Palladium, Rhodium and Ruthenium Catalysts Supported on Silica. Applied Surface Science, Vol.78, No.2, (June 1994), pp. 211-218, ISSN 0169-4332... 

Supported metal complexes and clusters with well-defined structures offer the advantages of catalysts that are selective and structures that can be understood in depth. Such catalysts can be synthesized precisely with organometallic precursors, as illustrated in this review. Synthetic methods are illustrated with examples, including silica-supported chromium and titanium complexes for alkene polymerization rhodium carbonyls bonded predominantly at crystallographically specific sites in a zeolite and metal clusters, including Ir4, Rhg, OsjC, and bimetallics. 

However, these results are not yet sufficient for a detailed determination of the structure of immobilized rhodium catalyst. The reason is that the broadening of the signal at 32 ppm can result either from a single phosphorus ligand or from two coalescent P chemical shifts related to the phosphine ligands with P3 and PI phosphorus atoms. In other words, there are two possible ways of binding of the Wilkinson s catalyst to the silica surface, namely a monopodal and a bipodal scenario, (see Fig. 9). In the... 

The presented 2D P J-resolved NMR experiments provide clear evidence that Wilkinson s catalyst immobilized on the amine functionalized silica SBA-3 material, possess only one triphenylphosphine ligand. The rhodium centre is coordinated to the silica surface through the two amine ligands. It reveals significant information about the structure of... 

All the catalysts have been tested in the selective hydrogenation of citral. This molecule suits very well to the study of the influence of the nature and the structure of the active phase on its catalytic properties, because it includes three kinds of unsaturations (1) an aldehydic function, (2) a conjugated olefinic bond and (3) an isolated olefinic bond. Moreover, rhodium or platinum supported on silica are not selective for the hydrogenation of citral to diolefinic alcohols (geraniol and nerol) (13, 14). The overall reaction path for reduction of citral trans is represented in figure 5. Depending on the selectivity of the first hydrogenation step, three... 

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