Anchored Wilkinson Catalyst

Abstract

A series of Anchored Wilkinson’s Catalysts were prepared by the reaction of the homogeneous Wilkinson catalyst with alumina/heteropoly acid support materials. It was found that the catalytically active species from these materials were unique in that they had only a single triphenylphosphine and a heteropoly acid as ligands giving these catalysts distinctive steric and electronic characteristics. These catalysts were used to promote the hydrogenation of 1-hexene and limonene with substrate to catalyst ratios of 10,000 and 7,500 respectively. The results were compared with those obtained using the homogeneous Wilkinson and 1% Rh/Al2O3 catalysts with respect to catalyst activity and stability as well as the reaction selectivity as measured by the amount of double bond isomerization observed. The observed rates of hydrogen uptake and double bond isomer formation in the hydrogenations of both 1-hexene and limonene follow the same order with respect to the nature of the heteropoly acid ligand used to anchor the Wilkinson catalyst to the alumina: silicotungstic acid > phosphotungstic acid > phosphomolybdic acid > silicomolybdic acid for hydrogen addition and the reverse for isomerization. This consistency provides a measure of the electronic character of these Keggin heteropoly acids when acting as ligands. In contrast to the reactions observed with the anchored catalysts the homogeneous Wilkinson catalyst was incapable of completing these high substrate/catalyst ratio hydrogenations. It became deactivated at about 85% 1-hexene conversion and only 10% limonene hydrogenation. As compared with the anchored catalysts the supported Rh promoted more isomerization of 1-hexene and limonene while the hydrogenation of the trisubstituted double bond in p-menthene was more difficult over the supported metal catalyst than with the sterically more accessible anchored Wilkinson catalysts.

Partial and Total Solvent-Free Limonene’s Hydrogenation: Metals, Supports, Pressure, and Water Effects

“…At low pressure, all catalysts, except Ru, independent of the supports were menthene selective. It was reported that hydrogenation of the limonene's endocyclic double bond was disfavored compared to the exocyclic double bond's hydrogenation [26]. It was also reported that Ru/C has smallest nanoparticles (1.5 nm), compared to the other investigated metals, which could explain its inactivity on our hydrogenation [29].…”

“…Partial hydrogenation of limonene to menthene tends to be problematic due to overreduction. Limonene hydrogenation using Wilkinson's catalyst confirmed that the hydrogenation of the endocyclic double bond is disfavored [26]. Following hydrogenation of limonene over Pd/C and Pd/ Alumina catalysts at room temperature and 0.1 MPa of hydrogen pressure, side products, such as terpinolene, g-terpinene, and p-cymene, were formed besides menthene and menthane [27].…”

Wilkinson‐Type Immobilized Catalyst on Diamond Nanoparticles for Alkene Reduction

“…functionalized a mesoporous SBA‐15 support with a triphenylphosphine rhodium carbonyl complex and found excellent activity for olefin hydrogenation . A series of alumina/heteropolyacid anchored Wilkinson catalysts have shown to be active towards the reduction of 1‐hexene with 85 % of conversion …”

“…[42] As eries of alumina/heteropolyacid anchored Wilkinson catalysts have shown to be active towards the re-ductionof1 -hexene with 85 %o fc onversion. [43] Herein, we describe the formation of rhodium(I)-modified NDs (NDs-Rh) using asurface-immobilized catechol phosphane ligand (1). While the catechol part provides immobilizationo f the ligand via interaction with the hydroxyl groups of oxidized NDs, [14,17] the phosphane functions will coordinate to transition metal centers and form surface-bound molecular complexes.…”

Optimization of Reaction Conditions and Regeneration Procedure of the PdSb/TiO2 Catalyst for Acetoxylation of Toluene

“…From the literature, it is known that Pd based catalysts are widely used for acetoxylation reactions [3][4][5][6] in general and toluene acetoxylation in particular [5,7,8]. Most of the work reported so far was carried out under liquid-phase conditions and in batch reactors [5,9].…”