Anchored catalysts

Catalysts Anchored to Inorganic Solids by Covalent Bonds... 

It has not been shown unambiguously, however, whether the rhodium remains coordinated to the ligands 2 and 3 during the catalysis. Kantam and associates [23] have used a Pd(II) catalyst anchored onto MCM-41/silylamine (MCM-41 a molecular-sieve) for hydrodehalogenation of aryl halides by atmospheric hydrogen. The catalyst was reused for several cycles with constant activity. 

Ribaudo F, van Leeuwen PWNM, Reek JNH (2006) Supramolecular Dendritic Catalysis Noncovalent Catalyst Anchoring to Fimctionalized Dendrimers. 20 39-59 Richmond TG (1999) Metal Reagents for Activation and Functionalization of Carbon-Fluorine Bonds. 3 243-269... 

Supramolecular chemistry also provides new tools for catalyst anchoring. We have shown that catalysts can be noncovalently attached to various soluble and insoluble supports, affording recyclable catalysts. Interestingly, the reversible nature of the noncovalent bond gives rise to new opportunities. In the first instance, we foresee an important role for supramolecular bidentate ligands in combinatorial catalysis - but as a consequence of the entirely new properties many new applications are envisioned. We look forward to new developments and results in this exciting emerging area of supramolecular catalysis. 

In this work the preparation of orthophenylenediamine (OPDA) from 4-chloro-2-nitroani1ine was studied on alumina supported palladium catalysts. High OPDA yields were obtained on catalysts containing stabilized ionic palladium. In the preparation of the given palladium containing catalysts anchoring type surface reactions were used. The existence of palladium in ionic form was evidenced by XPS and El R measurements. 

Figure 4.23 Second-generation W-and Re-alkylidene metathesis catalysts anchored on silica, with their corresponding TOF and TON values at25°C [131],...

Now let us discuss how one can conjugate the process of H2 evolution on the catalyst anchored to the membrane or located in a water phase with the vectorial PET across this membrane. 

The groups of Reek and Meijer have also applied the noncovalent approach for catalyst anchoring to a dendrimer support [62], Phosphine functionalized ligands were attached to the periphery of polypropylene imine) dendrimers via combined ionic interactions and H-bonding using a specific binding motif that is complementary to that of the support (Fig. 6). 

Supramolecular Dendritic Catalysis Noncovalent Catalyst Anchoring to Functionalized Dendrimers... 

Smet, R, Riondato, J., Pauwels, T., Moens, L. and Verdonck, L. Preparation and characterization of a titanium(IV) silsesquioxane epoxidation catalyst anchored into mesoporous MCM-41, Inorg. Chem. Commun., 2000, 3, 557-562. 

One example of a catalyst anchoring onto the hybrid xerogel s framework is the chemical modification of a dendrimer xerogel126. In the starting dendrimer xerogel, the high specific surface area (> 1000 m2 g-1) is combined with a good hydrothermal stability (up... 

I-IG. 19. Photoluminesccncc spectrum (a), its excitation spectrum (b), and UV absorption spectrum (c) of the vanadium oxide catalyst anchored to Vycor glass by the photo-CVD method. Photolumiiiescence spectrum recorded at 77 K excitation wavelength, 280 nm emission monitored at 500 iim UV absorption spectrum measured at 295 K vanadium content, 0.1 wt% [reproduced with permission from Anpo et al. (69)]. 

Fig. 20. Second-derivative photoluminescence spectrum of the vanadium oxide catalyst anchored to Vycor glass shown in Fig. 19 [reproduced with permis.sion from Anpo et al. (69). ...

Fk5. 21. Progression of the vibrational tine structure of the photoluminescence spectr um of vanadium oxide catalyst anchored to SiOj at 77 K. Theoretical results from a Franck-Condon analysis (striped bars) and experimental results (solid bars) [reproduced with permission from Patterson et al. (725)]. 

Fig. 26. Photoluminescence spectra of the molybdenum oxide catalyst anchored to Si02 (molybdenum oxide/Si02) at 77 K (a) and at 298 K (b) and their excitation spectrum. Excitation wavelength at 280 nm emission monitored at 520 nm [reproduced with permission from Anpo...

Fig. 28. UV-visible absorption spectra of porous Vycor glass (PVG) and the lilaniuni oxide catalyst anchored to PVG having one to five Ti-O layers. Dotted line is the absorption spectrum of the anchored titanium oxide having one Ti-O layer obtained by subtracting the PVG spectrum from the spectrum of the anchored titanium oxide/PVG catalyst [reproduced with permission from Anpo et al. (idS)].

Fig. 44. Relationship between the yields of the phosphorescence spectrum of the vanadium oxide catalyst anchored to Vycor glass and the yields of the photocatalytic isomerization of tTOra-2-butene on this catalyst. Phosphorescence yields measured at 280 K photocatalytic reaction temperature, 298 K. O, yields of cw-2-butene yields of 1-butene. Initial pressure of rranj-2-buteiie about 399 Pa [reproduced with permission from Anpo et at (69)].

The deposition of a suitable catalyst in the intimate body of the above-described filters is controlled primarily by the structure of the filter itself, but it is also influenced by the nature of its constituent material. In fact, shear stresses may arise at the interface between this material and the deposited catalyst, owing to thermal expansion mismatch between the two phases. Since most catalyst supports are based on inorganic oxides, this problem would be particularly serious for metal-based filters, owing to their much higher thermal expansion coefficients. However, in some metal alloys, such as the FeCrAlloy, a thin surface layer of a metal oxide (e.g., ALOO is formed at high temperatures, which improves their thermal resistance and allows a proper basis for catalyst anchoring. 

Shephard DS, Maschmeyer T, Johnson BFG, Thomas JM, Sankar G, Ozkaya D, Zhou WZ, Oldroyd RD, Bell RG (1997) Bimetallic nanoparticle catalysts anchored inside mesoporous silica. Angew Chem Int Ed Engl 36 2242... 

Miyabe H, Tuchida S, Yamauchi M, Takemoto Y (2006) Reaction of nitroorganic compounds using thiourea catalysts anchored to polymer support. Synthesis 3295... 

Early studies of the supported metal complexes utilized as hydrosilylation catalysts focused on the immobilization of H2PtCl6 on ion exchangers. Chloroplatinic acid and other Pt complexes have been used as efficient precursors of the catalysts anchored to silica or organic materials for the hydrosilylation of 1-alkenes, styrene, allyl derivatives, and acetylene [2, 84-87]. 

The positive situation with respect to catalyst life and metal leaching has been confirmed by a comparison of results obtained in a bydrosilylation reaction carried out with a homogeneous rhodium catalyst, a similar catalyst anchored to silica, and a corresponding organopolysiloxane-based system synthesized via route A [83]. 

Dendrimers are a class of macromolecules with highly branched and well-defined structures, and have recently attracted much attention as soluble supports for (chiral) catalyst immobilization [55-65]. As stated above, the catalysts anchored onto or into insoluble supports often possess an uneven catalytic site distribution and partly unknown structures, and generally suffer from diminished activity due to the mass transfer hmitations. Dendrimers, on the other hand, allow for the precise construction of catalyst structures with uniformly distributed catalytic... 

Thomas and Johnson described a direct asymmetric hydrogenation of ethyl nicotinate using Pd ferrocenyl catalyst anchored within MCM 41 [48]. The confined catalyst (5%) displayed a good activity (TON = 291), but no increase in enantioselec tivity (17% ee) was observed compared to the corresponding homogeneous catalyst (Scheme 10.35). 

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