Supported hydrogen bonded catalyst

An alternative to the supported liquid phase (SLP) method was recently proposed using the same type of solid the supported hydrogen bonded (SHB) catalysts. First demonstrated with the zwitteronic Rh1 catalysts [(sulphos)Rh(cod)] (1) and [(sulphos)Rh(CO)2] (2) (sulphos = 03S(Cr,I I4)CI I2C(CH2PPh2) ). the immobilization procedure is based on the capability of the sulfonate tail of sulphos to link the silanol groups of the support via hydrogen bonds (Figure 12). 

Figure 3.12. Silica grafted catalysts for hydroformylation and hydrogenation, the immobilisation is based on hydrogen bonding between the surface and the sulfonate group (supported hydrogen-bonded (SHB)...

For this reason, these catalysts are also known under the name of supported hydrogen-bonded (SHB) catalysts and, in conjunction with Pd° particles on the same support material, have contributed to generate active heterogeneous systems for the hydrogenation of benzenes in aprotic solvents. Irrespective of the substrate, the combined single-site/dispersed-metal catalyst RhI-Pd0/SiO2 shown in Figure 16.5a was from four- to six-fold more active than supported palladium... 

Fig. 16.5 Some examples of supported hydrogen-bonded catalysts (as described by Bianchini).

Weak Chemisorption Supported Hydrogen-Bonded (SHB) Catalysts... 

The formation of an complex has also been proposed to occur in the solid-liquid hydrogenation of alkenes with the supported hydrogen-bonded (SHB) catalyst [(sulphos)Rh(cod)]/Si02 (sulphos = 03S(C6H4)CH2C(CH2PPh2)3 cod = cyclo-octa-1,5-diene) (Scheme 10) [55-56]. 

Epoxidation with a Supported Hydrogen-Bonded Catalyst. 64... 

The formyl C-H O hydrogen bond idea (Fig. 1.4) was first conceived for the catalyst 9 and its existence is supported by several X-ray studies of BX3 aldehyde... 

It can be summarized from the available data in Table 3 that supported palladium catalysts selectively hydrogenated carbon-carbon double bonds in the presence of the nitrile group in NBR. However, there is no detailed fundamental study on heterogeneous catalytic hydrogenation of nitrile rubber in the literature that can provide an insight into the reaction. The available information is limited since most of the literature is patented. 

This involves deposition of the catalyst on the accessible surface of the support. The complex is held on the surface by rather weak interactions, such as van der Waals forces, hydrogen bonding, or a donating bond. The stability of the complex on the surface is determined by its solubility in the reaction solvent and/or the complexation of reagents and products. 

Renewed interest in this method came recently from its adaptation to the immobilization of water/ organic solvent biphasic catalysts, resulting in the so-called supported aqueous phase catalysts (SAPCs).117 The molecular catalyst is immobilized via water, which is hydrogen bonded to the surface silanol groups reactants and products are in the organic phase (Figure 11)... 

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