Catalysts immobilisation

Vankelecom IFJ, Jacobs PA (2000) In De Vos DE, Vankelecom IFJ, Jacobs PA (eds) Chiral catalyst immobilisation and recycling, chap 2. Wiley-VCH, Weinheim... 

Another successful approach to catalyst immobilisation involves attachment of the carbene precursor to a peptide on solid support. Treatment with base generates the corresponding carbenes that undergo in situ complexation to Pd(ll) centres (Scheme 6.33). Again, the main drawback of this approach was the low reactivity of the catalytic system that only allowed the coupling of aryl iodides and bromides [116], The reasons for this outcome are in need of further studies. 

Scheme 6.33 Pre-catalyst immobilisation by attachment to a peptide on solid support...

Since catalysts immobilised on hydrophilic silica gel often give superior performances to their polymer-bound or polymer-incorporated analogues for multiple applications, Heckel and Seebach have immobilised TADDOL derivatives on hydrophobic controlled-pore glass (CPG) silica gel. Indeed, CPG is... 

The method of catalyst immobilisation appeared to affect its performance in catalysis. Catalyst obtained by method II showed a low selectivity in the hydroformylation of 1-octene (l b aldehyde ratio was even lower than 2) at a very high rate and high yields of isomerised alkenes (Table 3.2, entry 2), whereas procedure IV resulted in a catalyst that was highly selective for the linear aldehyde (with a l b ratio of 37) (entry 5). In accordance with examples from literature it is likely that procedure II gave rise to the ionic bonding of ligand-free rhodium cations on the slightly acidic silica surface [29],... 

A summary of the research activities of the last four years reveals three different important trends (a) The design of new ionic ligands for excellent catalyst immobilisation in ionic liquids and high regioselectivity (b) the successful application of cheap, halogen-free ionic liquids in the biphasic Rh-catalysed hydroformylation (c) the successful development of unusual multiphasic reaction concepts for Rh-catalysed hydroformylation, namely catalysis in ionic liquid/supercritical C02 and SILP-catalysts. 

An alternative strategy for catalyst immobilisation uses ion-pair interactions between ionic catalyst complexes and polymeric ion exchange resins. Since all the rhodium complexes in the catalytic methanol carbonylation cycle are anionic, this is an attractive candidate for ionic attachment. In 1981, Drago et al. described the effective immobilisation of the rhodium catalyst on polymeric supports based on methylated polyvinylpyridines [48]. The activity was reported to be equal to the homogeneous system at 120 °C with minimal leaching of the supported catalyst. The ionically bound complex [Rh(CO)2l2] was identified by infrared spectroscopic analysis of the impregnated resin. 

Regulated Systems for Catalyst Immobilisation Based on Supercritical Carbon Dioxide... 

Keywords Biphasic systems Catalyst immobilisation Ionic liquids ... 

Langanke J, Leitner W (2008) Regulated Systems for Catalyst Immobilisation Based on Supercritical Carbon Dioxide. 23 91-108 Larock R (2005) Palladium-Catalyzed Annulation of Alkynes. 14 147-182 Larrow JF, Jacobsen EN (2004) Asymmetric Processes Catalyzed by Chiral (Salen)Metal Complexes 6 123-152... 

Phan, N T S. and Brown, D.H. and Styring, P. (2004). A faeile method for catalyst immobilisation on silica nickel catalysed Kumada reactions in mini-continuous flow and batch reactors. Green Chemistry, 6, 526-532. 

Jackson, T. and Clark, J.H. and Macquarrie, D.J. and Brophy, J. H. (2004). Base catalysts immobilised on silica coated reactor walls for use in continuous flow systems. Green Chem., 6, 193-195. 

Bell, R. C., Castleman, A. W. and Thorn, D. L., Vanadium oxide complexes in room-temperature chloroaluminate molten salts. Inorg. Chem., 38,5709,1999. Dyson, P. J., Mcindoe, J. S. and Zhao, D. B., Direct analysis of catalysts immobilised in ionic liquids using electrospray ionisation ion trap mass spectrometry. Chem. Commun., 508,2003. 

Despite the fact that, for the oxidation of sodium dithionite at unmodified gold electrodes, well-defined voltammetric waves are obtained12, the reaction still behaves irreversibly1214. Therefore, it is in principle possible to improve the oxidation rate of this reaction by using an appropriate catalyst immobilised at the gold electrode surface. The modified electrode used here was obtained by a 100-fold scanning experiment between -1.2 and... 

Mainly the hydrogenations are mediated through a platinum-group-metal-catalysed reaction with chiral ligands bound to the metal. Koten and coworkers210 proposed the use of Ru- and Rh-containing catalysts immobilised on silica in asymmetric hydrogenation. As a chiral compound, they used BINAP (2,2 -bis(diphenylphosphino)-1,1 -binaphthyl) (Scheme 4). 

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