Organometallic polymers hydrogenation catalyst

Last but not least, the success of aqueous-phase catalysis has drawn the interest of the homogeneous-catalysis community to other biphasic possibilities such as or-ganic/organic separations, fluorous phases, nonaqueous ionic liquids, supercritical solvents, amphiphilic compounds, or water-soluble, polymer-bound catalysts. As in the field of aqueous-phase catalysis, the first textbooks on these developments have been published, not to mention Job s book on Aqueous Organometallic Catalysis which followed three years after our own publication and which put the spotlight on Job s special merits as one of the pioneers in aqueous biphasic catalysis. Up to now, most of the alternatives mentioned are only in a state of intensive development (except for one industrial realization that of Swan/Chematur for hydrogenations in scC02 [2]) but other pilot plant adaptations and even technical operations may be expected in the near future. 

Transition-metal organometallic catalysts in solution are more effective for hydrogenation than are metals such as platinum. They are used for reactions of carbon monoxide with olefins (hydroformyla-tion) and for some ohgomerizations. They are sometimes immobihzed on polymer supports with phosphine groups. 

Polborn and Severin [23] recently reported ruthenium- and rhodium-based TSAs for the transfer hydrogenation reaction. These complexes were used as catalyst precursors in combination with molecular imprinting techniques. Phosphinato complexes were prepared as analogs for the ketone-associated complex. They demonstrated that the results obtained in catalysis were better in terms of selectivity and activity when these TSAs were imprinted in the polymer. This shows that organometallic complexes can indeed serve as stable TSAs (Figure 4.9). 

Additives. Certain additives may be included with the catalyst system of the transition metal catalyst and MAO or borate cocatalyst in order to improve the polymerization activity or perhaps to adjust a polymer property into a useful range. Activators that have been reported for sPS polymerization include aluminum alkyls, hydrogen, and organometallic compoimds of tin and zinc. 

Many studies have been carried out on the anionic polymerization of NIPAM using conventional organometallic catalysts. However, the acidic amide proton of NIPAM inhibited anionic polymerization, instead inducing hydrogen-transfer polymerization imder basic conditions, as shown in Scheme 2. The polymers obtained were insoluble in water and did not show LCST phase separation [14,15]. Recently, the polymerization of monomers in which this active hydrogen was protected by methoxymethyl or trialkylsi-lyl group 9,10 was examined and living anionic polymerization has become possible [60-62]. Ishizone et al. have prepared atactic PNIPAM with a narrow MWD via the anionic polymerization of N-methoxymethyl-NIPAM (9)... 

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