Hydrogenated polymers, ruthenium-based

Ruthenium catalysts, such as Ru(CHCH(Ph))Cl(CO)(PCy3)2, have been found to be active for catalyzing the hydrogenation of various diene-based polymers. The catalytic mechanism for the hydrogenation of NBR, SBR and PB has been investigated [68]. 

Adsorption is commonly used for catalyst removal/recovery. The process involves treating the polymer solution with suitable materials which adsorb the catalyst residue and are then removed by filtration. Panster et al. [105] proposed a method involving adsorbers made from organosiloxane copolycondensates to recover rhodium and ruthenium catalysts from solutions of HNBR. These authors claimed that the residual rhodium could be reduced to less than 5 ppm, based on the HNBR content which had a hydrogenation conversion of over... 

The use of catalysts based on polymers with inverse temperature solubility, often copolymers of TV-isopropy-lacrylamide, to allow recovery by raising the temperature to precipitate the polymer for filtration,9 was mentioned in Chap. 5. The opposite, if the catalyst is soluble hot, but not cold, has also been used in ruthenium-catalyzed additions to the triple bonds of acetylenes (7.1).10 The long aliphatic tail of the phosphine ligand caused the catalyst to be insoluble at room temperature so that it could be recovered by filtration. There was no loss in yield or selectivity after seven cycles of use. A phosphine-modified poly(A-iso-propylacrylamide) in 90% aqueous ethanol/heptane has been used in the hydrogenation of 1-olefins.11 The mixture is biphasic at 22°C, but one phase at 70°C, at which the reaction takes place. This is still not ideal, because it takes energy to heat and cool, and it still uses flammable solvents. 

Dendrimer based-BINAP polymers have been prepared from 124. A series of soluble dendritic mono-BINAP ligands with Frechet-type polyether wedges like 127 and dendritic poly-BlNAP ligands like 128 have been reported Ruthenium complexes of both classes of dendrimer were prepared and found to be comparable both in catalytic activity and enatioselectivity as homogeneous BINAP analogs in asymmetric hydrogenation reactions. 

Recently, a novel porphyrin-based polymer, namely a poly(CO-Ru(n)-64) (with CO-Ru(n)-64 = ruthenium carbonyl spirobifluorenylporphyrin), was prepared electrochemically and used for the transfer of carbene to olefins and sulphides in a solid-state reaction. In another original study, a bimetallic porphyrin film using 65 was studied as electrode modifier with catalytic activity for molecular oxygen reduction and hydrogen peroxide reduction " . 

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). 

The ruthenium initiators have also been used to conduct hydrogenations after the polymerization process. Polymers obtained from G1 or G3 have been shown to be readily hydrogenated upon addition of a base and hydrogen gas. This resulted in the decomposition of initiators and the formation of products acting as hydrogenation catalysts [152-155]. 

Recently, blocked polymeric isocyanates useful in the preparation of polyurethanes, have been prepared by direct carbonylation of a nitro-substituted polymer based on styrene with carbon monoxide in the presence of a catalyst at 60-200 "C and a pressure from atmospheric to 2000 psi in a hydrogen-donor solvent [64]. Catalysts such as PdL2X2 (X = halogen, L = heterocyclic ligand, e.g. pyridine) in the presence of [NEt4][Cl] have been used. However, from the abstract it is not clear if polynuclear ruthenium, iron, and platinum carbonyls are... 

---