Ligand polymer-bound

Polymer bound ligands, polymer bound metallocenes, catalyst systems, preparation, and use... 

The size-exclusion and ion-exchange properties of zeoHtes have been exploited to cause electroactive species to align at a zeoHte—water interface (233—235). The zeoHte thus acts as a template for the self-organization of electron transfer (ET) chains that may find function as biomimetic photosynthetic systems, current rectifiers, and photodiodes. An example is the three subunit ET chain comprising Fe(CN)g anion (which is charge-excluded from the anionic zeoHte pore stmcture), Os(bipyridine)3 (which is an interfacial cation due to size exclusion of the bipyridine ligand), and an intrazeoHte cation (trimethylamino)methylferrocene (F J ). A cationic polymer bound to the (CN) anion holds the self-assembled stmcture at an... 

A remarkable effect of the reaction temperature on the enantioselectivity of the addition of butyllithium to benzaldehyde was found with polystyrene-bound cvs-enofo-S-dimethylamino -(benzyloxy)bornane (8)12. When the soluble monomeric ligand 9 was tested, the enantioselectivity increased with decreasing temperature (53% ee at — 78 C). In contrast, the polymer-bound chiral additive 8 showed an optimum at — 20 C (32% ee). Although the enantioselectivity of this addition reaction is low, an advantage of a polymer-bound chiral auxiliary is that it can be removed by a simple filtration. 

A polymer-supported version of our optimal ligand was also developed [52]. Its preparation involves attachment of aziridine carbinols to polymer-bound triphenylchloromethane (Scheme 40). This polymer-bound ligand 53 was almost equally effective in the enantioselective addition of diethylzinc to aromatic and aliphatic aldehydes with ee s ranging from 77-97% for the latter type of substrate [52]. It is of practical interest that this polymer-supported ligand could be reused without losing much of its efficiency. 

The properties and yield of the polymer product were correlated to the NHC identity, providing clear evidence that the NHC ligand was bound and influenced the reaction. Smaller R groups (Me, Et) on 39-R provided low molecular weights, yields, and detectable amounts of impurity. Sugiyama only examined the influence of sterics on the formation of PC, but the initial success inspired Tanaka and coworkers to extend this application by tethering NHC ligands to styrene beads [48]. 

Transformations to polymer-bound amino compounds, which are often useful as ligands for metals ions or other free species (67), employ a wide selection of organic reactions. Quaternary ammonium salts result from heating isolated polymer tosylate with tertiary amine they may also be prepared in one step from (hydroxyethyl)polystyrene and toluenesulfonyl chloride and a two-fold excess of amine. 

A chiral diphosphine ligand was bound to silica via carbamate links and was used for enantioselective hydrogenation.178 The activity of the neutral catalyst decreased when the loading was increased. It clearly indicates the formation of catalytically inactive chlorine-bridged dimers. At the same time, the cationic diphosphine-Rh catalysts had no tendency to interact with each other (site isolation).179 New cross-linked chiral transition-metal-complexing polymers were used for the chemo- and enantioselective epoxidation of olefins.180... 

A comparison of the rates showed that the polymer-bound Ti-TADDOLate 88 and the dendritic polymer 89 catalyze the Et2Zn-to-PhCHO addition at a similar fast rate as the monomeric TADDOLate 86 and the dendritic TADDOLate 87 in homogeneous solution [107,112]. Further experiments also with other ligands are being carried out in our laboratories. 

In related work a library of 1,458 peptide ligands and various metal salts was tested in hydrolysis reactions of (p-nitrophenyl)phosphates.35 An active substructure composed of polymer-bound histidine in combination with Eu3+ was identified by further dissecting the original hit structure. It needs to be pointed out that catalytically active polymer beads can also be tested for catalytic activity using IR-thermography. In a seminal paper this was demonstrated using 7,000 encoded polymer beads prepared by split-and-pool methods, specifically in the metal-free acylation of alcohols.36... 

The separation of homogeneous catalysts by means of membrane filtration has been pioneered by Wandrey and Kragl. Based on the enzyme-membrane-reactor (EMR),[3,4] that Wandrey developed and Degussa nowadays applies for the production of amino acids, they started to use polymer-bound ligands for homogeneous catalysis in a chemical membrane reactor (CMR).[5] For large enzymes, concentration polarization is less of an issue, as the dimension of an enzyme is well above the pore-size of a nanofiltration membrane. 

Plenio et al. tested an adamantyl phosphine ligand bound to soluble polystyrene (Figure 4.43) in various palladium-catalyzed C-C coupling reactions.[62] The retention of metal complexes of the polymer-bound phosphine ligand were determined to be higher than 99.95%. 

Figure 4.43. Polymer-bound adamantyl phosphine ligands.[62]...

The sensors discussed so far are based on ligands covalently bound to the polymer backbone. Other methods of detection - often referred to as mix and detect methods - work by simple noncovalent incorporation of the polymer with the ligand of interest. Reichert et al. generated liposomes of polydiacetylene with sialic acid for the same purpose of detection as Charych s surface-bound polymers, but realized that covalent functionalization of the polymer was not necessary [17]. Through simple mixing of the lipid-bound sialic acid with the polymer before sonication and liposome formation, they were able to form a functional colorimetric recognition system (Fig. 8). 

Cross-linked polymers bearing IV-sulfonyl amino acids as chiral ligands were converted to polymer bound oxazaborolidine catalysts by treatment with borane or bromoborane. In the cycloaddition of cyclopentadiene with methacrolein, these catalysts afforded the same enantioselectivities as their non-polymeric counterparts238. 

At least two groups examined the issue of catalyst recycle by using polymer-bound or water-soluble ligands." " ... 

In view of the environmental issues and operational simplicity, heterogeneous catalytic systems have been suggested to be advantageous. Gibson and co-workers first introduced polymer-bound cobalts 27 and 28 to this end." Subsequently, Portnoy and Dahan immobilized cobalt on dendrimeric phosphane ligands, which have a partial structure of 29 (Figure 6)." ... 

A dry 50 mL Schlenk reaction tube was flushed with nitrogen and charged with a mixture of 7 (527mg, l.Ommol), 1,3-dicyclohexylcarbodiimide (1.04g, 5mmol), pentafluorophenol (920 mg, 5 mmol), 4-(dimethylamino)pyridine as the catalyst and the aminomethylated polystyrene (930 mg, 1.07 mmol g ) in dry dichloromethane (20 mL). The mixture was stirred at room temperature for 24h under a N2 atmosphere. The polymer was filtrated, rinsed sequentially with CH2CI2 and acetone and dried at 50 °C in vacuo to yield the polymer-bound ligand 8 as pale yellow beads. 

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