Recycling ligand

Unfortunately, the immobilization of the alkaloid ligands did not result in the simultaneous immobilization of the osmium catalyst due to the weak binding of cinchonidine to the osmium complexes. In most studies, leaching of the osmium catalyst was reported and supplementation of the osmium catalyst was necessary after recovery of the immobilized chiral ligand. In other studies, the recycled ligands were used without further addition of the osmium catalyst resulting in reduced yields or longer reaction times. 

Receptor recycles, ligand degraded Receptor recycles. Receptor transported, Re( ligand recycles ligand transported liga eptor recycles, nd released... 

They also employed 7V-heterocyclic carbene (NHC)-modified silica particles as efficient and recyclable ligands for the Huisgen cycloaddition (Scheme 4.2) (Li et al., 2008). A variety of 1,2,3-triazoles were generated in high yields from various organic azides and alkynes. 

Inspired by the helical structures of naturally occurring DNA, RNA, and polypeptides, the creation and application of helical chiral polymers have received extensive attention, recently evolving into a hot research topic but still challenging field [67]. Generally, helical chiral polymers, including the static helical polymers and the dynamic and responsive helical polymers, can be prepared via polymerization of chiral monomers, or with a chiral initiator or chiral catalyst in which either a left- or right-handed helical sense is prevalent. It is to be noted that helical chiral polymers as a novel class of recyclable ligands enable asymmetric induction for catalysis [68]. 

A fluorous 1,4-disubstituted [l,2,3]-trizole 26 was prepared from fluoroalkyl tosylate to replace the air- and moisture-sensitive phosphine ligand as a recyclable ligand for the palladium-catalyzed Suzuki-Miyaura reaction and Mizoroki-Heck reaction (Scheme 7.23) [36]. As expected, the fluorous ligand, together with palladium acetate, promoted these coupling reactions and the fluorous ligand was conveniently... 

The unit has virtually the same flow sheet (see Fig. 2) as that of methanol carbonylation to acetic acid (qv). Any water present in the methyl acetate feed is destroyed by recycle anhydride. Water impairs the catalyst. Carbonylation occurs in a sparged reactor, fitted with baffles to diminish entrainment of the catalyst-rich Hquid. Carbon monoxide is introduced at about 15—18 MPa from centrifugal, multistage compressors. Gaseous dimethyl ether from the reactor is recycled with the CO and occasional injections of methyl iodide and methyl acetate may be introduced. Near the end of the life of a catalyst charge, additional rhodium chloride, with or without a ligand, can be put into the system to increase anhydride production based on net noble metal introduced. The reaction is exothermic, thus no heat need be added and surplus heat can be recovered as low pressure steam. 

Since no special ligand design is usually required to dissolve transition metal complexes in ionic liquids, the application of ionic ligands can be an extremely useful tool with which to immobilize the catalyst in the ionic medium. In applications in which the ionic catalyst layer is intensively extracted with a non-miscible solvent (i.e., under the conditions of biphasic catalysis or during product recovery by extraction) it is important to ensure that the amount of catalyst washed from the ionic liquid is extremely low. Full immobilization of the (often quite expensive) transition metal catalyst, combined with the possibility of recycling it, is usually a crucial criterion for the large-scale use of homogeneous catalysis (for more details see Section 5.3.5). 

Good rhodium retention results were obtained after several recycles. However, optimized ligand/metal ratios and leaching and decomposition rates, which can result in the formation of inactive catalyst, are not known for these ligands and require testing in continuous mode. As a reference, in the Ruhrchemie-Rhone-Poulenc process, the losses of rhodium are <10 g Rh per kg n-butyraldehyde. 

The majority of functional assays involve primary signaling. In the case of GPCRs, this involves activation of G-proteins. However, receptors have other behaviors— some of which can be monitored to detect ligand activity. For example, upon stimulation many receptors are desensitized through phosphorylation and subsequently taken into the cell and either recycled back to the cell surface or digested. This process can be monitored by observing ligand-mediated receptor internalization. For... 

Similarly, allylbromide reacts to give the hexabutenyl complex. The latter can be photolyzed. The new hexabutenylbenzene ligand is recovered in the recycling reaction [77] Scheme XI. 

The search for even more active and recyclable ruthenium-based metathesis catalysts has recently led to the development of phosphine-free complexes by combining the concept of ligation with N-heterocyclic carbenes and benzyli-denes bearing a coordinating isopropoxy ligand. The latter was exemplified for Hoveyda s monophosphine complex 13 in Scheme 5 [12]. Pioneering studies in this field have been conducted by the groups of Hoveyda [49a] and Blechert [49b], who described the phosphine-free precatalyst 71a. Compound 71a is prepared either from 56d [49a] or from 13 [49b], as illustrated in Scheme 16. 

Cements, polyester, 30 CFCs. See Chlorofluorocarbons (CFCs) Chain conformation, 54 Chain extenders, 213-214 structure of, 219 Chain extension, 216 Chain-growth polymerizations, 4 Char formation, 421, 423 Chelated phosphine ligands, 488 Chemical recycling, 208 Chemical structure... 

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