Phosphines tagged

Figure 17.19 An azido-sialic acid derivative that gets incorporated into glycans in cells can be labeled specifically with a biotin-phosphine tag using the Staudinger ligation process. The result is an amide bond linkage with the glycan.

Therefore, a good catalyst leads to weak fluorescence in the Heck product (15). A relatively small library of 96 known phosphines was tested in the palladium-catalyzed Heck coupling. Several sterically hindered ligands led to high catalyst activity. Fluorescence tags have also been used in the combinatorial search for metal-free catalysts in other types of reaction.42,43... 

Fluorous ligands introduce an ease of purification in that the tagged phosphine ligand, the palladium catalyst complexed ligand, and the oxidized ligand can be completely removed by direct fluorous solid-phase separation (F-SPE) prior to product isolation. Similarly, an example of a fluorous palladium-catalyzed microwave-induced synthesis of aryl sulfides has been reported, whereby the product purification was aided by fluorous solid-phase extraction [91]. 

Tri-O-acylglycerols (TAGs), 70 281 Trioctylphosphine oxide (TOPO), 79 66 Triode gauge, 20 660-661 Triols, phosphine oxide, 77 501 Triorganohydridosilanes, in silicone chemistry, 22 555... 

Bifunctional reagents have recently been used to facilitate separations in the Mitsunobu reaction.39 Mitsunobu products are often hard to separate from excess reagents and byproducts, including phosphines and phosphine oxides. The tagged phosphine 21 and azodicarboxylate 22 and the byproducts formed from these are converted to the carboxylic acid forms by treatment with trifluoroacetic acid (TFA) at the end of the reaction. The excess reagents and byproducts could then be captured on an ion exchange resin for convenient removal. 

An der Heiden, M. and Plenio, H. (2004) Homogeneous catalysts supported on soluble polymers biphasic Suzuki— Miyaura coupling of aryl chlorides using phase-tagged palladium—phosphine catalysts. Chem. Ear. ]., 10, 1789. 

Scheme 8. Phase-tagged phosphines as ligands in Pd-catalyzed cross-coupling reactions.

Scheme 15 Supramolecular interaction between perfluoro-tagged palladium phosphine complex 35 and polyglycerol perfluoroalkyl ester 34...

The concept of ionic tagging in aryl phosphine design is made explicit by the structures of ligands collected in Table 1.5. 

Let us examine first the principal sites of tagging ruthenium complexes (Scheme 1.41) they include covalent ligands A [phosphines, N-heterocyclic carbenes (NHCs) or pyridine], anionic ligands B, or the carbene ligand C (either in the aromatic moiety or at the alkoxy ligand). 

Conventional reagents that cannot easily be removed by solid-phase extraction may be tagged in such a way that extraction by scavenger resins becomes possible. For example, for Mitsunobu reactions phosphines and azodicarboxylic acid derivatives of types 3 and 4... 

In a similar fashion, efforts for the development and application of supported phosphines as scavengers to remove various electrophiles have been reported. Reports demonstrate the diversity of resin-tags used, and their applications as both... 

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