Ligand substitution linker ligands

Fluoroarene-Cr(CO)2L complexes 33p [L = CO, PPh3, P(OPh)3, P(pyrrolyl)3, P(pyrolyl)2 (NMeBn)], where L is a potential linker ligand for solid-phase synthesis, have been evaluated with regard to the rates of nucleophilic substitution by amines [35]. The preparative and kinetic results indicate that SNAr reactions on tris(pyrrolyl)phosphine-modified fluoroar-enechromium complexes proceed rapidly and with high efficiency, and are thus appropriate for the development of solid-phase versions for use in combinatorial synthesis (Scheme 18). 

Inorganic PSM this involves a modification of the secondary building units (SBUs), which form the nodes of the MOF network, and includes substitution of the metal centers or linker ligands. 

Allthough this SPS route averted some of the problems inherent to the synthesis of substituted imidazoles via condensation approaches, the value of the synthesized libraries of compounds is of a limited interest for the histamine receptor research field. First, there is only a limited number of glyoxals, one of the four reaction components, available as precursor. Secondly, only tri- and tetra-substituted imidazoles can be prepared via this method. And finally, the linker (H0-C(=0)-(CH2)2-), a pharmacophore not common to histaminergic ligands, remains present in the final product. 

Finally, homopolymers of bis(oxazoline) ligands have been used to prepare efficient catalysts for cyclopropanation reactions. However, the reduced accessibility to most of the bis(oxazoline) moieties along with the high substitutional lability of copper(I)/(II) leads to a low degree of metal loading. As a consequence, the transmission of chiral information from the metallated polymer is inefficient. The use of suitable dendrimers as cross-linkers in the polymerization process allows a higher level of metallation. 

Poijarvi-Virta and co-workers synthesized di- and trinuclear zinc complexes from benzene substituted in the 1,3 or 1,3,5 positions by 1,5,9-triazacyclododecane ligands via methyloxy linkers [46] as shown in Fig. 4.23. 

Different polyethylene glycol polymers were used in various papers and proved to be very reliable and useful for different classes of molecules their use for the synthesis of peptides [180, 181], of peptidomimetics [182] and of oligosaccharide libraries [183] was reported as the development and the use of a new PEG-linked traceless linker [184, 185], the selection of ligands for asymmetric Sharpless dihydroxylation [186-188], the use of PEG-linked triarylphosphines for LPCS requiring Mitsunobu or Staudinger conditions [189], the use of PEG-based supports to prepare a library of [l,4]oxazepine-7-ones [190] and the use of PEG-supported Schiff bases for the synthesis of a-substituted amino acids [191], Other examples of soluble polymers used for LPCS may include cellulose[192], polyacrylamide [193] polyvinyl alcohol [194, 195], various copolymers [196, 197] and NCPS [198-200]. Three excellent reviews [201-203] summarized the properties of PEG and other soluble polymers and their applications to the synthesis of peptides, oligonucleotides,... 

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