Multifunctional organic linker

Fig. 3. Some examples of multifunctional organic linker molecules a) lactic acid, b) oxalic acid, c) adipic acid, d) azelaic acid, e) malonamide, f) oxodiacetate, g) iminodiacetate, h) oxypyridine-4-carboxylic acid, i) squaric acid, j) 1,3-benzenedicarboxylic acid, k) 1,3,5-benzenetricarboxylic acid, 1) isonicotinic acid, m) 2,6-pyridine dicarboxyUc acid, n) 3,5-pyrazoledicarboxyUc acid, o) 4,4 -dipyridyl...

An anchor for traceless linking might also have a safety-catch function or be suitable for multifunctional cleavage. Linker systems enable the introduction of certain atoms or molecule fragments and will play an important role in the development of diverse organic substance libraries. It is important to point out that the final diversity is achieved on cleavage, and not in an additional solution phase re-... 

It is well established that MOFs themselves can function as heterogeneous catalysts [10-13,108] due to the presence (either in the pristine MOF or introduced afterwards by post-synthesis modifications) of active sites located at the metallic nodes and/or functional organic linkers. Therefore, combination of two (or more) different framework active sites (such as acid/base), or a framework active site with encapsulated species located inside the pores, affords a means for preparing multifunctional catalysts. In this way, sequential catalytic transformation (usually referred to as tandem or cascade processes [24,109,110]) can... 

Nowadays, solid-phase synthesis has been used as a powerful tool in organic chemistry, especially to prepare small molecule libraries. New linkers to obtain different functionalities after cleavage have been developed. There are different linkers strategies (Fig. 3.2), for example traceless linkers, multifunctional linkers, safety catch linkers, fragmentation/ cycloreversion cleavage linkers, cyclization cleavage linkers, which are useful methods for combinatorial solid-phase chemistry. 

Simple procedures to prepare multifunctional ligands. Organic bridging ligands having multifunctionalities require many intricate synthetic steps while metalloligands with multifunctionalities can be obtained from combination of simple connectors and linkers. 

As the linker units described above have become ever more elaborate and sophisticated, they have evolved into multifunctional (or diversity) linker units. Multifunctional linker imits use the cleavage step in solid-phase organic synthesis for incorporation of additional diversity into compound libraries, and the main classes of such linker units wiU be discussed in this section, along with representative cleavage strategies. 

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