Silver electronically tuned

Macrocycles are well known to bind to a variety of metals in several oxidation states and the macrocycle cavity size can be varied to electronically tune redox couples. A number of electrochemical investigations have been conducted on gold and silver macrocycles55-79. 

Scheme 6J Synthetic route to an electronically tuned silver-NHC, 6.

The classical Hunsdiecker reaction (equation 18), involving the reaction of silver caiboxylates widi halogens, and the various associated side reactions, has been reviewed several tunes. Optimum yields are obtain widi bromine, followed by chlorine. Iodine gives acceptable yields provid diat the correct stoichiometry of 1 1 is used. The reaction is most frequently carried out in tetrachloromediane at reflux. From a practical pmnt of view, one drawback is the difficulty encountered in the preparation of dry silver caiboxylates the reaction of silver oxide on the acyl chloride in tetrachloromediane at reflux has been employed to circumvent diis problem. Evidendy the use of molecular bromine limits die range of functional groups compatible widi die reaction the different reaction pathways followed by the silver salts of electron poor (equation 19) and electron rich (equation 20) aryl carboxyl s illustrate this point well. 

Electronically different LGs have also been incorporated to tune the glycosyl donor reactivity (Scheme 6.8). One of the first examples described the use of selenoglycosids in the presence of thioglycosides. While Mehta and Pinto used silver triflate to selectively activate the seleno derivative 34-the benzylated sulfur compound 35 did not react-for the synthesis of disaccharide 36 [38, 39], iodonium sources became more common for numerous applications of this concept in one-pot... 

Subsequently, Schomaker and coworkers have developed the first example of ligand-controlled and tunable silver-catalyzed C(sp )-H amination method (Scheme 9.31) [37]. Simple silver catalysts supported by common nitrogenated ligands were used to tune a nitrene transfer reaction between two different types of C-H bonds while silver catalysts supported by Bubipy appear to prefer amination of the most electron-rich C-H bond, silver supported by a tpa ligand is more sensitive to the steric environment around the C-H bond, as well as the bond dissociation energy. 

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