1//-Imidazole properties

The introduction of monomers containing polar groups such as tertiary amines, imidazoles, pyrrolidones, pyridines, etc., gives the polymer dispersant properties that will be discussed in the article on dispersant additives for lubricants. 

Two new sections on the protection for indoles, imidazoles, and pyrroles, and protection for the amide — NH are included. They are separated from the regular amines because their chemical properties are sufficienth different to affect the chemistry of protection and deprotection. The Reactivity Charts in Chapter 8 are identical to those in the first edition. The chart number appears beside the name of each protective group when it is first discussed. 

Generally, PS containing amine groups are synthesized by condensation of chlorinated PS with amines. These type of resins are widely used as anionic resins.[8] PSs containing imidazol rings have antistatic properties and are used as additives to make dyeing of synthetic fiber materials easy [9] (Scheme [3]). 

Dibenzo[/),/]thiepin-10(l 1H)-one (1) is an important synthon for the transformation of thiepins into other heterocycles. Oxidation with selenium(IV) oxide gives dibenzo[7>,/]thiepin-10,l 1-dionc (2), in 45% yield,38 which can be condensed with a series of benzaldchydes in the presence of ammonium acetate to provide the substituted 2-aryldibenzo[2,3 6,7]thiepino[4,5-t/]imidazoles 3, known to have anti-inflammatory properties.38... 

Phosphazene polymers can act as biomaterials in several different ways [401, 402,407]. What is important in the consideration of skeletal properties is that the -P=N- backbone can be considered as an extremely stable substrate when fluorinated alcohols [399,457] or phenoxy [172] substituents are used in the substitution process of the chlorine atoms of (NPCl2)n> but it becomes highly hydrolytically unstable when simple amino acid [464] or imidazole [405-407] derivatives are attached to the phosphorus. In this case, an extraordinary demolition reaction of the polymer chain takes place under mild hydrolytic conditions transforming skeletal nitrogen and phosphorus into ammonium salts and phosphates, respectively [405-407,464]. This opens wide perspectives in biomedical sciences for the utilization of these materials, for instance, as drug delivery systems [213,401,405,406,464] and bioerodible substrates [403,404]. 

Maki Y, S Yamamoto, M Nozaki, O Hayaishi (1969) Studies on monooxygenases II. Crystallization and some properties of imidazole acetate monooxygenase. J Biol Chem 244 2942-2950. 

These results suggest that imidazolidin- and imidazol-based skeletons transfer similar amounts of electron density to the metal. The conclusion that changes in the bridge of the NHC skeleton have such a small effect on the electronic properties of the NHC is quite surprising, considering that SIMes- and IMes-based catalysts often show remarkably different catalytic behaviour. It is still unclear if these small changes in the electronic properties of the NHC ligand confer such different catalytic behaviours, or other effects (steric, flexibility, etc.) should be invoked. 

Bidentate NHC-Pd complexes have been tested as hydrogenation catalysts of cyclooctene under mild conditions (room temperature, 1 atm, ethanol). The complex 22 (Fig. 2.5), featuring abnormal carbene binding from the O carbon of the imidazole heterocycles, has stronger Pd-C jj, bonds and more nucleophilic metal centre than the bound normal carbene chelate 21. The different ligand properties are reflected in the superior activity of 22 in the hydrogenation of cyclooctene at 1-2 mol% loadings under mild conditions. The exact reasons for the reactivity difference in terms of elementary reaction steps are not clearly understood [19]. 

In the course of studying a large nnmber of examples where the side chains of the imidazol- and imidazolidin-2-ylidene were altered, several research groups found that NHCs bearing exclnsively alkyl side chains did not provide catalysts with better characteristics when compared to SIMes- and DVIes-derived systems 14 and 15. While Herrmann and co-workers showed that an unsaturated NHC bearing cyclohexyl wing tips conld be incorporated into a second-generation catalyst that was active in metathesis [20-23], more recent studies showed that similar complexes were either very difficult to prepare or were unstable and showed dramatically decreased catalytic properties [24-26] (complexes 17-19, Fig. 3.4). 

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