Selectivity enhancement in functionalization of C-H bonds: A review.

The selectivity is an extremely important characteristic of a chemical reaction. This review deals mainly with supramolecular and nano-chemical approaches to the problem of selectivity enhancement in various functionalizations of C-H compounds. Enzyme mimics is a very fruitful method to achieve the predominant formation of desirable products and isomers. By obstructing the approach of certain C-H bonds of a substrate to the active catalytic centre we simultaneously increase the relative reactivity of other fragments. This can be done by creating steric hindrance around the active centre. Spatial restrictions can be made if we place the catalyst into a nano-cavity. We can achieve discrimination in reactivity of different C-H bonds if we allow certain fragments to approach closely the active centre. In order to do this chemists use coordination of the catalyst to some groups of the substrate with the participation of relatively strong binding (chelate control) or relatively weak forces (molecular recognition).