Metal complexes-polybenzimidazoles

Polystyrene-based resins have been used widely as supports for metal complex catalysts and other reactive species. These polymers, however, have a drawback in their limited thermo-oxidative stability [1,2]. The scope for application is therefore restricted, particularly in polymer-supported transition metal complex oxidation catalysts [3]. Consequently there is a need for the development of polymer supports with a much higher intrinsic thermo-oxidative stability. Polybenzimidazoles and polyimides are likely candidates in this respect. 

Polybenzimidazole resin in a porous bead has been applied as a polymer support for homogeneous metal complexes [4-6], The polybenzimidazole-supported Mo(VI) species showed retention of high activity in the epoxidation of propylene, but progressive loss of activity on recycling in the epoxidation of cyclohexene. 

Redox metal centers can also be grafted on to the surface of silica, or on to the internal surface of a molecular sieve, by ligand displacement with pendant silanol groups [33]. Alternatively metal complexes can be tethered to silica or the internal surface of a molecular sieve via a spacer that is attached to the surface. This approach is analogous to the tethering of organic bases to solid surfaces referred to earlier. Metal complexes can also be attached to oxidatively stable organic polymers such as polybenzimidazole [34]. 

Sherrington and coworkers have used polybenzimidazoles and polymides to complex metal ion catalysts and thus avoid or minimize losses of the metal ions, some of which are expensive. The first has been used to complex palladium(II) for the Wacker reaction (5.47) of 1-octene and 1-decene to ketones.204 (The other reagents for this reaction are copper(II) chloride and oxygen.)... 

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