Pyridine complexes, polymer-bound

O-linked polymer-bound Af-substituted hydroxylamines are prepared by reduction of resin-bound oximes with borane-pyridine complex in the presence of dichloroacetic acid (Scheme 94). Other reducing systems commonly used for imine or oxime reduction are ineffective, including borane-pyridine in the presence of acetic acid. Subsequently, the A-substituted products are acylated and cleaved from the resin to afford Af-substituted hydroxamic acids 220. ... 

A material with nitrogen-coordinated Ru was obtained from a silica-linked 2-(phenylazo)pyridine ligand. Results for cyclobutanol oxidation with 02 and the sacrificial oxidant isobutyraldehyde indicate that one- and two-electron oxidations occur simultaneously. The stability of the catalyst is not always guaranteed, probably because acids may be formed in oxidations of alcohols (284). Leaching problems are also encountered with a polymer-bound Ru Schiff base complex, used in oxidation of benzyl alcohol (285). 

Amine complexes. The effect of immobilization of the Cu(II) complexes of polymeric amines has been examined and reviewed by Challa et al. ( ). The polymeric ligands were varied by using the following species polymer-bound dimethylbenzylamlne (formed by treatment of chloromethylated polystyrene with dimethylamlne), the copolymer of styrene and 4-vinyl-pyridine and the copolymer of styrene and N-vinylimidazole. The reaction examined was the Cu(II) oxidative dimerization of 2,6-disubstituted phenols (Equation 1). 

Pyridine Complexes. The addition of a halogen to pyridine affords a molecular complex The bromine complex Is capable of the halogen— atlon of olefins as reported by Lloyd and Durocher and Zupan et al (61-63). Anti stereoselectivity Is observed and a nucleophilic solvent can replace the second halogen, thus Implicating a bromonlum Ion. A similar complex with polyvinyl pyrldlne-N-oxlde acts In a similar fashion. The polymer-bound pyrldlnlum hydrobromide perbrom-Ide has also been formed by Frechet, Farrall and Nuyens. It reacts with olefins In the same fashion but has also been shown to halogenate ketones (64). 

Another approach is based on the application of redox polders, e.g. osmium complex-modified poly(vinyl pyridine) (9-11) or ferrocene-modified poly(siloxanes) (12,13X crosslinked together with an enzyme on the top of the electrode. The electron transfer fi-om the active site of the polymer-entrapped enzyme to the electrode surfece occurs to a first polymer-bound mediator which has suflSdently approached the prosthetic group to attain a fast rate constant for the electron-tranrfer reaction. From this first mediator the redox equivalents are transported along the polymer chains by means of electron hopping between adjacent polymer-linked mediator molecules (Fig. 2). Extremely fast amperometric enzyme electrodes have been obtained with si ificantly decreased dependence fi-om the oxygen partial pressure. However, die redox polymer/enzyme/crosslinker mbcture has to applied either manually or by dipcoating procedures onto the electrode surface. 

---