Pyridine-Cu complex

Tab. II Polymerization rate of XOH catalyzed by pyridine-Cu complex in several solvents...

Polymerization proceeded about 5 times faster in an alkaline solution, and the side reaction that forms biphenoquinone was suppressed151. The acceleration effect is due to the acid dissociation of XOH by alkali, but the monomeric pyridine-Cu complex was hydrolyzed at the same time, therefore the acceleration was not observed in the pyridine-Cu system. The PVP-Cu complex is relatively stable toward alkali due to its chelate structure thus, the PVP-Cu catalyst was active during the polymerization even in an alkaline solution. 

Evans et al. reported that the his(oxazolinyl)pyridine (pybox) complex of copper(II) 17 is a selective catalyst of Diels-Alder reactions between a-bromoacrolein or methacrolein and cydopentadiene affording the adducts in high enantioselectivity [23] (Scheme 1.30). Selection of the counter-ion is important to achieve a satisfactory reaction rate and enantioselectivity, and [Cu(pyhox)](ShFg)2 gave the best result. This catalyst is also effective for the Diels-Alder reaction of acrylate dieno-philes (vide infra). 

Evans s bis(oxazolinyl)pyridine (pybox) complex 17, which is effective for the Diels-Alder reaction of a-bromoacrolein and methacrolein (Section 2.1), is also a suitable catalyst for the Diels-Alder reaction of acrylate dienophiles [23] (Scheme 1.33). In the presence of 5 mol% of the Cu((l )-pybox)(SbF5)2 catalyst with a benzyl substituent, tert-butyl acrylate reacts with cyclopentadiene to give the adduct in good optical purity (92% ee). Methyl acrylate and phenyl acrylate underwent cycloadditions with lower selectivities. 

The oxidation of butanone-2, catalyzed by complexes of pyridine with cupric salts, appeared to be similar in its main features [191]. Butanone-2 catalytically oxidizes to acetic acid and acetaldehyde. The reaction proceeds through the enolization of ketone. Pyridine catalyzes the enolization of ketone. Enole is oxidized by complexes of Cu(II) with pyridine. The complexes Cu(II).Py with n = 2,3 are the most reactive. Similar results were provided by the study of butanone-2 catalytic oxidation with o-phenanthroline complexes, where Fe(III) and Mn(II) were used as catalysts [192-194],... 

The oxidation rates of XOH were measured for the PVP complexes of the transition metal ions of the 4th series, i.e., Cr, Mn, Fe, Co, Ni, Cu and Zn ion. As can be seen in Fig. 2 (a), the Cu complexes exhibit the highest activity and the activity of the PVP-Cu catalyst is higher than that of the monomeric pyridine-Cu catalyst. To this Cu complex, equivalent amount of the second metal component was added i.e., the PVP-Cu, secondary metal ion mixed complexes were prepared. The activities of these mixed complexes are summarized in Fig. 2 (b). One notices that Mn ion increases the catalytic activity of the Cu ion although Cr and Fe ion inhibit the catalytic activity. Another important result in Fig. 2 (b) is that the effect of secondary metal ion is more clearly observed in the PVP system, comparing to the monomeric pyridine catalysts. 

Fig. 7. Visible spectra of the Cu complex of poly(4-vinylpyridine) (a) and of pyridine (b)42,43 and ESR spectra of the Cu complex of poly(4-vinylpyridine) (c) and of pyridine (d)44,4S)...

The polymerization rate catalyzed by the Cu complex decreased in the following order QPVP-Cu > pyridine-Cu with benzylpyridinium chloride added as emul-... 

Manecke et al.16s synthesized a semiconducting polymeric complex which possessed both bis(ethylene-l,2-dithiolato)Cu(II) and a phthalocyanine-Cu(II)-type structure 54. This Cu complex exhibited high catalytic activity in the oxidative polymerization of XOH, about 50 times higher than that of pyridine-Cu. A synchronous four-electron-transfer mechanism was proposed for the catalysis of 54. The phthalo-cyanine-Cu(II) type structure of 54 is presumed to form a complex with molecular... 

In the polymerization of xylenol by partially quatemized poly(4-vinylpyridine)-Cu(II) complex, the binding between the positively charged polymer and the substrate, xylenol anion, is observed. The overall rate catalyzed by the polymer is five times higher than that catalyzed by the pyridine-Cu(II) complex (119-121). 

Shiga, T., Ohba, M., and Okawa, H. (2004) A series of trinuclear Cu Ln Cu complexes derived from 2,6-di(acetoacetyl)pyridine synthesis, structure, and magnetism. Inorganic Chemistry, 43, 4435 446. Albrecht, M., Schmid, S., Dehn, S., et al. (2007) Diastereoselective formation of luminescent dinuclear lan-thanide(III) helicates with enantiomerically pure tartaric acid derived bis(P-diketonate) ligands. New Journal of Chemistry, 31, 1755-1762. 

The cascade reaction for the preparation of anilines is particularly well suited to the synthesis of potential ligands, as is illustrated by the scorpion ligand A,A-4-tris(pyridin-2-ylmethyl)aniline (37), which forms a range of Cu complexes with widely varying solid-state structures.Clearly, from the metal coordination geometries illustrated in Figure 6.9, Horning-crown macrocycles may fulfill similar roles. 

The electrolytic oxidation was found to proceed much faster in the presence of Cu-pyridine as a redox mediator in the electrolytic cell divided with a membrane. The electrode coated with Cu/poly(4-vinylpyridine) was also effective for the oxidative polymerization, and what was more, without a partition membrane (Figure 8). Polymer-Cu complex film coated on the electrode prevented formation of the insulating film of the product polymer on the electrode surface and decreased the electrolytic potential. The oxidation using the electrode coated with a macromolecular Cu complex provides a facile method for forming poly(phenylene oxide)s. 

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