Oxidative coupling copper-polymer complex catalysts

Challa, G., Meinders, H. C. Copper-polymer complexes as catalysts for oxidative coupling reactions. J. Mol. Catal. 1977, 3,185-190. 

Copper-Polymer Complexes as Catalysts for Oxidative Coupling Reactions... 

We were interested in the behaviour of polymeric catalysts in order to confirm that typical polymer effects may occur. Oxidative coupling of 2,6-disubstituted phenols, as developped by Hay (7), was chosen as a model reaction and the catalytic activities of coordination complexes of copper with several polymeric tertiary amines were compared with the activities of their low molecular weight analogs. The overall reaction scheme is presented in scheme 1. 

Since the yield in the oxidative coupling is practically quantitative, the oxidative polymerization of a,( )-diethynyl monomers would be expected to yield high molecular weight, linear polymers, as shown in equation (18). Hay has reported that almost any diethynyl monomer, even organometallic monomers, can be polymerized to high molecular weight polymers in Ae presence of a soluble amine complex catalyst of a copper(I) salt (Hay modification). ... 

The oxidative coupling reaction of terminal alkynes is critically dependent on the water concentration in the reaction mixture (see Section 2.5.2). Since water is produced during the reaction, careful elimination of it may be required. Challa and Meinders have demonstrated that the polymer catalyst derived from copper(II) chloride and either N,/V-dimethylbenzylamine or N,/V-dimethylaminomethylated atactic polystyrene (37) provides an extra protection of the catalytic copper complexes against water in the coupling reaction of phenylacetylene (equation 23), resulting in a higher reaction rate than the low molecular weight catalyst. 

The last example to be mentioned deals with the application of coordination compounds attached to polymers and their use as immobilized catalysts. This technique has been used for a long time in organometallic catalysis. Similar reactions with biomimetic catalysts, as with Cu(II) oxidases, are less well known, and a review for polymeric copper imidazole complexes used in oxidative phenol coupling is available. 

They next studied the asymmetric oxidative polymerization of achiral 2,3-dihydroxynaphthalene (Scheme 42). The polymerization of this monomer with CuCl2-(-)-sparteine complex resulted in a low yield and gave a low molecular weight oligomer, whereas the polymerization with CuCl-(S)-Phbox quantitatively gave a polymer with Mn of 10 600-15 300. The enantioselectiv-ity attained in this polymerization, however, was estimated to be low, with 43% ee from the model reaction [169]. When vanadyl sulfate (VOSO -Phbox complex was used instead of the copper catalyst system, the enantioselectivity was improved up to 80% ee [170]. Asymmetric cross-coupling polymerization of two kinds of naphthol derivatives was also reported [171,172]. 

Poly(ionic liquid) brushes with terminated ferrocene units acted similarly, while the interfacial resistance was probed by hexacyanoferrate [457]. Chemical and electrochemical switching of local pH at an electrode-grafted poly(vinyl pyridine) brush again allowed modulation of hexacyanoferrate chemistiy (Fig. 43) [458]. Octacyanomolybdate was used as catalyst for the oxidation of ascorbic acid [459]. Even heteropolyanions (Keggin ions) could be entrapped in polymer films electrochemicaUy [460]. Further, thermoresponsive or pH-responsive cationic copolymer films modulated the hexacyanoferrate or ferrocenedicarboxyUc acid electrochemistry by temperature or variatimi of pH and perchlorate concentration, respectively [461-463]. Besides these complexes with cationic polyelectrolyte films, electroactive cationic counterions (e.g., the europium couple) interacted with anionic networks [464]. Similarly, copper ions within a PAA matrix [367] allowed the construction of actuators [465]. Besides these binary systems (poly-electrolyte/electroactive counterions), multiresponsive electrode modification with an interpenetrating gel network of poly(acrylic) acid and poly(diethyl acrylamide) allowed the modulation of hexacyanoferrate electrochemistry [368]. 

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