Phthalocyanines catalytic properties

Oxidation can also occur at the central metal atom of the phthalocyanine system (2). Mn phthalocyanine, for example, can be produced ia these different oxidation states, depending on the solvent (2,31,32). The carbon atom of the ring system and the central metal atom can be reduced (33), some reversibly, eg, ia vattiag (34—41). Phthalocyanine compounds exhibit favorable catalytic properties which makes them interesting for appHcations ia dehydrogenation, oxidation, electrocatalysis, gas-phase reactions, and fuel cells (qv) (1,2,42—49). 

The development of such a reaction proceeding under mild conditions is a technological challenge constituting one of the key points for the finalizing of efficient and low cost fuel cells. The catalytic properties of macrocyclic complexes like porphyrins and phthalocyanines for the reduction of molecular oxygen have been well known for four decades350,351 and numerous papers are devoted to this area. Here only some relevant and recent work in this field is described. 

Abstract In this chapter, recent progress in the synthesis, crystal structures and physical properties of monomeric phthalocyanines (Pcs) is summarized and analysed. The strategies for synthesis and modification of Pcs include axial coordination of central metal ions, peripheral substitution of Pc rings and the ionization of Pcs. The crystal structures of various typical Pcs, especially the effects of different synthetic and modification strategies on the supramolecular assemblies of Pcs via %—% interactions between Pc rings, are discussed in detail. Finally, the UV-vis spectroscopic, conducting, magnetic and catalytic properties of some Pcs with crystal structures are presented briefly, and the correlations between various properties and the molecular structure discussed. 

They comprise a comparison of the activities of polymeric phthalocyanines with various central atoms. The monomers always showed lower activity than the corresponding polymers. The nature of the substrate has a decisive influence on the catalytic properties of the chelate. Electrodes with gold substrate showed only very slight activity. 

Randin, in a recently-published paper 44>, investigated solely on the basis of results from the literature the relationship between electrocatalytic activity for 2 reduction on the one hand, and oxidation potential, magnetic moment, and catalytic properties in gas-phase reactions on the other. It was found for the transition-metal phthalocyanines that magnetic moment and activity for the dehydrogenation of cyclohexanedione increase together with the activity of the phthalocyanines for 2 reduction, while the oxidation potential becomes less. The last fact can be seen from Fig. 29, in which the first oxidation potentials in 1-chlomaphthalene, measured by Manassen and Bar-Ilan 45>, are plotted against electrochemical activity. This result shows that the more easily an electron can... 

Savy et al. 35> reach practically the same conclusion concerning the electron transitions during formation of the activated complex but consider an edge-on arrangement of the oxygen above the plane of the chelate molecule more probable. Their studies relate only to the catalytic properties of the phthalocyanines for 02 reduction. Their conclusion is that the conditions for optimal activation of oxygen... 

Phthalocyanine compounds exhibit favorable catalytic properties which makes them interesting for applications in dehydrogenation, oxidation, eleclrocalalysis, gas-phase rcacliuns, and fuel cells. 

Cook, A. H. Catalytic Properties of the Phthalocyanines. Part. I. Catalase Properties. 

Certain metal derivatives, particularly the ferrous and chloroferric complexes, catalyze the decomposition of hydrogen peroxide. They are themselves destroyed in the process (58, 127, 871). Paquot and his coworkers have extensively investigated the catalytic properties of the phthalocyanines (71, 270-277). Nickel phthalocyanine is a useful catalyst for the autoxidation of a-carbon atoms of ethylenic molecules. Thus nickel phthalocyanine (0.4%) catalyzes the aerial oxidation of cyclo-... 

Rigid spirocyclic linking groups can be introduced between porphyrin subunits to provide significant steric restriction to prevent structural relaxation, which in turn helps promote fruitful catalytic properties in PIMs. Phthalocyanine network PIMs are important catalysts for example, iron-porphyrin derivatives can permit the catalysis of hydrocarbon hydroxylations and alkene epoxidations." ... 

The redox electrochemistry of a Fe /Fe couple is easily accomplished on a phthalocyanine-coated electrode with peak separations comparable to that of platinum [141,142,163,164]. Phthalocyanine-coated electrodes are found to be efficient electrocatalysts to catalys catechol, p-benzoquinone and oxalic acid oxidations [120,150]. The electrochemical activity of these electrodes may be due to the high voltage, surface area, high electronic conductivity and redox behaviour of phthalocyanine, vanadium phthalocyanine and other phthalocyanines have been prepared by vapour deposition and show photoelectrochemical responses when dipped in aqueous electrolytes [244-249]. Polymeric phthalocyanines of Co and Fe are coated on active carbon and are shown to give catalytic properties for dioxygen reduction and thiol oxidations. Dioxygen chemisorption and ammonia absorption of metallo... 

Shao JG, Richards K, Rawlins D, Han BC, Hansen CA (2013) Synthesis, electrochemistry, spectroelectrochemistry and catalytic properties in DDT reductive dechlorinationin of hon(II) phthalocyanine, 2,3- and 3,4-tetrapyridinoporphyrazine complexes. J Porphyrins Phthalocyanines 17(4) 317-330... 

Substitution at axial sites in metalloporphyrins and phthalocyanins is important in the context of their behavior as models for biological systems and for their potential catalytic properties. The reaction of imidazole (Him) with phthalocyaninatoiron(II) in DMSO has been reinvestigated and shows two distinct relaxation processes as shown in Eq. (2) and (3). Forward rate constants were kif=9.8 0.2x 10 s , k2f= 5.4 + 0.15 s ... 

History. Braun and Tschemak [23] obtained phthalocyanine for the first time in 1907 as a byproduct of the preparation of o-cyanobenzamide from phthalimide and acetic anhydride. However, this discovery was of no special interest at the time. In 1927, de Diesbach and von der Weid prepared CuPc in 23 % yield by treating o-dibromobenzene with copper cyanide in pyridine [24], Instead of the colorless dinitriles, they obtained deep blue CuPc and observed the exceptional stability of their product to sulfuric acid, alkalis, and heat. The third observation of a phthalocyanine was made at Scottish Dyes, in 1929 [25], During the preparation of phthalimide from phthalic anhydride and ammonia in an enamel vessel, a greenish blue impurity appeared. Dunsworth and Drescher carried out a preliminary examination of the compound, which was analyzed as an iron complex. It was formed in a chipped region of the enamel with iron from the vessel. Further experiments yielded FePc, CuPc, and NiPc. It was soon realized that these products could be used as pigments or textile colorants. Linstead et al. at the University of London discovered the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines from 1929 to 1934 [1-11]. The important CuPc could not be protected by a patent, because it had been described earlier in the literature [23], Based on Linstead s work the structure of phthalocyanines was confirmed by several physicochemical measurements [26-32], Methods such as X-ray diffraction or electron microscopy verified the planarity of this macrocyclic system. Properties such as polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and reduc-... 

Interesting results have been obtained in studies of the catalytic activity for oxidation by phthalocyanine polymers, containing different metal ions in the same molecule 87-90>. If Fe was mixed with a series of other transition metal ions, differences in activity were found to be dependent on the metal ion, and correlations between the catalytic activity and the thermal activation energy of semiconductivity were found. With copper as the second metal ion, maximum activities were found at a ratio Fe/Cu = 1. Many other chelate polymers have been tested for their oxidation activity, and a dependence of the catalytic activity on the donor properties of the ligand was found 91>92). 

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