Phthalocyanine metallophthalocyanine salts

The first catalysts reported for the electroreduction of C02 were metallophthalocyanines (M-Pc).126 In aqueous solutions of tetraalkylammonium salts, current-potential curves at a cobalt phthalocyanine (Co-Pc)-coated graphite electrode showed a reduction current peak whose height was proportional to the C02 concentration and to the square root of the potential sweep rate at a given C02 concentration. On electrolysis, oxalic acid and glycolic acid were detected, but formic acid was not. Mn and Pd phthalocyanines were inactive, while Cu and Fe phthalocyanines were slightly active. At the potentials used for C02 reduction, M-Pc catalysts would be in their dinegative state, and the occupied dz2 orbital of the metal ion in the metallophthalocyanine was suggested to play an important role in the catalytic activity. 

Dilithium phthalocyanine is obtained as dark-blue crystals. The compound has high thermal stability, as is typical of many phthalocyanines. It is soluble in acetone, giving a deep-blue solution that deposits phthalocyanine when in contact with even trace amounts of water. The material is also soluble in ethanol and tetrahydrofuran, but it is insoluble in diethyl ether, hexane, or chloroform. Solutions of the dilithium complex in ethanol react rapidly and quantitatively with a variety of metal salts to give the metallophthalocyanines, which precipitate, in very pure form, from solution. The electronic spectrum contains the bands (acetone solution) 370 (e = 24,800), 596 (e = 17,300), 630 (e = 16,100), 655 nm (e = 11,100). 

Phthalocyanines could be prepared in high yields by reacting phthalo-nitriles with alcohols in the presence of DBU (80CL1277 83JAP(K)23854 83JAP(K)105962). If a metal salt was also present in the reaction mixture, metallophthalocyanines were obtained (83CL313 83JAP(K) 127763). 

The reaction between phthalonitrile and metals (finely divided or acid etched) is usually very vigorous at 250-300°C and sufficient heat is generated to maintain the reaction temperature. These compounds are monofianctional with respect to the formation of phthalocyanine rings [42,56-58]. The cyclo-tetramer-ization of four phthalonitrile molecules into a phthalocyanine macrocycle involves a reduction reaction which requires two electrons in addition to the 16 Ti-electrons from the 8 nitrile groups to yield the 18 7r-electron aromatic system. For metallophthalocyanine the two extra electrons are provided by metal or metal salts. The use of reducing coreactants such as 1,2,3,6-tetrahydropyridine or hydroquinone is effective for the conversion of phthalonitrile to phthalocyanine. The reactions are normally carried out under pressure. Bis-... 

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