Polymeric metal phthalocyanines

Li, H. and T.F. Guarr (1999). Reversible electrochromism in polymeric metal phthalocyanine thin films. J. Electroanal. Chem. 297,169-183. 

The impetus for the preparation of polymeric metal phthalocyanines is repeatedly traced to an early report on the thermal stability of copper phthalocyanine 24). Dent and Linstead 24) described it to be exceptionally resistant to heat and at about 580°C it may be sublimed at low pressure in an atmosphere of nitrogen or carbon dioxide. This description served to suggest to several groups that incorporation of a metal phthalocyanine structure into a polymeric repeat unit would yield polymers of exceptional thermal stability. 

Heating bis(l,2-dicarboxylic acids) or the corresponding dianhydrides with a nitrogen source (like urea) and a metal or metal salt has been used most frequently to prepare polymeric metal phthalocyanines (Vl-15). Ammonium molybdate is mentioned frequently as being a useful promoter for this reaction. Reaction in bulk at temperatures of >180°C is generally employed 4, 26, 55). The effect of certain reaction variables on the polymer molecular weight was... 

Pyromellitonitrile has been used as a reactant in this synthesis 34, 67). Heating this tetranitrile with metal salts at 150°-200°C in ethylene glycol or dimethylformamide yields polymeric metal phthalocyanines 34). The direct preparation of thin films of metal phthalocyanines on a substrate has been patented 64). In this method, pyromellitonitrile vapors are heated in the presence of the substrate which can either be a metal or an inert substrate possessing a metal coating. Films 10-300 microns thick are obtainable and are valuable for their semiconduction properties. Additionally, surfaces can be coated by immersing an object in a hot solution of pyromellitonitrile in an inert solvent. 

Another route to polymeric metal phthalocyanines that has been described for those containing silicon (2, 51, 59) or titanium 18) as the central atom employs [57] and [58] as monomers. 

The electrical properties of polymeric metal phthalocyanines are receiving rather extensive attention. There is general agreement that they are typical... 

Carbon suboxide, polymerization of, 131 Catalytic activity of, polymeric metal phthalocyanines, 159 o-Carboxybenzaldehyde, polymers with ferrocene, 128,129 4-Carboxy-1,6-heptadiene, polymers of, 79 Chelate polymers, 173,327 Chlorendic acid,... 

Most reported phthalocyanine derivatives (sulfo-, nitro-, amino-, triphenylmethyl-, polymeric, etc.) are copper complexes, although at present the synthetic chemistry of other d- and /-metal Pc derivatives is being rapidly developed (Examples 30-36) [5,6,116-118]. Some of them (in particular, copper phthalocyanine sulfonic acids) are of industrial interest because of their usefulness as dyes. Phthalocyanine sulfonic acids themselves are prepared both by urea synthesis from sulfonated phthalic anhydride and by the sulfonation of the phthalocyanine [6], Some substituted metal phthalocyanines can be obtained by chemical or electrochemical reduction [118e]. Among a number of reported peculiarities of substituted phthalocyanines, the existence of three electronic isomers for magnesium derivative PcMn was recently confirmed [118f]. 

Some papers have appeared that deal with the use of electrodes whose surfaces are modified with materials suitable for the catalytic reduction of halogenated organic compounds. Kerr and coworkers [408] employed a platinum electrode coated with poly-/7-nitrostyrene for the catalytic reduction of l,2-dibromo-l,2-diphenylethane. Catalytic reduction of 1,2-dibromo-l,2-diphenylethane, 1,2-dibromophenylethane, and 1,2-dibromopropane has been achieved with an electrode coated with covalently immobilized cobalt(II) or copper(II) tetraphenylporphyrin [409]. Carbon electrodes modified with /nc50-tetra(/7-aminophenyl)porphyrinatoiron(III) can be used for the catalytic reduction of benzyl bromide, triphenylmethyl bromide, and hexachloroethane when the surface-bound porphyrin is in the Fe(T) state [410]. Metal phthalocyanine-containing films on pyrolytic graphite have been utilized for the catalytic reduction of P anj -1,2-dibromocyclohexane and trichloroacetic acid [411], and copper and nickel phthalocyanines adsorbed onto carbon promote the catalytic reduction of 1,2-dibromobutane, n-<7/ 5-l,2-dibromocyclohexane, and trichloroacetic acid in bicontinuous microemulsions [412]. When carbon electrodes coated with anodically polymerized films of nickel(Il) salen are cathodically polarized to generate nickel(I) sites, it is possible to carry out the catalytic reduction of iodoethane and 2-iodopropane [29] and the reductive intramolecular cyclizations of 1,3-dibromopropane and of 1,4-dibromo- and 1,4-diiodobutane [413]. A volume edited by Murray [414] contains a valuable set of review chapters by experts in the field of chemically modified electrodes. 

Several attempts to employ this same route for the preparation of polymeric metal free phthalocyanines employing a bis-phthalo-nitrile were unsuccessful (1). 

To enhance the heat-resistance of metal phthalocyanines, the polymerization of silicon and germanium phthalocyanines was investigated by Jeffery et al.[8] of Admiralty Research Establishment, U.K. Metal phthalocyanine chlorides were autoclaved to form hydrates, followed by condensated to obtain thin pol)rmer films. 

The resistivities of metal dithienes compare with those of Ovalene (p = 2,3 X 10 ohm-cm), violanthrone (2.3 X 10 ohm-cm), or cy-ananthrone (1.2 X 10 ohm-cm) (19). Metal phthalocyanines with reported resistivities of between 10 and 10 ohm-cm, are worse semiconductors than the dithienes. The conductivity of some rhenium dithienes approaches that of intrinsic silicon even better conductors may result by synthesizing polymeric species. 

Polymeric metal-containing (Cu, Mg, Zn, and Ni) and metal-free phthalocyanine thin films were prepared from the gas phase by low-temperature plasma polymerization [115, 116]. The plasma-polymerized CuPc (pp-CuPc) obtained was a glossy greenish thin film with a thickness of 60-300 nm. The film was smooth and even, and was soluble neither in pyridine nor in concentrated sulfuric acid, both of which are good solvents for monomeric CuPc. 

Very recently, Abel and Clair described an elegant approach to address these issues, whereby they co-evaporated iron and 1,2,4,5-tetracyanobenzene (TCNB) 61 under UHV, not only onto Au(lll) and Ag(lll) surfaces but also onto an insulating NaCl film (Figure 28.27) [133]. While the polymerizations were found sensitive to the stoichiometric ratio of the two components, they could occur on the metal surfaces at room temperature, without the formation of byproducts. When TCNB was polymerized with iron in a 2 1 stoichiometric ratio on Au(lll) and Ag(lll), a 2-D polymeric Fe-phthalocyanine network was obtained. The resultant patchwork pattern composed of three differently oriented domains (ca. 10-30 nm wide) could be accounted for by the threefold symmetry of the substrates. On the other hand, when the polymerization was carried out on NaCl islands (50-100nm wide) deposited on Ag(lOO), the polymeric Fe-phthalocyanine was produced as a monodomain phase. In this way, a direct preparation of organic metal-on-insulator systems can be envisaged, as well as a smooth transferral of products onto various other substrates for device applications. 

As pointed out before when multilayers of metal phthalocyanines are deposited on an electrodic surface, only the outermost layer is active for the reduction of 02 and this is also true for other electrochemical reactions. This shows that multilayers of phthalocyanines or polymerized multilayers of phthalocyanines are rather compact and the inner layers are not accessible to O2 molecules. ... 

Abel M, Qair S, Ourdjini O, Mossoyan M, Porte L (2011) Single layer of polymeric Fe-phthalocyanine an otganometaUic sheet on metal and thin insulating film. J Am Chem Soc 133 1203-1205. doi 10.1021/jal08628r... 

The metal-ffee phthalocyanines are prepared either by hydrolysing the alkali metal phthalocyanine or via the thermal transformation of the diimino-isoindolene intermediate [63,64]. Polymeric phthalocyanines are prepared by the polycyclotetramerization of tetracya-nobenzene or pyromellitic dianhydride (PMDA) in the presence of urea, metal or metal salts and catalysts at about 400°C [65-69]. The mechanism of the reaction is explained by Wohrle et al. [66,67] and the reaction is shown in Scheme 17.2. 

In few cases linear chain structured polymeric metal complexes were prepared. A linear polymeric phthalocyanine 60 was obtained as film by the electrochemical polymerization of the corresponding monomer [260]. The synthesis of structural uniform ladder polymers 61 based on the hemiporphyrazine structures was achieved by a repetitive Diels-Alder reaction [261,262]. Recently, linear oligomeric porphyrines covalently connected via meso-meso-positions up to 128 units were synthesized [263]. 

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