Water metal phthalocyanine complexes

Hiratsuka et al102 used water-soluble tetrasulfonated Co and Ni phthalocyanines (M-TSP) as homogeneous catalysts for C02 reduction to formic acid at an amalgamated platinum electrode. The current-potential and capacitance-potential curves showed that the reduction potential of C02 was reduced by ca. 0.2 to 0.4 V at 1 mA/cm2 in Clark-Lubs buffer solutions in the presence of catalysts compared to catalyst-free solutions. The authors suggested that a two-step mechanism for C02 reduction in which a C02-M-TSP complex was formed at ca. —0.8 V versus SCE, the first reduction wave of M-TSP, and then the reduction of C02-M-TSP took place at ca. -1.2 V versus SCE, the second reduction wave. Recently, metal phthalocyanines deposited on carbon electrodes have been used127 for electroreduction of C02 in aqueous solutions. The catalytic activity of the catalysts depended on the central metal ions and the relative order Co2+ > Ni2+ Fe2+ = Cu2+ > Cr3+, Sn2+ was obtained. On electrolysis at a potential between -1.2 and -1.4V (versus SCE), formic acid was the product with a current efficiency of ca. 60% in solutions of pH greater than 5, while at lower pH... 

Copper, and occasionally silver, have been used as catalysts for hydroformylation of a-olefins. Phosphite complexes of copper(I) chloride have been claimed as catalysts (126). Phthalocyanine complexes of Group IB metals have been stated to show a low degree of catalytic activity (127). One of the more interesting examples of copper catalysis was disclosed by McClure (128). Copper powder, with a controlled amount of water (0.2-4.0 moles H20/mole Cu), gave a slow conversion of pro-... 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

This chapter deals with the provision of suitable starting materials for investigations in the noble metal porphyrin field (Sects. 2.1-2.4) and the establishment of their structures (Sect. 2.5). Most of these investigations are devoted to complexes with synthetic porphyrin ligands which are soluble in organic solvents [e.g. (OEP)- or (TPP) complexes Sect. 2.1]. Special mention is made to some novel porphycene derivatives (Sect. 2.2), to phthalocyanine systems (Sect. 2.3), and to water-soluble porphyrin complexes (Sect. 2.4). 

The alkali metal phthalocyanines are, with the exception of the dilithium derivative, fairly insoluble in most organic solvents. The dilithium complex is unique in being soluble in a wide range of organic solvents including alcohol and acetone 11). All the complexes are readily demetallated by dilute aqueous acid. Dilithium phthalocyanine is rapidly demetallated by cold water 11), while disodium phthalocyanine is more resistant to hydrolysis, reacting slowly with hot water. The dipotassium derivative is said to be more readily demetallated than the sodium complex, perhaps because of its larger size 10). 

The zerovalent dipotassium phthalocyanine cuprate(0) may be prepared by the reduction of the cupric complex with potassium in liquid ammonia. It was not possible to isolate a copper(I) derivative (870). Like other low oxidation state metal phthalocyanines, this complex is air- and water-sensitive. 

Cartoni et al. [88] studied perspective of the use as stationary phases of n-nonyl- -diketonates of metals such as beryllium (m.p. 53°C), aluminium (m.p. 40°C), nickel (m.p. 48°C) and zinc (liquid at room temperature). These stationary phases show selective retention of alcohols. The retention increases from tertiary to primary alcohols. Alcohols are retained strongly on the beryllium and zinc chelates, but the greatest retention occurs on the nickel chelate. The high retention is due to the fact that the alcohols produce complexes with jS-diketonates of the above metals. Similar results were obtained with the use of di-2-ethylhexyl phosphates with zirconium, cobalt and thorium as stationary phases [89]. 6i et al. [153] used optically active copper(II) complexes as stationary phases for the separation of a-hydroxycarboxylic acid ester enantiomers. Schurig and Weber [158] used manganese(ll)—bis (3-heptafiuorobutyryl-li -camphorate) as a selective stationary phase for the resolution of racemic cycUc ethers by complexation GC. Picker and Sievers [157] proposed lanthanide metal chelates as selective complexing sorbents for GC. Suspensions of complexes in the liquid phase can also be used as stationary phases. Pecsok and Vary [90], for example, showed that suspensions of metal phthalocyanines (e.g., of iron) in a silicone fluid are able to react with volatile ligands. They were used for the separation of hexane-cyclohexane-pentanone and pentane-water-methanol mixtures. 

Other researchers have reported electrochemical nitrite reduction using aquocobalamin " and water-insoluble metallo-phthalocyanines absorbed onto electrodes. Nyokong and coworkers found that the potential for catalytic nitrite reduction varied with metal in a series of metallo-phthalocyanine complexes adsorbed onto a glassy carbon electrode (GCE) in basic solutions, Cu(Pc) > Fe(Pc) > Ni(Pc) > Co(Pc) > Mn(Pc) > Zn(Pc). ... 

Water soluble cobalt(ll) 2,9,16,23-tetrasulfophthaloeyanine, zinc(II)-2,9,16,23-tetrasulfo-phthalocyanine, zinc(ll)tetracarboxyphthalocyanine, and non-metallic sulfophthalocyanine complexes are catalysts and photocatalysts for the oxidation of sulfide, sulfite and thiosulfate ions by dioxygen. Typical conditions are 293 K, 1 atm Oi and pH 9.24 in aqueous solutioaThe cobalt phthalocyanine complexes show high catalytic activity only in the... 

This class of PC catalysts has also been extensively studied as a potential substitute for Pt as they are low cost, methanol tolerant and have reasonably good activity and remarkable selectivity toward ORR [194]. They normally catalyze a direct 4e reduction of O2 to )deld water. The major drawback of this kind of catalyst is of low stability in acidic media [195]. However, when the catalyst is heat treated, the activity and stability of transition metal macrocycle complex (TMMC) are improved significantly [194]. The molecules of TMMC have a square planar structure with the metal ion symmetrically surrounded by four nitrogen atoms these nitrogen atoms are from each member of the ring systems which, in turn, are connected by carbon atoms (porphyrins) or nitrogen atoms (phthalocyanines). 

The reddish metal was already known in prehistoric times. It occasionally occurs as a native metal, but mostly in conspicuous green ores, from which it is extracted relatively easily. It is convenient to work, but not very hard. Not very optimal as a tool ("Otzi the Iceman" had a copper axe with him). Only through the addition of tin is the more useful bronze obtained. Its zinc alloy is the versatile and widely used brass. Copper is one of the coinage metals. Water pipes are commonly made of copper. Its very good thermal and electrical conductivity is commonly exploited (cable ), as well as its durability (roofs, gutters), as the verdigris (basic copper carbonate) protects the metal. Cu phthalocyanines are the most beautiful blue pigments. Seems to be essential to all life as a trace element. In some molluscs, Cu replaces Fe in the heme complex. A 70-kg human contains 72 mg. 

For systemic administration, the photosensitizer usually has to be delivered into the bloodstream by intravenous injection. Since the photosensitizer is a solid, this means that a solution or a stable suspension has to be provided. Metal complexes of the basic porphyrin and phthalocyanine nuclei are insoluble in water, so that some effort has to be made to render the system water soluble, or at least amphiphilic, by placing various substituents (e.g., S03H, C02H, OH, NR3+, polyether, aminoacid, sugar) on the periphery of the molecule. The aromatic character of the ligand offers a suitable opportunity for such substitutions to be made. Examples will appear frequently in the following sections. 

The phthalocyanines, naphthalocyanines, and certain of their metal derivatives (Figure 6.17) are infrared fluorophores. 61"64 As a class, they are exceptionally stable compounds, with copper (Cu) phthalocyanine (not a fluorophore) remaining intact above 300 °C in air. First used for textile dyeing in the last century and still widely used, there is a rich chemistry of phthalocyanines. Most derivatives can be made by prolonged heating of a phthalimide or phthalic acid derivative with a metal in powder or salt form at elevated temperature. Several derivatives absorb in the near-IR, and either fluoresce or phosphoresce. The electronic transitions of phthalocyanines are complex and have been extensively studied, at least in part because the symmetry of the molecule makes theoretical calculations of its spectroscopic behavior more tractable. Unsubstituted phthalocyanines and naphthalocyanines are, as a class, very insoluble in solvents other than, for instance, nitrobenzene. Sulfonated phthalocyanines are water soluble and exhibit spectra comparable to the parent derivative. Photolumines-cent phthalocyanines (Pcs) include SiPc, ZnPc, and PC itself. These compounds have been little used for practical infrared fluorometry to date however, Diatron Corpora-... 

We can now make sensible guesses as to the order of rate constant for water replacement from coordination complexes of the metals tabulated. (With the formation of fused rings these relationships may no longer apply. Consider, for example, the slow reactions of metal ions with porphyrine derivatives (20) or with tetrasulfonated phthalocyanine, where the rate determining step in the incorporation of metal ion is the dissociation of the pyrrole N-H bond (164).) The reason for many earlier (mostly qualitative) observations on the behavior of complex ions can now be understood. The relative reaction rates of cations with the anion of thenoyltrifluoroacetone (113) and metal-aqua water exchange data from NMR studies (69) are much as expected. The rapid exchange of CN " with Hg(CN)4 2 or Zn(CN)4-2 or the very slow Hg(CN)+, Hg+2 isotopic exchange can be understood, when the dissociative rate constants are estimated. Reactions of the type M+a + L b = ML+(a "b) can be justifiably assumed rapid in the proposed mechanisms for the redox reactions of iron(III) with iodide (47) or thiosulfate (93) ions or when copper(II) reacts with cyanide ions (9). Finally relations between kinetic and thermodynamic parameters are shown by a variety of complex ions since the dissociation rate constant dominates the thermodynamic stability constant of the complex (127). A recently observed linear relation between the rate constant for dissociation of nickel complexes with a variety of pyridine bases and the acidity constant of the base arises from the constancy of the formation rate constant for these complexes (87). 

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