Phthalocyanine ligands

Radical phthalocyanine species, e.g. 6, can be prepared by the reaction of thionyl chloride or thionyl bromide with metal phthalocyanines. In these cases, the phthalocyanine ligand only carries the charge — l.349... 

Only a handful of rr-bonded iron porphyrin complexes have been structurally characterized, listed in Table HI, and four of these contain porphycene. corrolc. or phthalocyanine ligands rather than porphyrins. " "" Selected data arc given in Table III, and X-ray crystal structures of methyl- and phenyliron porphyrin complexes are shown in Fig. 4. All of the iron(III) porphyrin complexes exhibit... 

In general, for a particular metal state, metallophthalocyanines are more difficult to demetallate than are metalloporphyrins (the central hole is marginally smaller in the phthalocyanine ligand). Thus, copper(II) phthalocyanine, dissolved in concentrated sulfuric acid, is precipitated unchanged when the solution is poured into ice/water. However, metallochlorins are demetallated more readily than the corresponding metalloporphyrins (basicity chlorin < porphyrin). 

Bocian, Lindsey and co-workers studied sandwich complex nanocapacitors comprised of porphyrin and phthalocyanine ligands separated by lanthanide metals [133]. A triple-decker sandwich of phthalocyanine-Eu-phthalocyanine-Eu-porphy-rin, with two phenylethynyl linker wires from the porphyrin, potentially has up to nine accessible oxidation states (—4 to +4). SAMs of monomers, dimers, trimers, and oligomers of this sandwich, anchored at one or both ends by thioacetyl groups, gave charge densities up to 10 10 mol cm-2, electron-transfer rates up to 105 electrons s-1, and charge-dissipation half-lives in the 10-50 s range. 

Relatively few chromium complexes with phthalocyanine ligands have been reported and, ir view of the chemical relationship between the few known compounds, all of them, irrespectivt of the metal oxidation state, are dealt with in this section. In the following discussion Pi represents the dianionic phthalocyanine ligand. 

The macrocyclic phthalocyanine ligand will form a complex Pt(phthalocyanine).1106 The crystal structure shows two polymorphs present because of molecular packing.1107 The platinum is in a square planar coordination geometry with a mean Pt—N distance of 1.98 A. The complex can be partially oxidized with iodine to give conducting mixed valence solids.1108 Eighteen fundamental and overtone combination bands are observed in the resonance Raman spectrum of platinum phthalocyanine, and from this data the symmetry of the excited singlets are found to be Dy.. Qlv or D2.1109... 

This chapter is concerned with dyes and pigments which are complexes of azo, formazan, azomethine, nitroso, anthraquinone and phthalocyanine ligands. Many of these compounds find important applications in other fields, particularly colour photography and reprography, analysis, catalysis, biology, and some modem high technology industries such as electronics. These applications are described in other chapters of this volume. 

EDTA ethylenediaminctetra-Af-acetic acid Pc phthalocyanine (ligand, sensitiser)... 

The reason of why such reactions are discussed separately stems from the fact that metal-metal (both a direct or a bridge mediated) interaction causes certain specific properties of polynuclear complexes, and cannot be, therefore taken as a simple sum of their independent mononuclear constituents. A particular case is some phthalocyanine dimers in which the monomers are bound via a close k-tz system contact of the phthalocyanine ligands. Such dimers are included in this Section too in spite of the fact that there is neither a direct metal-metal bond nor a bridge connection. 

Figure 4.38 Molecular formula of Cu-phthalocyanine and optimized geometry of the phthalocyanine ligand.

Since the pioneering work of Kirin et al. [5] various lanthanide(III) and cerium(IV) complexes containing phthalocyanine ligands have been synthesized (Table 17) [213-221]. Equations 15a,b give typical methods of preparation for Ln(III) derivatives. 

Metal phthalocyanine complexes are also frequently used as autoxidation catalysts (see Section II.B.2). They have generally been found to be more active than the corresponding stearates or acetylacetonates. Thus, Uri145 compared the catalytic activity of a series of transition metal stearates with the corresponding metal phthalocyanines in the autoxidation of methyl linoleate. The phthalocyanine complexes afforded faster rates of oxidation. In addition, the phthalocyanine ligand is stable and is not easily destroyed under autoxidizing conditions. Interest in metal phthalocyanine catalysts has also been stimulated by their resemblance to the metal-porphyrin structures contained in many oxidative enzymes (see Sections II.B.2 and V). 

Recently, a ruthenium-catalysed oxidation in water was published by d Alessandro et al. [34]. Water can be regarded as an environmentally friendly solvent which, because it is inert, reduces the risk of explosions. The oxidation of cyclohexane directly to adipic acid was performed using ruthenium catalysts bearing water-soluble phthalocyanine ligands RuPcS (where PcS is tetra-sodium 2,3-tetrasulfophthalocyaninato) with KHSOs (Eq. 4). However we note that very low TONs were observed and the use of KHSOs as a primary oxidant is not viable for industrial-scale oxidations. 

However, the relatively high enzyme costs form an obstacle to commercialization. Inefficient laccase use is a result of its instability towards the oxidizing reaction conditions. We have recently shown that the stability of the laccase under reaction conditions can be improved by immobilization as a cross-linked enzyme aggregate (see Chapter 9). It has also been shown that a water-soluble iron complex of a sulfonated phthalocyanine ligand is an extremely effective catalyst for starch oxidation with hydrogen peroxide in an aqueous medium [11]. 

The chemistry of Rh111 complexes with porphyrin and phthalocyanine ligands is quite distinctive, as these rigidly planar, tetradentate amine ligands form complexes via unique synthetic routes, and the chemistry of the resulting complexes differs substantially from that of complexes with less constrained ligands. A variety of porphyrin complexes of Rhm have been characterized, and a list of the abbreviations used in this section is found in (54) and Table 58. 

Figure 4.41 The structures of (a) [Sm(III) Pc(a-OC5Hn)4 (TClPP)] and (b) [Sm(IIIH Pc(a-OC5Hii)4 (TCIPP)] [66], (Reproduced with permission from R. Wang et ah, Controlling the nature of mixed (phthalocyaninato)(porphyrinato) rare-earth(III) double-decker complexes the effects of nonperipheral alkoxy substitution of the phthalocyanine ligand, Chemistry - A European Journal, 2006, 12, 1475. Wiley-VCH Verlag GmbH Co. KgaA.)...

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