Phthalocyanines superphthalocyanines

In presence of acids or other metal ions the five-unit macrocyclc of superphthalocyanines can be contracted to produce metal-free phlhalocyanine or metal phthalocyanines, respectively. This reaction might be more of scientific interest than of synthetic value. Nevertheless, one example is shown below. 

Addition of one more pyrrole unit to porphyrins, corroles or phthalocyanines gives pentaphyrin (38), sapphyrin (39), smaragdyrin (42) or superphthalocyanine (45) (Figures 16 and 17). 

Metal-free superphthalocyanine has not yet been obtained. The attempted demetallation in acidic media resulted in ring contraction to phthalocyanine or complete hydrolysis to phthalic acid (Scheme 110).201... 

Both porphyrins and phthalocyanines are prepared by template Schiff base type condensation rections. For example, the use of a large template is evident in the synthesis of the superphthalocyanine 3.83, in which five repeat units are organised about the pentagonal bipyramidal U022+ core, instead of four as in more traditional phthalocyanine complexes such as 3.82. Smaller templates result in the formation of the trimeric subphthalocyanine 3.84. The reversible nature of the condensation reaction means that both 3.83 and 3.84 can be converted into normal tetrameric phthalocyanine, 3.85, Scheme 3.23. 

Uranyl chloride, UO2CI2, reacts on heating with o-phthalodinitrile to form a so-called superphthalocyanine complex with 2-1-5 coordination (Figure 11.4) other metals (lanthanides, Co, Ni, Cu) react with this, forming a conventional phthalocyanine, so that the uranyl ion has an important role in sustaining this unusual structure. 

The first structurally characterized expanded porphyrin system to be reported in the literature was the so-called superphthalocyanine ligand [112]. This compound, which represents the first example of a well-characterized pentaligated complex prepared from any aromatic pentadentate macrocycle ligand, was obtained as an outgrowth of early efforts to prepare uranyl phthalocyanine and not as the product of a directed step-by-step synthesis. As such, the early literature associated with this species remains somewhat clouded and incomplete. 

In terms of spectroscopic properties, the uranyl superphthalocyanine complexes 160-162 display features which, although reminescent of, differ substantially from those of the phthalocyanine. The IR spectrum exhibits a strong v(OUO) stretching transition at 925 cm (KBr pellet) [112,118,119] or 933 cm" (evaporated film)... 

In addition, the electronic spectrum of uranyl superphthalocyanine 160 is significantly different from those of known metal phthalocyanine complexes... 

Many of the other properties of the uranyl superphthalocyanine complex 160 may also be explained in terms of the severe strain within the macrocycle. The reaction of 160 with acids, for instance, under conditions which readily demetalates many phthalocyanine and porphyrin complexes [130, 131], results in an unprecedented ring contraction giving ftee-base phthalocyanine as the product (Scheme 23)... 

Reactions of the uranyl superphthalocyanine complex 160 with anhydrous metal salts (e.g. C0CI2, NiClj, FeClj, CuClj, ZnClj, SnClj, and PbCl2) also results in a ring contraction. In this case, the corresponding metal phthalocyanine complexes are formed (Scheme 24) [132, 133], These contraction reactions indicate... 

Macrocycle 9.105, in the form of its pentaligated uranyl complex, was first characterized by Marks and Day. While earlier reports had claimed the successful preparation of normal U02-phthalocyanine from the reaction of U02 and phthalonitrile, the results of Marks and Day revealed that it is the pentameric uranyl superphthalocyanine, contaminated with only small quantities of metal-free phthalocyanine, that is the dominant product obtained as the result of such a process. The findings of Marks and Day were thus consistent with one other earlier report (see reference 57 and references therein) wherein mass spectrometric evidence... 

Scheme 1-4 Boron and uranyl templates direct the formation of sub- and superphthalocyanines respectively (12 and 13). Removing the template results in the formation of the normal phthalocyanine (15).

X-ray diffraction 113) reveals that the so-called uranyl phthalocyanine is in reality a complex of the superphthalocyanine ligand, an expanded five-subunit analog of phthalocyanine 112, 113), (The rigorous Chemical Abstracts name of this complex is 5,35 14,19-diimino-7,12 21,-26 28,33-trinitrilopentabenzo [c,h,m,r,w,] [1,6,11,16,21] pentaazacyclopen-tacosinatodioxouranium(VI). The molecular structure of this unique complex is depicted in Figures 9 and 10. The coordinative preferences of the uranyl ion can dramatically alter the normal course of the cyclization reaction (Equation 17). 

This tendency of superphthalocyanine to contract to phthalocyanine may be attributed to the internal ring strain, the impaired macrocyclic n system, the inadequately large centre hole and the unstable coordination geometry. In (45a) the ligand ring cannot take a planar conformation but is buckled severely, and the uranium atom is centred in a distorted pentagonal bipyramidal structure with an average U—Ngp, distance of 2.52 A. 

The ring contraction of dioxouranium(VI) superphthalocyanine to normal phthalocyanine is promoted by small metal ions. Mechanistic studies have not distinguished between proposals involving the intermediacy of metal super-... 

Thus, in examples of synthesis of tetraazamacrocyclic compounds on nickel ions (mainly) and on copper(II), square-planar system assembling is realised [38,47-49]. Guanidium ion promotes building of 27-crown-9-ether [60]. o-Aminobenzaldehyde self-condensation on the copper ion as matrix results exclusively in forming a complex with TAAB [67]. When using nickel(II) or cobalt(II) as templates under the same conditions, two types of macrocyclic azomethine systems - TAAB and TRI - may be synthesised [67-71]. Macrocychsation of phthalonitrile on the anisotropic matrix 0=U=0 ends with obtaining the so-called superphthalocyanine product [U02(L29)] [72, 73], rather than with the isolation of the corresponding complex with the phthalocyanine (Pc), as observed for other metal ions (Eq. 1.18) [11,74]. 

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