Superphthalocyanine

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. 

Superphthalocyanines are the products of the cyclopentamerization of phthalonitrile212 or of phthalonitriles with additional substituents.70113 The formation of structural isomers occurs if these precursors are unsymmetrically substituted at the benzene nucleus, (cf. p736). 

Complexes with 2,3,9,10,16,17,23,24,30,31-decaalkyl superphthalocyanines, (4,5-R2)5PcU02 (R = Me, Bu"), and the analogous pentamethylphthalocyanine complex, (4-Me)5PcU02, have been reported. In these the uranium atom is bonded to five nitrogen atoms of the superphthalocyaninate group.369... 

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. 

Invariably hydrolytic instability of lanthanide Por complexes, particularly that observed for the larger lanthanide elements, negatively influences their prospective application in terms of biomedicine (Sect. 7.4). As a response to this problem, larger porphyrin-like or expanded porphyrins , the so-called texaphyrins (Tx), have been examined by Sessler et al. [246]. The motivation, that expanded systems better accommodate larger ions, was previously demonstrated in a uranyl superphthalocyanine (SPc) complex [247], This SPc-complex contains an expanded, cyclic five-subunit pentakis(2-iminoisoindoline) which is formed by a template reaction of o-dicyanobenzene with anhydrous uranyl chloride. The uranium is displaced by only 0.02 A from the mean N5-plane. 

This superphthalocyanine (SPc) complex possesses a number of interesting chemical and physicochemical properties these are discussed in detail in Reference 6. The synthesis of uranyl superphthalocyanine, U(spc)02, can be... 

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. 

The apparent contradiction between the empirical stoichiometry and the spectral characteristics of these new uranyl complexes was finally resolved by X-ray crystallography. Specifically, a single crystal X-ray structural analysis of the blue-black material formed from the reaction of the anhydrous uranyl chloride and o-dicyanobenzene [112] (Figures 22 and 23) revealed that the complex obtained was in fact an expanded five-subunit superphthalocyanine macrocycle in which a pentagonal bipyramidal coordination geometry pertains about the centrally-bound uranium atom. 

As is apparent from Figs. 22 and 23 the superphthalocyanine ligands forms an hexagonal girdle around the uranium atom that is essentially perpendicular to... 

A variety of substituted uranyl superphthalocyanine complexes, such as the more soluble methyl 161 and butyl 162 substituted systems [118, 17] can be obtained from the general condensation reaction (Scheme 22). However, when the condensation reaction was carried out using 1,2-dicyanobenKnes with electron withdrawing substituents, or those which impose a greater steric congestion, no five subunit-containing macrocyclic products could be detected. 

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... 

With the original reports of the successM synthe of the sapphyrins [26,66,152] and uranyl superphthalocyanine [112, 118, 119], interest in other expanded porphyrin systems, was kindled. The next logical step (after sapphyrin), in the expanding series of all-pyrrole systems, was the pentaphyrin macrocycle 231 which contains five pyrroles and five meso-like methine bridgra. In 1983 Gossauer et al. reported the synthesis of the first prototypical member 231 of this macrocyclic family [158, 182, 183, 185-187]. This first synthesis was achieved by a 2 + 3 MacDonald-type condensation between an oc-firee dipyrromethane 233 and a tripyrrane dialdehyde 236. More recently, the synthesis of pentaphyrin 231 has l n achieve by using a dipyrromethane 5,5 -dicarboxylic acid 235 in place of an a-firee dipyrromethane [21]. Here, as is the case in many of these kind of reactions [21,26,27,66,155], decarboxylation occurs under the reaction conditions to produce the corresponding a-free species 233 in situ. (Scheme 40) [21]. 

Another expanded porphyrin previously known to form a complex with the uranyl cation was the pentaphyrin 232 [158, 187]. An improved synthesis of a new pentaphyrin derivative and its corresponding, structurally characterized, uranyl complex was recently reported [240]. This new uranyl pentaphyrin, has a very distorted solid state structure reminiscent of the closely related uranyl superphthalocyanine complex 160 [112] (Figures 22 and 23). 

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... 

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