Phthalocyanine-subphthalocyanine

Keywords Phthalocyanines - Subphthalocyanines-Boron-NonUnear Optics-Dipolar Compounds -... 

Abstract This chapter describes the synthesis of phthalocyanines, subphthalocyanines and porphyrazines bearing fluorine atoms and/or perfluorinated alkyl or aryl groups. Influence of fluorination of macrocycle on its physico-chemical properties and perspectives of application is also briefly considered. 

Although these methods were applied for the synthesis of a number of various phthalocyanines with different central atoms (e.g., H2, Cu, Zn, Ni, Pt, Pd, Lu, etc.) not all metal phthalocyanines can be prepared by one of these methods. For example, the synthesis of silicon phthalocyanine, rhenium phthalocyanine and boron subphthalocyanine need more drastic conditions. In the following, an overview of the synthesis of phthalocyanines containing all central metals which have hitherto been inserted into the ring is given. 

In contrast to phthalocyanines (tetra- or octasubstituted) in which the isoindoline units carry all the same substituents, reports of phthalocyanines with lower symmetry, which have been prepared by using two different phthalonitriles, have rarely appeared. This is due to the problems which are associated with their preparation and separation. For the preparation of unsymmetrical phthalocyanines with two different isoindoline units four methods are known the polymer support route,300 " 303 via enlargement of subphthalocyanines,304 " 308 via reaction ofl,3,3-trichloroisoindoline and isoindolinediimine309,310 and the statistical condensation followed by a separation of the products.111,311 319 Using the first two methods, only one product, formed by three identical and one other isoindoline unit, should be produced. The third method can be used to prepare a linear product with D2h symmetry formed by two identical isoindoline units. For the synthesis of the other type of unsymmetrical phthalocyanine the method of statistical condensation must be chosen. In such a condensation of two phthalonitriles the formation of six different phthalocyanines320 is possible. 

Ring enlargement from subphthalocyanines has been used to synthesize unsymmetrically substituted metal-free phthalocyanines of the AAAB type (see p 738). 

Figure 13 Ring expansion of a haloboron(III) subphthalocyanine (49) to give an unsymmetrically substituted phthalocyanine, here the zinc(II) benzonaphthoporphyrazine (51).252,253 As usual, the product is...

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. 

Some representative examples of fullerene-porphyrin dyads are shown in Scheme 9. In other examples, porphyrin analogs such as phthalocyanines and subphthalocyanines have been used for the construction of efficient dyads. Again, the most straightforward approach for their synthesis involved 1,3-dipolar cycloaddition of the appropriate azomethine ylides to C60 [203-205]. Also, with the aid of the Bingel reaction, other phthalocyanine-fullerene systems have been prepared [206,207] with the most prominent example being the one that contains a flexible linker possessing an azacrown subunit [208]. The novelty of this dyad can be found in the nature of the linker that could, in principle, induce conformational changes in the multicomponent system when certain ions (e.g., alkaline ions) are present. As a direct consequence this would potentially allow an external control over the electronic interactions between the phthalocyanine and fullerene units. 

The phthalocyanines (e.g., 2.277) are well known for their ready availability and their tendency to form stable complexes with a wide variety of metals. They are typically prepared via the metal-templated macrocyclization of a phthalonitrile derivative (e.g., 2.276) as shown in Scheme 2.3.1. The ease of preparation as well as the remarkable coordinative ability of the phthalocyanines led Meller and Ossko in 1972 to attempt to prepare boron-containing phthalocyanine derivatives. This they tried via the reaction of phthalonitrile with haloboranes. What they in fact obtained, however, was not the desired tetrameric phthalocyanine derivative, but rather a contracted trimeric phthalocyanine 2.284, a species that has since come to be known as subphthalocyanine (Scheme 2.3.2). A similar fluorine-containing subphthalocyanine 2.285 was also prepared using this procedure. 

A single crystal X-ray diffraction analysis has been carried out on both the chloro- and the phenyl-substituted subphthalocyanines 2.284 and 2.287 (Figures 2.3.2 and 2.3.3). These analyses served to show that subphthalocyanines lie in a bowl-shaped conformation. This is, of course, very different from the near-planar conformation of the parent phthalocyanines. Presumably, this bowl-shaped structure accounts, in part, for the decreased molar absorptivities of the subphthalocyanines relative to their phthalocyanine parents . Nevertheless, despite the non-planar nature of these macrocycles, the subphthalocyanines are capable of supporting an induced diamagnetic ring current (as judged by NMR spectroscopy). Thus, they may appropriately be considered as being aromatic. 

While the subphthalocyanines are interesting in their own right, much of the recent impetus for preparing these macrocycles derives from their use as precursors in the synthesis of unsymmetrically substituted phthalocyanines, which are otherwise... 

The first documented example of a ring-expansion reaction involving a sub-phthalocyanine came in 1990. Here, Kobayashi and Osa and coworkers reported that by treating the t-butyl-substituted subphthalocyanine 2.286 with succinimide (2.296), one could obtain the unsymmetrically substituted phthalocyanine 2.297 in 13% yield (Scheme 2.3.5). Similarly, treating subphthalocyanine 2.286 with the dii-minoisoindoline analogs 2.298-2.300, afforded the unsymmetrically substituted... 

In an attempt to explain these findings, Wohrle and coworkers found that subphthalocyanine 2.284 can be converted to unsubstituted phthalocyanine by treatment with the weak base, zinc(II) acetate dihydrate (Scheme 2.3.11). On the other hand, no reaction occurred when ZnCl2-H20 was used. This and other experiments... 

In an attempt to preclude the formation of the various side-products observed in the above reactions, Wohrle and coworkers developed a modified means of effecting this type of ring expansion.They found that reacting the subphthalocyanine 2.284 with a phthalonitrile derivative such as 2.328 or 2.329 in the presence of zinc(II) acetate led to reasonable yields of the zinc(II) mono-substituted phthalocyanine 2.308 or 2.330 (Scheme 2.1l3). Importantly, they also found that the amount of... 

One final example of a cryptand-like expanded porphyrin is the niobium(IV) bicyclophthalocyaninato system 9.132 reported by Gingl and Strahle in 1990. Interestingly, 9.132 was isolated as a by-product of a standard phthalocyanine-form-ing reaction (i.e., metal-templated cyclocondensation of phthalonitrile 9.102) in which NbOCls was used as the catalyst (Scheme 9.2.10). As such, it represents the fourth type of system to be prepared using this type of procedure (the other three being the parent phthalocyanines, the subphthalocyanines discussed in Chapter 2, and the superphthaolcyanines discussed in Section 9.2.1 of this chapter). 

Figure 1. Molecular structures of from left to right phthalocyanine porphyrins and subphthalocyanine...

In this chapter we report on some novel strategies that have been pursued to obtain efficient second-order nonlinear molecules starting from the well-known phthalocyanines. In principle, these planar centrosymmetric molecules do not present second-order activity and have been extensively studied for third-order applications. In order to induce asymmetry, two main approaches have been followed a) peripheral substitution of the macrocycle with donor and acceptor groups and b) structural modifications of the Pc core to reduce the symmetry, the resulting-noncentrosymmetric compounds (i.e. subphthalocyanines) presenting variable degrees of dipolarity/octupolarity in the nonlinear response. 

Claessens et al. reviewed the recent progress in studies of NLO properties of boron-subphthalocyanines (SubPcs). These phthalocyanine derivatives consist of three isoindole units N-fused around a central boron atom, which bear an axial ligand. These authors noted that the optical response of these nearly ocmpolar derivatives is associated to the charge transfer inside the macrocycle tt surface. Ihey... 

S.V. Kudrevich, S. Gilbert, J.E. van Lier (1996). Syntheses of trisulfonated phthalocyanines and their derivatives using boron(III) subphthalocyanines as intermediates. J. Org. Chem., 61, 5706-5707. 

A phthalocyanine may also have a chiral structure if the metallic centre coordinated by the nitrogen atoms is out of the plane defined by the Pc ligand. A subphthalocyanine (6.41) with C3 symmetry was resolved by HPLC. The CD showed dichroic effects at 560 and 570 nm (Qoo- band) and 280 and 300 nm (Soret band), being either positive or negative according to the enantiomer. Unfortunately, the authors were not able to assign configurations to the enantiomers. 

The subphthalocyanine (SubPc) macrocycles have been received a great deal of attention because of their interesting optical properties and their utility in the synthesis of asymmetrical non-planar phthalocyanines " SubPc compounds consist of three coupled isoindole units with a boron atom at the centre. One component of this series is the sub-2,3-boronnaphthalocyanine chlorine (subBClNPc) compound, Figure 14.31. This compound has been considered in this chapter since it represents a new challenge in the optic of the surface vibrational studies because of the structure of this compound is conic, as in the case of the sub-2,3-boronphthalocyanine chlorine macrocycle, instead of the planar structure of the naphtalocyanine complexes already mentioned. ... 

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