Porphycene

In the same paper, Limbach et al. (87AGE934) reported the study of the compound related to porphyrins, porphycene 79. Porphycene behaves very differently from FI2P in CPMAS DNMR experiments. Its behavior was explained assuming that the four porphycene tautomers (two cis and two trails) are present in the crystal and interconverting very rapidly due to short N-H...N distances in the seven-membered pseudorings. 

In (87BBPC941), Limbach made a major contribution to understanding crystalline and amorphous environments using compounds that in the gas phase show symmetric double minimum potentials. Several compounds were used to illustrate the periodic (crystal) and random (glass) distortions of the potential surface, among them H2P and porphycene. Tlie seminal paper on the tautomerism of porphyrins in the solid state is that of Limbach... 

Porphyrin and its isomers, porphycene, hemiporphycene, corphycene, and iso-porphycene, as high-technological dyes 99CFY767. 

The reductive coupling of the dicarbonyl compound 6 induced by a low-valent titanium species gives initially the dihydroporphycenes 7 which then spontaneously aromatize in the presence of oxygen to yield the porphycenes 8. 

Low-valent titanium was prepared from TiCl4 (9.5 g, 50 mmol) and activated zinc (6.55 g, 100 mmol) in the presence of pyridine (2.5 mL) in THF (400 mL) To this mixture was added all at once the corresponding bipyrroledicarbaldehyde (6 1.36 g, 5 mmol) and the mixture was refluxed for 30 min. After hydrolysis with a 10% aq K.2C03 (125 mL), aqueous extraction and chromatography (silica gel, CH2Cl,/hexane 1 1), the porphycene was obtained as the only nonpolymerized product. Recrystallization (hexane) gave red-violet needles of the porphycene yield 120 mg (10%). 

The reduction of porphycenes, e.g. 1, can be achieved by catalytic hydrogenation22-25 or chemical reduction with alkali metals.22 With alkali metals one of the C —C double bond bridges in 1 is reduced to yield a 19,20-dihydroporphycene2. On catalytic hydrogenation of porphycene (1), 2,3-dihydro porphycene (3) is formed which can be compared to chlorin, the dihydrogenated form of porphyrin. 

In contrast to porphyrin which is brominated in the meso positions, unsubstituted porphycene (1) is selectively brominated in the 2-position.26... 

The tetrabromo porphycene was used as a starting product for the first synthesis of isocorroles (see Section 1.8.) which are formed from the porphycene by ring contraction on treatment with base. 

The photophysical properties of porphycenes make these structures potential sensitizers for an application in Photodynamic Tumor Therapy (PDT). To improve the photophysical properties and to modify possible biological activity it is necessary to have porphycenes with an extended chromophore and/or with additional functional groups for further modifications. The Diels-Alder reaction of a vinyl porphycene allows for the preparation of benzoporphycenes with an extended chromophore9 and additional functional groups (cf. Section 1.1.2.4.). 

To form the desired vinyl group, the methoxyethyl-substituted porphycene 9, has to be converted into its nickel complex. In the nickel porphycene the methoxyethyl side chain is... 

As in the porphycene series one method to obtain an isocorroie is based on the McMurry coupling of a tetrapyrroledicarbaldehyde, e.g. 1.2 4 The reductive cyclization forms a C —C double bond bridge leading directly to the isocorroie, e.g. 2, which is at the correct oxidation level. 

Analogously, the tetrabromotetrapropylporphycene 9 furnishes the corresponding isocorroie-carbaldehyde 10 in good yields, but in this case no decarbonylated product was observed. The mechanism of these interesting ring contractions of porphycenes into isocorroles still needs to be determined. 

Organometallic complexes are known which contain a wide variety of macrocycles closely related to porphyrins corroles, porphycenes, tetraazaporphyrins. phthalocyanines, tetraazaannulenes, and porphyrinogens are the best known examples. Examples containing the first four of these macrocycles are included where there is a useful comparison or contrast with the relevant porphyrin chemistry, but the discussion will not be comprehensive. The four macrocycles are shown in Fig. 2. 

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... 

Szeimies RM, Karrer S, Abels C, Steinbach P, Fickweiler S, Messmann H, Baumler W, Landthaler M (1996) 9-Acetoxy-2,7,12,17-tetrakis-(beta-methoxyethyl)-porphycene (ATMPn), a novel photosensitizer for photodynamic therapy uptake kinetics and intracellular localization. J Photochem Photobiol B 34 67-72. 

In another work, the same authors demonstrated the versatility of graphene as donor material when preparing a similar nanographene hybrid with porphycenes, a well-known electron acceptor [120], The preparation was followed along the same lines that were established for the porphyrins. By using Raman, TEM, and AFM, the nature of the graphene moiety was clearly demonstrated. Contrary to the electron ac-... 

Fig. 18.9 Left part - device performance as a function of soaking time for Ti02-based devices using nanographene/porphyrin hybrids (closed) and porphyrin dyes (open). Right part - device performance as a function of soaking time for ZnO-based devices using nanographene/porphycene hybrids (closed) and porphycenes (open).

In a corresponding investigation, the application of a new nanographene hybrid that consists of negatively-charged GO and a positively-charged porphycene... 

Fig. 18.11 Upper part - chemical structures of negatively-charged porphyrin and positively-charged graphene. Lower part - chemical structures of positively-charged porphycene and negatively-charged graphene oxide.

One example of a tin porphycene has been reported, but as yet no organometallic derivatives have been reported." A small number of tin corrole complexes are known including one organotin example, Sn(OEC)Ph, prepared from the reaction of Sn(OEC)Cl with PhMgBr. A crystal structure of Sn(OEC)Ph shows it to have both shorter Sn—N and Sn—C bonds than Sn(TPP)Ph2, with the tin atom displaced 0.722 A above the N4 plane of the domed macrocycle (Fig. 6). The complex undergoes reversible one-electron electrochemical oxidation and reduction at the corrole ring, and also two further ring oxidations which have no counterpart in tin porphyrin complexes. " " ... 

Porphycenes (150) and corrphycenes (151) are porphyrin isomers, several of whose iron(III) complexes have been characterized. Examples include distorted square-pyramidal (12,17-diethox-ycarbonyl-2,3,6,7,1 l,18-hexamethylcorrphycenato)iodo-iron(III), [Fe(tprpc)X] (where tprpc = 2,7, 12,17-tetra-u-propylporphycene) with X = C1, Br, N3, 02CMe, or OPh and [Fe(tprpc)2]0. " Iron(II)- and iron(IV)-tproc complexes also exist, as established in an examination of oxygenation of iron(II) porphycene.The structure of chloro(3,6,13,16-tetraethyl-2,7,12,17-tetramethylpor-phycenato)iron(III), also distorted square-pyramidal, has been compared with those of chloro-iron(III) porphyrin complexes. ... 

Lauro, F. M., Pretto, P., Covolo, L., Jori, G., and Bertoloni, G. (2002). Photoinactivation of bacterial strains involved in periodontal diseases by porphycene-polylysine conjugates. Photochem. Photohiol. Sci. 1, 468 70. 

Finally, some aspects of the electrochemistry of cobalt(II) porphycenes (17) have been discussed in two relatively recent articles ]84, 85]. 

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