Porphyrin- 2.0.2.0 Porphycene

Notably, this metal-mediated concept, namely, coordination of a fullerene-pyridine ligand by a macrocyclic r-system, is very general and has been successfully extended to zinc complexes of phthalocyanines, porphycenes and corrphycene macrocycles. Interestingly, the binding strength reveals a close resemblance to the oxidation potential of the macrocyclic s -system porphycene > porphyrin. 

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 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... 

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... 

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).

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. ... 

This chapter deals with the provision of suitable starting materials for investigations in the noble metal porphyrin field (Sects. 2.1-2.4) and the establishment of their structures (Sect. 2.5). Most of these investigations are devoted to complexes with synthetic porphyrin ligands which are soluble in organic solvents [e.g. (OEP)- or (TPP) complexes Sect. 2.1]. Special mention is made to some novel porphycene derivatives (Sect. 2.2), to phthalocyanine systems (Sect. 2.3), and to water-soluble porphyrin complexes (Sect. 2.4). 

Porphyrin analogs, homologs, and porphyrinoids - The class of tetrapyrrole chromophores can be enlargened by alteration of the numbers of carbon atoms linking the pyrrole rings [101]. A beautiful porphyrin isomer, porphycene, has been prepared by Vogel and coworkers [102], This porphyrin isomer, H2(Pyc),... 

One of the widely studied, stable constitutional porphyrin isomers encompassing 18jt-electrons in a cyclic conjugated pathway is porphycene 38 (Scheme 17). Other isomers such as NCPs are much less stable and are not discussed here. Porphycenes consist of two 2,2 -bipyrrole subunits linked by two double bonds and are thus named as [18] porphyrin( 2.0.2.0). ... 

Corrphycenes and their metal complexes undergo four distinct one-electron redox steps, two are reduction steps and two are oxidation steps. A comparison with porphyrins and porphycenes indicates that the first reduction potentials of the free base and of metallo-corrphycenes are between those of porphycene 38, the easiest to reduce molecules, and those of porphyrins 2. The oxidation potentials of corrphycenes and porphyrins, however, are quite similar (00IC2850). The synthesis of hemi-porphycene 70 (Scheme 33) has been achieved (05ACI3047) from corrole 8 (R=C6H5). 

We have compiled synthetic chemistry and properties of porphyrin analogues containing only furan, imidazole, or thiophene subunits in place of pyrrole subunit(s). Expanded porphyrinoids have been excluded. This write-up is not intended to give a comprehensive treatment, but is aimed to complement earlier reviews (06CCR468, 08CSR215). In the following two sections, the chemistry of core-modified porphycenes and porphyrins is presented. 

Prototropic tautomerism in porphycenes exhibits characteristics that are vastly different from the behavior of regular porphyrins and has therefore been researched using a variety of techniques, including high-level electronic spectroscopy methods [41], Initial 15N CPMAS NMR experiments carried out on 30a revealed that proton... 

Octaethylcorrphycene exists in solution as the /ran.v-protonatcd tautomer 32a-l shown in Fig. 20. Unexpectedly, in the solid state, the presence of the cis tautomer 32a-2 (21/7,227/) was revealed by X-ray diffraction analysis. Rates of tautomerism determined for 32a in solution using dynamic NMR spectroscopy are higher than those in porphyrins but slower than in the case of porphycenes, indicating an intermediate strength of intramolecular hydrogen bonding. The AG for this process was estimated as 8.3 kcal mol-1. 

A theoretical study of the acidity (proton loss) of the porphyrin 266 and some related systems was carried out by means of the B3LYP/6-31+G(d,p) computational level. These include, on one hand, porphyrin fragments 267 and pyrrole 11 (X = H) and the monoanion and dianion of 266 and, on the other hand, chalcogen-related porphyrins 268,269, and 270 and their anions, as well as cyclic nitrogen derivatives 271, 272, 273, and 274, simplified models of porphyrin, dibenzo[14]annulene, phthalocyanine, and porphycene. 

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