Tetra-substituted porphyrins

In a later article, complexes of Ni(II), Cu(II), Pd(II), and V02+ ions with the same tetra-substituted porphyrin were reported. Stepwise oxidation of these complexes gave products for which the authors proposed quinonoid, monoradical, and diradical structures. The most prolonged oxidations yielded the diradical products, which were isolated as dark purple crystals, relatively stable in air (40). The monoradical vanadyl complex was observed to be diamagnetic, suggesting antiferromagnetic coupling between the phenoxyl radical and unpaired electron on vanadium, whereas in the copper complex no such coupling was observed. More detailed studies of these systems seem warranted. 

Figure 11. Structure of Nolte s mesomorphic inducing "clipper" molecule and schematic representation of a tetra-substituted porphyrin guest being held by the "clipper" molecule. Reprinted with permission from van Nunen,. L. M. Folmer, B. F. B. Nolle, R.. M. y. Amer. Chem. Soc. 1997, 7 79, 283. 1997 American Chemical Society.

Functionalization of 5,10,15,20-Tetra-Substituted Porphyrins Laurent jaquinod... 

Selective complexation of di- and tetra-substituted porphyrins with cerium(III) ion led to novel double- and triple-decker sandwich complexes. In such complexes, the two or three porphyrin macrocyles were rotated by ca. 20-45. The various complexes were prepared by reaction of the parent porphyrins with cerium acetate. 

Following this methodology, discrete information on the present tautomers for a number of unsymmetrically mono- [116], di- [115, 116], tris- [117], and tetra-substituted porphyrins [118], Nnatural chlorin derivatives [123] was derived. 

Tetra(o-aminophenyl)porphyrin, H-Co-Nl TPP, can for the purpose of electrochemical polymerization be simplistically viewed as four aniline molecules with a common porphyrin substituent, and one expects that their oxidation should form a "poly(aniline)" matrix with embedded porphyrin sites. The pattern of cyclic voltammetric oxidative ECP (1) of this functionalized metal complex is shown in Fig. 2A. The growing current-potential envelope represents accumulation of a polymer film that is electroactive and conducts electrons at the potentials needed to continuously oxidize fresh monomer that diffuses in from the bulk solution. If the film were not fully electroactive at this potential, since the film is a dense membrane barrier that prevents monomer from reaching the electrode, film growth would soon cease and the electrode would become passified. This was the case for the phenolically substituted porphyrin in Fig. 1. 

The functionalization of zinc porphyrin complexes has been studied with respect to the variation in properties. The structure and photophysics of octafluorotetraphenylporphyrin zinc complexes were studied.762 Octabromoporphyrin zinc complexes have been synthesized and the effects on the 11 NMR and redox potential of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraarylporphyrin were observed.763 The chiral nonplanar porphyrin zinc 3,7,8,12,13,17,18-heptabromo-2-(2-methoxyphenyl)-5,10,15,20-tetraphenylporphyrin was synthesized and characterized.764 X-ray structures for cation radical zinc 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin and the iodinated product that results from reaction with iodine and silver(I) have been reported.765 Molecular mechanics calculations, X-ray structures, and resonance Raman spectroscopy compared the distortion due to zinc and other metal incorporation into meso dialkyl-substituted porphyrins. Zinc disfavors ruffling over doming with the total amount of nonplanar distortion reduced relative to smaller metals.766 Resonance Raman spectroscopy has also been used to study the lowest-energy triplet state of zinc tetraphenylporphyrin.767... 

Krai has recently reported a related system in which porphyrins bearing bicyclic guanidine substituents (such as the tetra-substituted species 70 shown is Scheme 35) form highly ordered chiral assemblies in aqueous solution [92]. 

The direct labelling of TOPO capped semiconductor CdSe or CdSe/ZnS QDs with tetra-pyridyl substituted porphyrin (Fig. 1). Here P is based on the coordination of the pyridyl N lone pair with Zn or Cd atoms on the surface of QD. 

Figure 1. Structural formulas of 5,10,1 S,20-tetra-meta-pyridyl substituted porphyrin, P (A), trioctyilphospWne oxide, TOPO (B) and schematical presaitation of heterocomposites CdSe/ZnS QD - poiphyrin (C). r = 7.55 A is P radius. All components in part (C) are presented in a real relative scale.

Another approach is the nucleophilic displacement of chloride from chloro-propyl-silica with a pyridine-substituted porphyrin. These materials are active in the epoxidation of alkenes, where iodosylbenzene is the preferred oxidant, and in the oxidation of alkanes to alcohols and ketones. The copolymerisation of a porphyrin containing four attached trimethoxysilane groups with tetra-ethoxysilane, leading to an active hybrid silica-porphyrin, offers another route to these important catalysts. 

Analogous condensations with a pyrrole aldehyde lead to mesomeric dipyrro-methene cations, which play an important part in porphyrin synthesis. Under appropriate conditions one can combine four mol equivalents of pyrrole and four of an aromatic aldehyde to produce a tetra-aryl substituted porphyrin in one pot. ... 

This instrument was employed to examine the excited state dynamics of supramolecular systems generated from self-assemblies between metal-substituted 18-crown-6 tetra-substituted phthalocyanines (McrPc) with ions contained in the crown sites (McrPcK) and metal-substituted weso-tetrakis(4-sulfonatophenyl)porphyrin (MTPPS) or meso-(4-carboxylphenyl)porphyrin (MTPPC). In the absence of added potassium ions, no hetero-complexes were formed. In the presence of K", absorption spectral changes indicated the formation of a... 

Tetra-substitution at the same meso positions of the porphyrin core by bulky ort/ru-terphenyl groups conferred to the macrocycle an overall macro-disk-like shape ((26) M = 2H, Cu). " In this case, both the free-base and the copper complex exhibited an enantiotropic Colt phase from room temperature up to 59 °C for the ligand and 57 °C for the copper complex. The comparison between these macrocycles with the related phthalocyanine derivatives confirmed the perturbing role of the side groups on the stability of the Colh phase, consequent to a disturbed molecular stacking. X-Ray diffraction suggested that the columns would be constituted by the stacking of dimer units, with a periodicity of about 9.5 A. 

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