Porphyrins peripheral groups

In the case of the hydroxylation of inactivated alkanes, the yields and distributions of products are sensitive to the peripheral substitution pattern of the porphyrin. Table 4 lists the results from the oxidation of adamantane with iodosylbenzene and three iron porphyrins Fe (TPP)Cl, Fe (TTP)Cl (TTP tetrakis(o-tolyl)porphyrin), and Fe (TMP)Cl [44]. Apparently, there is a high degree of selectivity for tertiary centers over secondary centers. In addition, with increasing substitution of the porphyrin peripheral groups, the relative reactivity of tertiary and secondary hydrogens decreased from 48 1 to 11 1. Details of the steric effect of the porphyrin peripheral groups to the selectivity will be discussed later. 

Meso substitution of porphyrines to give tetraazaporphyrines, so-called porphyrazines, modulates the electronic character of the macrocycle. While porphyrazines have received considerably less attention than porphyrines over many years, this has changed due to the development of efficient syntheses of soluble derivatives.1 6-1809 Also, various porphyrazines (and phtalocyanines) with peripheral groups for metal ion coordination have been prepared and used for the construction of multimetallic complexes.1806 Ni porphyrazines (695) typically show absorptions spectra with a strong Q band at around 615nm. 

As shown in Fig. 1-33, metalloporphyrins exhibit a number of porphyrin core vibrations in which local modes such as v(C=C) and v(C=N) are strongly coupled (Section 1.21) due to its planar 7r-conjugated structure. Several groups of workers (5-8) have carried out normal coordinate analysis on metalloporphyrins. If we consider the simplest metalloporphyrin in which all the peripheral groups are the hydrogen atoms, it should have 105 (3 x 37 - 6) normal vibrations, which can be classified under D4h symmetry as shown in Table 4-4. Table 4-5 shows major local coordinates that describe general characters of 35 Raman-active in-plane vibrations (8) together with observed frequencies for Ni(OEP) (Fig. 1-32). These normal mode descriptions are applicable to other metalloporphyrins with minor modifications. 

Abstract The metal-driven construction of multi-porphyrin assemblies, which exploits the formation of coordination bonds between exocyclic donor site(s) on the porphyrins and metal centers, has recently allowed the design and preparation of sophisticated supra-molecular architectures whose complexity and function begin to approach the properties of naturally occurring systems. Within this framework, meso-pyridyl/phenyl porphyrins (PyPs), or strictly related chromophores, can provide geometrically well-defined connections to as many as four metal centers by coordination of the pyridyl peripheral groups. Several discrete assemblies of various nuclearities, in which the pyridylporphyrins are connected through external coordination compounds, have been constructed in recent years. In this review, we summarize recent work in this field from our and other laboratories. The photophysical properties of some ruthenium-mediated assemblies of porphyrins prepared by our group are also described. 

Fig. 17 Measured Fe excitation probabilities for a series of iron porphyrins. All nitrosyl complexes have an Fe-NO stretch/bend mode in the 520-540 cm region. Comparison among the nitrosyl complexes (c-g) reveals that peripheral groups strongly influence the vibrational frequencies and amplitudes of the central Fe. Sample temperatures were 34 K for Fe(OEP), 30 K for Fe(OEP)(NO), 80 K for Fe(TPP)(NO), 35 K for Fe(DPIXDME)(NO), 34 K forFe(PPIXDME)(NO), and 64 K for Fe(MPIXDME) (NO). The Fe(OEP)(Cl) spectrum is an average over multiple scans with an estimated average temperature of 87 K. Reprinted from reference [192], with the permission of the American Chemical Society, copyright 2004...

Tanaka et al. [8] proposed a very elegant strategy based on porphyrins peripherally modified with dibenzol[24]crown-8 and a secondary ammonium ion, able to form rotaxanes. In fact, the interaction of a porphyrin with a phthalocyanine lead to the formation of a stable jt-stacked pseudo-rotaxane after end-capping the ammonium chains by reaction with Staudinger-phosphite in chloroform, followed by metallation with Cu(II). In acidic media, the ammine and phosphoramide groups are protonated generating a tetracationic species that can form ion-pairs with the tetraanionic [Cu-TSPP] species [9]. 

The electrochemical process in substituted porphyrins can be more or less localized at the peripheral groups, as demonstrated with wero-pyridyporphyrins coordinated to one to four transition metal complexes [236]. A study involving porphyrin derivatives substituted with diones and tetraones demonstrated that these redox-active sites can function independently of the central macrocycle [237]. The reduction of the 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin-2,3-diones, 2,3,-12,13-tetraones [L-(P-tetraone)M] and 2,3,7,8-tetraones [C-(P-tetraone)M], (where M is 2H, Cu ", Zn, Ni " and Pd " ) was investigated and the products characterized by ESR and thin-layer UV-Visible spectroelectrochemistry. In diones, the first two reduction processes occur at the peripheral units whereas in the... 

The effect of core shielding of a porphyrin moiety by peripheral dendrons has been carefully investigated on two series of Zn-phthalocyanine-cored dendrimers with aryl-ether branches [60]. Generation 0,1, and 2 (dendrimer 27) species, terminated with ester groups, are soluble in organic solvents, while the species terminated with carboxylate units (e.g., 28) are soluble in water. 

A detailed analysis of Ni11 complexes with mew-substituted porphyrins bearing zero, one, two, or four /-butyl groups revealed that both the out-of-plane and in-plane distortion depend on the perturbation symmetry of the peripheral substituents (number and position of substitutents), and their orientation.1775 These results have implications for understanding the role of nonplanar distortions in the function of metalloproteins containing nonplanar porphyrins.1776... 

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