Tetrakis porphyrin oxidation

Bruice, T.C. and G. He (1991). Nature of the epoxidizing species generated by reaction of aUcyl hydroperoxides with iron(III) porphyrins. Oxidations of cis-stilbene and (Z)-l,2-bis(trans-2, trans-3-diphenylcyclopropyl)ethene by tert-BuOOH in the presence of [meso-tetrakis(2,4,6-trimethylphenyl)porphinato]-, [meso-tetrakis(2,6-dichlorophenyl)-porphinato]-, and [meso-tetrakis(2,6-dibromophenyl)porphinato]rron(III) chloride. J. Am. Chem. Soc. 113, 2747-2753. 

In the case of an aminophenyl daivative with -NH2 groups at the para position of the phenyl substituents, for example in 5,10,15,20-tetrakis(4-aminophenyl)porphyrin or 5,15-bis(4-aminophenyl)-10,20-bis(4-carbomethoxyphenyl)porphyrin, oxidation gives a highly interconnected nanolibrous networic and a linear porphyrin polymer [94, 95]. The mechanism is considered analogous to that found for aniline polymerization, except that the attack of the electrophilic nitrogen must occur exclusively to the meta-positions of the aminophenyl substituents of another porphyrin molecule, as shown in Fig. 5. 

Quinoxaline gave quinoxaline 1-oxide [substrate, ACONH4, trace manganese tetrakis(2,6-dichlorophenyl)porphyrin, CH2Cl2-MeCN then 30% H2O2-MeCNi, 20°C, 2h 33% netj. ... 

Another iron porphyrin complex with 5,10,15,20-tetrakis(2, 6 -dichloro-3 -sulfonatophenyl)porphyrin was applied in ionic liquids and oxidized veratryl alcohol (3,4-dimethoxybenzyl alcohol) with hydrogen peroxide in yields up to 83% to the aldehyde as the major product [145]. In addition, TEMPO was incorporated via... 

DCE interface in the presence of TPBCl [43,82]. The accumulation of products of the redox reactions were followed by spectrophotometry in situ, and quantitative relationships were obtained between the accumulation of products and the charge transfer across the interface. These results confirmed the higher stability of this anion in comparison to TPB . It was also reported that the redox potential of TPBCP is 0.51V more positive than (see Fig. 3). However, the redox stability of the chlorinated derivative of tetra-phenylborate is not sufficient in the presence of highly reactive species such as photoex-cited water-soluble porphyrins. Fermin et al. have shown that TPBCP can be oxidized by adsorbed zinc tetrakis-(carboxyphenyl)porphyrin at the water-DCE interface under illumination [50]. Under these conditions, the fully fluorinated derivative TPFB has proved to be extremely stable and consequently ideal for photoinduced ET studies [49,83]. Another anion which exhibits high redox stability is PFg- however, its solubility in the water phase restricts the positive end of the ideally polarizable window to < —0.2V [85]. 

The consequences of polychlorination of porphyrins on redox properties of complexes has been investigated.1404 The highly chlorinated porphyrin 3-octachloro-/ /c.vo-tetrakis(3,5-dichloro-2,6-dimethoxyphenyl)porphyrin exhibits a substantial anodic shift for reduction of over 0.5 V and a smaller shift for oxidation versus the unchlorinated precursor. Contrastingly, small potential shifts for the octabromo-substituted 5,10,15,20-tetraphenylporphyrinate arise from the dominance of macrocycle ruffling over electronic effects. In the polychloro complex, distortion does not compensate fully for electron-withdrawing effects of the Cl substituents. 

The decay of zinc tetrakis(A -methylpyridinium-4-yl(porphyrin 7r-radical cations in the presence of poly(styrenesulfonate) and IrIV oxides or [Ir(OI I )r,]2 has been studied at high pH.46 The hexahydroxide species was found to be very reactive. 

Water soluble iron porphyrins [Fem(TPPS)(H20) ]3-330 and [Fem(TMPy)(H20)2]5+ 331 332 (TPPS = maso-tetrakis(/ -sulfonatophenyl)porphyrin, TMPyP = / /e.vo-tetrakis(7V-methyl-4-pyridi-nium)porphyrin331 or maso-tetrakis (A -methyl-2-pyridinium)porphyrin332 dications) act as effective electrocatalysts for the reduction of nitrite to ammonia in aqueous electrolytes (Equation (64) Ei/2= 0.103 V vs. SCE at pH 7), with NH2OH or N20 also appearing as products depending on the reaction conditions. Nitric oxide then ligates to the iron(III) porphyrin to form a nitrosyl complex [Fen(P)(NO+)] (P = porphyrin) as intermediate. 

Surface modified NO sensors incorporate an electrode surface that has been modified or treated in some way so as to increase the selectivity of the sensor for NO and promote catalytic oxidation of NO. An early example of such a sensor was presented by Malinski and Taha in 1992 [27], In this publication an —500nm diameter carbon fiber electrode was coated with tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin, via oxidative polymerization, and Nation. This electrode was shown to have a detection limit of — lOnM for NO and great selectivity against common interferences. However, recently it has been shown that this electrode suffers severe interference from H202 [28],... 

Collman et al.99 reported the asymmetric epoxidation of terminal olefins catalyzed by iron porphyrin complex 129. The catalyst was synthesized by connecting binaphthyl moieties to a readily available aa/ / -tetrakis(aminophenyl)-porphyrin (TAPP). Epoxidation of unfunctinalized olefins was carried out using iodosylbenzene as the oxidant. As shown in Scheme 4-46, excellent results were... 

Other examples of oxidant-iron(III) adducts as intermediates in iron porphyrin-catalyzed reactions have been published as listed in references 54a-k. Competitive alkene epoxidation experiments catalyzed by iron porphyrins with peroxy acids, RC(0)00F1, or idosylarenes as oxidants have been proposed to have various intermediates such as [(porphyrin)Fe (0-0-C(0)R] or [(porphyrin)Fe (0-I-Ar)]. Alkane hydroxylation experiments catalyzed by iron porphyrins with oxidant 3-chloroperoxybenzoic acid, m-CPBA, have been proposed to operate through the [(porphyrin)Fe (0-0-C(0)R] intermediate. J. P. CoUman and co-workers postulated multiple oxidizing species, [(TPFPP )Fe =0] and/or [(TPFPP)Fe (0-I-Ar)] in alkane hydroxylations carried out with various iodosylarenes in the presence of Fe(TPFPP)Cl, where TPFPP is the dianion of me50-tetrakis(pentafluorophenyl)porphyrin. ... 

The kinetics and mechanism for oxygen transfer between 4-cyano-V,V,-dimethylaniline V-oxide and a C2-capped mexo-tetraphenylporphyrinatoiron(III) and mc5 o-tetrakis(pentafiuorophenyl)-porphyrinatoiron(III) have been established. Addition of a copper(II) porphyrin cap to an iron(II)-porphyrin complex has the expected effect of reducing both the affinities and rate constants for addition of dioxygen or carbon monoxide. These systems were studied for tetradecyl-substituted derivatives solubilized by surfactants such as poly(ethylene oxide) octaphenyl ether. ... 

Nierengarten et al. looked at the effects of pendant fullerenes on the electrochemical potentials of a porphyrin core. Molecule 1 had an oxidation potential 175 mV higher than mes0-tetrakis(3,5-di-tert-butylphenyl)porphyrin (1195 mV compared... 

Although the cofacial diporphyrins represent a vibrant and innovative direction in dioxygen activation, simple porphyrins and their derivatives also remain an important research area. The dichlorophenyl-substituted porphyrin tdcpp [5,10,15,20-tetrakis(2,6-dichlorophenyl)-porphyrin] forms a complex with cobalt(II), [Co(tdcpp)], and catalyzes the oxidation of conjugated olefins to (after experimental workup) ketones in the presence of dioxygen and triethylsilane (80) a hydroperoxide intermediate has been isolated from these reactions (81). 

The kinetics of oxidation of aldehydes by the Fenton reagent [Fe(II)-H202-0H-] have been studied.89 It has been suggested that different reactivities of PhIO in iron(III)-porphyrin-catalysed alkene epoxidation may be due to the formation of a more reactive iron(IV)-0-IPh complex.90 The iron(m) complex of tetrakis(3,5-disulfonato-mesityl)porphyrin catalyses the oxidative degradation of 2,4,6-trichlorophenol to 2,6-dichloro-l,4-benzoquinone with KHSO5 as the oxygen atom donor a peroxidase-type oxidation is thought to be involved.91... 

A recent contribution to the chemoselectivity problem is the composite photocatalysis developed by Maldotti et al. [117]. Cyclohexene la was subjected to photo-initiated oxidation in Nation membranes containing Pd(II) porphyrin Pd(4-TMPyP) [4-TMPyP = weso-tetrakis(N-methyl-4-pyridyl)porphyrin] and Fe(III) porphyrin 11 to... 

Synthetic iron porphyrin complexes such as Fe(TPP) (tetraphenylporphyrin = TPP), Fe(TMP) (Tetramesitylporphyrin = TMP), and Fe(TDCPP) (tetrakis (dichlorophenyl)porphyrin = TDCPP) (Fig. 9) have been used as models for P450 and peroxidase (9, 50-54). Early pioneering work showed that epoxida-tion catalyzed by Feln(TPP) was successfully carried out by the use of iodosylbenzene (Ph—1=0) as an oxidant (50). A very interesting feature of this model epoxidation is that the cis olefin is readily oxidized while the trans olefin is hardly oxidized (e.g., d.v-stylbene can be oxidized in 80% yield, but fraws-stylbene gave only a trace amount of the epoxide under the same conditions) (50, 55). Most of the model reactions are carried out in homogeneous organic solvents such as chloroform, dichloromethane, and acetonitrile, thus, the c/.v-epoxidation is expected to be a kinetically favorable process over the trans-epoxidation. 

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