Corroles reactions

Protonation and deprotonation reactions of corroles have already been mentioned (see Introduction). Attempts to achieve electrophilic substitution reactions, at the corrole, e.g. Friedel-Crafts acylation, have been unsuccessful.1 Heating corroles with acetic anhydride yields the corresponding 21-acetyl derivatives l.8a,b... 

Chromium, (ri6-benzene)tricarbonyl-stereochemistry nomenclature, 1,131 Chromium complexes, 3,699-948 acetylacetone complex formation, 2,386 exchange reactions, 2,380 amidines, 2,276 bridging ligands, 2,198 chelating ligands, 2,203 anionic oxo halides, 3,944 applications, 6,1014 azo dyes, 6,41 biological effects, 3,947 carbamic acid, 2,450 paddlewheel structure, 2, 451 carboxylic acids, 2,438 trinuclear, 2, 441 carcinogenicity, 3, 947 corroles, 2, 874 crystal structures, 3, 702 cyanides, 3, 703 1,4-diaza-1,3-butadiene, 2,209 1,3-diketones... 

Octaethyl and tris(pentafluorophenyl) corroles, known as oec and tpfc, respectively, are also efficient for the stabilization of P(VI) phosphorus [53,54]. The electron-rich oec reacts with PCI3 to form (oec)P=0 40 that can be further derived into dihydrido 41a, dimethyl 41b and diphenyl 41c compounds by reduction with LiAlH4 and reactions with methyl and phenyl Grignard reagents. 

Carbenoid N-H insertion of amines with diazoacetates provides a useful means for the synthesis of ot-amino esters. Fe(III) porphyrins [64] and Fe(III/IV) corroles [65] are efficient catalysts for N-H carbenoid insertion of various aromatic and aliphatic amines using EDA as a carbene source (Scheme 16). The insertion reactions occur at room temperature and can be completed in short reaction times and with high product yields. It is performed in a one-pot fashion without the need for slow... 

A more practical, atom-economic and environmentally benign aziridination protocol is the use of chloramine-T or bromamine-T as nitrene source, which leads to NaCl or NaBr as the sole reaction by-product. In 2001, Gross reported an iron corrole catalyzed aziridination of styrenes with chloramine-T [83]. With iron corrole as catalyst, the aziridination can be performed rmder air atmosphere conditions, affording aziridines in moderate product yields (48-60%). In 2004, Zhang described an aziridination with bromamine-T as nitrene source and [Fe(TTP)Cl] as catalyst [84]. This catalytic system is effective for a variety of alkenes, including aromatic, aliphatic, cyclic, and acyclic alkenes, as well as cx,p-unsaturated esters (Scheme 28). Moderate to low stereoselectivities for 1,2-disubstituted alkenes were observed indicating the involvement of radical intermediate. 

The same strategy provides a useful tool to derivatize corrole 22 and sapphyrin 25 (Scheme 7). In the case of corrole 22, the reaction with pentacene (after 6 h at 200 °C) afforded mainly the dehydrogenated adduct 23 this is formed from the selective addition of pentacene to the befa-pyrrolic double bond near to the direct pyrrole-pyrrole link and subsequent dehydrogenation <04S 1291>. In minor amount, the reaction also gave rise to the dehydrogenated adduct 24 resulting from an unexpected thermal [4+4] cycloaddition reaction. 

Scheme 7. DA reactions of corrole 22 and sapphyrin 25 with pentacene.

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. " " ... 

Redox equilibrium of Ag(I I [-porphyrin /Ag(III) is characterized with = 0.59 V versus SCE [412]. Evidently, corroles and carbaporphyrins are able to stabilize the Ag(III) oxidation state, presumably due to the presence of 7r-electron donors, which reduce the formal oxidation state of the metal in such complex [396]. It is expected that such complexes have potential practical applications, for example, as the catalysts in the electron-transfer reactions. 

Bis(2-pyrrolyl) sulfides, prepared from the reaction of the pyrrole with sulfur dichloride, are useful precursors in the synthesis of corroles and related compounds, as it is possible to cause the extrusion of the sulfur atom with the consequent formation of a bipyrrolic unit within the macrocycle <72JCS(P1)1124). 

Fe111 and Co111 corroles catalyze the reaction between alkene and hydroxide. The product is either an alcohol or a ketone depending on the substrate.241 The kinetics are first order in both alkene and hydroxide ion, and the rate increases in the order ethoxyethylene > styrene > 1-octene. No intermediates such as alkylmetal complexes have been detected spectroscopically. These observations suggest a mechanism involving an initial metal-alkene n complexation followed by rate-determining hydroxylation (Scheme 80). 

Sapphyrin (39d) was the first cyclic pentapyrrole obtained by Woodward et al.114 The acid-catalyzed cyclization of the tetrapyrrole (46) gave (39d) instead of corrole (30) via a disproportionation reaction. Accordingly, addition of diformylpyrrole (47) to (46) leads to (39c) (Scheme 105). However, the [3 +2] route is facile and more satisfactory in general (Scheme 106).274,275... 

Coproporphyrin I synthesis, 816 Coronands classification, 919 metal ion complexes, 928,938 Corphins, 855 Coninoids, 983 Corrins, 871-888 demetallation, 882 deuteration, 879 electrophilic reactions, 879 metallation, 882 NMR, 878 nucleophilicity, 886 nucleophilic reactions, 879 oxidation, 879 oxidative lactamization, 880 oxidative lactonization, 880 photochemistry, 887 reactions, 879 at metal, 885 rearrangements, 879 redox chemistry, 888 spectra, 877 synthesis, 878 Corroles, 871-888 demetallation, 874 deuteration, 872 hydrogenation, 872 metallation, 874 reactions, 872 at metal, 875 redox chemistry, 876 synthesis, 871 Corticotropin zinc complexes medical use, 966 Cotton effect anils, 717... 

The first reports on iron-catalyzed aziridinations date back to 1984, when Mansuy et al. reported that iron and manganese porphyrin catalysts were able to transfer a nitrene moiety on to alkenes [90]. They used iminoiodinanes PhIN=R (R = tosyl) as the nitrene source. However, yields remained low (up to 55% for styrene aziridination). It was suggested that the active intermediate formed during the reaction was an Fev=NTs complex and that this complex would transfer the NTs moiety to the alkene [91-93]. However, the catalytic performance was hampered by the rapid iron-catalyzed decomposition of PhI=NTs into iodobenzene and sulfonamide. Other reports on aziridination reactions with iron porphyrins or corroles and nitrene sources such as bromamine-T or chloramine-T have been published [94], An asymmetric variant was presented by Marchon and coworkers [95]. Biomimetic systems such as those mentioned above will be dealt with elsewhere. 

Aviv and Gross developed an interesting insertion reaction of diazo compounds into a secondary amine-hydrogen bond in the presence of Fe-corrole complexes (Scheme 7.8) [12], Competition experiments performed in the presence of an amine and an alkene revealed the N—H-insertion reaction to be much faster than the cyclopropanation of the C=C bond. Apart from this chemoselectivity issue, the reactions are characterized by their very short reaction times most insertion reactions were completed within 1 min at room temperature. Most recently, Woo s group reported on a similar process using commercially available iron tetraphenyl-porphyrin [Fe(TPP)] dichloride [13]. 

Another procedure is the reaction of corrole with metal carbonyls in noncoordinating solvents such as toluene or benzene. Thus Mn2(CO)10, Fe(CO)5 and [Rh(CO)2Cl]2 lead to the formation of the corresponding metal3 + complexes. Also in this method the presence of an axial ligand is essential for the isolation of Rh3+ correlates [21, 24],... 

Zn2+ correlate can be obtained, as pyridinium salt, by reaction of corrole with zinc acetate in pyridine [25] in a procedure similar to that reported for the preparation of nickel and palladium complexes of corrole [11]. The zinc derivative is not paramagnetic and its formulation has been made on the basis of its proton NMR spectrum. Attempts to isolate the neutral zinc complex have been unsuccessful. 

The stabilizing effect of an axial ligand has been previously observed in the synthesis of cobalt corrolates. Such an effect has been used to synthesize the complex where no peripheral p substituents are present on the macrocycle, which decomposes if attempts are made to isolate it in the absence of triphenyl-phosphine [10]. The behavior of rhodium closely resembled that of cobalt and it seems to be even more sensitive to the presence of axial ligands. [Rh(CO)2Cl]2 has also used as a metal carrier with such a starting material a hexacoordinated derivative has been isolated. The reaction follows a pathway similar to that observed for rhodium porphyrinates the first product is a Rh+ complex which is then oxidized to a Rh3+ derivative [29]. 

The mechanism of cyclization has been investigated several times in the past [8]. It is catalyzed by the presence of a base the first step of the reaction is, in fact, the formation of a green dihydrobilin free base. Visible light can then furnish the necessary energy for cyclization. Otherwise, once the dihydrobilin free base is formed, coordination of a metal ion achieves the correct geometry for cyclization. The metal exerts a template action in holding the reactive sites in proximity. The participation of the metal in the cyclization process is demonstrated by the fact that metal free corrole has been isolated as reaction product when Cr or Ru salts have been used, but no light was needed for the reaction to occur [24]. 

Four different synthetic procedures have been examined for the preparation of the triphenyl derivative, the fourth one suggested by the synthetic conditions developed to obtain the diphenyl derivatives. In the first three procedures it has been impossible to isolate the triphenyl-dihydrobilin. Its formation has been demonstrated, however, by monitoring the electronic spectrum of the reaction mixture and the cyclization to corrole has been carried out in situ. The synthesis that gave the highest yield (20%) and that avoids tedious purification procedures is outlined in Fig. 10. It involved the acidic condensation of benzaldehyde with two equivalents of 3,3, 4,4 -tetramethyl-meso-phenyl-dipyrromethane-5,5 ... 

The cobalt atom is essential to drive the reaction towards the formation of the corrole ring other metals, such as Mn, Fe or Rh, in similar conditions give the expected meso-tetraphenyl-octamethylporphyrin in a mixture with its metal complexes. 

The synthesis of cobalt meso-diphenyl corrolates has also been reported [31]. The synthetic procedure involves the acidic condensation of 3,4-dimethyl-2-(a-hydroxybenzyl)pyrrole-5-carboxylic acid with 3,3, 4,4 -tetramethyl dipyrro-methane, followed by reaction with cobalt salts. The reaction afforded a mixture of two isomers Co(5,15-OMDPC)PPh3 and Co(5,10-OMDPC)PPh3. The formation of this latter isomer has been explained by the high tendency of self condensation of the starting pyrrole under the reaction conditions, 2-(a-hydroxybenzyl)meso-phenyl dipyrromethane can be formed. This species would afford the Co(5,10-OMDPC)PPh3 by further condensation with the dipyrromethane unit present in excess in the reaction mixture. 

It is well known that the oxidation state of the cobalt atom changes in the enzymatic B12 dependent reactions. The redox chemistry of cobalt corrinoids received a great deal of attention in the seventies. The Co3 +/Co2 + reaction of different corroles was investigated in the past although no mechanistic details have been reported. The resulting chemistry has already been reviewed [11]. 

The reduction peaks do not vary if the electrochemistry is carried out in the presence of excess PPh3. It is known that Co2+ porphyrinates can coordinate donor molecules along the z axis and the lack of occurrence of such reaction in the case of corroles has been attributed to the negative charge of the electrogenerated Co2+ complex. 

The first example reported in the literature is the cyclization of dihydrobilin to octadehydrocorrin [51-54]. The reaction is catalyzed by the presence of nickel or cobalt salts. As in the case of corrole and its metal complexes such ring closure reaction has been carried out in alcoholic solution, it is oxidative and base catalyzed. It has been demonstrated that the formation of the corrin ring is part of an equilibrium where the oxidative ring closure is coupled with a reductive ring opening reaction [55]. 

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