Corroles metallation

A. Mahammed, Z. Gross, Albumin-conjugated corrole metal complexes extremely simple yet very efficient biomimetic oxidation systems, J. Am. Chem. Soc., 2005, 127, 2883-2887. 

Epoxidation of alkenes with iodosylbenzene can be effectively catalyzed by the analogous salen or chiral Schiff base complexes of manganese(in), ruthenium(II), or ruthenium(III). For example, the oxidation of indene with iodosylbenzene in the presence of (/ ,5)-Mn-salen complexes as catalysts affords the respective (15,2/ )-epoxyindane in good yield with 91-96% ee [704]. Additional examples include epoxidation of alkenes with iodosylbenzene catalyzed by various metalloporphyrins [705-709], corrole metal complexes, ruthenium-pyridinedicarboxylate complexes of terpyridine and chiral bis(oxazoUnyl)pyridine [710,711]. 

Metallocorroles (M = Cu, Ni or Pd) can also be alkylated under the same conditions as the metal-free corroles23,24 to give the N2i-alkylated products together with a small amount of C3 alkylated product ( f = Pd). Allyl halides or bulky alkyl halides react with nickel corroles also at the 3-position. 

Licoccia S, Paolesse R (1995) Metal Complexes of Corroles and other Corrinoids. 84 71-134 Lin Z, Fan M-F (1997) Metal-Metal Interactions in Transition Metal Clusters with n-Donor Ligands. 87 35-80... 

The simple porphyrin category includes macrocycles that are accessible synthetically in one or few steps and are often available commercially. In such metallopor-phyrins, one or both axial coordinahon sites of the metal are occupied by ligands whose identity is often unknown and cannot be controlled, which complicates mechanistic interpretation of the electrocatalytic results. Metal complexes of simple porphyrins and porphyrinoids (phthalocyanines, corroles, etc.) have been studied extensively as electrocatalysts for the ORR since the inihal report by Jasinsky on catalysis of O2 reduction in 25% KOH by Co phthalocyanine [Jasinsky, 1964]. Complexes of all hrst-row transition metals and many from the second and third rows have been examined for ORR catalysis. Of aU simple metalloporphyrins, Ir(OEP) (OEP = octaethylporphyrin Fig. 18.9) appears to be the best catalyst, but it has been little studied and its catalytic behavior appears to be quite distinct from that other metaUoporphyrins [CoUman et al., 1994]. Among the first-row transition metals, Fe and Co porphyrins appear to be most active, followed by Mn [Deronzier and Moutet, 2003] and Cr. Because of the importance of hemes in aerobic metabolism, the mechanism of ORR catalysis by Fe porphyrins is probably understood best among all metalloporphyrin catalysts. 

Figure 18.13 Chemical structures of selected cofacial strapped diporphyrins (a), pillared diporphyrins (h), and pillared porphyrin/corrole, dicorrole, and diphthalocyanine derivatives (c) whose metal complexes have heen studied as ORR catalysts. Conventional notations for the structures are also hsted (in bold). Other molecular architectures of cofacial porphyrins are known, hut the corresponding complexes have not yet been studied as ORR catalysts.

The seiectivities of metal complexes of cofacial porphyrinoids (porphyrins, corroles, and phthalocyanines) reported in the literature by mid-2007 are summarized in Fig. 18.15. The data are organized by the type of catalyst as well as in order of decreasing Mav Whereas ORR catalysis by certain cofacial porphyrins, such as (FTF4)Co2 and (DPY)Co2 (Y = a, B) has been smdied extensively by a number of groups, and the values of av are known with high degree of confidence, those for most other catalysts... 

Radish KM, Shao J, Ou Z, Zhan R, Burdet E, Barhe J-M, Gros CP, Guilard R. 2005. Electrochemistry and spectroelectrochemistry of heterobimetalUc porphyrin-corrole dyads. Influence of the spacer, metal ion, and oxidation state on the pyridine binding ability. Inorg Chem 44, 9023-9038. 

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. 

The corrole ring is not strictly planar in the metal-free form.238 Because of the steric repulsion between inner protons, pyrrole ring A is tilted out of the mean plane. According to 7t-electron distribution calculations the three inner protons are attached to N-21, N-22 and N-24.aa>... 

Usually corroles are metallated with metal salts or metal carbonyls (Scheme 76).239,243,244... 

The metallation of corrole with Rh(CO)2Cl 2 gives an isomeric mixture of Rh HjCorXCO) 244 According to an X-ray structure analysis of the N-23,N-24 complex (N2l-Mc,N22-H), the two CO molecules coordinate to the approximately square planar Rh atom on the same side of the corrole which is considerably distorted and serves as a bidentate ligand. The N-23.N-24 isomer may be thermally equilibrated with the N-21,N-23 isomer (Scheme 79). 

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). 

Metallation of dioxacorrole with Rh(CO)2Cl 2 gives a mono-Rh complex in which the monovalent rhodium atom is coordinated by two corrole nitrogens (Scheme S4).244... 

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... 

Corroles and corrinoids - For results on the noble metal complexes of this interesting class of tetrapyrroles, see the article by S. Licoccia in this volume [105]. 

A most interesting example of the corrinoid structure is corrole, a macrocycle where an 18 electron aromatic it system analogous to that of a porphyrin is maintained. Corrole has been shown to be a versatile ligand capable of coordinating transition and main group metals without significant distortion of the macrocycle plane. 

The present article reviews the developments of the chemistry of corrole and its metal complexes considering the synthetic procedures that can be followed in order to prepare such compounds, their spectroscopic characterization and redox reactivity and demonstrates the peculiar ligand field effect of this macrocycle. 

Despite such great interest, a question that is still unanswered is why modified tetrapyrrole ligands, like those found in factor F430 and vitamin B12, are employed by natural systems to carry out specific chemistry rather than the porphyrin ligand. A possible explanation that has been proposed [1, 2] is that these modified tetrapyrrole ligands exhibit different flexibility as compared with porphyrins. Another very important factor, and probably the most important one in the case of corroles and corrinoids, is the difference in hole size between the various macrocycles. The tetrapyrrole that would most efficiently perform a specific function would be the one with the proper hole size for the radius of the metal ion involved in the process. 

The chemistry of corroles and their metal complexes has been reviewed by different authors in the past [7-11] and apart from necessary clarifications this paper will deal with the contributions to the chemistry of metallocorrolates and corrinoids published in the last ten years. 

The synthetic routes leading to corroles have been reviewed in the past [10]. The main procedure involves the cyclization of dihydrobilins either via a photochemical process or a metal assisted one. 

Because of its structure, corrole could be expected to stabilize the + 3 oxidation state for metal ions leading to the formation of neutral complexes. 

Several metal ions have been reacted with corroles or IV-alkylcorroles but, until 1980, the only example of a fully characterized metal3 + complex of corrole was a Co3 + derivative for which a crystal structure has been determined [11], The formation of an Fe3+ derivative has also been reported but no detailed characterization of this complex has been carried out although it has been used in a catalytic application [18]. 

In the last ten years, several metal ions have been inserted into the corrole moiety leading to the Periodic Table of Metallocorrolates shown in Fig. 9. 

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],... 

---