Iron complexes corroles

Addition of chloride anion to the ligand-free (i.e., four coordinate) iron(III) corrole leads to a complex with chloride coordinated apically to the iron center. To... 

Several other examples of metal(III) corroles prepared from free-base corroles have been reported. The first of these was the iron(III) corrole derivative 2.172. This complex was originally prepared in 1973 as the result of treating the free-base corrole 2.6 with phenyllithium in THF, followed by FeCl2 (Scheme 2.1.49). This same complex was later prepared from corrole 2.6 by reacting it with FeCl2 in the presence of pyridine. In both cases, the initially bound iron(II) center undergoes spontaneous oxidation (to iron(III)) during the reaction and/or workup. 

Recently, Vogel, et al. have described the synthesis of what may formally be considered as being an iron(IV) corrole. It was obtained as the result of a sequence of reactions that involved first treating octaethylcorrole 2.81 with Fc2(CO)9, followed by air. The intermediate p-oxo-iron(IV) dimer (2.175) that results was then, as the second step in the sequence, treated with HCl. This cleaves the dimer to form the iron(IV) corrole(Cl) monomer 2.176. This product can be treated with PhMgBr to afford the iron(IV) corrole complex 2.177 containing an axial phenyl substituent (Scheme 2.1.54). 

Single crystal X-ray diffraction studies of each of the above iron(III) and iron(IV) corrole complexes (2.175-2.178) showed that in each case the corrole macrocycles are nearly planar. In the case of both the iron(III) corrole 2.178 (Figure 2.1.11) and the a-phenyl iron(IV) corrole 2.177, the iron atom was found to lie 0.27 A above the mean plane of the macrocycle. The structures of the iron(IV) corrole species 2,175 (Figure 2.1.12) and 2.176, on the other hand, revealed the iron atom as being c. 0.40 A above the mean macrocycle plane. 

The conclusion that the cobalt and iron complexes 2.182 and 2.183 are formally TT-radical species is supported by a wealth of spectroscopic evidence. For instance, the H NMR spectrum of the cobalt complex 2.182 indicated the presence of a paramagnetic system with resonances that are consistent with the proposed cobalt(III) formulation (as opposed to a low-spin, paramagnetic cobalt(IV) corrole). Further, the UV-vis absorption spectrum recorded for complex 2.182 was found to be remarkably similar to those of porphyrin 7r-radicals. In the case of the iron complex 2.183, Mdssbauer spectroscopy was used to confirm the assignment of the complex as having a formally tetravalent metal and a vr-radical carbon skeleton. Here, measurements at 120 K revealed that the formal removal of one electron from the neutral species 2.177 had very little effect on the Mdssbauer spectrum. This was interpreted as an indication that oxidation had occurred at the corrole ligand, and not at the metal center. Had metal oxidation occurred, more dramatic differences in the Mdssbauer spectrum would have been observed. 

Oxidations of metallocorroles have also been investigated by Vogel and co-workers." For instance, these researchers found that treatment of a-phenyl-cobalt(III) corrole 2.182 with Fe(C104)3 resulted in oxidation to cation 2.191 (Scheme 2.1.64). They also found that iron(III) salts could be used to effect oxidation of nitrosyl iron(III) corrole 2.192. In this case, however, it was a ic-cation radical species (i.e., 2.193), which was obtained upon by treatment with, for instance, iron(III) chloride (Scheme 2.1.65)." Similar oxidations of tetravalent complexes have also been carried out by Vogel and coworkers (see Scheme 2.1.60)." ... 

Metal-catalysts that enable the direct transfer of an Ni-moiety from chloramine-T to alkenes with moderate efficiencies include metalloporphyrinoids. For example, in 2001, Simkhovich and Gross reported that iron (IV) corrole 21 (Scheme 2.29) catalyzed olefin aziridination with chloramine-T [44]. The use of porphyrine complexes of iron [Fe(TPP)Cl] and cobalt [Co(TDClPP)] in the presence of bromamine-T also allows for aziridinating a wide variety of alkenes [45,46]. A recyclable polymer-supported manganese (II) complex, which is readily prepared from chloromethy-lated poly(styrene-divinylbenzene) (PS-DVB) in two steps, transfers an Ni unit from bromamine-T to aliphatic alkenes in a heterogeneous system [47]. 

Similarly, the corresponding nickel complex, based on ESR spectroscopy, should be formulated as a nickel(II) corrole-71-radical. The iron corroles exist in the oxidation state + 111 or + IV depending on the nature of additional axial ligands. 

Corroles are porphyrins which lack the 20-methine group. (7,13-dimethyl-2,3,8,12,17,18-hexa-ethylcorrolato)iron chloride reacts with cyanide to form a low-spin dicyano complex, which is subsequently reduced by excess of cyanide to give (152). The iron in the dicyano complex is still in the 3+ oxidation state, with the reduced correlate as a dinegative radical ligand. ... 

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]. 

The iron porphyrins and related compounds constitute an extremely important class of coordination complex due to their chemical behaviour and involvement in a number of vital biological systems. Over recent years a vast amount of work on them has been published. Chapter 21.1 deals with the general coordination chemistry of metal porphyrins, hydroporphyrins, azaporphyrins, phthalocyanines, corroles, and corrins. Low oxidation state iron porphyrin complexes are discussed in Section 44.1.4.5 and those containing nitric oxide in Section 44.1.4.7, while a later section in this chapter (44.2.9.2) is mainly concerned with iron(III) and higher oxidation state porphyrin complexes. Inevitably however, a considerable amount of information on iron(II) complexes is contained in that section as well as in Chapter 21.1. Therefore in order to prevent excessive duplication, the present section is restricted to highlighting some of the more important aspects of the coordination chemistry of the iron(II) porphyrins while the related unusually stable phthalocyanine complexes are discussed in the previous section. 

Abstract The transition metal complexes of the non-innocent, electron-rich corrole macrocycle are discussed. A detailed summary of the investigations to determine the physical oxidation states of formally iron(IV) and cobalt(IV) corroles as well as formally copper(III) corroles is presented. Electronic structures and reactivity of other metallocorroles are also discussed, and comparisons between corrole and porphyrin complexes are made where data are available. The growing assortment of second-row corrole complexes is discussed and compared to first-row analogs, and work describing the synthesis and characterization of third-row corroles is summarized. Emphasis is placed on the role of spectroscopic and computational studies in elucidating oxidation states and electronic configurations. 

Abu-Omar MM (2011) High-valent iron and manganese complexes of corrole and porphyrin in atom transfer and dioxygen evolving catalysis. Dalton Trans 40 3435-3444... 

Murakami Y, Aoyama Y, Hayashida M (1980) Hydroxide-promoted reduction of the corrole complexes of cobalt(III) and iron(III) in the presence of olefin. J Chem Soc Chem Comm 501-502... 

Simkhovich L, Galili N, Saltsman I, Goldberg I, Gross Z (2000) Coordination chemistry of the novel 5,10,15-tris(pentafluorophenyl)corrole synthesis, spectroscopy, and structural characterization of its cobalt(III), rhodium(III), and iron(IV) complexes. Inorg Chem 39 2704-2705... 

Simkhovich L, Mahammed A, Goldberg I, Gross Z (2001) Synthesis and characterization of germanium, tin, phosphorous, iron and rhodium complexes of tris(pentafluorophenyl)corrole, and the utilization of the iron and rhodium corroles as cyclopropanation catalysts. Chem Eur J 7 1041-1055... 

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