Corroles, cobalt

The cobalt corroles are as expected isolated as neutral cobalt(III) complexes with an additional neutral axial ligand, which in most cases is triphenylphosphane or pyridine. 

Subsequent investigations were undertaken of cobalt corroles with modified structures [77] and with cobalt in higher oxidation states [78]. In addition, cobalt-containing corrole dimers were studied [79], cobalt biscorroles were investigated ]80, 81], the influence of various alkyl and aryl substituents on the electrochemical behavior of cobalt corroles was probed ]82], and the effects of solvents on the electrochemistry of these compounds was examined [83]. 

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]. 

Table 9. Electronic spectra of cobalt corrolates. According to Refs. [30, 31]...

The effect of peripheral substituents in the -NMR spectra of diamagnetic corrolates has been discussed for Co(OMC)PPh3 and the series of meso mono-, di- and triphenyl cobalt corrolates [30, 31]. 

Data relative to the 400 MHz H-NMR spectra of cobalt corrolates are reported in Table 16. The strong shift due to the macrocycle ring current demonstrates that the presence of the meso-phenyl substituents does not cause the loss of aromaticity. The meso-protons of the monophenyl derivative resonate at the same chemical shift value observed for the meso-unsubstituted complex. 

On the basis of spectroelectrochemistry it has been proposed that cobalt corrolate is reduced with a mechanism similar to that occurring in the case of cobalt porphyrinates as shown in Fig. 22 where the cyclic voltammograms in the four non-aqueous solvents investigated are also shown. 

Trivalent cobalt corroles may also be prepared from dideoxybiladienes-ac as... 

Cobalt(III) corroles can also be prepared from the free-base macrocycle. The first reported example of this came from Johnson and Kay in 1965. In this report, 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole 2.6 was treated with Co(OAc)2 in pyridine. The cobalt complex reportedly isolated was formulated as the cobaltic complex represented by structure 2.164 (Scheme 2.1.46). Johnson and Kay further reported in 1965 that heating this complex in methanol afforded a somewhat unstable pyridine-free cobaltous corrole (e.g., 2.165) for which no structure was offered. Treating this supposed cobaltous corrole with pyridine regenerated the cobaltic corrole 2.164. 

A diaxial, bis-pyridine ligation mode was also put forward for the cobalt corrole 2.166 (Figure 2.1.9). This complex, which was reported in 1971, was obtained... 

In 1974, Hush and Woolsey reported that treating the cobalt(II) corrole species discussed above with pyridine induced little in the way of spectral changes. These authors took this as an indication that the divalent cobalt corrole complex in question shows little or no tendency towards axial coordination. In 1978, however, Murakami, et al. reported a different result, stating that one pyridine molecule does in fact coordinate axially to the cobalt center of an anionic Co(II) corrole. 

Iron and Cobalt Corroles High-Valent or Non-innocent . 60... 

Monomeric Cobalt Corroles High-Valent and Covalent... 

Cobalt Corrole-Corrole and Porphyrin-Corrole Dimers... 

Conlon M, Johnson AW, Overend WR, Rajapaksa D, Elson CM (1973) Structure and reactions of cobalt corroles. J Chem Soc Perkin Trans 2281-2288... 

Murakami Y, Yamada S, Matsuda Y, Sakata K (1978) Transition-metal complexes of pyrrole pigments XV coordination of pyridine bases to the axial sites of cobalt corroles. Bull Chem Soc Jpn 51 123-129... 

Will S, Lex J, Vogel E, Adamian VA, Caemelbecke EV, Kadish KM (1996) Synthesis, characterization, and electrochemistry of o-bonded cobalt corroles in high oxidation state. Inorg Chem 35 5577-5583... 

Chattopadhyay P, Matsuo T, Tsuji T, Ohbayashi J, Hayashi T (2011) Thermal isomerization of A-bridged cobalt corrole complexes through a transiently formed axial carbenoid. Organometallics 30 1869-1873... 

Kadish KM, Shen J, Fremond L, Chen P, El Ojaimi M, Chkounda M, Gros CP, Barbe JM, Ohkubo K, Fukuzumi S, Guilard R (2008) Clarification of the oxidation state of cobalt corroles in heterogeneous and homogeneous catalytic reduction of dioxygen. Inorg Chem 47 6726-6737... 

Huang H-C, Shown I, Chang S-T, Hsu H-C, Du H-Y, Kuo M-C, Wong K-T, Wang S-F, Wang C-H, Chen L-C, Chen K-H (2012) Pyrolyzed cobalt corrole as a potential non-precious catalyst for fuel cells. Adv Func Mater 22(16) 3500-3508... 

The observed g value (2.0032) of the singly oxidized cobalt corrole, obtained by the chemical oxidation of (F5PhMes2Cor)Co with one equivalent of... 

Properties and Reactions.—Physicochemical studies of axial ligation of pyridine to cobalt corroles have been carried out/ and the kinetics and mechanism of cobalt-carbon bond cleavage in the alkylation of tin and mercury ions have also been studied. The mechanism of action of the vitamin coenzyme has been reviewed/ and several studies of the mechanism of cobalt-carbon bond cleavage and isomerization reactions of the model cobalt cobaloxime system have been published. ... 

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