Porphyrin-corrole dimers

The synthesis of the corrole-porphyrin pseudo-dimers 2.256a and 2.256b was also described by Paolesse and coworkers. These chimerical systems were prepared... 

The coordination chemistry of second-row transition metal corroles is less extensive than for first-row metals, but there are now numerous examples. The synthesis of brick red (oxo)Mo(mec) (mec = 2,3,17,18-tetramethyl-7,8,12,13-tetraethylcorrolate) was reported in a 1977 letter [63]. The first Ru corrole was synthesized as a cofacial Ru(III)-Ru(III) dimer in 2000 [64] the synthesis of a monomeric Ru corrole was achieved in 2003 [65]. A dicarbonylrhodium(I) A -me thy I corrole complex, where Rh(I) is bound to two of the ring nitrogen atoms, was reported in 1976 [66], while the synthesis of a Rh(III) corrole was published a dozen years later [67]. A series of Ag(III) corroles was described in 2003 [68]. This oxidation state assignment was supported by an X-ray photoelectron spectroscopy (XPS) comparison to cationic Ag(III) porphyrin complexes. 

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

It was observed in a 2005 article that Co(II) porphyrin-Co(III) corrole dimers are more effective dioxygen reduction electrocatalysts than analogous Co(III)-Co(III) corrole dimers or monomeric Co(III) corroles [145], The heterodimers operated effectively at lower overpotentials and promote complete reduction to water (the average number of electrons transferred per 02 molecule approaches 4 in the best porphyrin-corrole catalyst). It was suggested that the inferior catalytic performance of the corrole homodimers could be due to a reduction in the basicity of the activated intermediate when two Co(III) moieties are involved, leading to a less favorable 4-electron reduction. Heterobimetallic catalysts containing formally Co (IV) corroles were also examined as potential dioxygen reduction catalysts [146]. 

While the Co corrole-Fe/Mn porphyrin dyads were active electrocatalysts, the homobimetallic Co porphyrin-corrole dyads operate at lower overpotentials and favor 4-electron reduction to a greater extent. This was attributed to the locus of reduction in each complex apparently, the porphyrin is reduced first in the homometallic dimer, whereas the corrole is the site of the first reduction in the heterometallic dimers. A later article presented EPR and spectroelectrochemical evidence supporting the assignment of a Co(III) Ji-cation electronic configuration for the oxidized derivatives of monomeric Co triarylcorrolates, suggesting that the dimeric five-coordinate Co corrole catalysts are also Co(III) 7i-cation radicals [147]. Further study is needed to elucidate this point. 

Instead of using classical porphyrins, Verma and coworkers employed analogs of corroles to synthesize meso-meso corrole analog dimers (Fig. 22a) [167]. These dimers were prepared using AgOTf or FeCls as the chemical oxidant and isolated in about 90 % yield. Moreover, Osuka and coworkers also performed the synthesis of a (5-P dimer of A-fused porphyrins using AgOCOCFs as the chemical oxidant, with a yield of 61 % (Fig. 22b) [125]. 

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