Behavior of four anthracene-linked dimeric metalloporphyrins as electrocatalysts for the reduction of dioxygen

Abstract

Four new dimeric metalloporphyrins have been prepared in which the two porphyrin rings are linked by an anthracene bridge attached to meso positions. The electrocatalytic behavior of the diporphyrins toward the reduction of 02 at graphite electrodes has been examined for the following combination of metal centers: Co-Cu, Co-Fe, Fe-Fe, Fe-H2. The Co-Cu diporphyrin catalyzes the reduction of 02 to H202 but no further. The other three catalysts all exhibit mixed reduction pathways leading to both H202 and H20. However, the pathways that lead to H20 do not involve H202 as an intermediate. A possible mechanistic scheme is offered to account for the observed behavior.

Oxygen Activation Chemistry of Pacman and Hangman Porphyrin Architectures Based on Xanthene and Dibenzofuran Spacers

“…Seminal studies of Collman and Chang had already established that Pacman porphyrins containing late transition metals (e.g., Co). were effective electrocatalysts for the reduction of oxygen to water (54,55,63,64). The studies described below provide new mechanistic insights for the OÀ ÀO bond-breaking process, especially as it pertains to PCET reactivity.…”

“…1(a). These types of cofacial bisporphyrins containing either cobalt or iron are electrocatalysts for the reduction of dioxygen by two and four electrons (59)(60)(61)(62)(63)(64). Ruthenium and osmium cofacial bisporphyrin complexes reduce protons to dihydrogen (65), and dinitrogen by four and six electrons to generate hydrazine and ammonia (50,51,66), respectively.…”

Electrochemical Properties of a Porphyrin-Cobalt (II) Adsorbed on Silica–Titania–Phosphate Composite Surface Prepared by the Sol–Gel Method

“…UV-Visible spectra of nonmetallated SiTiP/TmPyP (A) and metallated SiTiP/CoTmPyP (B), suspended in liquid paraffin. solutions (5,(39)(40)(41)(42)(43)(44). In our case, when varying the solution pH between 1.6 and 6.8 the potential is only slightly changed staying between −0.22 and −0.29 V. Reduction of O 2 by the metal porphyrin on a rough electrode surface and that occurring on a very porous material surface can be quite different.…”

Metalloporphyrin Catalysts of Oxygen Reduction

“…In other cases, the reports are contradictory: for example, reported values of n av for a heterometallic complex, (DPA)CoFe, vary from 3.6 to 2, at the plateau of the first wave (the complex exhibits a voltammogram as in Fig. 18.10a) [Ni et al, 1987;Guilard et al, 1995]. As is the case for simple Fe and Co porphyrins, the catalytic performance of cofacial metalloporphyrins (and probably other porphyrinoids, although at present there are no data) appears to be quite sensitive to how the electrode surface was prepared and the catalyst deposited.…”

“…18.15). At least two hypotheses have been proposed: (i) polarization of the O-O bond in catalytic intermediates by the second ion (on an N -H moiety) acting as a Lewis acid [Collman et al, 1987[Collman et al, , 1994 and (ii) spatial positioning of H þ donors especially favorable for proton transfer to the terminal O atoms of coordinated O 2 [Ni et al, 1987;Rosenthal and Nocera, 2007]. To the best of my knowledge, neither hypothesis has yet been convincingly proven nor resulted in improved ORR catalysts.…”