Electrochemistry and Spectroelectrochemistry of Bismanganese Porphyrin-Corrole Dyads

Abstract

A series of homobimetallic manganese cofacial porphyrin-corrole dyads were synthesized and investigated as to their electrochemistry, spectroelectrochemistry, and ligand binding properties in nonaqueous media. Four dyads were investigated, each of which contained a Mn(III) corrole linked in a face-to-face arrangement with a Mn(III) porphyrin. The main difference between compounds in the series is the type of spacer, 9,9-dimethylxanthene, anthracene, dibenzofuran, or diphenylether, which determines the distance and interaction between the metallomacrocycles. Each redox process of the porphyrin-corrole dyads was assigned on the basis of spectroscopic and electrochemical data and by comparison with reactions and properties of the monocorrole and the monoporphyrin which were examined under the same solution conditions. The Mn(III) porphyrin part of the dyad undergoes two major one-electron reductions in pyridine and benzonitrile, the first of which involves a Mn(III)/Mn(II) process and the second the addition of an electron to the conjugated π-ring system of the macrocycle. The Mn(III) corrole part of the dyads also exhibits two major redox processes, one involving Mn(III)/Mn(II) and the other Mn(III) to Mn(IV) under the same solution conditions. The potentials and reversibility of each electron transfer reaction were shown to depend upon the solvent, type of spacer separating the two macrocycles, and the presence or absence of axial ligation, the latter of which was investigated in detail for the case of acetate ion which was found to bind within the cavity of the dyad to both manganese centers, both before and after the stepwise electroreduction to the Mn(II) forms of the two macrocycles. An intramolecular chloride ion exchange between the porphyrin part of the dyads which contain Mn(III)Cl and the singly oxidized corrole in the dyad is observed after the Mn(III)/Mn(IV) reaction of the corrole, suggesting that chloride is coordinated inside the cavity in the neutral compound.

Solvent and Anion Effects on the Electrochemistry of Manganese Dipyrrin-Bisphenols

“…The quasireversible (slow) electron transfer for the Mn III/II reduction process in CH 2 Cl 2 and C 2 H 4 Cl 2 (as indicated by a Δ E p ≫ 60 mV and the lack of a well-defined reoxidation) and the faster electron transfer for the first oxidation under the same solution conditions (Δ E p = 80 to 100 mV) is consistent with not only the different sites of electron transfer (i.e., a ligand-centered oxidation and a metal-centered reduction) as assigned above but also the possible presence of a coupled chemical reaction on reduction. The larger Δ E p value associated with a slow metal-centered reduction is also consistent for what has been reported for the Mn III/II process of many porphyrins − and also other Mn III macrocycles. − …”

“…A summary of the measured oxidation and reduction potentials for (Ph)DPPMn in these solvents containing 0.1 M TBAPF6 is given in Table 2 and examples of cyclic voltammograms are shown in Figure 5, where three types of current-voltage curves are seen for reduction. The first is in CH2Cl2 and C2H4Cl2 where the reduction peak is broad and no clear reoxidation peak is observed, perhaps due to the formation of dimers in solution as seen in the solid state 10 and also in the gas phase as seen by the ESI-MS results in Figures S4 and S5 Mn III/II process of many porphyrins [38][39][40] and also other Mn III macrocycles. [41][42][43] It is also worth noting that, with the exception of CH2Cl2 and C2H4Cl2, the cathodic peak currents for the first reduction (ipc) are essentially the same as the anodic peak currents for the first oxidation (ipa), consistent with the same number of electrons transferred in each step.…”

“…It should also be noted that a dimerization detectable during reduction but not oxidation can be rationalized by the different sites of electron transfer; i.e., an electron is added to the manganese center during reduction, while electron abstraction takes place on the (Ar)­DPP ring during oxidation. It should also be noted that ring-centered redox processes are typically rapid (reversible) electron transfers, while Mn III -centered reductions would be slower as is often observed for Mn III reductions at the metal center. − ,− …”

“…It should also be noted that ring centered redox processes are typically rapid (reversible) electron 21 transfers while Mn III -centered reductions would be slower as is often observed for Mn III reductions at the metal center. [16][17][18][38][39][40][41][42][43] Figure 12. Cyclic voltammograms of (a) (Ph)DPPMn and (b) (Mes)DPPMn at 10 -3 M in CH2Cl2 containing 0.1 M TBAPF6 before and after the addition of 2.0 eq TFA.…”

Pacman Compounds: From Energy Transfer to Cooperative Catalysis

“…Dyads with one cobalt(III) corrole and a noncobalt containing porphyrin showed a poor selectivity towards water formation . Similarly, dimanganese porphyrin–corrole dyads and heterobimetallic (M)‐porphyrin–Co‐corrole dyads (with M=Fe, Mn; Figure ) showed only insufficient selectivities.…”