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

Abstract

A series of "N2O2-type" manganese dipyrrin-bisphenols (DPP), formulated as (Ar)DPPMn, where Ar = pentafluorophenyl (F5Ph), phenyl (Ph) or mesityl (Mes), were electrochemically and spectroscopically characterized in nonaqueous media with and without added anions in the form of tetrabutylammonium salts (TBAX where X = ClO4 -, PF6 -, BF4 -, F -, Cl -, OHor CN -). Two major one-electron reductions are observed under most solution condition, the first of which is assigned as a Mn III/II process and the second as electron addition to the π-ring system as confirmed by spectroelectrochemistry. Each Mn III complex also exhibits one or two one-electron oxidations, the exact number depending upon the positive potential limit of the electrochemical solvent. The two oxidations are separated by 580-590 mV in CH3CN, 0.1 M TBAPF6 and are assigned as π-ring centered electron transfers to stepwise form a (Ar)DPPMn III π-cation radical and dication under these solution conditions. Comparisons are made between redox properties of (Ar)DPPMn and manganese(III) porphyrins, corroles and corrolazines each of which contains an innocent trianionic complexing ligand. The redox behavior and spectroscopic properties of [(Ar)DPPMn] n where n = 0, -1 or +1 are also compared to that of other structurally related [(Ar)DPPM] n complexes under similar solution conditions where M = Co II , Cu II , B III or Au III .

Synthesis, Characterization, and Electrochemistry of Copper Dibenzoporphyrin(2.1.2.1) Complexes

“…In this regard, it should be pointed out that if complexes 1a−1c contained a single π system, the appropriate linear freeenergy relationship (LFER) would use 2σ (one for each meso substituent) and the resulting slopes would then be half that in Figure 8, values too small for typical ligand-centered electron transfers based on a large amount of published data involving LFERs of meso-substituted porphyrins, 26 corroles, 25,65 dipyrrins, 60,66 and related compounds. 67,68 The last point to address is the 2.7-fold increase in the reaction constant for the second reduction (ρ = 192 mV) as compared to the first reduction (ρ = 70 mV) in Figure 8. The simplest explanation for this difference is that the site of the second electron addition is close to the meso-phenyl ring of the second dipyrrin.…”

“…In this regard, it should be pointed out that if complexes 1a – 1c contained a single π system, the appropriate linear free-energy relationship (LFER) would use 2σ (one for each meso substituent) and the resulting slopes would then be half that in Figure , values too small for typical ligand-centered electron transfers based on a large amount of published data involving LFERs of meso -substituted porphyrins, corroles, , dipyrrins, , and related compounds. , …”

Electrocatalytic Hydrogen Evolution of Bent Bis(dipyrrin) Ni(II) Complexes

“… The substituent effect was investigated for the redox potentials of bis­(dipyrrin) Ni­(II) complexes using Hammett substituent constants (σ) (Figures b and S16). The three redox potentials in MeCN form a linear slope with ρ = 0.09 V (1st Ox), 0.08 V (1st Red), and 0.11 V (2nd Red), indicating a weak substituent effect in bis­(dipyrrin) Ni­(II) complexes. − …”

Corroles at work: a small macrocycle for great applications

“…105). [289][290][291] Dipyrrin-bisphenol is a tetradentate ligand, like corrole and porphyrin, and interestingly, its chemical structure can be seen as the combination of half a salen unit and half of a porphyrin macrocycle (Fig. 105).…”

“…105). What makes the dipyrrin-bisphenol ligand closer to a corrole (and not a porphyrin) is that it presents, like corrole, a formal À3 charge and this molecule is able to coordinate quite a large variety of nonmetal or metal ions such as boron, 292 manganese, 291 cobalt, 290 gold. 289 Dipyrrin-bisphenol is a 12 p-conjugated system with only one meso-position and 4 beta-pyrrolic positions.…”