Crucial Roles of a Pendant Imidazole Ligand of a Cobalt Porphyrin Complex in the Stoichiometric and Catalytic Reduction of Dioxygen

Abstract

A cobalt porphyrin complex with a pendant imidazole base ([(L1)CoII]) is an efficient catalyst for the homogeneous catalytic two‐electron reduction of dioxygen by 1,1′‐dimethylferrocene (Me2Fc) in the presence of triflic acid (HOTf), as compared with a cobalt porphyrin complex without a pendant imidazole base ([(L2)CoII]). The pendant imidazole ligand plays a crucial role not only to provide an imidazolinium proton for proton‐coupled electron transfer (PCET) from [(L1)CoII] to O2 in the presence of HOTf but also to facilitate electron transfer (ET) from [(L1)CoII] to O2 in the absence of HOTf. The kinetics analysis and the detection of intermediates in the stoichiometric and catalytic reduction of O2 have provided clues to clarify the crucial roles of the pendant imidazole ligand of [(L1)CoII] for the first time.

A Cobalt(III) Corrole with a Tethered Imidazole for Boosted Electrocatalytic Oxygen Reduction Reaction

“…As shown in Figure 5a, the UV‐vis spectrum of 1 ‐ after reacting with O 2 is consistent with a Co III ‐superoxo species. [ 29,65 ] This result indicates that the reaction of O 2 with 1 ‐ gives 1 ‐superoxo. For the reduction of 2 , the bands at 383, 433, 584, and 607 nm were decreased, and new bands appeared at 420 and 564 nm (Figures 5b and S29b).…”

“…As shown in Figure 5, the EPR spectra of 1 ‐ and 2 ‐ both displayed eight‐line hyperfine spectral pattern under N 2 , confirming the formation of the Co II species. [ 64‐65 ] When O 2 was introduced into 1 ‐ , the different EPR signals revealed the formation of 1 ‐superoxo (Figure 5c). Notably, 2 ‐ cannot completely convert to 2 ‐superoxo under the same condition (Figure 5d).…”

Electrocatalytic oxygen reduction with cobalt corroles bearing cationic substituents

“…7,[16][17][18][19][20][21][22][23][24][25][26][27] Among the reported ORR catalysts, molecular complexes are of special interest because they are beneficial for obtaining a fundamental understanding of the structure-function relationships. 18,19,[28][29][30][31][32][33] In this regard, numerous molecular first-row transition metal complexes, including Mn, [34][35][36][37] Fe, [38][39][40][41] Co, [42][43][44][45] Ni [46][47][48] and Cu, [49][50][51][52] have been identified as active ORR electrocatalysts. In spite of these achievements, however, highly active and selective electrocatalysts for the 4e À ORR are still needed.…”

Dynamically Reversible Interconversion of Molecular Catalysts for Efficient Electrooxidation of Propylene into Propylene Glycol

“…As for the electrooxidation of propylene into PG, the generation of *OH and the transfer of *OH into the CC bond in propylene are both affected by the E B (*OH). , The strong E B (*OH) favors the dissociation of H 2 O into *OH, whereas the transfer of *OH to propylene would be impeded. , On the contrary, the weak E B (*OH) is beneficial to the combination of *OH and propylene but detrimental for *OH generation. , As such, the catalytic performance for propylene electrooxidation would be restricted due to the scaling relationship of the E B (*OH) over the conventional catalysts. If the electrocatalysts could undergo dynamically reversible interconversion during propylene electrooxidation, the scaling relationship of the E B for the specific intermediates could be effectively regulated. − Generally, molecular catalysts feasibly undergo configuration evolution due to the flexible interaction between the ligand and intermediates. − Therefore, regulating the dynamically reversible interconversion of molecular catalysts provides a promising pathway to promote the catalytic performance toward propylene electrooxidation.…”