Steering acidic oxygen reduction selectivity of single-atom catalysts through the second sphere effect.

Natural enzymes feature distinctive second spheres near their active sites, leading to exquisite catalytic reactivity. However, incumbent synthetic strategies offer limited versatility in functionalizing the second spheres of heterogeneous catalysts. Here, we prepare an enzyme-mimetic single Co-N atom catalyst with an elaborately configured pendant amine group in the second sphere via 1,3-dipolar cycloaddition, which switches the oxygen reduction reaction selectivity from the 4e to the 2e pathway under acidic conditions.

Diiron Complexes with Rigid and Conjugated S-to-S Bridges for Electrocatalytic Reduction of CO.

Electroreduction of CO to value-added low-carbon chemicals is a promising way for carbon neutrality and CO utilization. It was found that the diiron complex [(μ-bdt)Fe(CO)] (bdt = benzene-1,2-dithiolate) has high catalytic activity for electrocatalytic CO reduction. To further study the effect of the S-to-S bridge on the catalytic performances of diiron complexes for electrochemical CO reduction, four diiron complexes - with different rigid and conjugated S-to-S bridges were either selected or designed.

Photocatalytic H production using a hybrid assembly of an [FeFe]-hydrogenase model and CdSe quantum dot linked through a thiolato-functionalized cyclodextrin.

It is a great challenge to develop iron-based highly-efficient and durable catalytic systems for the hydrogen evolution reaction (HER) by understanding and learning from [FeFe]-hydrogenases. Here we report photocatalytic H production by a hybrid assembly of a sulfonate-functionalized [FeFe]-hydrogenase mimic (1) and CdSe quantum dot (QD), which is denoted as 1/β-CD-6-S-CdSe (β-CD-6-SH = 6-mercapto-β-cyclodextrin). In this assembly, thiolato-functionalized β-CD acts not only as a stabilizing reagent of CdSe QDs but also as a host compound for the diiron catalyst, so as to confine CdSe QDs to the space near the site of diiron catalyst.

Effect of the S-to-S bridge on the redox properties and H activation performance of diiron complexes related to the [FeFe]-hydrogenase active site.

Three biomimetic models of the [FeFe]-hydrogenase active site, namely diiron dithiolates of [(μ-edt){Fe(CO)}{Fe(CO)(κ-PNP)}] (1, edt = ethane-1,2-dithiolate, PNP = PhPCHN(nPr)CHPPh), [(μ-bdtMe){Fe(CO)}{Fe(CO)(κ-PNP)}] (2, bdtMe = 4-methylbenzene-1,2-dithiolate), and [(μ-adtBn){Fe(CO)}{Fe(CO)(κ-PNP)}] (3, adtBn = N-benzyl-2-azapropane-1,3-dithiolate), were prepared and structurally characterized. These complexes feature the same PNP ligand but different S-to-S bridges. Influence of the S-to-S bridge on the electrochemical properties and chemical oxidation reactivity of 1-3 was studied by cyclic voltammetry and by in situ IR spectroscopy.

Effect of Bridgehead Steric Bulk on the Intramolecular C-H Heterolysis of [FeFe]-Hydrogenase Active Site Models Containing a P2N2 Pendant Amine Ligand.

A series of pendant amine-containing [FeFe]-hydrogenase models, [X(CH2S-μ)2{Fe(CO)3}{Fe(CO)(P2(Ph)N2(Bn))}] (1H, X = CH2; 2Me, C(CH3)2; 3Et, C(CH2CH3)2; and P2(Ph)N2(Bn) = 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) with different groups at the bridgehead carbon of the S-to-S linker were synthesized. The oxidations of these complexes as well as the reverse reduction reaction were studied by cyclic voltammetry and in situ IR spectroscopy. Regardless of the bridgehead steric bulk, all three complexes demonstrate intramolecular iron-mediated C(sp(3))-H bond heterolytic cleavage with the assistance of the pendant amine base within the chelating diphosphine ligand in the two-electron oxidation process.

The influence of a S-to-S bridge in diiron dithiolate models on the oxidation reaction: a mimic of the H(air)(ox) state of [FeFe]-hydrogenases.

Two-electron oxidation of a diiron complex (1) containing a bulky S-to-S bridge with an exocyclic carbonyl group affords [1(OH)](+), which replicates the coordination structure and electronic configuration of H(air)(ox), and the chemically reversible reaction between 1 and [1(OH)](+) mimics the bioprocess of interconversion of the inactive H(air)(ox) and the active Hred states of the [FeFe]-hydrogenases.