Synthesis and Characterization of Bio‐Inspired Diiron Complexes and Their Catalytic Activity for Direct Hydroxylation of Aromatic Compounds

Abstract

Three [FeFe]‐hydrogenase model complexes [(μ‐dmedt){Fe(CO)3}2] [1; dmedt = SCH(CH3)CH(CH3)S], [(μ‐dmedt){Fe(CO)3}{Fe (CO)2PPh3}] (1‐PPh3), and [(μ‐dmest){Fe(CO)3}2] [1‐O; dmest = SCH(CH3)CH(CH3)S(O)], 1‐O were synthesized and characterized. These model complexes, which are generally used as the functional biomimics of the hydrogen‐producing dinuclear active site in [FeFe]‐hydrogenase, were used as efficient catalysts for the selective hydroxylation of aromatic compounds to phenols under mild conditions. Because both the dithiolato‐sulfur site and the Fe–Fe bond in the model complexes were possible active oxidation sites, DFT calculations were used to investigate the oxygenated products, that is, the S‐oxygenated products or the Fe‐oxygenated forms of the model complexes, which may be involved in the catalytic cycle. The experimental and computational results indicate that the thermodynamically favored Fe‐oxygenated intermediates dominate the hydroxylation of the aromatic compounds. A possible mechanism for the hydroxylation is also proposed.

A Functional Hydrogenase Mimic Chemisorbed onto Fluorine‐Doped Tin Oxide Electrodes: A Strategy towards Water Splitting Devices

“…Hydrogenases, metalloenzymes that utilize iron, diiron or iron–nickel as metallic components, are able to perform reversible proton reduction at ambient temperature and pressure with activities, efficiencies, and overpotentials that are comparable to platinum . It is thus not surprising that chemists take inspiration from nature to mimic the active site of these metalloenzymes to develop new classes of proton reduction catalysts . Although several hundreds of hydrogenase model systems have been reported to date, most have been studied as homogeneous catalysts in organic solvents .…”

Effect of the Terminal Ligands of [FeFe]‐Hydrogenase Model Complexes on Proton Reduction Properties and Catalytic Hydroxylation of Benzene

“…As shown in Figure S1 , the IR spectra of the two complexes were measured in CH 2 Cl 2 solution, the IR spectra data between 2076 and 1900 cm −1 are characteristic of the carbonyl absorption peaks of these two compounds. Displacement of CO‐group of complex 1 by strong donating ligands of 2‐fluoropyridine and 3‐fluoropyridine to prepare complex 2 and 3 . Complexes 2 and 3 have a higher electron density compared with the all‐carbonyl parental [FeFe]‐hydrogenase model complex 1 .…”

“…Hence, the study about the relationship between the reduction potential and complex structure is very meaningful. We chose the all‐carbonyl [FeFe]‐hydrogenase model complex (μ‐dmedt)Fe 2 (CO) 6 (dmedt=2,3‐butanedithiol) as the parent complex and introduced the structurally similar 2‐fluoropyridine and 3‐fluoropyridine ligands to synthesize two new [FeFe]‐hydrogenases model complexes 2 and 3 , respectively. A simple synthetic route of complexes 2 and 3 is shown in Scheme .…”

“…Electrochemical property tests demonstrated the relationship between the variable structure of these different complexes and related electrocatalytic properties. Moreover, preliminary works have discovered that the Fe−Fe bond based oxygenated μ‐O complex was capable of transferring oxygen atom to the aromatic substrates based on the DFT predicted results and the catalytic activity towards hydroxylation. The Fe−Fe bond electron density is closely related to the catalytic activity.…”

Synthesis, spectroscopic characterization, and crystal structures of diiron pentacarbonyl complexes with monosubstituted tris(3-chlorophenyl)phosphine or cyclohexyldiphenylphosphine ligands

“…It is generally accepted that phosphine ligands are good substitutes for the cyanide ligands found in the natural enzymes [10]. Recent studies on bridging dimethylethanedithiolate complexes have been reported in the literature [11,12], involving substitution of the parent complex [l-SCH(CH 3 )CH(CH 3 )S]Fe 2 (CO) 6 with PPh 3 or N-heterocyclic carbenes. The electrochemical properties and catalytic hydroxylation reactions of these complexes have also been studied.…”