Diiron models for active site of FeFe-hydrogenase with aromatic thiolate bridges: Structures and electrochemistry

[FeFe]-Hydrogenases: maturation and reactivity of enzymatic systems and overview of biomimetic models

[FeFe]-hydrogenases recieved increasing interest in the last decades. This review summarises important findings regarding their enzymatic reactivity as well as inorganic models applied as electro- and photochemical catalysts.

Biochemical and artificial pathways for the reduction of carbon dioxide, nitrite and the competing proton reduction: effect of 2nd sphere interactions in catalysis

Reduction of oxides and oxoanions of carbon and nitrogen are of great contemporary importance as they are crucial for a sustainable environment.

Electron-Rich, Diiron Bis(monothiolato) Carbonyls: C-S Bond Homolysis in a Mixed Valence Diiron Dithiolate

The synthesis and redox properties are presented for the electron-rich bis(monothiolate)s Fe₂(SR)₂(CO)₂(dppv)₂ for R = Me ([1]⁰), Ph ([2]⁰), CH₂Ph ([3]⁰). Whereas related derivatives adopt C₂-symmetric Fe₂(CO)₂P₄ cores, [1]⁰-[3]⁰ have C_s symmetry resulting from the unsymmetrical steric properties of the axial vs equatorial R groups. Complexes [1]⁰-[3]⁰ undergo 1e^- oxidation upon treatment with ferrocenium salts to give the mixed valence cations [Fe₂(SR)₂(CO)₂(dppv)₂]⁺. As established crystallographically, [3]⁺ adopts a rotated structure, characteristic of related mixed valence diiron complexes. Unlike [1]⁺ and [2]⁺ and many other [Fe₂(SR)₂L₆]⁺ derivatives, [3]⁺ undergoes C-S bond homolysis, affording the diferrous sulfido-thiolate [Fe₂(SCH₂Ph)(S)(CO)₂(dppv)₂]⁺ ([4]⁺). According to X-ray crystallography, the first coordination spheres of [3]⁺ and [4]⁺ are similar, but the Fe-sulfido bonds are short in [4]⁺. The conversion of [3]⁺ to [4]⁺ follows first-order kinetics, with k = 2.3 × 10^-6 s^-1 (30 °C). When the conversion is conducted in THF, the organic products are toluene and dibenzyl. In the presence of TEMPO, the conversion of [3]⁺ to [4]⁺ is accelerated about 10×, the main organic product being TEMPO-CH₂Ph. DFT calculations predict that the homolysis of a C-S bond is exergonic for [Fe₂(SCH₂Ph)₂(CO)₂(PR₃)₄]⁺ but endergonic for the neutral complex as well as less substituted cations. The unsaturated character of [4]⁺ is indicated by its double carbonylation to give [Fe₂(SCH₂Ph)(S)(CO)₄(dppv)₂]⁺ ([5]⁺), which adopts a bioctahedral structure.

Intramolecular stabilization of a catalytic [FeFe]-hydrogenase mimic investigated by experiment and theory

The mono-substituted complex [Fe2(CO)5(μ-naphthalene-2-thiolate)2(P(PhOMe-p)3)] was prepared taking after the structural principles from both [NiFe] and [FeFe]-hydrogenase enzymes. Crystal structures are reported for this complex and the all carbonyl analogue. The bridging naphthalene thiolates resemble μ-bridging cysteine amino acids. One of the naphthyl moieties forms π-π stacking interactions with the terminal bulky phosphine ligand in the crystal structure and in calculations. This interaction stabilizes the reduced and protonated forms during electrocatalytic proton reduction in the presence of acetic acid and hinders the rotation of the phosphine ligand. The intramolecular π-π stabilization, the electrochemistry and the mechanism of the hydrogen evolution reaction were investigated using computational approaches.

Direct synthesis of phenol by novel [FeFe]-hydrogenase model complexes as catalysts of benzene hydroxylation with H2O2

Compared the catalytic performance of complexes 1–3, the complex 2 has the highest phenol yield (24.6%) and phenol selectivity (92%), which has the highest electron densities of the catalytically active sites.

Synthesis of Diiron(I) Dithiolato Carbonyl Complexes

Virtually all organosulfur compounds react with Fe(0) carbonyls to give the title complexes. These reactions are reviewed in light of major advances over the past few decades, spurred by interest in Fe2(μ-SR)2(CO)x centers at the active sites of the [FeFe]-hydrogenase enzymes. The most useful synthetic route to Fe2(μ-SR)2(CO)6 involves the reaction of thiols with Fe2(CO)9 and Fe3(CO)12. Such reactions can proceed via mono-, di-, and triiron intermediates. The reactivity of Fe(0) carbonyls toward thiols is highly chemoselective, and the resulting dithiolato complexes are fairly rugged. Thus, many complexes tolerate further synthetic elaboration directed at the organic substituents. A second major route involves alkylation of Fe2(μ-S2)(CO)6, Fe2(μ-SH)2(CO)6, and Li2Fe2(μ-S)2(CO)6. This approach is especially useful for azadithiolates Fe2[(μ-SCH2)2NR](CO)6. Elaborate complexes arise via addition of the FeSH group to electrophilic alkenes, alkynes, and carbonyls. Although the first example of Fe2(μ-SR)2(CO)6 was prepared from ferrous reagents, ferrous compounds are infrequently used, although the Fe(II)(SR)2 + Fe(0) condensation reaction is promising. Almost invariably low-yielding, the reaction of Fe3(CO)12, S8, and a variety of unsaturated substrates results in C-H activation, affording otherwise inaccessible derivatives. Thiones and related C═S-containing reagents are highly reactive toward Fe(0), often giving complexes derived from substituted methanedithiolates and C-H activation.