Photoelectron spectroscopy of dithiolatodiironhexacarbonyl models for the active site of [Fe–Fe] hydrogenases: Insight into the reorganization energy of the “rotated” structure in the enzyme

[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.

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.

Hydrogen generation: aromatic dithiolate-bridged metal carbonyl complexes as hydrogenase catalytic site models

The design, syntheses and characteristics of metal carbonyl complexes with aromatic dithiolate linkers reported as bioinspired hydrogenase catalytic site models are described and reviewed. Among these the complexes capable of hydrogen generation have been discussed in detail. Comparisons have been made with carbonyl complexes having alkyl dithiolates as linkers between metal centers.

New insights into solvolysis and reorganization energy from gas-phase, electrochemical, and theoretical studies of oxo-Tp*Mo(V) molecules

Molecules of the general form Tp*MoO(OR)(2) [where Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate and (OR)(2) = (OMe)(2), (OEt)(2), and (O(n)Pr)(2) for alkoxide ligands and (OR)(2) = O(CH(2))(3)O, O(CH(2))(4)O, and O[CH(CH(3))CH(2)CH(CH(3))]O for diolato ligands] were studied using gas-phase photoelectron spectroscopy, cyclic voltammetry, and density functional theory (DFT) calculations to examine the effect of increasing ligand size and structure on the oxomolybdenum core. Oxidation potentials and first ionization energies are shown to be sensitive to the character of the diolato and alkoxide ligands. A linear correlation between the solution-phase oxidation potentials and the gas-phase ionization energies resulted in an unexpected slope of greater than unity. DFT calculations indicated that this unique example of a system in which oxidation potentials are more sensitive to substitution than vertical ionization energies is due to the large differences in the cation reorganization energies, which range from 0.2 eV or less for the molecules with diolato ligands to around 0.5 eV for the molecules with alkoxide ligands.