Synthesis of Diiron(I) Dithiolato Carbonyl Complexes

Abstract

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.

Hydrogenase Enzymes and Their Synthetic Models: The Role of Metal Hydrides

“…216 Yet, in reality the latter are too stable, to the point that their oxidations are strongly anodic (e.g., E 1/2 ([ 4 ] +/0 ) = 0.65 V vs Fc +/0 ) 217 and their Brønsted basicities are low. As discussed above, a requirement of the [FeFe]- and [NiFe]-H 2 ases is their participation in both acid–base and redox at mild pH and potentials.…”

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

“…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 . Strategies to afford robust immobilization on conductive electrode surfaces, which are key for the development of devices, are relatively limited.…”

[FeFe]‐hydrogenase H‐cluster mimics mediated by mixed (S, Se) and (S, Te) bridging moieties: Insight into molecular structures and electrochemical characteristics

“…The active site of this system contains an organometallic Fe/S cluster, the so‐called H‐cluster (Figure A), that is, responsible for the hydrogen evolution reaction . Over the past few decades, several diiron dithiolato complexes that mimic the butterfly [Fe 2 S 2 ] sub‐unit of the H‐cluster have been synthesized and tested as electrocatalysts . Moreover, these complexes have been modified to contain heavier chalcogen donor atoms such as selenium or tellurium instead of sulfur .…”