Templated Total Synthesis of Cu(I)-Methanobactin OB3b.

Methanobactin OB3b (Mbn-OB3b) is a unique natural product with stunning affinity for copper ions (Ka ≈Cu(I) 1034 ). Here, we report the first total synthesis of Cu(I)-bound methanobactin OB3b featuring as key transformations a cyclodehydration-thioacylation sequence, to generate the conjugated heterocyclic systems, and a copper-templated cyclization, to complete the caged structure of the very sensitive target compound.

Activating a [FeFe] Hydrogenase Mimic for Hydrogen Evolution under Visible Light.

Inspired by the active center of the natural [FeFe] hydrogenases, we designed a compact and precious metal-free photosensitizer-catalyst dyad (PS-CAT) for photocatalytic hydrogen evolution under visible light irradiation. PS-CAT represents a prototype dyad comprising π-conjugated oligothiophenes as light absorbers. PS-CAT and its interaction with the sacrificial donor 1,3-dimethyl-2-phenylbenzimidazoline were studied by steady-state and time-resolved spectroscopy coupled with electrochemical techniques and visible light-driven photocatalytic investigations. Operando EPR spectroscopy revealed the formation of an active [FeI Fe0 ] species-in accordance with theoretical calculations-presumably driving photocatalysis effectively (TON≈210).

Iron(0)-Mediated Stereoselective (3+2)-Cycloaddition of Thiochalcones via a Diradical Intermediate.

Reactions of α,ß-unsaturated aromatic thioketones 1 (thiochalcones) with Fe3 (CO)12 leading to η4 -1-thia-1,3-diene iron tricarbonyl complexes 2, [FeFe] hydrogenase mimics 3, and the thiopyrane adduct 4 are described. Obtained products have been characterized by X-ray crystallography and by computational methods. Completely regio- and diastereoselective formation of the five-membered ring system in products 3, containing four stereogenic centers, can be explained by an unprecedented, stepwise (3+2)-cycloaddition of two thiochalcone molecules mediated by Fe3 (CO)12 . Quantum chemical calculations aimed at elucidation of the reaction mechanism, suggest that the formal (3+2)-cycloaddition proceeds via sequential intramolecular radical transfer events upon homolytic cleavage of one carbon-sulfur bond leading to a diradical intermediate.

NMP makes the difference - facilitated synthesis of [FeFe] hydrogenase mimics.

To overcome the limitations of high reaction temperatures and long reaction times of conventional synthesis routes towards [FeFe] hydrogenase (H2ase) mimicking complexes, we introduced a more efficient synthesis route in the presence of aprotic polar co-solvents such as N-methyl-2-pyrrolidone (NMP). Versatile (di)thiol or disulfide ligands as well as selenium and tellurium analogues were converted to their corresponding complexes. While both reaction times and temperatures were reduced significantly, yields could be increased. Intensive kinetic monitoring of the formation of two [FeFe] H2ase mimics via UV-vis spectroscopy was performed, revealing an increase of the rate constant by one order of magnitude compared to that obtained in the same reaction without NMP. IR spectroscopic examination of the formation of the 1,3-propandithiole analogue (2a) revealed the appearance of a side product, analyzed by IR and UV-vis spectroscopy and mass spectrometry, which was proposed to be a NMP monosubstituted triirondodecacarbonyl (Fe3(CO)11NMP) cluster. Reacting triirondodecacarbonyl (Fe3(CO)12) with NMP in the absence of any additional ligand yielded this species as well. Quantum chemical simulations of Fe3(CO)11NMP indicated structural rearrangements including the omission of bridging carbonyls (µ-CO). Similar observations were made on utilizing other aprotic polar co-solvents.