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

Abstract

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.