Mononuclear manganese complexes as hydrogen evolving catalysts.

Molecular hydrogen (H) is one of the pillars of future non-fossil energy supply. In the quest for alternative, non-precious metal catalysts for hydrogen generation to replace platinum, biological systems such as the enzyme hydrogenase serve as a blueprint. By taking inspiration from the bio-system, mostly nickel- or iron-based catalysts were explored so far.

Mechanism of Diiron Hydrogenase Complexes Controlled by Nature of Bridging Dithiolate Ligand.

Bio-inorganic complexes inspired by hydrogenase enzymes are designed to catalyze the hydrogen evolution reaction (HER). A series of new diiron hydrogenase mimic complexes with one or two terminal tris(4-methoxyphenyl)phosphine and different μ-bridging dithiolate ligands and show catalytic activity towards electrochemical proton reduction in the presence of weak and strong acids. A series of propane- and benzene-dithiolato-bridged complexes was synthesized, crystallized, and characterized by various spectroscopic techniques and quantum chemical calculations.

Mitigating losses: how scientific organisations can help address the impact of the COVID-19 pandemic on early-career researchers.

Scientific collaborations among nations to address common problems and to build international partnerships as part of science diplomacy is a well-established notion. The international flow of people and ideas has played an important role in the advancement of the 'Sciences' and the current pandemic scenario has drawn attention towards the genuine need for a stronger role of science diplomacy, science advice and science communication. In dealing with the COVID-19 pandemic, visible interactions across science, policy, science communication to the public and diplomacy worldwide have promptly emerged.

Correction: Mitigating losses: how scientific organisations can help address the impact of the COVID-19 pandemic on early-career researchers.

[This corrects the article DOI: 10.1057/s41599-021-00944-1.].

Switching Site Reactivity in Hydrogenase Model Systems by Introducing a Pendant Amine Ligand.

Hydrogenases are versatile enzymatic catalysts with an unmet hydrogen evolution reactivity (HER) from synthetic bio-inspired systems. The binuclear active site only has one-site reactivity of the distal Fe atom. Here, binuclear complexes [Fe(CO)(μ-Mebdt)(P(4-CHOCH))] and [Fe(CO)(μ-Mebdt)(PPhPy)] are presented, which show electrocatalytic activity in the presence of weak acids as a proton source for the HER.

Nickel(ii) PECEP pincer complexes (E = O, S) for electrocatalytic proton reduction.

Nickel(ii) chloride and thiolate complexes with PECEP (E = O, S) pincer ligands were investigated as electrocatalysts for the hydrogen evolution reaction in CHCN in the presence of acetic acid and trifluoroacetic acid. The bis(thiophosphinite) (S,S) chloride complex reduced protons at the lowest overpotential in comparison with the bis(phosphinite) (O,O) and mixed phosphinite-thiophosphinite (O,S) complexes. A combination of electrochemical, NMR and UV-vis spectroscopic and mass spectrometric experiments provides mechanistic insights into the catalytic cycle for proton reduction to dihydrogen.

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.

A mononuclear iron carbonyl complex [Fe(μ-bdt)(CO)(PTA)] with bulky phosphine ligands: a model for the [FeFe] hydrogenase enzyme active site with an inverted redox potential.

A mononuclear hexa-coordinated iron carbonyl complex [Fe(μ-bdt)(CO)(PTA)] 1 (bdt = 1,2-benzenedithiolate; PTA = 1,3,5-triaza-7-phosphaadamantane) with two bulky phosphine ligands in the trans position was synthesized and characterized by X-ray structural analysis coulometry data, FTIR, electrochemistry and electronic structure calculations. The complex undergoes a facilitated two-electron reduction 1/1 and shows an inverted one-electron reduction for 1/1 at higher potentials. Electrochemical investigations of 1 are compared to the closely related [Fe(bdt)(CO)(PMe)] compound.

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.

[NiFe] hydrogenases: how close do structural and functional mimics approach the active site?

Hydrogen is being considered as a versatile alternative fuel with the ever increasing energy demand and oil prices. Hydrogenases (H2ases) found in bacteria, archaea and eukaryotes are very efficient catalysts for biological hydrogen production. An important and unique hydrogenase enzyme is the [NiFe] H2ase, with an unusual heterobimetallic site.

Microbial hydrogen splitting in the presence of oxygen.

The origin of the tolerance of a subclass of [NiFe]-hydrogenases to the presence of oxygen was unclear for a long time. Recent spectroscopic studies showed a conserved active site between oxygen-sensitive and oxygen-tolerant hydrogenases, and modifications in the vicinity of the active site in the large subunit could be excluded as the origin of catalytic activity even in the presence of molecular oxygen. A combination of bioinformatics and protein structural modelling revealed an unusual co-ordination motif in the vicinity of the proximal Fe-S cluster in the small subunit.

Effect of cyanide ligands on the electronic structure of [FeFe] hydrogenase active-site model complexes with an azadithiolate cofactor.

A detailed characterization of a close synthetic model of the [2 Fe]H subcluster in the [FeFe] hydrogenase active site is presented. It contains the full primary coordination sphere of the CO-inhibited oxidized state of the enzyme including the CN(-) ligands and the azadithiolate (adt) bridge, [((μ-SCH2 )2 NR)Fe2 (CO)4 (CN)2 ](2-) , R=CH2 CH2 SCH3 . The electronic structure of the model complex in its Fe(I) Fe(II) state was investigated by means of density functional theory (DFT) calculations and Fourier transform infrared (FTIR) spectroscopy.