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The reduction of SO2 to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO2 to H2S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO2 to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO2 by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that FeIITPP reduces SO2 by 2e−/2H+ to form an intermediate [FeIII−SO]+ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO2 could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide. [ABSTRACT FROM AUTHOR]

Reduction of oxides and oxoanions of carbon and nitrogen are of great contemporary importance as they are crucial for a sustainable environment. Substantial research has been dedicated to these areas in the last few decades. These reductions require both electrons and protons and their thermodynamic potentials often make them compete with hydrogen evolution reaction i.e., the reaction of protons and electrons to generate H2. These reactions are abundant in the environment in microorganisms and are facilitated by naturally occurring enzymes. This review brings together the state-of-the-art knowledge in the area of enzymatic reduction of CO2, NO2− and H+ with those of artificial molecular electrocatalysis. A simple ligand field theory-based design principle for electrocatalysts is first described. The electronic structure considerations developed automatically yield the basic geometry required and the 2nd sphere interactions which can potentially aid the activation and the further reduction of these small molecules. A systematic review of the enzymatic reaction followed by those reported in artificial molecular electrocatalysts is presented for the reduction of CO2, NO2− and H+. The review is focused on mechanism of action of these metalloenzymes and artificial electrocatalysts and discusses general principles that guide the rates and product selectivity of these reactions. The importance of the 2nd sphere interactions in both enzymatic and artificial molecular catalysis is discussed in detail. [ABSTRACT FROM AUTHOR]

A new synthetic approach, which involved ring-closing metathesis of dienols, derived from a (R)-(+)-glyceraldehyde derivative to form the substituted cyclopentenol and cyclohexenol in enantiomerically pure form is described. It is observed that stereocontrolled addition of hydroxyl groups followed by conversion of the ketal unit to hydroxymethyl group in these intermediates led to carbapentoses and hexoses.

A bio‐inspired FeFe hydrogenase model which catalyses hydrogen evolution reaction (HER) in acidic solutions is immobilized in polyaniline (PANI)‐based nanotubes. A combination of analytical techniques reveals that this construct maintains both the molecular signatures of the bio‐inspired complex and the material properties of PANI. The amine and imine‐rich environment of the PANI chain amplifies the inherent HER activity of the bio‐inspired complex, allowing electrocatalytic HER at neutral pH, with lower overpotentials and higher current densities compared to the bio‐inspired complex alone. This construct retains the oxygen stability of the bio‐inspired complex and remains stable through several hours of aerobic electrolysis, producing only 6.5 % H₂O₂ from the competing oxygen reduction reaction (ORR). [ABSTRACT FROM AUTHOR]

The advantage of a pre-organized π-cavity of Fe(II) complex of a newly developed macrobicycle cryptand is explored for CO 2 reduction by overcoming the problem of high overpotential associated with the inert nature of the cryptate. Thus, a bipyridine-centered tritopic macrobicycle having a molecular π-cavity capable of forming Fe(II) complex as well as potential for CO 2 encapsulation is synthesized. The inert Fe(II)-cryptate shows much lower potential in cyclic voltammetry than the Fe(II)-tris-dimethylbipyridine (Fe-MBP) core. Interestingly, this cryptate shows electrochemical CO 2 reduction at a considerably lower potential than the Fe-MBP inert core. Therefore, this study represents that a well-structured π-cavity may generate a new series of molecular catalysts for the CO 2 reduction reaction (CO 2 RR), even with the inert metal complexes., (© 2023 Wiley-VCH GmbH.)

An azadithiolate bridged CN - bound pentacarbonyl bis-iron complex, mimicking the active site of [Fe-Fe] H 2 ase is synthesized. The geometric and electronic structure of this complex is elucidated using a combination of EXAFS analysis, infrared and Mössbauer spectroscopy and DFT calculations. The electrochemical investigations show that complex 1 effectively reduces H + to H 2 between pH 0-3 at diffusion-controlled rates (10 11 M -1 s -1 ) i.e. 10 8 s -1 at pH 3 with an overpotential of 140 mV. Electrochemical analysis and DFT calculations suggests that a CN - ligand increases the p K a of the cluster enabling hydrogen production from its Fe(i)-Fe(0) state at pHs much higher and overpotential much lower than its precursor bis-iron hexacarbonyl model which is active in its Fe(0)-Fe(0) state. The formation of a terminal Fe-H species, evidenced by spectroelectrochemistry in organic solvent, via a rate determining proton coupled electron transfer step and protonation of the adjacent azadithiolate, lowers the kinetic barrier leading to diffusion controlled rates of H 2 evolution. The stereo-electronic factors enhance its catalytic rate by 3 order of magnitude relative to a bis-iron hexacarbonyl precursor at the same pH and potential., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

With the price-competitiveness of solar and wind power, hydrogen technologies may be game changers for a cleaner, defossilized, and sustainable energy future. H 2 can indeed be produced in electrolyzers from water, stored for long periods, and converted back into power, on demand, in fuel cells. The feasibility of the latter process critically depends on the discovery of cheap and efficient catalysts able to replace platinum group metals at the anode and cathode of fuel cells. Bioinspiration can be key for designing such alternative catalysts. Here we show that a novel class of iron-based catalysts inspired from the active site of [FeFe]-hydrogenase behave as unprecedented bidirectional electrocatalysts for interconverting H 2 and protons efficiently under near-neutral aqueous conditions. Such bioinspired catalysts have been implemented at the anode of a functional membrane-less H 2 /O 2 fuel cell device.

Reduction of oxides and oxoanions of carbon and nitrogen are of great contemporary importance as they are crucial for a sustainable environment. Substantial research has been dedicated to these areas in the last few decades. These reductions require both electrons and protons and their thermodynamic potentials often make them compete with hydrogen evolution reaction i.e., the reaction of protons and electrons to generate H 2 . These reactions are abundant in the environment in microorganisms and are facilitated by naturally occurring enzymes. This review brings together the state-of-the-art knowledge in the area of enzymatic reduction of CO 2 , NO 2 - and H + with those of artificial molecular electrocatalysis. A simple ligand field theory-based design principle for electrocatalysts is first described. The electronic structure considerations developed automatically yield the basic geometry required and the 2 nd sphere interactions which can potentially aid the activation and the further reduction of these small molecules. A systematic review of the enzymatic reaction followed by those reported in artificial molecular electrocatalysts is presented for the reduction of CO 2 , NO 2 - and H + . The review is focused on mechanism of action of these metalloenzymes and artificial electrocatalysts and discusses general principles that guide the rates and product selectivity of these reactions. The importance of the 2 nd sphere interactions in both enzymatic and artificial molecular catalysis is discussed in detail.

[reaction: see text] A simple approach for asymmetric induction in Cu(I)-catalyzed [2 + 2] photocycloaddition, where asymmetric catalysts or chiral auxiliaries were inefficient, has been developed using the concept of chirality transfer from the readily available 2, 3-di-O-cyclohexylidine-(R)-(+)-glyceraldehyde. An anion-induced cleavage of the tetrahydrofuran ring of the resulting oxa-bicyclo[3.2.0]heptanes led to a convenient access to the synthetically useful cis-1,2-disubstituted cyclobutanes in enantiomerically pure form.