No abstract

Imitating nature'sapproach in nucleophile-activated formaldehyde dehydrogenation, air-stable ruthenium complexes proved to be exquisite catalysts for the dehydrogenation of formaldehyde hydrate as well as for the transfer hydrogenation to unsaturated organic substrates at loadings as low as 0.5 mol %. Concatenation of the chemical hydrogen-fixation route with an oxidase-mediated activation of methanol gives an artificial methylotrophic in vitro metabolism providing methanol-derived reduction equivalents for synthetic hydrogenation purposes.M oreover,f or the first time methanol reforming at room temperature was achieved on the basis of this bioinduced dehydrogenation path delivering hydrogen gas from aqueous methanol.Inlight of anthropogenic global warming and the depletion of ecologically and economically reasonable sources for fossil fuels,inrecent years,one-carbon molecules have emerged as highly attractive renewable hydrogen carriers. [1][2][3][4][5][6][7][8][9][10][11] Owing to difficulties in the selective activation of methane at low temperatures and the rather poor energy balance of formic acid, methanol is currently discussed as most promising C 1 unit.[12] Combining ahigh hydrogen content (12.5 wt %) with the convenience of al iquid fuel, catalytic methods for the dehydrogenation of methanol as well as its production from CO 2 and H 2 have attracted major interest from the scientific community over the past decade to establish acarbon-neutral methanol economy.[13] However,d espite an umber of successful examples on the methanol-to-H 2 conversion, in particular this process is still in great need for further improvement. Herein we present ac onceptually unprecedented strategy for the hydrogen generation from aqueous methanol based on am ulticatalytic system implementing enzyme catalysis as new player in the field.[14] Theinterplay of methanol-activating biocatalysts with H 2 -liberating metal complexes is opening up new opportunities en route to ambient-temperature hydrogen-production systems or enzyme-driven hydrogen fuel cells.In contrast to the recent history of ex vivo approaches utilizing the C 1 feedstock, millions of years of evolution have provided solutions to the problems of the activation and use of organic one-carbon entities by creating well-defined lowtemperature pathways for methane-or methanol-feeding organisms. [15,16] Interestingly,a so pposed to the chemical objective aiming for full dehydrogenation processes (e.g. aqueous methanol yielding the maximum three equivalents of H 2 ), in aerobic methylotrophic yeasts and bacteria, formaldehyde is found to play acentral role in the cells metabolism. Once formed by oxidase/catalase-catalyzed formal oxygenation of methanol, formaldehyde hydrate serves both as source of reduction equivalents,such as NAD(P)H, as well as the actual carbon feedstock for the generation of carbohydrates.[17] Dehydrogenation generally proceeds by nucleophilic activation of formaldehyde through enzyme cofactors, such as pterins (e.g. tetrahydrofolate) or me...

At the palladium: Dimeric palladium bromide complexes bearing monodentate N-heterocyclic carbene ligands have been identified as efficient catalysts for the chemoselective racemization of axially chiral allenyl alcohols. In combination with porcine pancreatic lipase as biocatalyst, a dynamic kinetic resolution has been developed, giving access to optically active allenes in good yield and high enantiomeric purity (see scheme).

Novel hybrids containing silver or gold nanoparticles have been synthesized in aqueous media and room temperature using enzymes or tailor-made enzyme-polymer conjugates, which directly induced the formation of inorganic silver...

Alcohol dehydrogenases can act as powerful catalysts in the preparation of optically pure γ-hydroxy-δ-lactones by means of an enantioconvergent dynamic redox isomerization of readily available Achmatowicz-type pyranones. Imitating the traditionally metal-mediated "borrowing hydrogen" approach to shuffle hydrides across molecular architectures and interconvert functional groups, this chemoinspired and purely biocatalytic interpretation effectively expands the enzymatic toolbox and provides new opportunities in the assembly of multienzyme cascades and tailor-made cellular factories.

Crude Porcine pancreatic lipase was successfully used for the kinetic resolution of axially chiral primary allenic alcohols providing very high enantioselectivities with E values above 200. This simple access to optically active allenes was applied to the total synthesis of the fungal metabolite (-)-striatisporolide A, allowing its unambiguous stereochemical assignment.

Despite the outstanding power conversion efficiency of triple-cation perovskite solar cells (PSCs), their low long-term stability in the air is still a major bottleneck for practical applications. The hygroscopic dopants...

Over the years, the oxidative ring enlargement of furfuryl alcohols, known as the Achmatowicz reaction, has been developed into a powerful and versatile synthetic tool for the preparation of 6-hydroxypyranones. This review provides a comprehensive collection of the various ways to perform Achmatowicz rearrangement reactions and explores the role of this ring-expansion process in contemporary organic synthesis. 1 Introduction 2 Classical Methods and Variants 3 Single-Electron-Transfer Oxidations 4 Metal-Catalyzed Ring Expansions 5 Photolytic Oxygenations 6 Enzymatic Transformations 7 Conclusions