A manganese-based catalyst system for general oxidation of unactivated olefins, alkanes, and alcohols.

Non-noble metal-based catalyst systems consisting of inexpensive manganese salts, picolinic acid and various heterocycles enable epoxidation of the challenging (terminal) unactivated olefins, selective C-H oxidation of unactivated alkanes, and O-H oxidation of secondary alcohols with aqueous hydrogen peroxide. In the presence of the in situ generated optimal manganese catalyst, epoxides are generated with up to 81% yield from alkenes and ketone products with up to 51% yield from unactivated alkanes. This convenient protocol allows the formation of the desired products under ambient conditions (room temperature, 1 bar) by employing only a slight excess of hydrogen peroxide with 2,3-butadione as a sub-stoichiometric additive.

Cobalt nanoparticle-catalysed N-alkylation of amides with alcohols.

A protocol for efficient N-alkylation of benzamides with alcohols in the presence of cobalt-nanocatalysts is described. Key to the success of this general methodology is the use of highly dispersed cobalt nanoparticles supported on carbon, which are obtained from the pyrolysis of cobalt(ii) acetate and o-phenylenediamine as a ligand at suitable temperatures. The catalytic material shows a broad substrate scope and good tolerance to functional groups. Apart from the synthesis of a variety of secondary amides (>45 products), the catalyst allows for the conversion of more challenging aliphatic alcohols and amides, including biobased and macromolecular amides. The practical applicability of the catalyst is underlined by the successful recycling and reusability.

Unprecedented Mo3S4 cluster-catalyzed radical C-C cross-coupling reactions of aryl alkynes and acrylates.

A new method for the generation of benzyl radicals from terminal aromatic alkynes has been developed, which allows the direct cross coupling with acrylate derivatives. Our additive-free protocol employs air-stable diamino Mo3S4 cubane-type cluster catalysts in the presence of hydrogen. A sulfur-centered cluster catalysis mechanism for benzyl radical formation is proposed based on catalytic and stoichiometric experiments. The process starts with the cluster hydrogen activation to form a bis(hydrosulfido) [Mo3(µ3-S)(µ-S)(µ-SH)2Cl3(dmen)3]+ intermediate. The reaction of various aromatic terminal alkynes containing different functionalities with a series of acrylates affords the corresponding Giese-type radical addition products.

Photocatalytic CO2 Reduction Using CO2-Binding Enzymes.

Novel concepts to utilize carbon dioxide are required to reach a circular carbon economy and minimize environmental issues. To achieve these goals, photo-, electro-, thermal-, and biocatalysis are key tools to realize this, preferentially in aqueous solutions. Nevertheless, catalytic systems that operate efficiently in water are scarce. Here, we present a general strategy for the identification of enzymes suitable for CO2 reduction based on structural analysis for potential carbon dioxide binding sites and subsequent mutations. We discovered that the phenolic acid decarboxylase from Bacillus subtilis (BsPAD) promotes the aqueous photocatalytic CO2 reduction selectively to carbon monoxide in the presence of a ruthenium photosensitizer and sodium ascorbate. With engineered variants of BsPAD, TONs of up to 978 and selectivities of up to 93 % (favoring the desired CO over H2 generation) were achieved. Mutating the active site region of BsPAD further improved turnover numbers for CO generation. This also revealed that electron transfer is rate-limiting and occurs via multistep tunneling. The generality of this approach was proven by using eight other enzymes, all showing the desired activity underlining that a range of proteins is capable of photocatalytic CO2 reduction.

Regiodivergent Carbonylation of Alkenes: Selective Palladium-Catalyzed Synthesis of Linear and Branched Selenoesters.

An unprecedented regiodivergent palladium-catalyzed carbonylation of aromatic alkenes has been developed. Utilizing commercially available Pd(CH3 CN)2 Cl2 in the presence of 1,1'-ferrocenediyl-bis(tert-butyl(pyridin-2-yl)phosphine) ligand L8 diverse selenoesters are obtained in a straightforward manner. Key to success for the control of the regioselectivity of the carbonylation step is the concentration of the acidic co-catalyst. This general protocol features wide functional group compatibility and good regioselectivity. Mechanistic studies suggest that the presence of stoichiometric amounts of acid changes the properties and coordination mode of the ligand leading to reversed regioselectivity.

A general and robust Ni-based nanocatalyst for selective hydrogenation reactions at low temperature and pressure.

Catalytic hydrogenations are important and widely applied processes for the reduction of organic compounds both in academic laboratories and in industry. To perform these reactions in sustainable and practical manner, the development and applicability of non-noble metal-based heterogeneous catalysts is crucial. Here, we report highly active and air-stable nickel nanoparticles supported on mesoporous silica (MCM-41) as a general and selective hydrogenation catalyst. This catalytic system allows for the hydrogenation of carbonyl compounds, nitroarenes, N-heterocycles, and unsaturated carbon─carbon bonds in good to excellent selectivity under very mild conditions (room temperature to 80°C, 2 to 10 bar H2). Furthermore, the optimal nickel/meso-silicon dioxide catalyst is reusable (4 cycles) without loss of its catalytic activity.

Synthesis of piperidines and pyridine from furfural over a surface single-atom alloy Ru1CoNP catalyst.

The sustainable production of value-added N-heterocycles from available biomass allows to reduce the reliance on fossil resources and creates possibilities for economically and ecologically improved synthesis of fine and bulk chemicals. Herein, we present a unique Ru1CoNP/HAP surface single-atom alloy (SSAA) catalyst, which enables a new type of transformation from the bio-based platform chemical furfural to give N-heterocyclic piperidine. In the presence of NH3 and H2, the desired product is formed under mild conditions with a yield up to 93%. Kinetic studies show that the formation of piperidine proceeds via a series of reaction steps. Initially, in this cascade process, furfural amination to furfurylamine takes place, followed by hydrogenation to tetrahydrofurfurylamine (THFAM) and then ring rearrangement to piperidine. DFT calculations suggest that the Ru1CoNP SSAA structure facilitates the direct ring opening of THFAM resulting in 5-amino-1-pentanol which is quickly converted to piperidine. The value of the presented catalytic strategy is highlighted by the synthesis of an actual drug, alkylated piperidines, and pyridine.

Applying green chemistry principles to iron catalysis: mild and selective domino synthesis of pyrroles from nitroarenes.

An efficient and general cascade synthesis of pyrroles from nitroarenes using an acid-tolerant homogeneous iron catalyst is presented. Initial (transfer) hydrogenation using the commercially available iron-Tetraphos catalyst is followed by acid catalysed Paal-Knorr condensation. Both formic acid and molecular hydrogen can be used as green reductants in this process. Particularly, under transfer hydrogenation conditions, the homogeneous catalyst shows remarkable reactivity at low temperatures, high functional group tolerance and excellent chemoselectivity transforming a wide variety of substrates. Compared to classical heterogeneous catalysts, this system presents complementing reactivity, showing none of the typical side reactions such as dehalogenation, debenzylation, arene or olefin hydrogenation. It thereby enhances the chemical toolbox in terms of orthogonal reactivity. The methodology was successfully applied to the late-stage modification of multi-functional drug(-like) molecules as well as to the one-pot synthesis of the bioactive agent BM-635.

Atomically Dispersed Cobalt/Copper Dual-Metal Catalysts for Synergistically Boosting Hydrogen Generation from Formic Acid.

The development of practical materials for (de)hydrogenation reactions is a prerequisite for the launch of a sustainable hydrogen economy. Herein, we present the design and construction of an atomically dispersed dual-metal site Co/Cu-N-C catalyst allowing significantly improved dehydrogenation of formic acid, which is available from carbon dioxide and green hydrogen. The active catalyst centers consist of specific CoCuN6 moieties with double-N-bridged adjacent metal-N4 clusters decorated on a nitrogen-doped carbon support. At optimal conditions the dehydrogenation performance of the nanostructured material (mass activity 77.7 L ⋅ gmetal -1 ⋅ h-1 ) is up to 40 times higher compared to commercial 5 % Pd/C. In situ spectroscopic and kinetic isotope effect experiments indicate that Co/Cu-N-C promoted formic acid dehydrogenation follows the so-called formate pathway with the C-H dissociation of HCOO* as the rate-determining step. Theoretical calculations reveal that Cu in the CoCuN6 moiety synergistically contributes to the adsorption of intermediate HCOO* and raises the d-band center of Co to favor HCOO* activation and thereby lower the reaction energy barrier.

Water-Promoted Carbon-Carbon Bond Cleavage Employing a Reusable Fe Single-Atom Catalyst.

The development of methods for selective cleavage reactions of thermodynamically stable C-C/C=C bonds in a green manner is a challenging research field which is largely unexplored. Herein, we present a heterogeneous Fe-N-C catalyst with highly dispersed iron centers that allows for the oxidative C-C/C=C bond cleavage of amines, secondary alcohols, ketones, and olefins in the presence of air (O2 ) and water (H2 O). Mechanistic studies reveal the presence of water to be essential for the performance of the Fe-N-C system, boosting the product yield from <1 % to >90 %. Combined spectroscopic characterizations and control experiments suggest the singlet 1 O2 and hydroxide species generated from O2 and H2 O, respectively, take selectively part in the C-C bond cleavage. The broad applicability (>40 examples) even for complex drugs as well as high activity, selectivity, and durability under comparably mild conditions highlight this unique catalytic system.

Streamlining the synthesis of amides using Nickel-based nanocatalysts.

The synthesis of amides is a key technology for the preparation of fine and bulk chemicals in industry, as well as the manufacture of a plethora of daily life products. Furthermore, it constitutes a central bond-forming methodology for organic synthesis and provides the basis for the preparation of numerous biomolecules. Here, we present a robust methodology for amide synthesis compared to traditional amidation reactions: the reductive amidation of esters with nitro compounds under additives-free conditions. In the presence of a specific heterogeneous nickel-based catalyst a wide range of amides bearing different functional groups can be selectively prepared in a more step-economy way compared to previous syntheses. The potential value of this protocol is highlighted by the synthesis of drugs, as well as late-stage modifications of bioactive compounds. Based on control experiments, material characterizations, and DFT computations, we suggest metallic nickel and low-valent Ti-species to be crucial factors that makes this direct amide synthesis possible.

Bis(N-Heterocyclic Carbene) Manganese(I) Complexes: Efficient and Simple Hydrogenation Catalysts.

The use of bis(NHC) manganese(I) complexes 3 as catalysts for the hydrogenation of esters was investigated. For that purpose, a series of complexes has been synthesized via an improved two step procedure utilizing bis(NHC)-BEt3 adducts. By applying complexes 3 with KHBEt3 as additive, various aromatic and aliphatic esters were hydrogenated successfully at mild temperatures and low catalyst loadings, highlighting the efficiency of the novel catalytic system. The versatility of the developed catalytic system was further demonstrated by the hydrogenation of other substrate classes like ketones, nitriles, N-heteroarenes and alkenes. Mechanistic experiments and DFT calculations indicate an inner sphere mechanism with the loss of one CO ligand and reveal the role of BEt3 as cocatalyst.

Towards "homeopathic" palladium-catalysed alkoxycarbonylation of aliphatic and aromatic olefins.

Palladium-catalysed alkoxycarbonylation of alkenes allows for atom-efficient synthesis of esters from easily available alkenes in an industrially viable manner. One of the major costs associated with this process is the consumption of the catalyst system. Hence, for economic and ecologic reasons it is desirable to minimize the amount of metal and ligands wherever possible. Herein, we report "a homeopathic" palladium-catalysed alkoxycarbonylation of olefins under comparably mild conditions. The key to success is the homemade ligand LIKATphos providing good to excellent yields of ester products with catalyst turnover numbers in the range of 106.

Carbon neutral hydrogen storage and release cycles based on dual-functional roles of formamides.

The development of alternative clean energy carriers is a key challenge for our society. Carbon-based hydrogen storage materials are well-suited to undergo reversible (de)hydrogenation reactions and the development of catalysts for the individual process steps is crucial. In the current state, noble metal-based catalysts still dominate this field. Here, a system for partially reversible and carbon-neutral hydrogen storage and release is reported. It is based on the dual-functional roles of formamides and uses a small molecule Fe-pincer complex as the catalyst, showing good stability and reusability with high productivity. Starting from formamides, quantitative production of CO-free hydrogen is achieved at high selectivity ( > 99.9%). This system works at modest temperatures of 90 °C, which can be easily supplied by the waste heat from e.g., proton-exchange membrane fuel cells. Employing such system, we achieve >70% H2 evolution efficiency and >99% H2 selectivity in 10 charge-discharge cycles, avoiding undesired carbon emission between cycles.

{µ-2,2'-(Ethane-1,2-di-yl)bis-[4,6-bis-(tri-methyl-sil-yl)-1,3-di-hydro-cyclo-penta-[c]pyrrol-5-one]}bis-[tri-carbonyl-iron(0)].

The binuclear title compound, [Fe2(C28H48N2O2Si4)(CO)6], consists of two central iron(0) atoms, each of them surrounded by a cyclo-penta-dienone moiety and three carbonyl ligands in a three-legged piano-stool shape. Furthermore, the bis-(cyclo-penta-dienone) ligand acts as a bridge between the two metal atoms.

Catalytic utilization of converter gas - an industrial waste for the synthesis of pharmaceuticals.

Converter gas is a large scale waste product that is usually burned to carbon dioxide and contributes to the world emission of greenhouse gases. Herein we demonstrate that instead of burning the converter gas can be used as a reducing agent in organic reactions to produce valuable pharmaceuticals and agrochemicals. In particular, amide-based selected drug molecules have been synthesized by a reaction of aromatic nitro compounds and carboxylic acids in the presence of converter gas. In addition, we showed that this gas can also be conveniently utilized to carryout classical reductive amination reaction.

Activation of perfluoroalkyl iodides by anions: extending the scope of halogen bond activation to C(sp3)-H amidation, C(sp2)-H iodination, and perfluoroalkylation reactions.

A simple, efficient, and convenient activation of perfluoroalkyl iodides by tBuONa or KOH, without expensive photo- or transition metal catalysts, allows the promotion of versatile α-sp3 C-H amidation reactions of alkyl ethers and benzylic hydrocarbons, C-H iodination of heteroaryl compounds, and perfluoroalkylations of electron-rich π bonds. Mechanistic studies show that these novel protocols are based on the halogen bond interaction between perfluoroalkyl iodides and tBuONa or KOH, which promote homolysis of perfluoroalkyl iodides under mild conditions.

Hydrogenation of Carboxylic Acids, Esters, and Related Compounds over Heterogeneous Catalysts: A Step toward Sustainable and Carbon-Neutral Processes.

The catalytic hydrogenation of esters and carboxylic acids represents a fundamental and important class of organic transformations, which is widely applied in energy, environmental, agricultural, and pharmaceutical industries. Due to the low reactivity of the carbonyl group in carboxylic acids and esters, this type of reaction is, however, rather challenging. Hence, specifically active catalysts are required to achieve a satisfactory yield. Nevertheless, in recent years, remarkable progress has been made on the development of catalysts for this type of reaction, especially heterogeneous catalysts, which are generally dominating in industry. Here in this review, we discuss the recent breakthroughs as well as milestone achievements for the hydrogenation of industrially important carboxylic acids and esters utilizing heterogeneous catalysts. In addition, related catalytic hydrogenations that are considered of importance for the development of cleaner energy technologies and a circular chemical industry will be discussed in detail. Special attention is paid to the insights into the structure-activity relationship, which will help the readers to develop rational design strategies for the synthesis of more efficient heterogeneous catalysts.

Development of a General and Selective Nanostructured Cobalt Catalyst for the Hydrogenation of Benzofurans, Indoles and Benzothiophenes.

The selective hydrogenation of benzofurans in the presence of a heterogeneous non-noble metal catalyst is reported. The developed optimal catalytic material consists of cobalt-cobalt oxide core-shell nanoparticles supported on silica, which has been prepared by the immobilization and pyrolysis of cobalt-DABCO-citric acid complex on silica under argon at 800 °C. This novel catalyst allows for the selective hydrogenation of simple and functionalized benzofurans to 2,3-dihydrobenzofurans as well as related heterocycles. The versatility of the reported protocol is showcased by the reduction of selected drugs and deuteration of heterocycles. Further, the stability, recycling, and reusability of the Co-nanocatalyst are demonstrated.