Cobalt-catalyzed double hydroboration of pyridines.

Cobalt(ii) complexes were prepared from a modular phosphinopyridonate platform and applied to the hydroboration of pyridines. The synthetically useful, yet challenging, double hydroboration toward tetrahydropyridine derivatives was successfully performed with high activity and regiocontrol. This new method enabled the direct synthesis of -heterocyclic allylic boronates from commercial pyridines and pinacolborane (HBpin).

Counterion Effect in Cobaltate-Catalyzed Alkene Hydrogenation.

We show that countercations exert a remarkable influence on the ability of anionic cobaltate salts to catalyze challenging alkene hydrogenations. An evaluation of the catalytic properties of [Cat][Co(η -cod) ] (Cat=K (1), Na (2), Li (3), ( nacnac)Mg (4), and N( Bu) (5); cod=1,5-cyclooctadiene, nacnac={2,6-Et C H NC(CH )} CH)]) demonstrated that the lithium salt 3 and magnesium salt 4 drastically outperform the other catalysts. Complex 4 was the most active catalyst, which readily promotes the hydrogenation of highly congested alkenes under mild conditions.

Iron(ii) carboxylates and simple carboxamides: an inexpensive and modular catalyst system for the synthesis of PLLA and PLLA-PCL block copolymers.

The combination of inexpensive Fe(ii) acetate with low molecular weight aliphatic carboxamides generates an effective catalyst system for the ring opening polymerisation of lactones. PLLAs were produced in melt conditions with molar masses of up to 15 kg mol, narrow dispersity ( = 1.03), and without racemisation.

Synthesis and Catalysis of Anionic Amido Iron(II) Complexes.

Low-coordinate, open-shell 3d metal complexes have attracted great attention due to their critical role in several catalytic transformations but have been notoriously difficult to prepare and study due to their high lability. Here, we report the synthesis of a heteroleptic tri-coordinate amidoferrate that displays high catalytic activity in the regioselective hydrosilylation of alkenes.

Stereoselective Semi-Hydrogenations of Alkynes by First-Row (3d) Transition Metal Catalysts.

The chemo- and stereoselective semi-hydrogenation of alkynes to alkenes is a fundamental transformation in synthetic chemistry, for which the use of precious 4d or 5d metal catalysts is well-established. In mankind's unwavering quest for sustainability, research focus has considerably veered towards the 3d metals. Given their high abundancy and availability as well as lower toxicity and noxiousness, they are undoubtedly attractive from both an economic and an environmental perspective.

Redox-active ligands as a challenge for electronic structure methods.

To improve the catalytic activity of 3d transition metal catalysts, redox-active ligands are a promising tool. These ligands influence the oxidation state of the metal center as well as the ground spin-state and make the experimental determination of both properties challenging. Therefore, first-principles calculations, in particular employing density functional theory with a proper choice of exchange-correlation (xc) functional, are crucial.

The Diverse Modes of Oxygen Reactivity in Life & Chemistry.

Oxygen is a molecule of utmost importance in our lives. Beside its vital role for the respiration and sustaining of organisms, oxygen is involved in numerous chemical and physical processes. Upon combination of the different forms of molecular oxygen species with various activation modes, substrates, and reaction conditions an extremely wide chemical space can be covered that enables rich applications of diverse oxygenation processes.

BIAN-Aluminium-Catalysed Imine Hydrogenation.

Hydrogenations have been dominated by transition metal catalysis, while the use of more abundant and inexpensive main group metal catalysts has remained a great challenge. Here, a bimetallic Li/Al dihydride was successfully applied to catalytic hydrogenations of imines. The catalyst [(BIAN)Al(μ-H)Li(OEt)] was easily prepared from the 2e-reduced BIAN derivative and LiAlH.

Redox-active BIAN-based Diimine Ligands in Metal-Catalyzed Small Molecule Syntheses.

α-Diimine ligands have significantly shaped the coordination chemistry of most transition metal complexes. Among them, bis(imino)acenaphthene ligands (BIANs) have recently been matured to great versatility and applicability to catalytic reactions. Besides variations of the ligand periphery, the great versatility of BIAN ligands resides within their ability to undergo facile electronic manipulations.

Polynuclear Iron(II) Pyridonates: Synthesis and Reactivity of Fe and Fe Clusters.

The combination of pyridonate ligands with transition metal ions enables the synthesis of an especially rich set of diverse coordination compounds involving various κ- and μ-bonding modes and higher nuclearities. With iron(II) ions, this chemical space is rather poorly explored beyond some biomimetic models of the pyridone iron-containing hydrogenase. Here, the topologically new Fe and Fe clusters, Fe(L)[N(SiMe)] () and Fe(L)[N(SiMe)] (), were synthesized (L = 2-pyridonate; L = 6-methyl-2-pyridonate).

Photoredox-Catalyzed Synthesis of α-Amino Acid Amides by Imine Carbamoylation.

An operationally simple protocol for the photocatalytic carbamoylation of imines is reported. Easily available, bench-stable 4-amido Hantzsch ester derivatives serve as precursors to carbamoyl radicals that undergo rapid addition to -aryl imines. The reaction proceeds under blue light irradiation in the presence of the photocatalyst 3DPAFIPN and Brønsted/Lewis acid additives.

Next generation luminol derivative as powerful benchmark probe for chemiluminescence assays.

Chemiluminescence (CL) provides outstanding analytical performance due to its independence from external light sources, background-free nature and exceptional sensitivity and selectivity. Yet, ultra-sensitive (bio)analysis is impeded by low hydrophilicity, poor quantum yields, fast kinetics or instability of most CL reagents such as luminol, acridinium esters, dioxetanes or peroxyoxalic derivatives. Photophysical studies show that m-carboxy luminol overcomes these limitations as its hydrophilic design provides a 5-fold increase in relative quantum yield resulting in superior performance in HO-dependent bioassays with 18-fold higher sensitivity for the quantification of its co-reactant HO, and 5-times lower detection limits for the luminophore.

Selective Benzylic CH-Borylations by Tandem Cobalt Catalysis.

Metal-catalyzed C-H activations are environmentally and economically attractive synthetic strategies for the construction of functional molecules as they obviate the need for pre-functionalized substrates and minimize waste generation. Great challenges reside in the control of selectivities, the utilization of unbiased hydrocarbons, and the operation of atom-economical dehydrocoupling mechanisms. An especially mild borylation of benzylic CH bonds was developed with the ligand-free pre-catalyst Co[N(SiMe ) ] and the bench-stable and inexpensive borylation reagent B pin that produces H as the only by-product.

Light-Driven Waste-To-Value Upcycling: Bio-Based Polyols and Polyurethanes from the Photo-Oxygenation of Cardanols.

The upcycling of waste biomass into valuable materials by resource-efficient chemical transformations is a prime objective for sustainable chemistry. This approach is demonstrated in a straightforward light-driven synthesis of polyols and polyurethane foams from the multi-ton waste products of cashew nut processing. The photo-oxygenation of cardanol from nutshell oil results in the formation of synthetically versatile hydroperoxides.

Manganese-Catalyzed Hydroborations with Broad Scope.

Reductive transformations of easily available oxidized matter are at the heart of synthetic manipulation and chemical valorization. The applications of catalytic hydrofunctionalization benefit from the use of liquid reducing agents and operationally facile setups. Metal-catalyzed hydroborations provide a highly prolific platform for reductive valorizations of stable C=X electrophiles.

Planar Iron Hydride Nanoclusters: Combined Spectroscopic and Theoretical Insights into Structures and Building Principles.

The controlled assembly of well-defined planar nanoclusters from molecular precursors is synthetically challenging and often plagued by the predominant formation of 3D-structures and nanoparticles. Herein, we report planar iron hydride nanoclusters from reactions of main group element hydrides with iron(II) bis(hexamethyldisilazide). The structures and properties of isolated Fe , Fe , and Fe nanoplatelets and calculated intermediates enable an unprecedented insight into the underlying building principle and growth mechanism of iron clusters, metal monolayers, and nanoparticles.

Aryl Pyrazoles from Photocatalytic Cycloadditions of Arenediazonium.

A photocatalytic synthesis of 1,5-diaryl pyrazoles from arenediazoniums and arylcyclopropanols is reported. The reaction proceeded under mild conditions (rt, 20 min) with catalytic [Ru(bpy)] under blue-light irradiation and exhibited compatibility with several functional groups (e.g.

Photoredox-Catalyzed Addition of Carbamoyl Radicals to Olefins: A 1,4-Dihydropyridine Approach.

Functionalization with C1-building blocks are key synthetic methods in organic synthesis. The low reactivity of the most abundant C -molecule, carbon dioxide, makes alternative carboxylation reactions with CO -surrogates especially important. We report a photoredox-catalyzed protocol for alkene carbamoylations.

Heterogeneous Olefin Hydrogenation Enabled by a Highly-Reduced Nickel(-II) Catalyst Precursor.

Invited for the cover of this issue is the group of Robert Wolf at the University of Regensburg and colleagues at the University of Hamburg. The image depicts the hydrogenation of triphenylethylene. Read the full text of the article at 10.

Combined Photoredox and Iron Catalysis for the Cyclotrimerization of Alkynes.

Successful combinations of visible-light photocatalysis with metal catalysis have recently enabled the development of hitherto unknown chemical reactions. Dual mechanisms from merging metal-free photocatalysts and earth-abundant metal catalysts are still in their infancy. We report a photo-organo-iron-catalyzed cyclotrimerization of alkynes by photoredox activation of a ligand-free Fe catalyst.

Heterogeneous Olefin Hydrogenation Enabled by a Highly-Reduced Nickel(-II) Catalyst Precursor.

The hydrogenation of olefins, styrenes, enoates, imines, and sterically hindered tri-substituted olefins was accomplished using the pre-catalyst dilithiumbis(cycloocta-1,5-diene)nickelate(-II) (1). The mild conditions tolerate hydroxyl, halide, ester, and lactone functionalities. Mechanistic studies, including reaction progress analyses, poisoning experiments, and multinuclear NMR monitoring, indicate that a heterotopic (nickel nanoparticle) catalyst is in operation.

The Role of Organoferrates in Iron-Catalyzed Cross-Couplings.

Recent groundbreaking studies on organoferrates have demonstrated that coordinatively unsaturated three-coordinate-σ-alkylferrates are active catalysts in Fe-catalyzed cross-couplings with Grignard reagents and that pronounced solvent and counterion effects dictate metalate speciation and catalyst activity. Thanks to modern spectroscopic methods, sensitive catalyst intermediates could be analyzed.

Catalyst-Free -Deoxygenation by Photoexcitation of Hantzsch Ester.

A mild and operationally simple protocol for the deoxygenation of a variety of heteroaryl -oxides and nitroarenes has been developed. A mixture of substrate and Hantzsch ester is proposed to result in an electron donor-acceptor complex, which upon blue-light irradiation undergoes photoinduced electron transfer between the two reactants to afford the products. -oxide deoxygenation is demonstrated with 22 examples of functionally diverse substrates, and the chemoselective reduction of nitroarenes to the corresponding hydroxylamines is also shown.

A Carbene-Extended ATRA Reaction.

Atom-transfer radical addition (ATRA) reactions have gained a strong foothold in organic synthesis by virtue of their operational simplicity, synthetic versatility, and perfect atom economy. A rich chemical space can be accessed through clever combinations of the simple starting materials. Many variations of this general motif have been reported.

Iron-catalysed allylation-hydrogenation sequences as masked alkyl-alkyl cross-couplings.

An iron-catalysed allylation of organomagnesium reagents (alkyl, aryl) with simple allyl acetates proceeds under mild conditions (Fe(OAc) or Fe(acac), EtO, r.t.) to furnish various alkene and styrene derivatives.