Iron and cobalt catalysis: new perspectives in synthetic radical chemistry

Iron and cobalt complexes are at the origin of high valuable synthetic pathways involving radical intemediates.

Direct Synthesis of N-Heterocyclic Carbene-Stabilized Copper Nanoparticles from an N-Heterocyclic Carbene-Borane

N-Heterocyclic carbene (NHC)-stabilized copper nanoparticles (NPs) were synthesized from an NHC-borane adduct and mesitylcopper(I) under thermal conditions (refluxing toluene for 2.5 h). NPs with a size distribution of 11.6±1.8 nm were obtained. The interaction between Cu NPs and NHC ligands was probed by X-ray photoelectron spectroscopy, which showed covalent binding of the NHC to the surface of the NPs. Mechanistic studies suggested that NHC-borane plays two roles: contributing to the reduction of [CuMes]₂ to release Cu⁰ species and providing NHC ligands to stabilize the copper NPs.

Cross coupling of alkylsilicates with acyl chlorides via photoredox/nickel dual catalysis: a new synthesis method for ketones

Photoredox/nickel dual catalysis using silicates and acyl chlorides allows a new method of formation of ketones. Flow chemistry can be applied.

The Invention of New Methodologies: An Opportunity for Dating Natural Products

This Account surveys almost two decades of methodological developments and their straightforward applications to the total synthesis of simple natural products. The main directions covered include radical chemistry and cascades, electrophilic catalysis based on coinage metals, and asymmetric synthesis based on bis(sulfoxides) auxiliaries.

1 Introduction

2 Radical Cascades

2.1 N-Cyanamides

2.2 Homolytic Substitution at Sulfur Atom to Give Sultines

3 Electrophilic Catalysis Based on Platinum(II) and Gold(I) Complexes

4 From Alkylydene Bis(sulfoxides) to Chiral Carboxylic Acids

5 Conclusion and Perspectives

N-Heterocyclic carbene-stabilized gold nanoparticles with tunable sizes

A simple and straightforward synthesis of N-heterocyclic carbene (NHC)-protected gold nanoparticles is derived from (benz)imidazolium-AuX4 complexes and NaBH4 only. The proposed method allows size tuning, from 3 to 6 nm, by adding (benz)imidazolium bromide. Changing the reducing agent to tBuNH2BH3 shifts the size range to ca. 6-12 nm. A one pot protocol is also reported from AuCl, (benz)imidazolium bromides and NaBH4, thereby providing an even more straightforward way of producing NHC-capped gold nanoparticles. In addition, X-ray photoelectron spectroscopy (XPS) is used to unambiguously evidence, on the nanoparticles, the covalent bond formed between the NHC and the surface gold atoms.

Copper-Catalyzed Aziridination with Redox-Active Ligands: Molecular Spin Catalysis

Small-molecule catalysts as mimics of biological systems illustrate the chemists' attempts at emulating the tantalizing abilities displayed by nature's metalloenzymes. Among these innate behaviors, spin multistate reactivity is used by biological systems as it offers thermodynamic leverage towards challenging chemical reactivity but this concept is difficult to translate into the realm of synthetic organometallic catalysis. Here, we report a rare example of molecular spin catalysis involving multistate reactivity in a small-molecule biomimetic copper catalyst applied to aziridination. This behavior is supported by spin state flexibility enabled by the redox-active ligand.

Themed collection: Synthetic approaches to natural products via catalytic processes

Guest editors Louis Fensterbank, Shuanhu Gao and Armen Zakarian introduce this Organic Chemistry Frontiers themed collection entitled “Synthetic approaches to natural products via catalytic processes”.

Microfluidic chips for plasma flow chemistry: application to controlled oxidative processes

A novel biphasic gas/liquid plasma microreactor performed controlled oxidation of cyclohexane into “KA oil” with more than 70% selectivity and more than 10% conversion.

Circumventing Intrinsic Metal Reactivity: Radical Generation with Redox-Active Ligands

Nickel complexes have gained sustained attention as efficient catalysts in cross-coupling reactions and co-catalysts in dual systems due to their ability to react with radical species. Central to this reactivity is nickel's propensity to shuttle through several accessible redox states from Ni⁰ to Ni^IV . Here, we report the catalytic generation of trifluoromethyl radicals from a nickel complex bearing redox-active iminosemiquinone ligands. This unprecedented reactivity is enabled through ligand-based oxidation performing electron transfer to an electrophilic CF₃⁺ source while the nickel oxidation state is preserved. Additionally, extension of this reactivity to a copper complex bearing a single redox equivalent is reported, thus providing a unified reactivity scheme. These results open new pathways in radical chemistry with redox-active ligands.

Niobium-Catalyzed Intramolecular Addition of O-H and N-H Bonds to Alkenes: A Tool for Hydrofunctionalization

A convenient, versatile, and easy to handle intramolecular hydrofunctionalization of alkenes (C-O and C-N bonds formation) is reported using a novel niobium-based catalytic system. This atom economic and eco-friendly methodology provides an additional synthetic tool for the straightforward formation of valuable building blocks enabling molecular complexity. Various pyran, furan, pyrrolidine, piperidine, lactone, and lactam derivatives as well as spirocyclic compounds are produced in high yields and selectivities.

Gold(i)-catalyzed access to neomerane skeletons

The gold(i) catalyzed cycloisomerization of an enynyl propargylic ester, featuring a 1,2-acyloxy migration/intramolecular cyclopropanation sequence, opens a straightforward access to the 5,7,3-tricyclic skeleton of neomerane sesquiterpenes. The first total synthesis of 5-epi-valeneomerin B in 12 steps with an overall yield of 5.3% is reported.

Photochemical studies on bis-sulfide and -sulfone tethered polyenic derivatives

This study focusses on the [2 + 2]-photocycloaddition of a symmetric polyenic system tethered by an aryl bis-sulfide or sulfone platform.