Cobalt nanoparticles-catalyzed aerobic oxygenation and esterification of alkynes via C≡C bonds cleavage

An unprecedented efficient protocol is developed for the oxidative cleavage of C≡C bonds in alkynes to produce structure-diverse esters using heterogeneous cobalt nanoparticles as catalyst with molecular oxygen as the oxidant. A diverse set of mono- and multisubstituted aromatic and aliphatic alkynes can be effectively cleaved and converted into the corresponding esters. Characterization analysis and control experiments indicate high surface area and pore volume, as well as nanostructured nitrogen-doped graphene-layer coated cobalt nanoparticles are possibly responsible for excellent catalytic activity. Mechanistic studies reveal that ketones derived from alkynes under oxidative conditions are formed as intermediates, which subsequently are converted to esters through a tandem sequential process. The catalyst can be recycled up to five times without significant loss of activity.

Photocatalyzed oxidative cleavage of CC bond to carbonyl compounds by a recyclable homogeneous carbon nitride semiconductor/aqueous system

The development of methods based on direct oxidative cleavage of alkynes to carbonyls is an extremely challenging task. In this work, we describe a UV light-driven, potassium/sodium poly(heptazine imide) (K,Na-PHI)-catalyzed protocol for the selective oxidative cleavage of alkynes to acids under an O₂ atmosphere using water as a solvent. Various aromatic alkynes can be selectively cleaved to afford aromatic acids in good to high yield under clean, mild conditions. Mechanistic investigation indicates that the photogenerated hydroxyl radicals in situ act as green oxidation active species. Moreover, this protocol could be further developed as a sequential oxidative cleavage/esterification process for the preparation of aryl esters. Notably, the KNaPHI-II/water catalyst system could be used several times without significant loss of activity.

Applications of Photoredox Catalysis for the Radical-Induced Cleavage of C–C Bonds

Selective cleavage of C–C bonds forms one of the greatest challenges in current organic chemistry, due to the relative strength of these bonds. However, such transformations are an invaluable instrument to break down and construct new carbon–carbon bonds. To achieve this, photochemistry can be used as a tool to generate radicals and induce the cleavage of these bonds due to their high reactivity. This review examines some of the most influential contributions in this field since 2010.

1 Introduction

2 C–C Bond Cleavage

2.1 Homogeneous Catalyst

2.1.1 N-Centered Radical

2.2.2 O-Centered Radical

2.2 Heterogeneous Catalyst

3 C=C Bond Cleavage

3.1 Homogeneous Catalyst

3.2 Heterogeneous Catalyst

4 C≡C Bond Cleavage

4.1 Homogeneous Catalyst

4.2 Heterogeneous Catalyst

5 Conclusion

Visible-light-promoted thiocyanation of sp2 C–H bonds over heterogeneous graphitic carbon nitrides

Mesoporous graphitic carbon nitride (mpg-C₃N₄) is developed as a practical heterogeneous photocatalyst for C–S bond formation.