Organosulphur and organoselenium compounds as emerging building blocks for catalytic systems for O-arylation of phenols, a C-O coupling reaction

Diaryl ethers form an important class of organic compounds. The classic copper-mediated Ullmann diaryl ether synthesis has been known for many years and involves the coupling of phenols with aryl halides. However, the use of high reaction temperature, high catalyst loading and expensive ligands has created a need for the development of alternative catalytic systems. In the recent past, organosulphur and organoselenium compounds have been used as building blocks for developing homogeneous, heterogeneous and nanocatalysts for this C-O coupling reaction. Homogeneous catalytic systems include preformed complexes of metals with organosulphur and organoselenium ligands. The performance of such complexes is influenced dramatically by the nature of the chalcogen (S or Se) donor site of the ligand. Nanocatalytic systems (including Pd₁₇Se₁₅, Pd₁₆S₇ and Cu_1.8S) have been designed using a single-source precursor route. Heterogeneous catalytic systems contain either metal (Cu or Pd) or metal chalcogenides (Pd₁₇Se₁₅ or Cu_1.8S) as catalytically active species. This article aims to cover the simple and straightforward methodologies and approaches that are adopted for developing catalytically relevant organosulfur and organoselenium ligands, their homogeneous metal complexes, heterogeneous and nanocatalysts. The effects of chalcogen (S or Se) donor, halogen (Cl/Br/I) of aryl halide, nature (electron withdrawing or electron donating) of substituents present on the aromatic ring of aryl halides or substituted phenols and position (ortho or para) of substitution on the results of catalytic reactions have been critically analyzed and summarized. The effect of composition (Pd₁₇Se₁₅ or Pd₁₆S₇) on the performance of nanocatalytic systems is also highlighted. Substrate scope has also been discussed in all three types of catalysis. The superiority of heterogeneous catalytic systems (e.g., Pd₁₇Se₁₅ immobilised on graphene oxide) indicates the bright future possibilities for the development of efficient catalytic systems using similar or tailored ligands for this reaction.

Copper supported silica-based nanocatalysts for CuAAC and cross-coupling reactions

Recent advances in Cu/SiO2-based heterogeneous catalysts for click reaction, C–N, C–S, and C–O coupling reactions are reviewed and summarized.

Recent Advancement of Ullmann Condensation Coupling Reaction in the Formation of Aryl-Oxygen (C-O) Bonding by Copper-Mediated Catalyst

Transition metal-catalyzed chemical transformation of organic electrophiles and organometallic reagents belong to the most important cross coupling reaction in organic synthesis. The biaryl ether division is not only popular in natural products and synthetic pharmaceuticals but also widely found in many pesticides, polymers, and ligands. Copper catalyst has received great attention owing to the low toxicity and low cost. However, traditional Ullmann-type couplings suffer from limited substrate scopes and harsh reaction conditions. The introduction of homogeneous copper catalyst with presence of bidentate ligands over the past two decades has totally changed this situation as these ligands enable the reaction promoted in mild condition. The reaction scope has also been greatly expanded, rendering this copper-based cross-coupling attractive for both academia and industry. In this review, we will highlight the latest progress in the development of useful homogeneous copper catalyst with presence of ligand and heterogeneous copper catalyst in Ullmann type C-O cross-coupling reaction. Additionally, the application of Ullmann type C-O cross coupling reaction will be discussed.