(735f) C-C Coupling Reactions Using Cuprous Oxide Nanoparticles through Heterogeneous Pathway

Metal-catalyzed Carbon-carbon (C-C) coupling reactions are a diverse set of reactions that are used in making a wide range of compounds including pharmaceuticals,aromatic-polymers and agrochemicals.These reactions are traditionally executed using homogeneous palladium (Pd) based catalysts.In recent times substantial attention has been devoted to,metal and metal-oxide nanoparticle-based heterogeneous catalysts have emerged as striking-catalysts for these reactions, though identification of the catalytic pathway remains a challenge in the field.

In this work,we show that by selecting suitable reaction-conditions, the reaction pathway can be controlled to occur via a truly homogeneous or heterogeneous pathway in cuprous oxide (Cu₂O)-nanoparticle-catalyzed C-C coupling reactions.When the reactions are carried out in the liquid phase using dimethylformamide as the solvent, the surface atoms of Cu₂O nanoparticles undergo leaching and form homogenous Cu-complex in the presence of the base.The in-situ formed homogenous Cu-complexes can successfully catalyze oxidative C-C homo-coupling of terminal alkynes and C-C cross-coupling reactions between aryl halides and terminal alkyne.In contrast, when the reactions are performed in the absence of base, the C-C coupling reactions occur truly heterogeneous pathway.Role of oxygen was also studied by performing nitrogen and air switch conditions.The molecular reaction mechanisms are proposed for both homogeneous and heterogeneous pathways.The ramifications this work has the potential for the development of(a) an inexpensive Cu-based catalyst as a suitable replacement for Pd based catalysts, and (b)a heterogeneous catalyst capable of exhibiting long term stability to develop energy-efficient and nature friendly flow processes.

Reference:

1. Tirumala, R. A., Dadgar, A., Mohammadparast, F., Ramakrishnan, S., Mou, T., Wang, B., Marimuthu, A. Homogeneous versus Heterogeneous Catalysis in Cu₂O Nanoparticles Catalyzed C-C Coupling Reactions. Green Chemistry, 2019, 21, 5284-5290.

2. Pary, F. F., Tirumala, R. T., Andiappan, M.*, Nelson, T. L.* “Copper (I) oxide nanoparticle-mediated synthesis of polyphenylenediethynylenes: Evidence for homogeneous catalytic pathway”. Catalysis Science and Technology, 2021, DOI:10.1039/d1cy00039j, In Press.