Multi-walled Carbon Nanotubes Functionalized with a Palladium(II)-Schiff Base Complex: A Recyclable and Heterogeneous Catalyst for the Copper-, Phosphorous- and Solvent-free Synthesis of Ynones

During the last decade, studies on the isolation, characterization and catalytic activity of functionalized carbon nanotubes (CNTs) received particular attention because of their specific catalytic applications compared to homogeneous catalysts. Schiff bases, which are an important class of ligands with extensive applications in different fields, showed excellent catalytic activity when grafted on CNTs.¹ Conjugated alkynyl ketones, best known as ynones, have received considerable synthetic interest due to their occurrence in a wide variety of bioactive molecules and natural products.² This class of compounds are synthesized through various reported methods.³ Some of the disadvantages of these protocols include high temperatures, long reaction times, use of air and moisture sensitive catalysts such as phosphorous containing catalysts, use of copper catalysts which are very much prone to form diyne side products, use of hazardous organic solvents, use of toxic carbon-monoxide gas and need of special instruments. In this work, we presented a solvent-, copper- and phosphorous-free cross-coupling reaction of terminal alkynes with acyl halides catalyzed by Pd-Schiff base@MWCNTs in the presence of triethylamine as base. The catalyst was reusable and air-stable which showed high activity for this simple, mild and green reaction with good to excellent yields of the product. References: [1] M. Salavati-Niasari, M. Bazarganipour, Appl. Surf. Sci. 2009, 255, 7610-7617. [2] C. A. Quesnelle, P. Gill, M. Dodier, D. St-Laurent, M. Serrano- Wu, A. Marinier, A. Martel, C. E. Mazzucco, T. M. Sticle, J. F. Barrett, D. M. Vyas, B. N. Balasubramanian, Bioorg. Med. Chem. Lett. 2003, 13, 519-524. [3] (a) Perrone, S.; Bona, F.; Troisi, L. Tetrahedron, 2011, 67, 7386; (b)Shen, Q.; Huang, W.; Wang, J.; Zhou, X. Organometallics,2008, 27, 301.