Palladium complexes of pyridine-2,6-dicarboxamide NNN pincer-type ligands: Synthesis, characterization and catalytic application

Since the discovery of pincer ligands, a wide variety of transition metal complexes with pincer ligand backbones have been synthesized, and these complexes have become more prominent due to their superior properties and have gained a comprehensive place in many different application areas. In particular, the fact that pincer-structured complexes synthesized with palladium metal play an active role as catalysts in coupling reactions has made the development of palladium complexes with different structures and their use as catalysts in these reactions extremely common. In this Ph.D. thesis study, nine new ligands with a pyridine-2,6-dicarboxamide structured NNN pincer-type skeleton and palladium complexes of these ligands were synthesized. The structures of all synthesized compounds were characterized by 1H NMR, 13C NMR, COSY, HMQC, FT-IR, and UV-Visible techniques. In addition, the suitable crystals obtained from the ligands and complexes were analyzed by the X-ray single-crystal diffraction method. The catalytic activities of the palladium complexes, whose structures were confirmed by various characterization techniques, were tested through the Suzuki-Miyaura carboncarbon cross-coupling reaction between phenylboronic acid and 4-bromotoluene, 1-bromo-4- isobutylbenzene, and 2-bromo-6 methoxynaphthalene substrates. As a result of the catalytic activity analysis, high conversion rates and coupling products were obtained in a short time with all three substrates, using the palladium complexes as catalyst. Among the palladium complexes whose activities were examined as catalysts, the [Pd(H2L 9 )] complex was found to have the highest activity. In reactions in which [Pd(H2L 9 )] is used as a catalyst; more than 99% conversion and more than 99% yield were achieved in one hour with the 4-bromotoluene substrate, and more than 98% conversion and more than 98% yield were achieved after one hour with the substrate 1-bromo-4-isobutylbenzene. In the reaction in which 2-bromo-6-methoxynaphthalene was used as the substrate, it was determined that a yield of more than 99% was achieved with 100% conversion at the end of one hour. A mercury test was carried out to determine the nature of the catalyst. According to the results of the mercury test, it was determined that although mercury did not completely quench the activity, it caused a decrease in the activities of the catalysts at varying rates. According to the mercury test results, a reusability test was carried out to test the activities of black amorphous particles obtained from the reaction of [Pd(H2L 8 )], which is the complex with the highest decrease in activity. Four reactions were able to be performed in the reusability analysis. While 87% conversion was achieved in the first reaction, it was determined that this conversion amount decreased to 34% in the fourth reaction. Keywords: Pyridine-2,6-dicarboxamide derivative compounds, NNN pincer type ligands, Palladium complexes, Suzuki-Miyaura carbon-carbon cross-coupling reaction, X-ray single crystal diffraction analysis.