Synthesis and characterization of ionic liquid based phosphinite ligands and metal complexes; investigation of their catalytic conversions in transfer hydrogenation reactions and biological activity

The first study on an ionic liquid (IL) was carried out in 1914 by Paul Walden, who observed certain physical properties of ethylammonium nitrate ([EtNH3][NO3]; mp 13–14 °C). The discovery of a new class of materials did not receive much attention at the time, but today this work is generally accepted as the starting point for the field of ionic liquids. Ionic liquids are widely used as catalysts or reaction media in organic synthesis due to their environmentally friendly chemical and physical properties and especially their structural adjustability. In the present study, two ionic liquids 3-(3-chloro-2-hydroxypropyl)-1-vinyl-1H-imidazole-3-ium chloride (1) and 3-(3-chloro-2-hydroxypropyl)-1-butyl-1H-imidazole-3-ium chloride (2) was synthesized according to the literature. Phosphinite ligands 3, 4, and 5 were synthesized by reacting the imidazole derivative ionic liquids with PPh2Cl or PCy2Cl at -78 °C using the Schlenk-line technique. Since the ligands are unstable, they could not be characterized. Nevertheless, Ru (II), Ir (III) and Rh(I) complexes (3a-5c) of the phosphinite ligands were synthesized and characterized. Ionic liquids 1 and 2 were synthesized in approximately 87 % yield, while Metal-P-IL complexes were synthesized in 85% yields for 3a-3c, 90% for 4a-4c, and 89% for 5b-5c. When the thermal analysis results were considered, it was observed that the 3a-4c complexes could be safely used without decomposition between 138 ºC and 194 ºC. When the catalytic activity of Ru (II) complexes 3a and 3b was investigated in TH of acetophenone, TOF value of 388 h-1 and 64 h-1 were obtained for 3a and 3b, respectively, at reflux temperature, indicating that Ru-benzene complex was more efficient than Ru-p-cymene complex. When the TH results of Ir (III) complexes were examined, 98% conversion was obtained for 3c in 45 min, while 93% conversion was obtained for 4c in 5 h. When the TH reactions of all complexes were considered, it was observed that Ru-arene complexes gave better results. When the TH reactions of substituted acetophenone for the 3a complex were investigated, it was seen that 99% conversion was obtained for 4-F acetophenone in 10 min, while 93% conversion was obtained for 2-MeO acetophenone in 90 min. Many complexes containing transition metals have attracted attention due to their effectiveness in biological activities such as antimicrobial, antioxidant, and anticancer. In many cases the metal complex showed better activity than the free ligand. When the % DPPH inhibition results were taken into account, it was observed that Ru (II) complex 4b showed 24.19% radical scavenging activity at 25 mg L-1, while it showed 72.27% radical scavenging activity at 200 mg L-1. Test compound 4b showed the highest activity at all concentrations compared to other test compounds. All test compounds showed no significant chelating activity. All of the test compounds showed varying levels of antibacterial activity on the five bacteria used in the study (E. coli (ATCC 10536), P. aeruginosa (ATCC 9027), S. aureus (ATCC 6538), E. hirea (ATCC 10541), B. cereus). Among the synthesized imidazole containing derivatives (1-4c), compound 4c containing Ir (III) transition metal exhibited the highest antibacterial activity (13 mm), while ionic liquid including vinyl group (1) showed no antibacterial activity.