Investigating the catalytic properties of Pd-NHC catalyst system with benzimidazole skeleton in Sonogashira reactions.

Sonogashira coupling reaction of phenylacetylene with aryl halides catalyzed with Pd complexes in the presence of copper reagent is one of the most powerful tools in organic synthesis and has been widely applied to various areas such as natural product synthesis, biologically active molecules and material science. Concerns for maximal use of raw materials and minimal generation of waste products stimulate the search for appropriate catalyst and environmental friendly synthesis methods for the reactions both in laboratory and industry. On the other hand the use of microwave irradiation which known as a green synthesis method for promoting chemical reactions has recently become a versatile tool in organic synthesis. Rapid heating, reduced reaction times and, in many cases, increased yields have made microwave irradiation a commonly used tool. In this context the use of Pd-NHC catalysis in conjunction with microwaves may have significant advantages over conventional heating since the inverted temperature gradient under microwave conditions may lead to increased lifetime of the catalyst. It has been known that, Pd-NHCs efficient catalyst for several C-C coupling reactions and these type catalysts have been used less often in Sonogashire reaction comparing with Suzuki-Miyaura, Heck-Mizoroki and Buchwald–Hartwig reactions. In order to extend Pd-NHC catalyzed Sonogashira reactions, in this thesis, new benzimidazole salts as carbene precursors were synthesized and their catalytic properties were investigated in Sonogashira reactions presence of Copper nanoparticle co-catalyst under microwave irradiation. The catalytic activities of the catalyst system consist of benzimidazole salt, Pd(OAC)2, copper nanoparticle, base and solvent were determined in the selected reactions using by GC-MS techniques. The optimum catalytic activity of the catalyst system in Sonagashira reactions was obtained in 10 minutes under microwave irradiation. Structure of all new benzimidazole compounds synthesized in this work were identified by 1H-NMR, {1H}-13C-NMR, FT-IR spectroscopic techniques, and elemental analysis. The structure of the compounds were tested as catalyst both new synthesized (1-20) and known (I-XX) and optimized reaction conditions for Sonogashira reaction are given below.