The focus of this investigation is to carry out a comparative study focusing on three distinct methods of synthesizing 2,2’-bipyridines. Target 2,2’-bipyridines include unsubstituted, as well as 5,5’-methylated or 5,5’-brominated heterocyclics. The goal is to provide an affordable process of obtaining these 2,2’-bipyridine building blocks without exposing undergraduate students to severely high risk synthetic steps. As building blocks in analytical chemistry and materials science, 2,2’-bipyridines continue to have an increased role as a favored bidentate ligand, with excellent complexing capabilities. However, due to the highly drained nucleophilicity of pyridines, they serve as a poor starting material toward the preparation of the 2,2’-bipyridines, which tends to require multiple-step routes, severe reaction conditions, and often results in only mediocre yields. Considerations taken for this project are the timeliness of the reactions, as well as the safety and affordability of the starting materials and the consecutive reagents used. The project introduced herein compares a traditional synthetic organic route, the Kröhnke cyclization method, with more recent approaches of metal-catalyzed coupling reactions, namely a Ni-catalyzed homo-coupling, and the Stille-type cross-coupling process relying on an organotin reagent. Routes tested will focus on improving/maintaining time frames and yields for the reactions, concurrently. Compound purification will rely on CombiFlash RF200, column chromatography and HPLC methods. Characterization methods will rely on our available instruments, such as FT-IR, GC-MS and NMR. Synthesized ligands will be further utilized by a collaborative project to be incorporated into Ruthenium complexes.

Comparative investigation of "student-friendly" synthetic routes to prepare 2,2’-bipyridines as precursors for Ru-complexes

251st National Meeting (2016)

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