The focus of this investigation is to carry out a comparative study focusing on distinct coupling reactions to synthesize 2,2’-bipyridines. The current target 2,2’-bipyridine is either a 4-methylated or a 4,4’-dimethylated compound, while future targets include dihalogenated 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, and a mixture of products with varying ring connectivity, such as 2,2’ 2,4’ or 4,4’. Considerations taken for this project were the safety and affordability of the starting materials and the consecutive reagents used. Efforts are made to optimize reaction conditions focusing on singular product formation, to upscale the reaction from the initial 1-3 mmol scale, and to decrease total reaction time. The project introduced herein specifically compares a Ni-catalyzed homo-coupling and an organotin catalyzed Stille-type cross-coupling method. Moisture sensitivity of the reagents require the use of a glove box to prepare the catalysts, while coupling reactions need to be carried out on a Schlenk line. Compound purification relies on extraction and sublimation methods. Characterization methods utilize 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.

Guided inquiry approach to design student-friendly coupling methods for 2,2’-bipyridines as precursors for Ru-complexes

253rd National Meeting (2017)

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