Comparative study of homocoupling reactions to create 2,2’-bipyridine adducts

The project focuses on investigating the synthesis of 2,2’-bipyridine adducts for potential future use as ligands in novel organometallic ruthenium complexes. The bipyridine building blocks, due to their excellent bidentate ligands with complexing abilities, will be incorporated into ruthenium complexes in a collaborative project, increasing the photosensitivity of these complexes, and opening the doors for many applications ranging from synthetic photovoltaics to anti-cancer activity.
The first aim is to carry out a comparative study on the effects of electron donating substituents of variously substituted pyridines. The second aim is to compare the efficacy of two different palladium-based catalysts, namely, tetrakis (triphenylphosphine) palladium (0) and bis (triphenylphosphine) palladium (II) chloride, in order to optimize the preparation of these 2,2’-bipyridine adducts.
To support the goal of the first aim, substrates 2-bromo-6-(1H-pyrazol-1-yl) pyridine, 2-bromo-3-hydroxypyridine, 2-bromo-4-methylpyridine, and 2-bromo-5-methylpyridine will be employed, to obtain the expected final adducts of 6,6’-(1H-pyrazol-1-yl)-2,2’-bipyridine, 2,2′-bipyridine-3,3′-diol, 4,4’-dimethyl-2,2’-bipyridine, and 5,5’-dimethyl-2,2’-bipyridine, respectively.
To attain the second aim, reactions with all four substrates will be carried out utilizing both catalysts.
Prior studies done in our lab have focused on optimizing the synthetic routes and have compared several homo and cross coupling reactions. It was determined that homocoupling offers a more efficient route than cross coupling, based on both the obtained product yield, as well as providing the desired symmetrical bipyridine adducts.
The procedure for each reaction is conducted in an inert, moisture-free environment. First, the reaction chamber is assembled in a glovebox protecting the air-sensitive catalysts and substrates. The reaction chamber is then moved onto a Schlenk-line assembly, where an inert argon atmosphere is provided for the reactions to progress under. Reaction times vary from 12 to 72 hours based on the starting substrate, while the reaction progress is monitored with thin layer chromatography. Final products are isolated and purified via acidic extraction, and if needed recrystallization. Compound characterization is carried out utilizing NMR and FT-IR.