Study On The Synthesis, Characterization Of [N, N] Bidentate Ligands And Their Applications In Suzuki Reaction

Palladium catalyzed Suzuki reaction is one of the most effective methodologies incarbon-carbon bond formation, which plays an important role in organic synthesis.Palladium catalysts also play a very important role in Suzuki reaction. Choosing a properpalladium catalyst not only improves the reaction conditions but also enhance the reactionyields. Palladium sources and ligands are usually mainly the two components of thepalladium catalysts. And palladium acetate and palladium dichloride are used widely in thereaction while ligands mainly consisit of phosphanes, carbenes and nitrogen donor ligands.Ligand designing and synthesis are becoming more extensively researched because of itsgreat importance in catalyzing Suzuki reactions. Different ligands usually have differenteffects on Suzuki reactions.In this study, fourteen [N, N] bidentate ligands were synthesized and characterized,including pyridylbenzamidine ligands(L1-L6), N-acylpyridylbenzamidine ligands(L7-L10)and aminoimino ligands(L11-L14). These ligands were applied in Suzuki reactions of arylbromides and aryl chlorides with arylboronic acids to examine their catalytic activities.In the series of six pyridylbenzamidine ligands, the experiments showed that L5exhibited the best catalytic efficiency. Screening of the ligands indicated that the catalyticactivities of the ligands were mainly controlled by the electronic and steric effecs of thebackbone structures of the ligands. Ligands with stronger electronic effects and steric bulks were more catalytically active than those with less electronic and sterically bulkysubstituents. L5did also worked well on the Suzuki reactions of other aryl bromides andaryl chlorides with arylboronic acids except for sterically hindered aryl bromides anddeactivated aryl chlorides. However, dehalogenation and homocoupling of some activatedaryl chlorides were observed.N-acylpyridylbenzamidine ligands were more active, indicating that the introductionof the benzoyl group increased the steric bulk of the ligands which promoted the reductiveelimination process of the reaction. In this catalytic system, dehalogenation andhomocoupling of the substrates were not obserbved.Aminoimino ligands showed the best catalytic activities.Especially reactions ofdeacticated4-chlorotoluene and phenylboronic acid catalyzed by L12gave66%yield. C-Nδbond was introduced into the structures which made the ligands structures more flexible,promoting both the oxidative addition and eliminative reduction processes of the reactions.