| A series of functionalized ionic liquids (IL), including nitrile, ether, and hydroxyl-functionalized, have been synthesized and were evaluated as solvents in Suzuki, Heck, Stille and hydrogenation reactions.Highly stable palladium nanoparticles (Pd NPs), protected by an imidazolium-based ionic polymer (IP) in a functionalized IL, have been prepared. Transmission electron microscopy (TEM) analysis reveals that the Pd NPs have elliptical shape with average size of 5.0±0.2 nm. These Pd NPs are excellent pre-catalysts for Suzuki, Heck and Stille coupling reactions. For comparison, coupling reactions were catalyzed by lager Pd NPs synthesized by seeding growth method. On the basis of evidences by UV-Vis the mechanism catalyzed Pd NPs in ILs was proposed which follows classic catalytic cycle, involved oxidative addition, chemical etching, transmetalation, reductive elimination. The system may therefore be considered as an alternative to the traditional palladium on carbon (Pd/C) pre-catalyst employed in many C-C coupling reactions, also allowing reactions to be conducted under'solvent-free'conditions.Imidazolium- and pyridinium-based ILs with ether/polyether substituents have been evaluated as solvents for palladium catalyzed Suzuki C-C coupling reactions. In general, reactions proceed more efficiently in these solvents compared to other ILs, which is believed to be due to better stabilization of the palladium catalyst, involving weak interactions with the ether groups. Both position and the number of the oxygen atoms in the ether side-chain strongly influence the outcome of the coupling reactions in the imidazolium-based ILs, whereas for the pyridinium-based liquids no influence is observed. Carbene derivatives, generated from the imidazolium-based ILs, are synthesized, isolated, characterized by X-ray single crystal diffraction from stoichiometric reactions and believed to play a role by terminating the catalytic cycle.A highly efficient system for the Suzuki reaction based on hydroxyl- functionalized ILs has been established. 1H NMR analysis reveals that hydroxyl group has strong interaction with Br- and Cl- which leads to higher solvation of halide than in unfunctionalized ILs. The role of the OH group appears to be multifactoral, with facilitating oxidative addition and generation of the catalytic active Pd(0), enhancing the metathesis step between base and halide, preventing catalyst poisoning by solvation, decreasing its nucleophilicity.PVP stabilized rhodium nanoparticles are highly soluble in hydroxyl-functionalized ILs, providing an effective and highly stable catalytic system. Solubility of PVP is enhanced more than ten times by hydroxyl-functionalized ILs therefore provides an ability of Rh NPs to catalyze more efficiently in hydrogenation of unsaturated double and triple bonds. The combination of imidazolium-based cation and tetrafluoroborate is found to be the most efficient one in hydrogenation reactions. This system can be recycled more than nine times without significantly decreasing of catalytic activity in hydrogenation of styrene. However the slight drop of yields from seven batches is not due to catalyst leaching or decomposition which appears to be due to the formation of polystyrene identified by IR spectroscopy.
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