Development Of Highly Active Benzimidazolium Salt-Palladium Catalyst Systems And Applications In Carbon-Carbon Bond Forming Reactions

The dissertation consists of the construction of palladium-benzimidazolium salt catalyst systems and their applications in the Suzuki cross-coupling and Heck reaction.A practical and highly active palladium catalyst system, PdCl₂- benzimidazoliumfor the Suzuki coupling of aromatic halides with arylboronic acids has been constructed from direct combination of PdCl₂ with N,N'-dialkylbenzimidazolium chloride in DMF-H2O. A different substitutent effect has been uncovered with respect to nitrogen substituents in the benzimidazolium salts from the palladium-imidazolium salt analogs. That is the system with N-alkyl substitutes shows higher catalytic activity that that with N-aryl substitutes in the PdCh- benzimidazolium system while a reverse trend has been identified for the Pd-imidazolium systems. The coupling of a wide array of aromatic halides with arylboronic acids with the PdCl₂-benzimidazolium catalyst systems gave good to excellent yields. The effective palladium loading could be as low as 0.0001 mol% and 0.01-0.1 mol% for iodide and bromide substrates, respectively. The coupling of unactivated aromatic chlorides with arylboronic acids also gave good results using Cs₂CO₃ as base with a 2 mol% palladium loading. The aromatic halides with modest steric hindrance could also couple smoothly with phenylboronic acids using the catalyst system. The electronic factors from aromatic halides exert a significant influence on the Suzuki coupling catalyzed by the PdCl₂- benzimidazolium system while the electronic effect from the arylboronic counterparts is negligible.The Heck reactions of aryl bromides and chlorides are efficiently catalysed by the palladium-N,N-dialkylbenzimidazolium catalyst system in molten tetrabutylammonium bromide (TBAB) as ionic liquid reaction medium. Remarkable electronic effects from the benzimidazoliums on the catalysis have been observed. The comparative electron-donating substituent at positions 5 and 6 in benzimidazolium salts displayed higher catalytic activity than electron-neutral and electron-withdrawing benzimidazolium salts analogs. Reaction of 4-chloroacetophone...