[1- (N-methylphthalimide)-3-alkylbenzimidazol-2-ylidene] synthesis and properties of silver and palladium complexes

The N-heterocyclic carbene (NHC) precursors and their transition metal complexes are draw great attention and the number of studies on their use as catalyst increases. Some of the catalysts developed in this regard have been used on an industrial scale. Among the synthetic methods, palladium-catalyzed cross-coupling reactions are one of the most useful and most important methods for organic chemists to achieve C-C bonding at the intended aim and in moderate conditions. Over the last 15 years, the Pd-based NHC complexes have the high conversion in cross-coupling reactions and led to the choice of NHCs instead of phosphines as ligands. The Pd-NHC complexes contain a strong Pd-C bond, low ligand / Pd ratio and contribute to the high stability of the active species, even at high temperatures. In addition, a new approach to the metal center in the metal-NHC complexes in recent years has been developed to link a second ligand with the NHC ligand. Thus, the new complexes are more stable, effective and selective. The studies and results obtained within the scope of this thesis can be summarized under six headings: 1) In this study, N-methylphthalimide substituted benzimidazolium bromide and benzimidazolium chloride (2a-ı) were synthesized as carbene precursor and their structures were elucidated by appropriate spectroscopic methods. 2) Synthesized benzimidazolium salts were reacted with PdCl2 in 3-chlorpyridine to give NHC-Pd(II)-3-chlorpyridine complexes (3a-c) and their structures were elucidated by appropriate spectroscopic methods. 3) Synthesized benzimidazolium salts were reacted with PdCl2 in pyridine to give NHC-Pd(II)pyridine complexes (4a-e) and their structures were elucidated by appropriate spectroscopic methods. 4) When the benzimidazolium salts containing butyl, isopropyl, benzyl and phthalimide substituents were activated in pyridine with PdCl2, the coordinated complexes of phthalimido-PdBr2-pyridine (5a) or pyridine-PdBr2-pyridine (5b) were obtained instead of the expected NHC-Pd-Pyridine complex, and the structures were determined by appropriate spectroscopic methods. 5) Synthesized benzimidazolium salts were activated with Ag2O in dichloromethane to obtain Ag(I)NHC complexes (6a-g) and their structures were elucidated by appropriate spectroscopic methods. 6) The catalytic activity of (NHC)Pd(II)X2 complexes (3, 4) were investigated in direct arylation reactions. KEYWORDS: N-heterocyclic carbene; benzimidazole; NHC-Pd(II)-pridine (PEPPSI) complexes; Arylation reaction.