Studies On The Synthesis Of Chiral Multi-dentated N-Heterocyclic Carbene Precursors And The Catalytical Properties

Due to the strong electronic σ-donor property, N-heterocyclic carbenes (NHCs) have been recongnized as a new class of ligand. Besides the coordinating abilites, they display good air stability, and their versatile structure can be modified easily. The catalytic property of their metal complexes(M-NHC) in homogeneous catalysis including asymmetric reaction has been a focused research field. Many successful results have been reported in recent years, such as C-C coupling reaction catalyted by Pd-NHC and olefin metathesis reaction promoted by Ru-NHC. The design, synthesis of efficient, high selective M-NHC complexes, especially the NHC ligands or their precursors, is of great importance in the field of organic synthesis, catalysis and organometallic chemistry.In this thesis, reported are the synthesis of a series of multi-dentated precursors of N-heterocyclic carbene C2-symmetric imidazol(in)ium salts and their application in the transition metal-catalyzed reactions. The main research contents of the thesis were shown as follows:1) The C2-symmetric chiral imidazolinium tetrafluoroborate L1-L6which have hydroxyl, and L7-L9with methoxyl linked to the branchs of heterocycle have been synthesized via the conversion of optically pure β-amino alcohol or β-amino ether to substituted1,2-diamine using two methods, and the followed cyclization of the diamines. The C2-symmetric chiral imidazolium bromide L10-L15with aryloxy branchs have been synthesized though the substitution reaction between imidazole and chiral alkyl bromides prepared from optically pure a-hydroxyl carboxylates via arylation of hydroxy, reduction of ester group, and conversion of the hydroxyl. to bromide.2) Copper-NHC complexes generated in situ from Cu(OTf)2and NHC derived from chiral imidazolinium salts L1-L9and a base eg. KOBut or n-BuLi were applied to the enantioselective hydrosilylation of acetophenone with diphenylsilane. The multi-dentate NHC-Cu complex which derived from imidazolinium salt Li with KOBu/as the base were found to be able to catalyze the reaction, giving high conversions and up to87%yield in20min at room temperature. Up to97%yield was obtained with w-BuLi as the base at0-5℃, and the enantioselectivity was raised to25%. 3) Pd-NHC complexes generated from racemized imidazolium salts L10-L15and chiral imidazolium salts L12-L15, Pd(OAc)2and K2CO3in situ were utilized to catalyze the Suzuki coupling reaction of aryl halides with phenylboronic acids. The use of racemized precursors imidazolium salt L10resulted in the highest catalytic activity and the applicability of different substrates, including the substrates with various electronic effects and spatial effects.90-99%Isolated yields were obtained for the coupling reaction of aryl bromides substrates in5min to3h. The maximum of TOF value5.0×103h-were obtained with0.005mol%NHC precatalyst and the maximum of TON value105were observed with0.0005mol%NHC precatalyst respectively. It is also effective to the reaction aryl chlorides.71%Isolated yield is achieved.