Synthesis And Application Of N-Heterocyclic Carbene Ligands With A Biphenyl Backbone

This dissertation has mainly described some studies on the synthesis of axially chiral N-heterocyclic carbene (NHC) ligands with a biphenyl backbone, their coordination with transition metals (metal=Pd, Rh, Au), and the application of these NHC-metal complexes in the catalytic reactions. It was divided into three parts.1 A new family of imidazole-coordinated monodentate NHC-Pd complexes?-10a-d was obtained as well as cis-chelated bidentate NHC-Pd complexes?-lla-b from novel bis(imidazolium) salts with a biphenyl backbone, which derived racemic from 6,6'-dimethoxybiphenyl-2,2'-diamine. From the coordination of bis(imidazolium) salts with difference N-alkyl groups, it was found that?-10a-d could be obtained when the alkyl group has?-H. Applied this type of Pd complexes in Mizoroki-Heck coupling reaction under very mild conditions, it was found that good to excellent catalytic activities were obtained. Using chiral 6,6'-dimethoxybiphenyl-2,2'-diamine as starting material, axially chiral bidentate NHC-Pd complex?-11b was obtained, which was used to catalyze the oxidation kinetic resolution of secondary alcohols. Appropriate conversions (48-68% conv.) and moderate to good enantioselectivities (53-94%ee) were obtained.2 A new bidentate NHC-Rh(?) complex (R)-?-1, was synthesized from axially chiral bis(imidazolium) salt, and its structure has been confirmed by X-ray diffraction. This NHC-Rh complex was further applied in the asymmetric hydrosilylation reaction, which showed good to excellent catalytic activities in most ketones with 68-86%yields and moderate to good enantioselectivities (59-98%ee), with the exception of?-keto esters (20% ee).3 A series of axis chiral N-heterocyclic carbene precursors and NHC-Au complexes?-6a-c, were synthesized from chiral single-sided acylation of 6,6'-dimethoxybiphenyl-2,2'-diamine, and the structure of III-6a has been confirmed by X-ray diffraction. These NHC-Au complexes were applied to catalyze intramolecular hydroxylamine reaction. It was found that 2-adamantane carbonyl substituents with bigger steric hindrance afforded the higher enantioselectivity (43%ee), but with lower yiled (47%). A novel NHC-coordinated allylpalladium(?) complex?-8 was also synthesized, and its structure was confirmed by X-ray diffraction.?-8 complex as catalyst was applied in Suzuki-Miyaura and Mizoroki-Heck coupling reactions, and good to excellent yields of coupling products were afforded.