Highly Efficient Nitrogen-Phosphine Ligand:Synthesis And Application On C-N Coupling Reaction

Aromatic amines,heterocyclic amines and their derivatives are of great importance in organic chemistry,and act a key role as intermediates for synthesizing natural products,drugs,conductive polymers,organic light-emitting materials and dyes.Transition metal palladium-catalyzed C-N cross-coupling reaction is an effective way to build these compounds with advantage of high activity and mild reaction conditions.The general method for synthesis of amines is mainly palladium-catalyzed C-N coupling reaction of primary aromatic amine or alkyl amine with aryl bromides and iodides.However,the literature reports for the synthesis of triarylamines by using readily available and low-activity aryl or heteroaryl chlorides with poorly nucleophilic secondary aromatic amine are rare.The ligand structure defines the steric and electronic properties of the palladium catalyst,therefore plays a crucial role in the efficiency of C-N cross-coupling reaction.The development of highly efficient ligands has promoted the application of palladium-catalyzed C-N cross-coupling reaction.Most of highly efficient phosphine ligands that have been reported for the construction of C-N bonds of aromatic compounds are neutral phosphine ligands.Therefore,the development of highly efficient and novel anionic phosphine ligands to perform the amination of low-activity aryl and heteroaryl chlorides with secondary aromatic amines is of great significance.Based on that,the synthesis and structure characterization of three novel nitrogen-phosphine ligands and the activity test of 2 in palladium-catalyzed C-N cross-coupling reaction of aryl or heteroaryl chlorides with poorly nucleophilic secondary aromatic amines were carried out.In addition,we studied its mechanism of 2 in catalytic reactions.Details of the work are described as follows:1.Three highly efficient and borane protected nitrogen-phosphine ligands(1·BH3,2·BH,3·BH3)which are based on indenyl were synthetized.Their structures were characterized by 1H NMR,13C NMR,31P NMR and elemental analysis.The structures of borane protected ligands 1·BH3 and 2·BH3 were confirmed by X-ray diffraction techniques.2.Studies on the activity of novel ligand 2 for palladium-catalyzed C-N bond forming reaction of aryl or heteroaryl chlorides with secondary aromatic amines were carried out.The experimental results showed that pd(dba)2/2(2-(I,3-bis(dicyclohexyl phosphino)-1H-inden-2-yl)-N,N-dimethylaniline)catalytic system can effectively catalyze C-N coupling reaction.Coupling of an diverse array of aryl and heteroaryl chlorides with secondary aromatic amines were realized in good to excellent yields.3.We explored the high efficiency of ligand 2 and studied its mechanism of action in catalytic reactions.