Synthesis Of Tetraarylethylene Catalyzed By Non-phosphine Palladium Complexes And Study On C-N Activation Reaction

Tetraarylethylene and its derivatives and（hetero）biaryl compounds are widely used in drugs,biological activities,functional materials and aggregation-induced luminescence.These structures can be constructed by the three-component coupling reaction of internal alkynes,（hetero）aryl halides and（hetero）aryl boronic acid,and the C-N bond activation reaction of arylhydrazine.However,the existing palladium catalytic systems have shown higher palladium loading,lower catalytic activity or harsher reaction conditions in the catalytic construction of this kind of structural reactions,and most of the phosphine ligands are unstable in the air,toxic and seriously polluting to the environment.Therefore,this paper attempts to designα-diimine palladium complexes and nitrogen heterocyclic carbene palladium complexes to solve the above problems.1.Theα-diimine palladium complexes C1-C13 with different frameworks and ligand structures were designed and synthesized,and their structures were characterized by ¹H NMR and ¹³C NMR,and the single crystal structure of C4 was characterized by X-ray single crystal diffraction,and its catalytic performance for the reaction of internal alkynes,（hetero）aryl brominates with（hetero）arylphenylboric acid was evaluated.The effects of the relationship between the framework and ligand structure of the precatalyst and the steric hindrance of the substrate on the regio and stereoselectivity were further investigated.The palladium complex firstly reacts with brominated aromatics,and then the intermediate（Ⅱ）is coordinated with diphenylacetylene,migrated and inserted to undergo carbon-palladium reaction,and then the intermediate（Ⅳ）is metallized under the action of arylboric acid and alkali,and finally reduced and eliminated to form Z-or E-type tetraaryl substituted ethylene.The results show that the formation of Z or E type tetraaryl substituted ethylene depends on the steric hindrance interaction of diimine palladium complexes with aryl brominates and arylboric acids.Among them,when the steric hindrance of ortho substituents on arylboric acid is large,C4shows excellent selectivity and produces Z-based tetraaryl ethylene.The reason may be that the disubstituted large hindrance tert-butyl group was introduced into the 4,7-position of the C4 quinone skeleton,which increased the steric hindrance of aromatic amines and the repulsion between Ar²,borate and Ar¹due to the increase of substrate hindrance,which should have been easier to promote isomerization.However,at this time,the reaction temperature is low and the activation energy is high,and the free space is small,so that the configuration of olefins can not be reversed and isomerization does not occur,thus the highly selective Z-type tetra（hetero）aryl ethylene is obtained.2.Seven nitrogen heterocyclic carbene palladium complexes（Pd-NHCs）were synthesized,and the relationship between ligand structure and catalytic performance of palladium complexes was studied,the results show that their structures have an important effect on the catalytic performance of cross-coupling reaction.The mechanism shows that oxidation from intermediate LPd（0）to intermediate LPd（Ⅱ）is very important for conversion.Because of their strongσ-electron donor ability,these"large volume but flexible"Pd-NHCs,can form stable Pd-C bonds,thus promoting the cross-coupling reaction of Pd catalytic cycle.Based on this,we describe a kind of Suzuki-Miyaura cross-coupling catalyzed by C-N bond cleavage of arylhydrazine under the condition of air reaction in the presence of Pd-NHCs pre-catalyst,in which phenylhydrazine is used as an electrophilic reagent.It is found that Pd-PEPPSI-IPr is proved to be the best pre-catalyst,and various（hetero）biaryl compounds can be obtained in good to excellent yield in only 3 h at50℃.3.The precatalysts with different skeletons and ligand structures designed and synthesized in this paper can efficiently catalyze the reaction of a variety of functional group substrates,and the skeleton and N-aryl parts are included in the ligand design at the same time.Furthermore,disubstituted large hindered tert-butyl groups were introduced into the 4,7-position of the perylene quinone skeleton,which achieved another breakthrough and innovation in the design of the catalyst structure.At the same time,it provides a reference value for other researchers in this field in the structural design and synthesis of metal catalysts.