Synthesis And Application Of Redox-Active Ligands: Preparation Of Oxindoles Via Quinone-Catalyzed Radical Cyclization And Design Of New Sterically Bulky N-Ligands

Redox active ligands Due to their unique electronic properties,the oxidation state of the ligand leads to paramagnetism,mimicking biochemical processes such as respiration and photosynthesis.9,10-phenanthrene is a common redox ligand,because o-quinone can undergo a continuous one-electron reduction process to produce semiquinone radical anions and catechol dianions,respectively.Quinones and their derivatives are involved in various electron transport processes in various chemical and biological systems because of their remarkable electron transport capacity.Quinones in particular are often used to promote oxidation or photocatalytic processes.Indoleone is a kind of common nitrogen heterocyclic structure skeleton,which is known to have good biological activity and has many biological functions such as anti-cancer,anti-oxidation and anti-bacterial.3,3-indole ketone is more common type of structure of indole ketone,in recent years,the intramolecular reaction synthesis of3,3-instead of indole ketone synthesis method has made considerable progress,however,the synthetic strategies also have some shortcomings,such as the need for expensive metals and some complex organic ligands,demanding reaction temperature is higher,need strong acid,alkali,It even requires toxic free radical initiators.In this study,a new method of metal-free intramolecular synthesis of 3,3-indoleone was developed and its reaction mechanism was studied.First of all,we optimized the reaction conditions and determined the optimal reaction conditions.Under this condition,most of the substrates showed good yield,which reflected the good functional group tolerance of the catalytic method.In addition,ideal yield can be obtained in gram-order reaction,which has good application prospect.Finally,we also carried out a preliminary study on the mechanism of the reaction,and the free radical trapping experiment confirmed that the reaction underwent a free radical process.We suggest that 9,10-phenoxone（PQ）,K₂CO₃,and 1,4-dioxane may act in a similar way and form a complex[PQ-K₂CO₃-dioxane],which participates in the reaction cycle,in which a single electron transfer process also occurs.In addition,the reaction of n-butyl lithium with a variety of[NN]redox active ligands with diphenylmethyl substitution was studied.Redox active ligand is a kind of ligand that can also undergo electron transfer reaction when it is coordinated with metal center.Due to its rich tunable electronic structure and reactivity properties,it has attracted extensive attention in coordination chemistry.On the basis of our previous work,a series of diaryl methyl substituted redox ligands withα-diimine,bis（arylimino）acenaphthene（BIAN）or imine pyridine（IP）skeleton structures were prepared by condensation reaction using aniline derivatives substituted by ortho diaryl methyl as precursors.Further,the possible C=N bond addition or deprotonation reaction mode was revealed by its reaction with a strong base reagent such as n-butyl lithium.The solid molecular structure of the obtained lithium complex（or its hydrolysate）was determined by single crystal X-ray diffraction method,which provided experimental support for the design and construction of a novel multi-tooth redox active ligand.