Study On Synthesis Of Hydroxypyridyl/Pyridonate Complexes And Their Applications In Borrowing Hydrogen/Acceptorless Dehydrogenative Condensation Reactions

In recent years,a large number of metal-ligand cooperative catalysts have been reported.The ligands of these metal catalysts often contain some proton sensitive groups,such as-OH,-NH₂ and-CH₂.These proton sensitive groups can undergo dearomatization in the presence of alkali,which will change the structure of their ligands and affect the density of electron cloud in the metal center.In addition,borrowing hydrogen and acceptorless dehydrogenative condensation reactions have been considered as green and environmentally friendly strategies with high atom economy in these years.The earliest research in this field mainly focused on noble metal complexes such as ruthenium and iridium-based catalysts.However,many catalytic reaction conditions are relatively harsh,the reaction selectivity is poor,and the application range of substrates is limited.Moreover,the ligands of many catalysts are very sensitive to oxygen and water,and the synthesis path is complex.Combined with the recent research on hydroxy-pyridine synergistic catalysts in our group,a series of stable metal Ru,Mn and Ni catalysts with 2-hydroxypyridyl structure were designed and synthesized in this thesis.The reaction conditions of borrowing hydrogen/dehydrogenation were optimized by changing the structure of ligands or metal centers.Finally,a series of Ru,Mn and Ni catalysts containing 2-hydroxypyridyl group were designed to catalyze the synthesis of various alcohols,ketones,amines and N-heterocyclic compounds by borrowing hydrogen and acceptorless dehydrogenative condensation reactions,which has important implications for green chemistry.First,three bidentate ruthenium(?)complexes with a pyridonate fragment were prepared and fully characterized.These complexes are structurally similar,but differ in their pendant substituents.Complex[(O-C₅H₃N-C₅H₃N-CH₂-C₆H₅)RuH(PPh₃)₂(CO)](1)contains a phenyl unit,whereas complexes[(O-C₅H₃N-C₅H₃N-CH₂-C₄H₃S)RuH(PPh₃)₂(CO)](2)and[(O-C₅H₃N-C₅H₃N-CH₂-C₃H₂NS)RuH(PPh₃)₂(CO)](3)have uncoordinated thienyl and thiazolyl groups,respectively.These complexes were tested as catalysts for?-alkylation of secondary alcohols with primary alcohols,and 3 shows the highest activity,suggesting the thiazolyl ring participates in the catalytic process.Furthermore,3 is an excellent catalyst for?-alkylation of ketones with primary alcohols.Various?-alkylated ketones were synthesized in high yields,by using 0.05 mol%3 and 0.25 equiv of t-BuOK within 30 min,and the highest yield could reach up to 92%.To the best of our knowledge,complex 3 is the best catalyst for?-alkylation of ketones with primary alcohols up to the time of publication,with TOF up to 3680 h^-1.On the basis of the obove results,the metal Ru(?)catalysts were further applied to N-alkylation of aromatic amines with primary alcohols.After the screening of catalysts,complex 3 is also the best catalyst,which is consistent with the previous work.It once again showed that the uncoordinated N-heterocycle in the ligand played an important role in the catalytic cycle.A series of chain amine compounds with different substituent groups were synthesized via 0.1 mol%complex 3 and 1.5 equiv of KOH in refluxing toluene for 1 h,and the highest yield could reach up to 94%,with TOF up to 940 h^-1.Then,the metal Ru(?)catalysts were further applied to the synthesis of quinoline and naphthyridine derivatives via acceptorless dehydrogenative condensation(ADC)strategy,using o-aminobenzyl alcohol and ketones as the starting materials.Similarly,complex 3 has the higher activity.With 0.3 mol%catalyst loading and 1.0 equivalent of KOH,26 quinoline derivatives were isolated in high yields within 2 h at 120?,and the highest yield could reach up to 90%.Moreover,under similar conditions,this multifunctional catalyst is also applicable to the preparation of other N-heterocycles,and a series of naphthyridines,pyridines and pyrroles were generated.Next,a series of bidentate manganese(?)complexes were synthesized and characterized.And these manganese(?)complexes were used to catalyze the synthesis of quinolines and 1,2-disubstituted benzimidazoles via acceptorless dehydrogenative condensation(ADC)strategy.A series of quinoline and naphthyridine derivatives with different substituent groups were obtained by using2 mol%[(C₈H₅N₂-C₅H₃N-OH)Mn(CO)₃Br](9)as catalyst,1 equivalent of t-BuOK,and o-aminobenzyl alcohol and acetophenone as standard reaction substrates in refluxing toluene for 20 h,and the highest yield was 75%.Under the similar conditions,the complex 9 can also catalyze the synthesis of 1,2-disubstituted benzimidazoles(2 mol%,1.5 equivalent t-BuOK and 20 h),and the highest yield could reach up to 85%.In addition,a series of tridentate NNN-Mn(?)complexes were also synthesized and characterized.For the synthesis of quinoline compounds,the catalytic activity of complex[(O-C₅H₃N-C₅H₃N-CH₂-C₅H₄N)Mn(CO)₃](12)is better than that of complex[(HO-C₅H₃N-C₅H₃N-CH₂-C₅H₄N)Mn(CO)₃]Br(11),therefore,complex 12 is the intermediate of catalytic process.Finally,we synthesized and characterized five NNN-nickel(?)metal complexes.These complexes were also used to catalyze the synthesis of quinolines via acceptorless dehydrogenative condensation(ADC)strategy.After the screening of catalysts,complex[(HO-C₅H₃N-CH₂-C₅H₃N-C₅H₄N)Ni(CH₃O)₂Cl](15)showed the highest activity,and various quinolines and naphthyridines were synthesized in good yields,by using 10 mol%15 and 1.0 equiv of t-BuOK within 24 h at 130?,and the highest yield could reach up to 85%,at the same time,the variety of cheap metal catalyst is expanded.