Ruthenium Complexes With A Pincer Ligand Bearing 1,2-Dihydropyrimidine:Synthesis And Catalysis In Oppenauer-type Oxidation

1,2-Dihydropyrimidine is an important member of unsaturated N-heterocycles,in which a unique conjugate structure supplies the imine nitrogen atom as an excellent electron-donor with a lone pair unshared in addition to electron cloud shared by the conjugate system.Although metal complexes(such as of Cr,Co,Ni,Cu,Zn,Ru,Pd,Ir and Pt)coordinating with 1,2-dihydropyrimidine have been widely reported,there is no report available on a pincer ligand or its complexes bearing such a unit.Oppennauer-type oxidation is a powerful method in transforming alcohol into ketone,and has been applied widely in the synthesis and derivation of natural products and in chemical industry.Compared with other oxidations,there are several advantages in this reaction,such as simple operation,mild and environment-benign conditions,and high selectivity.A variety of ruthenium complexes have been reported on this catalysis.However,examples under phosphine-free conditions are scarce.This thesis desicribes the synthesize of the first pincer ligand containing a 1,2-dihydropyrimidine unit and its ruthenium(II)complexes as well as their catalytic application in Oppenauer-type oxidation.The contents of this thesis are mainly as follows:1.The synthetic method and coordination of 1,2-dihydropyrimidine are introduced as well as the Oppenauer-type oxidation catalyzed by ruthenium complexes,followed by the ideas on design of this work.2.The first pincer ligand containing a 1,2-dihydropyrimidine unit and its ruthenium(II)complexes were synthesized.On the basis of improvement upon the reported method,the rearrangement of pyrazolium with sodium hydroxide at room temperature gives the corresponding 1,2-dihydropyrimidine as a part of pincer ligand in excellent yield.Ligands exchange between the ligand and cis-Ru Cl₂(DMSO)₄ was investigated to afford meridional ruthenium complex Ru Cl₂(DMSO)(L)(Ru1),from which removal of chlorides produces ruthenium(II)complexes[Ru(L)(CH₃CN)₃](BF₄)₂(Ru2)and[Ru(L)(CH₃CN)₃](PF₆)₂(Ru3).New compounds were characterized by NMR spectroscopy and MS or elemental analysis,in addition,the structures of the ligand precursor pyrazolium and the ruthenium complex Ru2 were confirmed by single crystal X-ray diffraction.3.The Oppenauer-type oxidation catalyzed by the synthetic ruthenium complexes was investigated.After the reaction conditions were carefully optimized,the scope of substrates was screened.Secondary alcohols,including natural product cholesterol,can be oxidized efficiently to ketones under mild conditions in high yields with the ruthenium complex Ru1 as a catalyst.Distinct steric effects were observed from the outcome of substituted acetophenones.