Synthesis And Catalysis For Alcohol Oxidation Of An Oligomer Ruthenium Complex

The oxidation of alcohols to their corresponding carbonyl compounds is a fundamental transformation in organic synthesis.Traditional oxidation processes usually were realized with stoichiometric or even over-stoichiometric amounts of metal oxides or metal salts,which might bring about serious environmental problems and could not meet the development requirements of "green chemistry".Ruthenium complexes have emerged as efficient catalysts for the oxidation of various alcohols using environmentally benign oxidants such as molecular oxygen,hydrogen peroxide and tert-butyl hydroperoxide(TBHP).However,it is difficult to separate the expensive homogeneous catalysts from the reaction mixture,which makes them impossible to be employed in large scales.Thus,investigating the heterogenization of the ruthenium complexes for its recycling in the oxidation of alcohols is meaningful both in theory and potential application.In this thesis,a ligand with both a terpyridine and a pyridine-2,6-dicarboxylate groups(abbreviated as terpy-pydic)was designed and synthesized.This ligand reacted with [Ru(p-cymene)Cl2]2 to afford a novel oligomer ruthenium complex named as oligomer-Ru(terpy)(pydic).The intermediates and oligomer-Ru(terpy)(pydic)were characterized thoroughly by NMR,HR-MS,FT-IR,UV-Vis DRS,ICP,TG-DTA,XRD,SEM and EDX analysis.The catalytic performances of the oligomer ruthenium complex were evaluated in the oxidation of secondary alcohols.With 1-phenylethanol as the model substrate,the parameters such as reaction temperature,solvent,the loadings of TBHP and the catalyst were investigated,respectively.Meanwhile,the optimal reaction conditions of the oxidation of alcohols were obtained,which were 1-phenylethanol 2 mmol,oligomer-Ru(terpy)(pydic)0.1 mol%,molar ratio of TBHP to substrate 3:1,reaction temperature 50 °C,and n-hexane 2 mL.Under these conditions,both the conversion of 1-phenylethanol and the selectivity toward acetophenone reached up to > 99% in 9.5 h.The substrate tolerance of the catalytic oxidation system was also investigated under the optimal reaction conditions.It was found that the secondary benzylic alcohols with whether an electron-donating or an electron-withdrawing group could be oxidized to the corresponding ketones quantitatively.Though long reaction time and high TBHP loading were required,some aliphatic secondary alcohols were also oxidized to their corresponding ketones in excellent yields.For primary benzylic alcohols,over oxidation to the corresponding carboxylic acids were observed.Further experiments were performed to examine the reusability of oligomer-Ru(terpy)(pydic)with 1-phenylethanol as a model substrate.The results indicated that the catalyst could be recycled at least four cycles without a large reduction in its activity and selectivity.