The Design,Synthesis And Application Of Ionic Manganese Porphyrin And Ionic Liquid System In The Oxidation Of Hydrocarbon

Metalloporphyrin complexes have been widely used as the bimimetic oxidationcatalysts to mimic the behavior of mono-oxygenase cytochrome P-450.In this work,we proposed a strategy to modify the conventional neutral metalloporphyrin complexesinto the ionic ones to facilitate its compatibility with the ionic liquid(IL)solvent.Thecatalytic performance of the developed ionic metalloporphyrins in the ILs was theninvestigated towards hydrocarbon selective oxidations.The obtained results weresummarized as follows.(1) Design,synthesis and characterization of the ionic metalloporphyrins and thecorrespongding ionic liquidsBy modifying the conventional neutral manganese porphyrin with differentquaternary ammonium cations along with PF_~- as the counteranions,we synthesizedfour kinds of ionic manganese porphyrins which could be regarded asporphyrin-functionalized ILs.The ionic porphyrin free bases and the manganese ionicmetalloporphytins were characterized by ~1HNMR,UV-Vis,IR,ESI-MS,and TDG.According to the literature,a number of the ionic liquids with the similar structures tothe ionic manganese porphyrins were also synthesized and characterized thoroughly.(2) Investigation on the selective oxidations of hydrocarbons catalyzed by thedeveloped ionic mamganese porphyrins in EL solutionIn this part the catalytic performance of ionic metalloporphyrins immobilized in thesimilar structured ILs were studied for selective oxidations of styrene and ethylbenzene.After screening a series of the ionic mamganese porphyrins and the ILs,the followingthree systems were the optimal ones in terms of activities,stability and the recyclability. It was found that,without the auxiliary involvement of axial ligands and organic solvents,A efficiently catalyzed the epoxidations of styrene and its derivatives under mild conditions,affording high activity/oxide selectivity and good stability even after 5 recycling uses.The conversion of styrene and the selectivity to styrene oxide were 96% and 90% respectively under the optimal conditions.In system B,the conversion of styrene and the selectivity to styrene oxide were 96% and 96%,respectively,under the optimal conditions.It was also found that in system B water could accelerate the reaction rate greatly.Through UV-vis analysis,wefound that the interaction between B and water gave rise to stabilize the activeintermediate species of Mn~V=O porphyrin.C is not only an efficient catalytic system for the epoxidation of styrene and itsderivatives with high activity/oxide selectivity,but also exhibited high activity tooxidation of ethylbenzene and its derivatives,affording 65% ethylbenzene conversionand acetophenone 75% selectivity under the optimal conditions.The UV-Vischaracterization revealed that system C was more favorable to the formation andstability of the active intermediate species Mn~V=O porphyrin than the other twosystems.The systems of A,B,and C all showed good generality to the substrates with theconjugated nature like styrene derivatives and ethylbenzene derivatives.Compared with the conventional neutral manganese porphyrins towards hydrocarbonoxidations in organic solvents,the developed ionic manganese porphyrins immobilizedin the similar structured IL solvents were endowed with advantageous activity/stabilitywhich depended on many factors including that:①the IL solvent dually acted as theaxial ligands,avoiding the involvement of the imidazole or pyridine(derivatives),which is susceptible to oxidation and then sacrificed by excess oxidant;②the ILsbased on pyridiniurn or imidazolium with conjugated features could interact with thesuper-conjugated porphyrin throughπ-πinteractions;and the strongelectron-withdrawing effect of the cation in metalloporphyrin could decrease theelectron density of porphyrino ring;③the compatibility between the ionicmetalloporphyrins,the ILs,and the substrates avoided the mass transfer limitation.