蒽醌基金属-有机笼光氧化性能.pdf

第39卷第9期2023年9月Vol.39 No.916491660无机化学学报CHINESE JOURNAL OF INORGANIC CHEMISTRY收稿日期：20230404。收修改稿日期：20230605。国家自然科学基金(No.21861132004)资助。通信联系人。Email：蒽醌基金属-有机笼光氧化性能于艺彩1王海玲1李丽丽2何成,1(1大连理工大学精细化工重点实验室，大连116024)(2河南师范大学材料科学与工程学院，新乡453007)摘要：将光活性蒽醌配体L1和L2(L1=N2，N7双(2，2联吡啶)5基)9，10蒽醌2，7双酰胺，L2=N2，N7双(4(2，2联吡啶)5基)苯基)9，10蒽醌2，7双酰胺)与锌离子和亚铁离子通过配位自组装构筑得到一系列配合物1Zn、2Zn和2Fe，单晶X射线衍射和电喷雾质谱等表征表明这一系列配合物为“2+3”的M2L3型金属-有机超分子结构。将蒽醌基金属-有机笼1Zn与2Zn应用于甲苯光催化氧化反应中，结果表明笼状催化剂和底物分子间形成超分子主客体化合物是其能有效氧化甲苯的关键。通过对芳香醇的光氧化反应进一步探究1Zn与2Zn的光氧化性能，实验结果表明催化产率受到取代基的电子效应和底物分子的尺寸的影响。关键词：金属-有机笼；蒽醌；光催化氧化；超分子中图分类号：O614.24+1；O614.81+1文献标识码：A文章编号：10014861(2023)09164912DOI：10.11862/CJIC.2023.139Anthraquinonebased metalorganic cages as efficientphotocatalysts for oxidation reactionsYU YiCai1WANG HaiLing1LI LiLi2HE Cheng,1(1State Key Laboratory of Fine Chemicals,Dalian University of Technology,Dalian,Liaoning 116024,China)(2School of Materials Science and Engineering,Henan Normal University,Xinxiang,Henan 453007,China)Abstract:Anthraquinonebased metalorganic cages 1Zn,2Zn and 2Fe were constructed from ligands L1and L2(L1=N2,N7di(2,2bipyridin)5yl)9,10dioxo9,10dihydroanthracene2,7dicarboxamide,L2=N2,N7bis(4(2,2bipyridin)5yl)phenyl)9,10dioxo9,10dihydroanthracene2,7dicarboxamide)with Zn and Fe by coordination selfassembly.Single crystal Xray diffraction and electrospray mass spectrometry showed that this series ofcomplexes were M2L3type metalorganic structures.The 1Zn and 2Zn supramolecular systems were successfullyapplied to explore the oxidation of toluene into benzaldehyde,and the experiments suggested that the formation ofsupramolecular hostguest compounds between anthraquinonebased metalorganic cages and toluene was the key toeffective oxidation of toluene.The photooxidation performance of 1Zn and 2Zn was further investigated by thephotooxidation reaction of aromatic alcohols,and the results indicated that the catalytic yields are affected by theelectronic effects of the substituents and the size of the substrate molecules.CCDC:2251202,2Fe.Keywords:metalorganic cage;anthraquinone;photocatalytic oxidation;supramolecule无机化学学报第39卷0IntroductionAn artificial photocatalytic system inspired by natural enzymes that react under an ambient atmosphereand use moderate solvents and clean energy is a majorendeavor in catalytic chemistry13.To mimic the selectivity and efficiency of enzymatic systems,chemistshave constructed supramolecular systems with definedhydrophobic cavity sites to catalyze specific chemicaltransformations based on their special microenvironments46.Coordinationdriven selfassembled metalorganic cages(MOCs)are outstanding candidates foremulating the qualities of enzyme active sites well712due to the exquisite structures and high order functionssuch as catalysis1316,separation17,drug delivery1819,andstabilizingactivatedspecies2021.Inaddition,MOCs can be used as hosts to encapsulate guest molecules22,allowing the components to be forced closerwithin the confined space and efficiently enhanced inelectron,energy,or substance transfer,which has alsobrought about widespread attention2324.The photocatalytic system,as a highly selectiveconversion and clean method for the synthesis of finechemicals,has been attracting much attention due tomild reaction conditions2526.More than ever,the selective oxidation of organic compounds by molecule dioxygen(O2)or air under light conditions is considered tobe availably and environmentally friendly and thus ofgreatacademicandapplicationsignificance2728.Anthraquinones(AQs)as favorable photocatalysts aregenerally applied in organic reactions29.In biochemistry,AQs which are components of redox proteins andenzymes30have been considered as the charge acceptors and carriers in electron transport reactions,suchas natural photosynthesis31and aerobic respiration32.AQs and its derivatives are well known for theirremarkable redox properties34.They can be employedas redox catalysts in organic reactions to generate reactive oxygen species(ROS),which have powerful oxidization,including hydroxyl radicals(OH),superoxideradical(O2-),and singlet oxygen(1O2)35.Recently,they have been proven to be effective in oxidizing inertC(sp3)H bonds33.Apart from the redox properties,AQsalso have excellent photocatalytic properties35.Withthe combined above two characteristics,we can assumethat AQs can be photocatalysts for aerobic oxidativereactions.Herein,weconstructednovelsupramolecularstructures featuring large hydrophobic cavities andfavorable light absorption,which were obtained by theself assembly of metal ions with well functionalizedand qualifiable AQsbased ligands to increase the levelof structural complexity and functional diversity.Benefiting from these characteristics,we have presented anaerobic oxidation system using metalorganic cages asphotocatalysts for the highly selective production ofrelevant carbonyl compounds through the oxidation oftoluene and aromatic alcohols using O2as the oxidantunder mild conditions and without the addition of additives.1Experimental1.1Materials and physical measurementsAllchemicalswereofreagentgradequalityobtained from commercial sources and used as supplied unless otherwise stated.1H NMR spectra weremeasured on a Varian DLG 400M spectrometer.Electrospray ionization mass spectrometry(ESI MS)wascarried out on an HPLCQTof MS spectrometer.UVVis spectra were measured on an HP 8453 spectrometer.Gas chromatographymass spectrometry was carried out in Agilent 6890N GC.Elemental analysis wasperformed on the Elementar Vario EL cube.Thermogravimetric analysis(TGA)was performed on SDTQ600 V20.9 Build 20 instrument.1.2Synthesis of the ligandsand cagesLigands L1and L2(L1=N2,N7di(2,2bipyridin)5yl)9,10dioxo9,10dihydroanthracene2,7dicarboxamide,L2=N2,N7bis(4(2,2bipyridin)5yl)phenyl)9,10dioxo9,10dihydroanthracene2,7dicarboxamide)were synthesized according to established methods bycoupling 9,10quinone2,7dicarboxylic acid36to 5amino2,2bipyridine37and 5(4aminophenyl)2,2bipyridine38,respectively.A detailed description ofeach of these steps followed.1.2.1Synthesis of L1and L220 mL thionyl chloride and 9,10quinone2,71650第9期dicarboxylic acid(0.8 g,2.7 mmol)were added into a100 mL roundbottom flask,then three drops of DMFwere added.The mixture was heated at 80 for several hours.The solvent was spun off after the reactionsolution was clarified to obtain a yellowgreen solid.The obtained solid was dissolved in 80 mL of dry tetrahydrofuran,and 80 mL of tetrahydrofuran solution of 5amino2,2bipyridine(1.4 g,8.1 mmol)containing 3mL of triethylamine was added dropwise.After the mixture was stirred at room temperature overnight,the temperature was raised to 85 and the reaction was continued for 10 h.Then the solution was cooled to roomtemperature and suction filtered.The upper filter cakewas washed with dichloromethane,methanol,and waterin turn and dried to obtain buff ligand L1(1.4 g,2.3mmol)with a yield of 85.6%.1H NMR(400 MHz,DMSOd6):11.07(s,2H),9.10(s,2H),8.84(d,J=12.0 Hz,2H),8.67(d,J=4.1 Hz,2H),8.51(s,2H),8.38(dd,J=21.6,7.6 Hz,8H),7.93(s,2H),7.43(s,2H).Elemental analysis Calcd.for C36H22N6O4(%):H,3.68;C,71.75;N,13.95.Found(%):H,3.91;C,71.63;N,12.53.The ligand L2was synthesized in a similar way toL1except that 5amino2,2bipyridine was replacedby 5(4aminophenyl)2,2bipyridine,claybank ligandL2(1.6 g,2.2 mmol)was obtained with a yield of79.5%.1H NMR(400 MHz,DMSOd6):10.92(s,2H),9.07(s,2H),8.85(d,J=7.6 Hz,2H),8.72(d,J=6.2 Hz,2H),8.54(d,J=8.1 Hz,2H),8.508.41(m,6H),8.29(d,J=8.5 Hz,2H),8.057.96(m,6H),7.90(d,J=8.7Hz,4H),7.47(s,2H).Elemental analysis Calcd.forC48H30N6O4(%):H,4.01;C,76.38;N,11.13.Found(%):H,4.63;C,75.53;N,10.16.1.2.2Synthesis of 1Zn and 2ZnTreating L1(180.6 mg,0.3 mmol)or L2(226.2 mg,0.3 mmol)with Zn(BF4)2(47.8 mg,0.2 mmol)in 30 mLDMF at 80 for 16 h resulted in the formation of anew set of“2+3”type cages 1Zn and 2Zn(Scheme1),respectively in yields of 75.8%and 72.1%,basedon the solid dried on vacuum.Elemental analysisCalcd.for Zn2(C36H22N6O4)34BF4C3H7NO(%):H,3.12;C,56.52;N,11.28.Found(%):H,3.05;C,56.34;N,11.35.Elemental analysis Calcd.for Zn2(C48H30N6O4)34BF4C3H7NO(%):H,3.47;C,62.71;N,9.45.Found(%):H,3.54;C,62.49;N,9.36.The characterizationsof1H NMR,ESIMS spectra,and TGA of the cages areshown in subsequent results and discussion.1.2.3Synthesis of 2FeIn the presence of Ar,treating L2(226.2 mg,0.3mmol)with Fe(BF4)26H2O(67.5 mg,0.2 mmol)in 30mL DMF at 65 for 12 h resulted in the formation of2Fe in yields of 76.9%,based on the solid dried on avacuum.Elemental analysis Calcd.for Fe2(C48H30N6O4)34BF4H2OC3H7NO(%):H,3.55;C,62.73;N,9.46.Found(%):H,3.53;C,62.21;N,9.80.The single crystal Xray analysis and TGA of 2Fe are shown in subseScheme 1Schematic representation of the synthesis of cages于艺彩等：蒽醌基金属-有机笼光氧化性能1651无机化学学报第39卷quent results and discussion.1.3Xray crystallographyA brown red crystalline product of 2 Fe wasobtained by diffusion of diethyl ether into the mixtureof ligand L2and Fe(BF4)26H2O in DMF solution.Xrayintensities of the complex were collected on a BrukerD8 Venture diffractometer with graphite monochromated Mo K(=0.071 073 nm)using the SMART andSAINT programs.The structure was solved by directmethods and refined on F2by fullmatrix leastsquaresmethods with SHELXTL2018.In the structural refinement,except the partly occupied solvent molecules andthe disordered parts in the cage,the other nonhydrogen atoms were refined anisotropically and hydrogenatoms within the ligand backbone were fixed geometrically at calculated distances and allowed to ride on theparent nonhydrogen atoms.The highly disorderedstate of the incorporated molecule solvents meant thatlots of them could not be located,and hence in thefinal refinement,the electron density was treated withthe SQUEEZE routine in the PLATON program package.One of the benzene rings,and the BF4-counterions were disordered into two parts with the site occupied factors(s.o.f.)of each part being fixed in suitablevalue.To assist the stability of refinements,several restraints were applied:(1)geometrical constraints of idealized regular polygons for the disordered benzene ringin the ligand were used,with phenyl ring CC bondlengths of 0.139 nm,and CC distances diagonallyacross the phenyl ring of 0.278 nm;(2)the respectivebond distances in the BF4-anions were restrained tothe idealized geometry;(3)thermal parameters on adjacent atoms the disorder parts and the BF4-anions wererestrained to be similar.The A alert in checkcif wascaused by the weak diffraction intensity of the crystal.The crystal data of complex 2Fe are summarized inTable 1.CCDC:2251202,2Fe.Table 1 Crystal data and refinement details for complex 2FeParameterFormulaFormula weightCrystal systemSpace groupa/nmb/nmc/nm2FeFe2C144H96B4F16N18O15xsolvent2 777.32TrigonalR32.002 1(2)2.002 1(2)7.025 7(8)ParameterV/nm3ZDc/(gcm-3)F(000)Reflection measured,independent,observed I2(I)Rint2Fe24.389(6)61.1358 53237 512,5 624,2 5980.0742Results and discussion2.1Characterization and crystal structureThe formation of the cages was characterized by1H NMR analysis and ESIMS.The1H NMR spectra ofcomplexes 1Zn and 2Zn showed one set of signalsafter coordination,which suggested the formation ofdiscrete and symmetric assemblies,and most signals of1Zn and 2Zn showed slight downfieldshifted resonance concerning the free ligands,respectively(Fig.1aand 1b).ESIMS spectrum was conducted for supporting the formations and stability of these cages in solution.The spectrum of 1Zn exhibited signals displaying the expected isotopic patterns at m/z 484.59,675.12,and 1056.18(Fig.1c).A simple comparisonwith the simulation results based on the natural isotopic abundances indicated that the peaks correspond toZn2(L1)3(BF4)n(4-n)+(n=02).In the same way,as shownin Fig.1d,the main peaks in the ESIMS spectrum of2Zn were observed at m/z 598.64,827.19,and1 284.28,which are assigned to Zn2(L2)3(BF4)n(4-n)+(n=02),respectively.The results revealed the formation ofstable Zn2L3species for each complex.The TGA showed that solvent molecules in powders dried on a vacuum of 1Zn,2Zn,and 2Fe couldbe removed in a temperature range of room temperature to 110,120,and 110,respectively(Fig.2).Theresults indicated that the complexes 1Zn and 2Zncould maintain structures stabilization during the catalytic process at room temperature.1652第9期Fig.11H NMR spectra of(a)1Zn and L1,(b)2Zn and L2in DMSOd6(298 K,400 MHz)and ESIMS spectra ofcages(c)1Zn and(d)2Zn with an inset showing the observed and calculated isotope patternsThe data was collected under N2followed by a ramp of 10 min-1up to 1 000.Fig.2TGA curves of(a)1Zn,(b)2Zn,and(c)2Fe于艺彩等：蒽醌基金属-有机笼光氧化性能1653无机化学学报第39卷The lightharvesting capability of the complexeswas investigated by UVVis absorption spectra and fluorescence spectrum.The UV Vis absorption spectraabsorption peaks of 1Zn were similar to that of L1,but the maximum absorption peak position of 1 Znshowed a significant redshift,however,the UV Visabsorption spectra of 2Zn revealed a new absorptionband at 335 nm compared with that of the ligand L2(Fig.3a and 3b).At an excitation wavelength of 350nm,1 Zn exhibited a strong fluorescence emissionpeak at 432 nm,which occurred a little red shift compared to L1,while the fluorescence emission peak at419 nm for 2Zn revealed a little blue shift comparedto that of L2(Fig.3c and 3d)at an excitation wavelengthof 320 nm.Therefore,the above photophysical studiesdisclosed that the complexes have good photoactivityand can be applied in the photocatalytic field.Since the quality of single crystals for 1Zn and 2Zn was too poor to get structural information,the single crystal analysis of 2Fe with a similar coordinatedconfiguration was carried out to show the M2L3structural feature of these complexes(Fig.4).Singlecrystal Xray diffraction study revealed that 2Fe crystallizes inthe trigonal crystal system with the R3 space group.Each L2ligand coordinates with two Fe centersthrough its two chelating 2,2bipyridine groups.And,two Fe ions located in the vertexes are linked bythree L2ligands to form a C3symmetric“2+3”helicatecage.In each of the three ligands,the 2,2bipyridinering planes are not coplanar with the anthraquinonebackbone,and the two planes are approximately perpendicular to each other.The anthraquinone rings areoriented with their edges directed to the center of thecage.2.2Photooxidation reactionEncouraged by the photoredox activity of anthraquinone groups and the welldefined cavities,we decided to evaluate the usefulness of cages 1Zn and 2Znas photocatalysts for oxygenation.In a typical experiment,the oxidation reaction employing the photocataFig.3UVVis absorption spectra and fluorescence spectrum of L1,L2,1Zn,and 2Zn1654第9期lyst 1Zn/2Zn(0.1 mol)and toluene(0.03 mmol)ina Schlenk quartz tube containing 3.0 mL MeCN/H2O(1 1,V/V)as the solvent in the presence of O2at roomtemperature gave product benzaldehyde with yields of16.9%and 12.8%,and the turnover number(TON)values were 50.8 and 38.5 within 3.5 h under 365 nmLED irradiation(Table 2,Entry 1).It is worth notingthat benzaldehyde pr