兩個菲咯啉銅配合物的合成、晶體結(jié)構(gòu)和催化性能

肖艷華 孫志康 胡星星 李亮 楊小俊 袁華 吳元欣 杜治平＊,,

兩個菲咯啉銅配合物的合成、晶體結(jié)構(gòu)和催化性能

肖艷華1孫志康1胡星星1李亮2楊小俊1袁華1吳元欣1杜治平＊,1,2

(1武漢工程大學(xué)，綠色化工過程省部共建教育部重點實驗室，湖北省新型反應(yīng)器與綠色化學(xué)工藝重點實驗室，武漢430073)
(2湖北迅達藥業(yè)股份有限公司，武穴435400)

在醇溶劑中合成了2個銅配合物[Cu(Ⅱ)(phen)2Br]2[Cu(Ⅰ)4Br6](1)和[Cu(Ⅱ)(phen)2Br]Br·CH3OH(2)(phen=菲咯啉)，并采用紅外光譜、元素分析、熱重和X射線單晶衍射對其進行了分析。1是Cu(Ⅱ)-Cu(Ⅲ)混價態(tài)化合物，并通過π-π作用和C-H…Br氫鍵作用形成了一個超分子網(wǎng)絡(luò)結(jié)構(gòu)。該化合物的結(jié)構(gòu)單元包括2個[Cu(Ⅱ)(phen)2Br]+陽離子和1個[Cu(Ⅰ)4Br6]2-四核陰離子；陰離子中的4個銅原子組成四面體結(jié)構(gòu)，而6個溴原子分別沿銅四面體的6個邊橋聯(lián)銅原子，形成八面體結(jié)構(gòu)。2由[Cu(Ⅱ)(phen)2Br]+、Br-和CH3OH組成，并通過π-π作用也形成了一個超分子網(wǎng)絡(luò)結(jié)構(gòu)。當(dāng)它們催化甲醇氧化羰基化合成碳酸二甲酯(DMC)時，2僅顯示了5.9的DMC轉(zhuǎn)化數(shù)，而1中的[Cu(Ⅰ)4Br6]2-陰離子能為甲醇的氧化羰基化反應(yīng)提供適宜的合成環(huán)境，DMC的轉(zhuǎn)化數(shù)達到54.7。

銅配合物；溶劑熱法；氧化羰基化；碳酸二甲酯

0 Introduction

Copper-haloid complexes have rich structural motifs,such as monomeric species[1],rhomboid Cu2×2dimers[2],cubane or stepped-cubane Cu4×4tetramers[3], Cu6×6clusters[4],zigzag[CuX]nchains[5],double-stranded [Cu2×2]nladders[6],[Cu6×6]nbanded ribbons[7],and 2D [CuX]nlayers[8].Among them,monovalent copper compounds exhibit strong fluorescence,electrical conductivity,and catalytic properties[9],divalent copper compounds exhibit magnetic,biological and catalytic properties[10],and mixed-valent Cu(Ⅱ)-Cu(Ⅲ)copper compounds exhibit biological and electronic properties[11].For controlling the topologies and properties of these copper-haloid complexes,it is important to rationally select ligands,type of the anions,and reaction conditions.Hence,the design and assembly of copper-haloid complexes have attracted increasing interestas an expanding field[12].

Herein,a Cu(Ⅱ)-Cu(Ⅲ)mixed-valent Cu complex, [Cu(phen)2Br]2[Cu4Br6](1)(phen=1,10-phenanthroline) was obtained from CuBr2and phen in alcoholby autoreduction,and the other Cu complex,[Cu(phen)2Br] Br·CH3OH(2),was synthesized from CuBr and phen in methanol by oxidation.Their structures were investigated by infrared spectroscopy,thermal analysis, and X-ray diffraction(XRD)single-crystal structure analysis,and their catalytic activities were investigated for the oxidative carbonylation ofmethanol.

1 Experimental

1.1 Materials and measurements

Methanol and anhydrous ethanol were freshly distilled prior to use.Other reagents were used as received without further purification.Elemental analyses were carried out on an elemental Vario EL analyzer.Diffraction intensity data were collected on a Bruker SMART APEX-ⅡCCD diffractometer.The thermal investigations were done on a Q50 thermalanalyzer under a dynamic nitrogen environment with a heating rate of 10℃·min-1.Infrared spectra were recorded on a Nicolet 6700 FT-IR spectrophotometer in the form of KBr pellets.

1.2 Syntheses of the complexes

Synthesis of[Cu(phen)2Br]2[Cu4Br6](1):First,4 mmol(0.792 g)of 1,10-phenanthroline dihydrate in 15.0 mL of ethanol was added dropwise to a solution containing 4 mmol(0.893 g)of CuBr2and 15.0 mL of methanol,followed by stirring for 30 min at25℃and filtered.Second,the residue and 25.0 mL of ethanol were added into a Parr Teflon-lined autoclave(50 mL) and heated at 150℃for 3 days.After cooling down to room temperature,dark green crystals were obtained. Yield:52.7%(based on Cu).Anal.Calcd.for C24H16Br4Cu3N4(%):C,33.11;H,1.85;N,6.43;Found(%): C,32.90;H,1.85;N,6.27.FT-IR(KBr,cm-1):3 048 (w),1 622(m),1 605(w),1 582(w),1 519(s),1 428 (s),858(s),721(s),493(m).

Synthesis of[Cu(phen)2Br]Br·CH3OH(2):First, CuBr(0.431 g,3 mmol)was added into methanol(20 mL).Second,the mixture was refluxed for 6 h under oxygen,followed by the addition of1,10-phenanthroline dihydrate(0.594 g,3 mmol).Third,the solution was refluxed again for 8 h,followed by filtration.After the solution was cooled to room temperature,the filtrate was placed in a refrigerator for two weeks to afford green crystals.Yield:53.1%(based on phen).Anal. Calcd.for C25H20Br2CuN4O(%):C,48.76;H,3.27;N, 9.10.Found(%):C,49.09;H,2.99;N,9.38.FT-IR (KBr,cm-1):3 030(vw),1 627(m),1 605(w),1 586 (m),1 518(s),1 427(s),1 104(m),852(s),722(s), 430(m).

1.3 X-ray data collection and structure refinements

Reflection intensities of the two crystals were collected on a Bruker APEX-ⅡCCD diffractometer with Mo Kαradiation(λ=0.071 073 nm).Lp correction and aψempirical absorption correction were made for intensity data.The structures of 1 and 2 were solved by direct methods,and further refined by the fullmatrix least-squares method on F2with anisotropic displacementparametersforallnon-hydrogen atoms[13-16]. Hydrogen atoms associated with carbon atoms were geometrically generated,and the remaining hydrogen atoms were located from the difference Fourier maps. Hydrogen atoms were further refined isotropicallyusing the riding model.In the final refinement,four copper atoms in 1 were found to be disordered and were represented by two sets ofatomic positions(Cu(2), Cu(3),Cu(4),Cu(5)and Cu(2A),Cu(3A),Cu(4A), Cu(5A))．The occupancy for each of them was 0.5. The solvate methanol in 2 was orientational disorder, and the occupancies for all the atoms were 0.25. Table 1 summarizes the details of crystallographic data and structure refinementfor two complexes.

CCDC:1437662,1;1014482,2.

1.4 Oxidative carbonylation of methanoland the analysis of the product

The oxidative carbonylation of methanol with CO and O2was conducted in a 250 mL stainless steel autoclave lined with Teflon.First,40 mL of methanol and 0.44 mmol of the catalyst were loaded into the autoclave.Second,the air in the autoclave was displaced three times with O2,followed by pressurization to 4.0 MPa with CO and O2(pCO/pO2=19)at room temperature.Third,the system was heated to 120℃and maintained for 4 h.After the reaction,the reactor was cooled down to room temperature.Next,the reaction mixture was analyzed on a Shimadzu GC-2014 equipped with an RTX-50 capillary column(30 m×0.32 mm×0.25μm)and a FID.The conditions employed are as follows:column temperature,60℃; injector temperature,250℃;detector temperature,300℃;FID detection,calibration normalization method.

Table 1 Crystallographic data of complexes 1 and 2

2 Results and discussion

2.1 Structure description of 1

The Cu complex 1 is a Cu(Ⅱ)-Cu(Ⅲ)mixed-valentcomplex.The unit cell structure of 1(Fig.1)contains two[Cu(Ⅱ)(phen)2Br]+cations and one tetranuclear [Cu(Ⅰ)4Br6]2-anion.

Fig.1 Structure of 1

Table 2 Selected bond lengths(nm)and angles(°)for complex 1

Comparison with the[Cu(Ⅱ)(phen)2Br]+isomers reported in the literature[17],the[Cu(Ⅱ)(phen)2Br]+cation of 1 has a square based pyramidal distorted trigonal bipyramidal(SBPDTB)stereochemistry,as the τvalue,whereτ=(α8-α1)/60°[18](α8:N(4)-Cu(1)-N(1), α1:N(2)-Cu(1)-Br(1)),is 0.88.The[Cu(Ⅰ)4Br6]2-anion is a Cu(Ⅰ)tetranuclear structure composed of four monovalent copper atoms and six bromine atoms.The four copper atoms Cu(2),Cu(3A),Cu(4)and Cu(5A)in Fig.2b exhibitapproximate trigonalplanar coordination with slight deviations from the planes through three bromine atoms,constituting a distorted tetrahedron with bond angles varying from 57.06(7)°to 64.05(7)° (Table 2).Because copper atoms in the[Cu(Ⅰ)4Br6]2-anion are positional disorder,the Cu(Ⅰ)tetrahedron can assume either of two equivalent orientations,as shown in Fig.2b and 2c.Six bromine ligands lie onthe six edges of the Cu(Ⅰ)tetrahedron to bridge four copper atoms;thus,the[Cu(Ⅰ)4Br6]2-anion is an aggregate composed of an octahedron of bromide ligands containing a tetrahedron of trigonal-planar-coordinated Cu(Ⅰ)atoms.

Fig.2[Cu4Br6]2-anion in 1 showing two types of orientations of the copper(Ⅰ)tetrahedron

In the[Cu(Ⅰ)4Br6]2-anion,the copper-copper distances(Cu(4)…Cu(3A)0.268 7(3)nm,Cu(2)…Cu(4) 0.269 2(3)nm,Cu(2)…Cu(5A)0.269 4(3)nm,Cu(3)…Cu(5)0.278 6(3)nm)are shorterthan two times the sum of the van der Waals radii of Cu atoms(0.280 nm), exceptfor Cu(2)…Cu(3A)(0.285 2(3)nm)and Cu(4)…Cu(5A)(0.283 8(3)nm),suggesting strong Cu(Ⅱ)-Cu(Ⅲ)interac-tion[19].

The distances ofπ-πinteractions between the phen six-membered rings for 1 vary from 0.341 96 to 0.351 76 nm.Table 3 lists the values of the C-H…Br hydrogen bond constituting the Br atom in the [Cu(Ⅰ)4Br6]2-anion and the C atom in the offset phen ring.The structure of 1 can be described as a supramolecular network assembled via the combination of π-πinteractions and C-H…Br hydrogen bonds,in which tetranuclear Cu(Ⅰ)anions reside inside the cavities of the frameworks(Fig.3).

2.2 Structuraldescription of 2

X-ray crystal-structure analysis reveals that 2 crystallizes in the C2/c space group.Table 4 lists the selected bond distances and angles of 2,and Fig.4 and 5 summarize the asymmetry unit and packing projection of 2,respectively.

Fig.3 Packing diagram of the unit cell of 1

Fig.4 Structure of 2

Table 3 Hydrogen bond parameters for complex 1

Complex 2 consists of[Cu(Ⅱ)(phen)2Br]+,Br-and CH3OH(Fig.4).None of the anions or methanol mole-cules are close enough(＜0.3 nm)to be considered even weakly semi-coordinated to the Cu(Ⅰ)cation[17]. The[Cu(Ⅱ)(phen)2Br]+cation of 2,also involves a near trigonal bipyramidal stereochemistry having a square based pyramidal distortion(SBPDTB),withτ=0.67 (α8:N(1)-Cu(1)-N(1A),α1:N(2)-Cu(1)-Br(1)).The structural data show that the Cu and Br atoms in 2 lie on a 2-fold axis of symmetry(Table 4),while those in 1 and[Cu(phen)2Br]Br·H2O[17]do not.The corresponding Cu-N bond distances in 2,which are in the normal range(0.199 7～0.215 0 nm)[20],are longer than those in[Cu(phen)2Br]Br·H2O[17],and comparable to those in 1.Meanwhile,the Cu-Br bond distances in the[Cu(Ⅱ)(phen)2Br]+cations of 1 and 2,are shorter than that in[Cu(phen)2Br]Br·H2O[17].

Table 4 Selected bond lengths(nm)and angles(°)for complex 2

Viewing from the direction shown in Fig.5,the most remarkable structural feature is that 2 exhibits a supramolecular framework.In 2,there areπ-π stacking interactions during the six-membered rings of phen with centroid-centroid distance varying from 0.337 07 to 0.338 34 nm.The solvent methanol molecules in an orientational disorder state reside inside the gaps of the frameworks,indicating that methanol can evaporate easily.

Fig.5 Packing diagram of 2 along the c-axis

2.3 TG analysis of complexes

Thermogravimetric analysis of 1 shows that 1 begins to lose weight at approximately 290℃(Fig.6), indicating that1 is stable below 290℃.A weightloss of 41.35%is observed in the temperature range of 290～500℃,which is close to the mass fraction of phen(38.38%).Taking into account thatthe phen unit exhibits a melting point of 99℃and a boiling point of 300℃,the weight loss of 41.35%is attributed to the complete decomposition of phen.At temperatures greaterthan 500℃,the residue beginsto lose weight.

Fig.6 TGA curves of complexes 1 and 2

Thermogravimetric analysis of 2 shows that a 2.84%weight loss of 2 is observed from 50 to 110℃, close to the half of the methanol mass fraction (5.20%).This shows that methanol in 2 is easily removed,which is consistent with the result analyzed by the single-crystal XRD.In the temperature range of 110～260℃,a very flat line is observed on the TG curve,with no weight loss,indicating that[Cu(phen)2Br]Br is very stable.Continuous decomposition is observed during 260～430℃,and a weight loss of 54.53%is close to the mass fraction ofphen(58.46%),indicating that phen is completely decomposed.At temperatures greater than 430℃,the weight loss is ascribed to the decomposition ofthe residue.

2.4 Catalytic activity of complexes

Transition-metal complexes are frequently employed as important catalysts in several catalytic reaction[21],hence,the oxidative carbonylation of methanol to DMC is selected as the probe reaction, and the catalytic performances of 1 and 2 are investigated in this reaction.

As shown in Table 5,when CuBr2was used as the catalyst,the turnover number(TON)of DMC is 5.2 with a selectivity of 67.8%for DMC;however,the selectivity for the byproduct dimethoxy methane (DMM)is up to 32.2%.On the other hand,when 2 replaced CuBr2,the TON is 5.9.The central copper atom in 2 is penta-coordinated,and the steric hindrance from phen ligands blocks the coordination of the copper with CO and methanol;hence,the activity is low.Although the increase of the TON is not clear, the selectivity to DMC is close to 100%.Notably,the TON for 1 is up to 54.7 with 97.5%selectivity of DMC,exhibiting activity and DMC selectivity higher than those reported previously for Cu(phen)Cl2[22]and (C3H7)4NBr/CuBr2[23].Complexes 1 and 2 have the same [Cu(Ⅱ)(phen)2Br]+cation;however,from the catalytic property of 2 in Table 5,the activity of the[Cu(Ⅱ)(phen)2Br]+cation is very low;hence,the high activity and DMC selectivity of 1 are attributed to the[Cu(Ⅰ)4Br6]2-anion.Four copper atoms in the[Cu(Ⅰ)4Br6]2-anion are bridged by six bromine atoms(Fig.2),and this structure might be in favor of the oxidative carbonylation of methanol[24];thus,1 exhibits activity very higher than 2.

Table 5 Effect of different catalysts on the oxidative carbonylation of methanol*

3 Conclusions

In this study,1 with a mixed-valent Cu(Ⅱ)-Cu(Ⅲ)system was synthesized from CuBr2and phen in alcohol by autoreduction,while 2 was prepared from CuBr and phen in methanol by oxidation,both of which can assemble into supramolecular frameworks by various interactions.The[Cu(Ⅱ)(phen)2Br]+cations of 1 and 2 have a square based pyramidal distorted trigonal bipyramidal stereochemistry,while the Cu and Br atoms in 2 lie on a crystallographic 2-fold axis of symmetry.The[Cu(Ⅰ)4Br6]2-ion in 1 is composed of an octahedron of bromide ligands containing a tetrahedron of coordinated Cu(Ⅰ)atoms,each of which exhibits approximate trigonal planar coordination and is bridged by three bromine atoms.Four copper atoms are found to be disordered,resulting in two equivalent Cu(Ⅰ)tetrahedrons observed,and there is the strong interaction between them.When both 1 and 2 were tested as catalysts for the oxidative carbonylation of methanol to DMC,2 exhibits the TON of only 5.9, while the TON on 1 was up to 54.7.

Supporting information is available athttp://www.wjhxxb.cn

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Syntheses,Crystal Structures and Catalytic Performances of Two Cu Complexes with 1,10-Phenanthroline Ligand

XIAO Yan-Hua1SUN Zhi-Kang1HU Xing-Xing1LI Liang2YANG Xiao-Jun1YUAN Hua1WU Yuan-Xin1DU Zhi-Ping＊,1,2
(1Hubei Key Laboratory of Novel Reactor&Green Chemical Technology,Key Laboratory for Green Chemical Process of Ministry of Education,Wuhan Institute of Technology,Wuhan 430073,China)
(2Hubei Xunda Pharmaceutical Co.,Ltd.,Wuxue,Hubei 435400,China)

Two novel Cu complexes,[Cu(Ⅱ)(phen)2Br]2[Cu(Ⅰ)4Br6](1)and[Cu(Ⅱ)(phen)2Br]Br·CH3OH(2)(phen= 1,10-phenanthroline),have been synthesized in alcohol and characterized by infrared spectroscopy,elemental analysis,thermal analysis,and X-ray diffraction single-crystal structure analysis.The structure of 1 with a Cu(Ⅱ)-Cu(Ⅲ)mixed valence can be described as a supramolecular network assembled via the combination ofπ-π interactions and C-H…Br hydrogen bonds.Its unit cell structure contains two[Cu(Ⅱ)(phen)2Br]+ions and one tetranuclear[Cu(Ⅰ)4Br6]2-ion;four Cu atoms in the[Cu(Ⅰ)4Br6]2-anion are at corners of a tetrahedron,and six bromine atoms bridging along its six sides constitute an octahedron.The complex 2 consists of[Cu(Ⅱ)(phen)2Br]+,Br-and CH3OH,and a supramolecular framework is formed byπ-πinteractions.When 1 and 2 were used as catalysts for the oxidative carbonylation of methanol to dimethyl carbonate(DMC),2 exhibits a turnover number of only 5.9 for DMC,while the[Cu(Ⅰ)4Br6]2-anion in 1 provides a suitable environmentfor the oxidative carbonylation ofmethanol,and the turnover number for DMC are up to 54.7.CCDC:1437662,1;1014482,2.

Cu complexes;solvothermal synthesis;dimethyl carbonate;oxidative carbonylation

O614.121

A

1001-4861(2016)09-1659-08

10.11862/CJIC.2016.214

2016-06-21。收修改稿日期：2016-08-06。

國家自然科學(xué)基金(No.21276201)資助項目。

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