双胺配体[K2(L)(THF)2](L=[Ph2Si(NAr)2]2-，Ar=2,6-iPr2C6H3)构筑的两个低价稀土镱化合物

徐敬尧 张雷 胡劲松＊,,2 邵雪嫚 潘成岭＊,

双胺配体[K2(L)(THF)2](L=[Ph2Si(NAr)2]2-，Ar=2,6-iPr2C6H3)构筑的两个低价稀土镱化合物

徐敬尧1张雷1胡劲松＊,1,2邵雪嫚1潘成岭＊,1

(1安徽理工大学材料科学与工程学院，多尺度材料与分子催化实验室，淮南232001)
(2南京大学配位化学国家重点实验室，南京210093)

以双胺类配体[K2(L)(THF)2](1)(L=[Ph2Si(NAr)2]2-，Ar=2,6-iPr2C6H3)与二价稀土YbI2(THF)2的交换反应得到2个不同类型的化合物[Yb(L)(THF)3](2)和{Yb(L)2[K(THF)2]2}(3)。对化合物进行X-射线单晶结构解析，核磁共振和元素分析表征。研究结果表明：化合物2中，通过1个双齿含氮配体和3个中性THF分子配位，以五配位模式稳定二价镱稀土中心。而化合物3中二价稀土镱是与2个螯合胺类配体配位，以共平面、四配位模式稳定其金属中心。K+恰好在配体的2个苯环之间，形成独特的三明治结构，有助于化合物的稳定。

稀土化学；胺基配体；镱

In the past decades,there has been a growing interestin the chemistry oforganolanthanide complexes supported by various non-cyclopentadienyl ligands[1-3]. Nitrogen donors are commonly used to support lanthanide metals,and the significance of sterically encumbered amido ligands was first demonstrated in the successfully isolation of lanthanide(Ⅱ)complex {Ln[N(SiMe3)2]3},as exemplified by the pioneering work of Bradley and co-workers[4-5].In the past years, there has been increasing interest in the developmentof various amido ligands that have been widely used to stabilize lanthanide(Ⅱ)metals such as{Na Ln[N (SiMe3)2]3}(Ln=Yb,Eu)and rich chemistry has been demonstrated in terms of structures and reactivity[6-9]. Besides these three traditional lanthanide(Ⅱ)(Sm,Eu and Yb)ions,it has also been shown that a reaction system with the[N(SiMe3)2]-ligand and the more reducing Tm(Ⅱ),Dy(Ⅱ)and Nd(Ⅱ)ions has led to a facile reduction of N2and the isolation of the corresponding(N2)2-complexes[10-11].Generally speaking, divalent lanthanide complexes with high reactive metal centers are very difficult to prepare.Thus the synthesis of a wide variety of lanthanide amido complexes remains an importantwork.

Chemical properties are always affected to some extent by the steric and electronic environment of the metal center.Therefore,to synthesize low-valent lanthanide complexes,the highly reducing nature of metal centers and their large ionic radii require that special care must be taken in the choice of the ligand with its proper steric bulk surrounded by the stabilization of lanthanide(Ⅱ)and reaction conditions to prevent unexpected results[12].In recentyears,N,N′-chelatingβ-diketiminates[(R1NCR2)2CR3]-(nacnac-)[13]and guanidinate ligands[(ArN)2CN(C6H11)2]-(Giso-)[14-15]have been utilized in the preparation and characterization of homoleptic four-coordinate Ln(Ⅱ)(Yb and Sm)complexes.In addition,Prof.Lee group reported divalent lanthanide complexes supported by a bulky 2-pyridyl amido and unsymmetrical benzamidinate ligands,which were very interesting[16-17].

In our previous work,we directly obtained planar four-coordinate Ln(Ⅱ)diamido complexes{Ln(L)2[K (solv.)x]2}(Ln=Sm and Eu),which represent the first example of lanthanide bearing heteroleptic sandwich structures[18-21].These results inspired us to extend the coordination chemistry of bulky diamido ligands to ytterbium(Ⅱ)by taking advantage of related synthetic routes.We have explored the coordination of amido ligand H2L(L=[Ph2Si(NAr)2]2-,Ar=2,6-iPr2C6H3)[22]to stabilize the ytterbium(Ⅱ)complex,{Yb(L)2[K(THF)2]2} (3),by the reaction of[Yb(L)(THF)3](2)and one eqivement of[K2(L)(THF)2](1)[18],as shown in Scheme 1.Herein,we reported the synthesis and structural studies of these complexes.According to our experimental results,it was difficult to isolate monometallic complex 2,and easy to obtain heterotrimetallic sandwich complex 3.To the best of our knowledge, homoleptic and heterotrimetallic divalent ytterbium complexes with diamido ligands are meaningful in the lanthanide chemistry.

Scheme 1

1 Experimental

1.1 Materials and methods

All procedures were performed under vacuum using standard Schlenk techniques or in a nitrogenfilled drybox.THF was pretreated with KOH and was then distilled from sodium benzophenone ketyl prior to use.Hexane and toluene were purified by distillation from sodium/triglyme benzophenone ketyl or CaH2.All other commercially available chemicals were used after appropriate purification.NMR spectra were recorded on a Bruker DPX 300 spectrometer. Elemental analyses(C,H,N)were carried out in the microanalytical laboratory of Shanghai Institute of Organic Chemistry,Chinese Academy of Sciences.

1.2 Synthesis of compounds

Synthesis of[Yb(L)(THF)3](2).A solution of[K2(L)(THF)2](1.15 g,1.5 mmol)in THF(15 mL)was treated with YbI2(THF)2(0.84 g,1.5 mmol)at room temperature to give the title compound 2 as red crystals(0.70 g,49.5%).1H NMR(C6D6,300 MHz):δ 7.62(d,J=4.8 Hz,4H,ArH),7.11～7.21(m,10H,ArH), 6.93(t,J=7.2 Hz,2H,ArH),3.26～3.52(m,12H,THF), 4.33(sept,J=6.9 Hz,4H,CHMe2),1.25～1.45(br,12H, THF),1.11(d,J=6.9 Hz,24H,CHMe2).13C NMR(C6D6,75.47 MHz):δ159.3,154.7,148.6,142.9,135.8,126.8, 124.9,116.4(Ar),69.1,28.2(OCH2CH2(THF)),25.7, 23.9(CHMe2).Anal.Calcd.for C48H68N2O3SiYb(%):C, 62.52;H,7.43;N,3.04.Found(%):C,62.59;H,7.38; N,3.32.

Synthesis of{Yb(L)2[K(THF)2]2}(3).A green suspension of YbI2(THF)2(0.59 g,1 mmol)in THF was added to a solution of[K2(L)(THF)2](1.54 g,2 mmol)to give the compound 3 as green crystals(0.79 g,45.0%).1H NMR(C6D6,300 MHz):δ7.71(d,J=3 Hz,8H,ArH),7.12～7.16(m,12H,ArH),7.08(s,12H, ArH),3.56(br,16H,THF),3.39(sept,J=6.6 Hz,8H, CHMe2)1.43(br,16H,THF),1.00(d,J=6.6 Hz,48H, CHMe2).13C NMR(C6D6,75.47 MHz):δ143.1,139.8, 135.8,130.4,124.1,123.4(Ar),68.1,66.2,29.4, (OCH2CH2(THF)),26.1,23.9,22.9,15.9(ArCHMe2). Anal.Calcd.for C80H104K2N4O2Si2Yb(3·2THF)(%):C, 65.76;H,7.17;N,3.83.Found(%):C,65.38;H,7.31; N,3.94.

1.3 Crystalstructure determination

X-ray crystallographic data of 2 and 3 were collected under polybutenes,isobutylene oil at room temperature.All measurements were made on a Bruker Smart Apex CCD diffractometer with graphitemonochromated Mo Kαradiation(λ=0.071 073 nm). The structure ofcomplexes 2 and 3 are solved by direct methods,and the non-hydrogen atoms are located from the trial structure and then refined anisotropically with SHELXTL using a full-matrix least-squares procedure based on F2values[23].The hydrogen atoms positions are fixed geometrically atcalculated distances and allowed to ride on the parent atoms.The crystallographic data are summarized in Table 1,while the selected bond lengths and angles are given in Table 2.

CCDC:689221,2;689222,3.

Table 1 Crystal data and structure refinement for complexes 2 and 3

Table 2 Selected bond lengths(nm)and angles(°)for the complexes 2 and 3

2 Results and discussion

The use of a dry-box and access to single crystal for X-ray diffraction techniques made it possible to safely handle and characterize the complex.Heterometallic complex with sandwich structure{Yb(L)2[K (THF)2]2}(3)was readily synthesized as green crystals in one step by 0.5 equiv[K2(L)(THF)2].YbI2(THF)2in THF at room temperature(Scheme 1).Importantly, when an addition of YbI2(THF)2was allowed,another new complex[Yb(L)(THF)3](2)was isolated as a red solid.Alternatively complex 3 can be synthesized from further reaction of 2 with[K2(L)(THF)2],indicating that 2 is an intermediate to the formation of 3. However,we failed to isolate the other lanthanide(Ⅱ) (Sm and Eu)complexes with homoleptic type like complex 2.

Compound 2 crystallizes in a monoclinic crystal system with space group P21.X-ray crystallographic analysis revealed that 2 is mononuclear homoleptic complex with ligand ions coordinated ytterbium center. The structure consists of two independent molecules. This structure differs from homoleptic complexes stabilized by related{[(R1)NC(R2)]2C(R3)}-(nacnac-)[13]and guanidinate[(ArN)2CN(C6H11)2]-(Giso-)[14-15]ligands including unprecedented examples of 4-coordinate. The coordination geometry of complex 2 is fivecoordinated,and the Yb metal center isη2(N,N)-coordinated by one amido ligand and three THF molecules,forming a distorted square pyramidal geometry, with N(1),N(2),O(1)and O(3)forming the basalplane whilst O(2)occupying the apical position,as shown in Fig.1.The Yb(Ⅱ)-N bond distances fall in the range of 0.234 6(4)～0.239 4(4)nm,and the N-Yb-N′angles are 68.8(1)°and 69.1(1)°.The Yb(Ⅱ)-O bond distances range from 0.237 0(4)to 0.249 5(4)nm.Lappert andco-workers have reported several homolepticβdiketiminato ytterbium(Ⅱ)complexes.The Yb(Ⅱ)-N bond distances in the latter complexes range from 0.238 6(4)to 0.242 3(9)nm[13],which are slightly longer than those observed for complex 2.

Fig.1 Molecular structure of 2 with 30%thermal ellipsoids

Over the past years,there has been significant interest in low-coordination-number(＜6)lanthanide complexes.Here the coordination sphere includes two chelating L ligands,as shown in Fig.2.Two potassium ion is sandwiched between two phenyl rings via cation -πinteractions.In addition to the cation-πinteractions with two arene rings,each potassium ion is further bound to two THF molecules.The bis(amido)ligands coordinate in a chelating fashion with Yb-N lengths (Yb(1)-N(1)0.245 4(2)nm,Yb(1)-N(2)0.241 6(2)nm) notably longer than those observed in related divalent ytterbium amido species such as complex 2(Yb(1)-N(1)0.234 6(4);Yb(1)-N(2)0.239 4(4)nm).The K-C bond distances ranged from 0.303 2(3)to 0.354 5(4) nm and K(1)-O(1)and K(1)-O(2)bond distances are 0.275 1(4),0.277 8(4)nm,respectively.

Fig.2 Molecular structure of 3 with all hydrogen atoms omitted for clarity

Over the past several decades,complex[(C5Me5)2Sm]with a sandwich structure has attracted considerable attention in divalent lanthanide chemistry[24-25]. A novel class of triple-decker bent metallocenes complexes of divalent lanthanide{(μ-η8,η8-cot)[Ln (C5Me5)2]2}(cot=cyclooctatetraenyl)was reported by Evans[26-27].The excellentexample has a rare tetradecker sandwich complex of a divalent lanthanide[(C5Me5)Yb (μ-η8,η8-cot‴)Yb(μ-η8,η8-cot‴)Yb(C5Me5)](cot‴=1,3,6-tris(trimethylsilyl)cyclo-octatetraenyl-dianion)[28].Complexes with one,two,or three lanthanide centers can give different types of sandwich structures[23-27].However,the current type of heterotrimetallic sandwich complex 3 was interesting in lanthanide chemistry.

3 Conclusions

In summary,we have successfully achieved the synthesis of two amido Yb(Ⅱ)complexes 2 and 3. Complex 2 is an intermediate to the formation of 3. The structure of complex 3 showed that potassium ions are sandwiched between two phenyl rings and help to stabilize the divalent ytterbium center.We believe that this method should be applicable for the synthesis of complexes of transition metal elements, and this work is in progress in our laboratory and will be reported in due course.

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Two Divalent Ytterbium Complexes with Diamido Ligands [K2(L)(THF)2](L=[Ph2Si(NAr)2]2-,Ar=2,6-iPr2C6H3)

XU Jing-Yao1ZHANG Lei1HU Jin-Song＊,1,2SHAO Xue-Man1PAN Cheng-Ling＊,1
(1Laboratory of Multiscale Materials and Molecular Catalysis,School of Materials Science and Engineering, Anhui University of Science and Technology,Huainan,Anhui 232001,China)
(2State Key Laboratory of Coordination Chemistry,Nanjing University,Nanjing 210093,China)

The reaction of diamido ligand[K2(L)(THF)2](1)(L=[Ph2Si(NAr)2]2-,Ar=2,6-iPr2C6H3)with YbI2(THF)2afforded two complexes[Yb(L)(THF)3](2)and{Yb(L)2[K(THF)2]2}(3),which were characterized by X-ray structure analysis,NMR and elemental analysis.The coordination geometry of complex 2 is five-coordinated,and Yb metal center is coordinated by one amido ligand and three THF molecules.Complex 3 adopts a four-coordinated,nearly planar geometry around the Yb(Ⅱ)center.Two potassium ion is sandwiched between two phenyl rings via cationareneπ-interactions,which helps to stabilize the metalcenter.CCDC:689221,2;689222,3.

lanthanide chemistry;amido ligand;ytterbium

O614.346

A

1001-4861(2015)07-1433-06

10.11862/CJIC.2015.203

2015-03-17。收修改稿日期：2015-06-06。

国家自然科学基金(No.21201006)，南京大学配位化学国家重点实验室开放基金，高等学校博士点基金(No.26920123415120002)，安徽理工大学博士启动基金资助项目。

＊通讯联系人。E-mail：jshu@aust.edu.cn;clpan@aust.edu.cn；会员登记号：S06N5201M1405(胡劲松)；S06N4958S1006(潘成岭)。