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* E-mail: yaoym@suda.edu.cn; Tel.: 0086-0512-65882806; Fax: 0086-0512-65880305 Received December 29, 2009; revised and accepted February 6, 2010. Project supported by the National Natural Science Foundation of China (Nos. 20771078 and 20972108), the Major Basic Research Project of the

Natural Science Foundation of the Jiangsu Higher Education Institutions (No. 07KJA15014), and the Qing Lan Project. † Dedicated to Professor Qi Shen on the occasion of her 70th birthday.

Chin. J. Chem. 2010, 28, 1013—1018 © 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1013

Synthesis and Structural Characterization of Lanthanide Amides Stabilized by an N-Aryloxo Functionalized

β-Ketoiminate Ligand†

Xu, Bin(徐宾) Han, Xiangzong(韩祥宗) Yao, Yingming*(姚英明) Zhang, Yong(张勇) Shen, Qi(沈琪)

Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering & Materials Science, Dushu Lake Campus, Soochow University, Suzhou, Jiangsu 215123, China

The synthesis and characterization of dimeric lanthanide amides stabilized by a dianionic N-aryloxo functional-ized β-ketoiminate ligand are described in this paper. Reactions of 4-(2-hydroxy-5-tert-butyl-phenyl)imino-2-pen-tanone (LH2) with Ln[N(SiMe3)2]3(µ-Cl)Li(THF)3 in a 1∶1 molar ratio in THF gave the dimeric lanthanide amido complexes [LLn{N(SiMe3)2}(THF)]2 [Ln＝Nd (1), Sm (2), Yb (3), Y (4)] in good isolated yields. These complexes were characterized by IR spectroscopy, elemental analysis, and 1H NMR spectroscopy in the case of complex 4. The definitive molecular structures of complexes 1, 3, and 4 were determined. It was found that complexes 1 to 4 can initiate the ring-opening polymerization of L-lactide.

Keywords organolanthanides, β-ketoiminate ligand, synthesis, crystal structure, polymerization, L-lactide

Introduction

Over the past decade, significant efforts to explore ligands other than the traditional ancillary ligand bis(cyclopentadienyl) set in organometallic lanthanide chemistry have led to the fruitful design of new nonlan-thanocene complexes.1-3 Of these new alternatives, ni-trogen-containing ligands, such as guanidinate, amidi-nate4 and β-diketiminate5 ligands, have received much attention, because their electronic properties and steric bulkiness can be modified by variation of the substitu-ents on the nitrogen atoms. Furthermore, a lot of lantha-nide complexes stabilized by such ligand systems have been reported to exhibit interesting catalytic activity for the polymerization of some polar and nonpolar mono-mers.6-9 β-Ketoiminate ligands, as one kind of nitro-gen-containing ligands, can be easily prepared from inexpensive and readily available starting materials and simply modified of their both steric and/or electronic properties. β-Ketoiminate ligands have become among the most attractive chelating systems in main group and transition metal coordination chemistry, and some of these metal complexes exhibit exciting reactivity in homogeneous catalysis, such as for the polymerization and copolymerization of olefins,10-14 and the ring- opening polymerization of cyclic esters,15-17 etc. How-ever, these ligands have seldom been used in organo-lanthanide chemistry, and only few lanthanide com-

plexes stabilized by β-ketoiminate ligands have been reported.18-20

Recently, we became interested in studying the syn-thesis and reactivity of organolanthanide complexes supported by N-aryloxo functionalized β-ketoiminate ligands, which contains a pendant phenol functional-ity.21,22 In our earlier work, a series of new lanthanide chlorides and aryloxides based on this ligand were syn-thesized and it was found that the corresponding lantha-nide aryloxides are active initiators for the ring-opening polymerization of L-lactide.22 In order to elucidate the effect of active group on the catalytic activity, we have synthesized some new lanthanide amido complexes sta-bilized by N-aryloxo functionalized β-ketoiminate ligand and examined their catalytic activity for the ring- opening polymerization of L-lactide. Herein, we report these results.

Experimental

The complexes described below are extremely sensi-tive to air and moisture. Therefore, all manipulations were performed under pure argon with rigorous exclu-sion of air and moisture using Schlenk techniques. Sol-vents were dried and freed of oxygen by refluxing over sodium/benzophenone ketyl and distilled prior to use. 4-(2-Hydroxy-5-tert-butyl-phenyl)imino-2-pentanone (LH2)

22 and Ln[N(SiMe3)2]3(µ-Cl)Li(THF)3 (Ln＝Nd,

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Sm, Yb, Y)23 were prepared according to the literature procedure. The uncorrected melting points of crystalline samples in sealed capillaries (under argon) are reported as ranges. Lanthanide metal analyses were performed by EDTA titration with a xylenol orange indicator and a hexamine buffer. Carbon, hydrogen and nitrogen analy-ses were performed by direct combustion with a Carlo-Erba EA-1110 instrument. The IR spectra were recorded with a Nicolet-550 FT-IR spectrometer as KBr pellets. The 1H NMR spectra were recorded in C6D6 solution for the yttrium complexes with a Unity Var-ian-400 spectrometer. Molecular weight and molecular weight distribution (PDI) were determined against a polystyrene standard by gel permeation chromatography (GPC) on a PL 50 apparatus, and THF was used as an eluent at a flow rate of 1.0 mL/min at 40 ℃.

Synthesis of [LNd{N(SiMe3)2}(THF)]2 (1)

A THF solution (10 mL) of Nd[N(SiMe3)2]3(µ-Cl)-Li(THF)3 (1.75 mmol) was added to the suspension of LH2 (0.43 g, 1.75 mmol) in toluene (10 mL). The solu-tion became clear immediately. The mixture was stirred at 0 ℃ for 20 min, and then precipitate formed gradu-ally. The precipitate was separated from the solution by centrifugation, and then the powder was dissolved with THF. Blue crystals were obtained from a concentrated THF/toluene solution (10 mL) at －10 ℃ (0.73 g, 67%). m.p. 186—188 ℃; IR (KBr) v: 2954, 1532, 1526, 1499, 1403, 1366, 1287, 1242, 1156, 1026, 939, 827, 744, 686, 512 cm－1. Anal. calcd for C50H90N4Nd2O6Si4: C 48.27, H 7.29, N 4.50, Nd 23.19; found C 48.65, H 7.50, N 4.39, Nd 22.97. Crystals suitable for an X-ray structure analysis were obtained from the concentrated THF/toluene solution.

Synthesis of [LSm{N(SiMe3)2}(THF)]2 (2)

The synthesis of complex 2 was carried out in the same way as that described for complex 1, but Sm[N(SiMe3)2]3(µ-Cl)Li(THF)3 (1.83 mmol) was used instead of Nd[N(SiMe3)2]3(µ-Cl)Li(THF)3. Yellow mi-crocrystals were obtained from a concentrated THF so-lution at －10 ℃ (0.95 g, 83%). m.p. 185—187 ℃; IR (KBr) v: 2953, 1587, 1555, 1497, 1405, 1360, 1284, 1243, 1130, 1022, 937, 825, 752, 680, 515 cm－1. Anal. calcd for C50H90N4Sm2O6Si4: C 47.80, H 7.22, N 4.46, Sm 23.94; found C 47.63, H 7.43, N 4.77, Sm 23.51.

Synthesis of [LYb{N(SiMe3)2}(THF)]2 (3)

The synthesis of complex 3 was carried out in the same way as that described for complex 1, but Yb[N(SiMe3)2]3(µ-Cl)Li(THF)3 (1.60 mmol) was used instead of Nd[N(SiMe3)2]3(µ-Cl)Li(THF)3. Yellow mi-crocrystals were obtained from a concentrated THF so-lution at room temperature (0.93 g, 89%). m.p. 199—201 ℃; IR (KBr) v: 2956, 1593, 1500, 1405, 1358, 1289, 1253, 1182, 1129, 1022, 934, 886, 840, 754, 685, 634, 525 cm－1. Anal. calcd for C50H90N4Yb2O6Si4: C 46.14, H 6.97, N 4.30, Yb 26.59; found C 46.64, H 6.65,

N 4.53, Yb 26.92. Crystals suitable for an X-ray struc-ture analysis were obtained from the concentrated THF/toluene solution.

Synthesis of [LY{N(SiMe3)2}(THF)]2 (4)

The synthesis of complex 4 was carried out in the same way as that described for complex 1, but Y[N(SiMe3)2]3(µ-Cl)Li(THF)3 (1.84 mmol) was used instead of Nd[N(SiMe3)2]3(µ-Cl)Li(THF)3. Yellow mi-crocrystals were obtained from a concentrated THF so-lution at room temperature (0.91 g, 87%). m.p. 187—189 ℃; 1H NMR (C6D6, 400 MHz) δ: 0.17 (s, 36H, N(CH3)3), 1.32 (s, 8H, THF), 1.42 (s, 18H, C(CH3)3), 2.08 (s, 6H, CH3C＝N), 2.13 (s, 6H, CH3C＝O), 3.80 (s, 8H, THF), 5.36 (s, 2H, CH), 7.10—7.20 (6H, Ar); 13C NMR (C6D6, 400 MHz) δ: 178.13 (CO), 168.71 (CN), 152.37 (Ph), 146.92 (Ph), 139.78 (Ph), 127.23 (Ph), 123.52 (Ph), 118.82 (Ph), 91.43 (CH), 70.63 (α-CH2 THF), 38.42 (C(CH3)3), 32.48 (C(CH3)3), 27.75 (β-CH2 THF), 25.81 (CH3), 19.51 (CH3), 6.35 (TMS); IR (KBr) v: 2956, 1592, 1499, 1405, 1358, 1286, 1253, 1182, 1129, 1021, 934, 886, 840, 756, 682, 633, 527 cm－1. Anal. calcd for C50H90N4Y2O6Si4: C 52.98, H 8.00, N 4.94, Y 15.69; found C 53.44, H 8.41, N 4.78, Y 15.92. Crystals suitable for an X-ray structure analysis were obtained from the concentrated THF/toluene solution.

Typical procedure for the polymerization reaction

The procedures for the polymerization of L-lactide initiated by complexes 1—4 were similar, and a typical polymerization procedure is given below. A 50 mL Schlenk flask, equipped with a magnetic stirring bar, was charged with a solution of L-lactide in toluene. To this solution was added the desired amount of initiator in toluene by syringe. The contents of the flask were then stirred vigorously at 70 ℃ for the desired time. The reaction mixture was quenched by the addition of 1 mol/L HCl-ethanol solution and then poured into metha-nol to precipitate the polymer, which was dried in a vacuum and weighed.

X-ray crystallography

Suitable single crystals of complexes 1, 3 and 4 were sealed in a thin-walled glass capillary for determining the single-crystal structures. Intensity data were col-lected with a Rigaku Mercury CCD area detector in ω scan mode using Mo Kα radiation (λ＝0.71070 Å). The diffracted intensities were corrected for Lorentz polari-zation effects and empirical absorption corrections. De-tails of the intensity data collection and crystal data are given in Table 1.

The structures were solved by direct methods and refined by full-matrix least-squares procedures based on |F|2. All the non-hydrogen atoms were refined anisot-ropically. The hydrogen atoms in these complexes were all generated geometrically, assigned appropriate iso-tropic thermal parameters, and allowed to ride on their parent carbon atoms. All the H atoms were held station-

Lanthanide Amides Stabilized by an N-Aryloxo Functionalized β-Ketoiminate Ligand

Chin. J. Chem. 2010, 28, 1013—1018 © 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cjc.wiley-vch.de 1015

Table 1 Crystallographic data for complexes 1, 3 and 4

Compound 1 3 4

Formula C50H90N4Nd2O6Si4 C50H90N4O6Si4Yb2 C50H90N4O6Si4Y2

Mr 1244.10 1301.70 1133.44

T/K 293(2) 223(2) 223(2)

Crystal system Monoclinic Monoclinic Monoclinic

Space group P21/n P21/n P21/n

Crystal size/mm3 0.30×0.30×0.27 0.48×0.38×0.24 0.70×0.60×0.40

a/Å 12.852(3) 12.622(2) 12.671(3)

b/Å 16.434(3) 16.171(3) 16.260(4)

c/Å 14.984(3) 14.808(3) 14.799(3)

β/(°) 100.551(6) 99.698(2) 99.558(3)

V/Å3 3111.2(12) 2979.4(9) 3006.6(11)

Z 2 2 2

Dcalcd/(g•cm－3) 1.328 1.451 1.252

µ/mm－1 1.771 3.245 2.045

F(000) 1284 1324 1200

θmax/(°) 25.35 27.48 25.50

Collected reflns 29478 14034 12283

Unique reflns 5693 6765 5504

Obsd reflns [I＞2.0σ(I)] 4645 5531 4665

No. of variables 301 292 292

GOF 1.146 1.022 1.130

R 0.0810 0.0384 0.0546

wR 0.1812 0.0793 0.1253

Largest diff peak, hole/(e•Å－3) 0.838, －1.239 1.279, －1.174 1.063, －0.980

ary and included in the structure factor calculation in the final stage of full-matrix least-squares refinement. The structures were solved and refined using SHELEXL-97.

Results and discussion

Synthesis and characterization of the lanthanide amides 1—4

Lanthanide amido complexes stabilized by the N-aryloxo functionalized β-ketoiminate ligand can be conveniently prepared through protonolysis reactions of Ln[N(SiMe3)2]3(µ-Cl)Li(THF)3 (Ln＝Nd, Sm, Yb, Y) with 1 equiv. of LH2 in THF. Reaction of Ln[N(SiMe3)2]3(µ-Cl)Li(THF)3 with LH2 in THF at 0 ℃, after workup, the final products were obtained as blue (for Nd), and yellow (for Sm, Yb and Y) powder, respectively, in 67%—89% isolated yields as summa-rized in Scheme 1. The compositions of complexes 1—4 were established as LLnN(SiMe3)2(THF) by elemental analysis and 1H NMR spectroscopy in the case of com-plex 4. X-ray structure determination of complexes 1, 3, and 4 revealed that these complexes have solvated dimeric structures [LLnN(SiMe3)3(THF)]2 in the solid state. All of these complexes are soluble in THF, and slightly soluble in DME and toluene.

The molecular structures of complexes 1, 3, and 4

Scheme 1

are shown in Figures 1—3, with their selected bond lengths and bond angles, respectively. These complexes are isostructural, and they have centrosymmetric dimeric structures containing Ln2O2 core. These lantha-nide amido complexes possess bridging phenoxo oxy-gen atoms, which is similar to those found in the corre-sponding lanthanide chlorides and aryloxide.22 The metal centers in these complexes are six-coordinated with two oxygen atoms and one nitrogen atom from one β-ketoiminate ligand, one nitrogen atom from the amido group, one oxygen atom from one THF molecule, and one oxygen atom from another β-ketoiminate ligand. Each metal center has a highly distorted octahedral co-

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Figure 1 ORTEP diagram of complex 1 showing an atom numbering scheme. Thermal ellipsoids are drawn at the 20% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Nd(1)—O(1) 2.252(6), Nd(1)—O(2A) 2.373(6), Nd(1)—O(2) 2.407(6), Nd (1)—O(3) 2.551(7), Nd(1)—N(1) 2.482(7), Nd(1)—N(2) 2.344(8), Nd(1)—C(11) 3.078(8); O(2A)-Nd(1)-O(2) 68.3(2), O(2)-Nd(1)-N(1) 65.5(2), N(1)-Nd(1)-O(1) 73.3(2), O(1)-Nd(1)-N(2) 121.2(3), O(2A)-Nd(1)-N(2) 132.1(2), N(2)-Nd(1)-O(2) 105.4(2), O(2A)-Nd(1)-O(3) 78.2(2), O(2A)-Nd(1)-N(1) 119.2(2), O(1)-Nd(1)-O(2) 120.4(2), N(2)-Nd(1)-N(1) 97.3(2).

ordination geometry, in which O(2), O(2A), O(3), and N(1) can be considered to occupy equatorial positions and O(1) and N(2) occupy axial positions.

In complex 1, the terminal Nd—O(alkoxo) bond length of 2.252(6) Å is comparable well with the corre-sponding bond lengths in neodymium β-ketoiminate complexes [L'Nd(OAr)(THF)]2 (2.260(5) Å) (L' ＝OC(Me)CHC(Me)N(2-O-5-Me-C6H3), ArO ＝ O-2,6- t-Bu2-4-Me-C6H3),

22 but slightly smaller than that in Nd2[{OC(t-Bu)CHC(But)N}2(CH2)3]3 (2.304(3) Å).20 Two phenoxo groups are unsymmetrically coordinated to the central metal atoms. The average Nd—O(Ar) bond length of 2.390(6) Å is comparable with the cor-responding value in [L'Nd(OAr)(THF)]2 (2.371(5) Å).22

The Nd—N(amido) bond length of 2.344(8) Å is com-parable with those values in β-ketoiminato samarium and erbium amido complexes when the difference in ionic radii is considered.19 It is worth noting that there is remote π interaction of one carbon atom of the aryloxo group with the neodymium metal atom, which is differ-ent from that observed in N-aryloxo functionalized β-ketoiminato lanthanide aryloxide.22 The Nd(1)—C(11) distance of 3.078(8) Å falls in the range of π-Ph—Nd interactions [2.898(12)—3.183(10) Å] observed in a range of neutral and anionic neodymium aryloxides.24

Figure 2 ORTEP diagram of complex 3 showing an atom numbering scheme. Thermal ellipsoids are drawn at the 20% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Yb(1)—O(1) 2.140(3), Yb(1)—O(2A) 2.233(3), Yb(1)—O(2) 2.281(3), Yb(1)—O(3) 2.403(3), Yb(1)—N(1) 2.371(3), Yb(1)—N(2) 2.229(3), Yb(1)—C(6) 3.066(4), Yb(1) — C(11) 3.017(4); O(2A)-Yb(1)-O(2) 68.1(1), O(2)-Yb(1)-N(1) 68.4(1), N(1)-Yb(1)-O(1) 76.6(1), O(1)-Yb(1)-N(2) 122.0(1), O(2A)-Yb(1)-N(2) 132.2(1), N(2)-Yb(1)-O(2) 100.9(1), O(2A)-Yb(1)-O(3) 79.9(1), O(2A)-Yb(1)-N(1) 119.8(1), O(1)-Yb(1)-O(2) 126.5(1), N(2)-Yb(1)-N(1) 95.4(1).

In complex 3, the Yb—N(amido) bond length of 2.229(3) Å is comparable with that observed in complex 1 when the difference in ionic radii is considered. The terminal Yb—O(alkoxo) bond length of 2.140(3) Å is comparable well with the corresponding bond lengths in ytterbium β-ketoiminate complex [L'YbCl(DME)]2 (2.140(4) Å).22 Two phenoxo groups are also unsym-metrically coordinated to the central metal atoms, and the bridging Yb—O(Ar) bond lengths (2.233(3) and 2.281(3) Å) are in accordance with the corresponding value in [L'YbCl(DME)]2 (2.269(3) Å).22 There are re-mote π interactions of two carbon atoms of the aryloxo group with the ytterbium metal atom. The Yb(1)—C(6) and Yb(1)—C(11) distances of 3.066(4), and 3.017(4) Å, respectively, are in accordance with those observed of 2.814(4) to 3.148(6) Å for chelating η6-, η1-Ph—Yb bonding in [Yb(Odpp)3]2 (Odpp＝2,6-diphenylphenol-ate).25 In complex 4, the Y—N(amido) and Y—

O(alkoxo) bond lengths are 2.269(3) and 2.168(3) Å, respectively, which are comparable with the corre-sponding values in complexes 1 and 3, when the differ-ence in ionic radii is considered. The two phenoxo groups are also unsymmetrically coordinated to the yt-trium metal atoms with the deviation of 0.048 Å. There

Lanthanide Amides Stabilized by an N-Aryloxo Functionalized β-Ketoiminate Ligand

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Figure 3 ORTEP diagram of complex 4 showing an atom numbering scheme. Thermal ellipsoids are drawn at the 20% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Y(1)—O(1) 2.168(3), Y(1) — O(2A) 2.257(3), Y(1) — O(2) 2.322(3), Y(1) — O(3) 2.427(3), Y(1)—N(1) 2.406(3), Y(1)—N(2) 2.269(3), Y(1)—C(11) 3.028(4); O(2A)-Y(1)-O(2) 68.16(10), O(2)-Y(1)-N(1) 67.80(10), N(1)-Y(1)-O(1) 75.67(11), O(1)-Y(1)-N(2) 120.36(11), O(2A)-Y(1)-N(2) 130.90(12), N(2)-Y(1)-O(2) 101.63(11), O(2A)-Y(1)-O(3) 79.41(10), O(2A)-Y(1)-N(1) 120.36(11), O(1)-Y(1)-O(2) 124.98(11), N(2)-Y(1)-N(1) 95.87(12).

is remote π interaction of one carbon atom of the ary-loxo group with the yttrium metal atom, which is dif-ferent from that observed in complex 3. The Y(1)—C(11) distance of 3.028(4) Å accords with that in com-plex 3.

Ring-opening polymerization of L-lactide by com-plexes 1—4

To further elucidate the effect of active group on the catalytic activity, the catalytic behavior of these lantha-nide amido complexes 1—4 for the ring-opening po-lymerization of L-lactide was examined. The polymerization results are summarized in Table 2.

All of the lanthanide amido complexes can initiate the polymerization of L-lactide in toluene. Complex 1 polymerizes 200 equiv. of L-lactide to give 30% yield after 2 h, and to give 95% yield after 4 h (Entries 1 and 2). However, the catalytic activity of the β-ketoiminate lanthanide amido complex is lower than that of the cor-responding lanthanide aryloxide. For example, the β-ketoiminate neodymium aryloxide gives 85% yield of 200 equiv. of L-lactide after 2 h.22 These results re-vealed that the initiating groups in organolanthanide catalysts also have apparent effect on the catalytic activ-ity for L-lactide polymerization. This difference should be attributed to that the silylamide group is less nucleo-

Table 2 Polymerization of L-lactide initiated by complexes 1—4a

Entry Initiator [M]0/[I]0b Tp/℃ t/h Yieldc/% Mn×10−4 d PDI

1 1 200 70 2 30 2.49 2.39

2 1 200 70 4 95 8.08 2.02

3 1 300 70 2 17 0.74 1.50

4 1 300 70 4 84 9.62 1.90

5 1 400 70 2 15 — —

6 2 200 70 4 64 3.22 1.68

7 2 300 70 4 53 2.67 1.89

8 3 100 70 4 20 0.75 2.44

9 4 100 70 4 52 1.26 2.03 a Polymerization conditions: toluene as solvent, [L-LA]＝1 mol• L－1. b [M]0/[I]0＝[monomer]/[initiator]. c Yield: weight of poly-mer obtained/weight of monomer used. d Measured by GPC cali-brated with standard polystyrene samples.

philic than aryloxide, which is disadvantageous for the nucleophilic attack on the carbonyl carbon of the coor-dinated lactide. As that in β-ketoiminate lanthanide ary-loxo system,22 the central metal ion has a significant effect on the catalytic activity, and the catalytic activity decreased dramatically with the decrease of the ionic radii. The neodymium amido complex catalyzes L-lactide polymerization to give 84% yield in toluene in 4 h at 70 ℃ when the molar ratio of monomer to ini-tiator ([M0]/[I0]) is 300 (Entry 4), whereas the yield is only 20% even when the molar ratio of monomer to initiator decreased to 100 when the ytterbium complex (3) was used as the initiator (Entry 8). All of the polymers obtained have high molecular weights, and the molecular weight distributions (PDIs) of the resultant polymers were relatively broad, which indicated that these polymerization systems are not well-controlled. One possibility is that these lanthanide amido com-plexes are multi-center catalysts for L-lactide polymeri-zation, because all of the Ln—O(alkoxo), Ln—O(Ar) and Ln—N(amido) bonds in these complexes might be active for the polymerization.

Conclusion

In summary, a series of new soluble lanthanide amido complexes stabilized by a dianionic N-aryloxo- functionalized β-ketoiminate ligand were synthesized, and their structural features were provided via X-ray diffraction study. These β-ketoiminate lanthanide amido complexes can initiate the ring-opening polymerization of L-lactide, and the ionic radii have a significant effect on the catalytic activity. In comparison with the corre-sponding lanthanide aryloxides, these amido complexes exhibited relatively lower catalytic activity.

References

1 Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283.

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2 Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Chem. Rev. 2002, 102, 1851.

3 Piers, W. E.; Emslie, D. J. H. Coord. Chem. Rev. 2002, 233—234, 131.

4 Edelmann, F. T. Chem. Soc. Rev. 2009, 38, 2253. 5 Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev.

2002, 102, 3031. 6 Luo, Y. J.; Yao, Y. M.; Shen, Q.; Sun, J.; Weng, L. H. J.

Organomet. Chem. 2002, 662, 144. 7 Luo, Y. J.; Yao, Y. M.; Shen, Q. Macromolecules 2002, 35,

8670. 8 Luo, Y. J.; Yao, Y. M.; Shen, Q.; Yu, K. B.; Weng, L. H.

Eur. J. Inorg. Chem. 2003, 318. 9 Yao, Y. M.; Zhang, Z. Q.; Peng, H. M.; Zhang, Y.; Shen, Q.;

Lin, J. Inorg. Chem. 2006, 45, 2175. 10 Huang, Y. B.; Jin, G. X. Dalton Trans. 2009, 767. 11 Huang, Y. B.; Tang, G. R.; Jin, G. X. Organometallics 2008,

27, 259. 12 Tang, L. M.; Li, Y. G.; Ye, W. P.; Li, Y. S. J. Polym. Sci.,

Part A: Polym. Chem. 2006, 44, 5846. 13 Li, X. F.; Li, Y. G.; Li, Y. S.; Chen, Y. X.; Hu, N. H.

Organometallics 2005, 24, 2502. 14 He, X. H.; Yao, Y. Z.; Luo, X.; Liu, Y. H.; Zhang, L.; Wu,

Q. Organometallics 2003, 22, 4952.

15 Tang, H. Y.; Chen, H. Y.; Huang, J. H.; Lin, C. C. Macromolecules 2007, 40, 8855.

16 Doherty, S.; Errington, R. J.; Housley, N.; Clegg, W. Or-ganometallics 2004, 23, 2382.

17 Yu, R. C.; Huang, C. H.; Huang, J. H.; Lee, H. Y.; Chen, J. T. Inorg. Chem. 2002, 41, 6450.

18 Schuetz, S. A.; Silvernail, C. M.; Incarvito, C. D.; Rhein-gold, A. L.; Clark, J. L.; Day, V. W.; Belot, J. A. Inorg. Chem. 2004, 43, 6203.

19 Schuetz, S. A.; Day, V. W.; Sommer, R. D.; Rheingold, A. L.; Belot, J. A. Inorg. Chem. 2001, 40, 5292.

20 Rees Jr., W. S.; Just, O.; Castro, S. L.; Matthews, J. S. Inorg. Chem. 2000, 39, 3736.

21 Han, X. Z.; Wu, L. L.; Yao, Y. M.; Zhang, Y.; Shen, Q. Chin. Sci. Bull. 2009, 54, 3795.

22 Peng, H. M.; Zhang, Z. Q.; Qi, R. P.; Yao, Y. M.; Zhang, Y.; Shen, Q.; Cheng, Y. X. Inorg. Chem. 2008, 47, 9828.

23 Zhou, S. L.; Wang, S. W.; Yang, G. S.; Liu, X. Y.; Sheng, E. H.; Zhang, K. H.; Cheng, L.; Huang, Z. X. Polyhedron 2003, 22, 1019.

24 Deacon, G. B.; Feng, T.; Junk, P. C.; Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1997, 1181.

25 Deacon, G. B.; Nickle, S.; Mackinnon, P. I.; Tiekink, E. R. T. Aust. J. Chem. 1990, 43, 1245.

(E0912295 Pan, B.)