Synthesis and structural diversity of lanthanide amidate complexes and their catalytic activities for the ring-opening polymerization of rac-lactide

Article abstract of DOI:10.1016/j.jorganchem.2013.02.022

Anionic lanthanide amidate complexes, Li(THF)Ln[C₆H ₅C(O)NC₆H₃(ⁱPr)₂] ₄(THF)_n·(sol)_m (Ln = La (1), Nd (2), Sm (3), Yb (4), Y (5), n = 0 or 1; sol = THF or n

Full text of DOI:10.1016/j.jorganchem.2013.02.022

Journal of Organometallic Chemistry 732 (2013) 92e101
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and structural diversity of lanthanide amidate complexes and their
catalytic activities for the ring-opening polymerization of rac-lactide
,
a
,
a,b
Xiaolin Hu a, Chengrong Lu a, Bing Wu a, Hao Ding a, Bei Zhao a , Yingming Yao
*
**
, Qi Shen
a Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, PR China
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, PR China
a r t i c l e i n f o
a b s t r a c t
Anionic lanthanide amidate complexes, Li(THF)Ln[C6H5C(O)NC6H3(iPr)2]4(THF)n$(sol)m (Ln ¼ La (1), Nd
(2), Sm (3), Yb (4), Y (5), n ¼ 0 or 1; sol ¼ THF or n-Hex), were synthesized for the first time by direct
protonolysis reaction of LiLn(NiPr2)4(THF) with benzamide proligand, C6H5CONHC6H3(iPr)2 (HL). It was
confirmed by their characterization data that complexes 1e5 presented rich and varied structures with
changeable coordination modes of the amidate ligands. On the other hand, similar reactions of HL with
neutral homoleptic lanthanide amides, Ln[N(SiMe3)2]3, cleanly yielded the neutral lanthanide amidate
complexes, {PhC(O)NC6H3(iPr)2}2Ln{OC(Ph)(C6H3(iPr)2)NeHeN(C6H3(iPr)2)C(Ph)O}(THF)2 (Ln ¼ La (6),
Nd (7), Sm (8)). Single-crystal X-ray structural determination revealed that complexes 6e8 featured an
unprecedented NeHeN bond between two of the amidate ligands, making it the most notable difference
from normal neutral analogs. Complexes 1e8 were characterized by elemental analysis and IR spec-
troscopy, with additional 1H NMR spectroscopy in the case of complexes 1, 5 and 6. Furthermore, both
the anionic and neutral lanthanide amidate complexes proved to be efficient catalysts for the ring-
opening polymerization of rac-lactide, affording heterotactic-rich polylactides. The anionic lanthanide
amidate complexes exhibited significantly higher activities than their neutral counterparts due to the
cooperative effect.
Article history:
Received 16 October 2012
Received in revised form
10 February 2013
Accepted 14 February 2013
Keywords:
Amidate ligand
Structural diversity
rac-Lactide
Polymerization
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
modes when bound to a metal center [2a,10]. A survey of the
literature reveals that most characterized transition metal amidate
The use of readily accessible classes of organic compounds as
ancillary ligands is a key facet of organometallic and coordination
chemistry. In the past two decades, a very simple group of N,O-
chelating molecules, namely deprotonated organic amides (ami-
dates), has received considerable attention in organotransition
metal chemistry because of such attractive features as ease of
preparation and tunability of steric and electronic properties [1].
Furthermore, some of these transition metal amidate complexes
have shown great potential applications in catalytic trans-
formations, such as hydroamination and hydroamination/cycliza-
complexes fall into one of the following three categories: i) mon-
odentate: O-bound or N-bound, ii) bridging and iii) chelating (see
Fig. 1). It is well-known that the lanthanide metals display more
varied coordination numbers compared to the transition metals in
their complexes. Hence, the amidate group may give rise to addi-
tional coordination modes in organolanthanide chemistry. How-
ever, to date, studies on the synthesis and reactivity of the
lanthanide amidate complexes remain rather limited, and only a
few papers have been published in this field to our best knowledge
[11]. There are different methods reported for the synthesis of
lanthanide amidate complexes, including the insertion of isocya-
nate into LneC bonds [12], the insertion of CO into organo-
lanthanide azobenzene derivative [13], the one-electron reduction
and coupling reaction using bisaryloxo samarium(II) complex and
phenyl isocyanate [14], and the disruptive acylation of dianionic
guanidiate ligand using PhCOCl [15]. Nevertheless, the most direct
method to access lanthanide amidate complexes involves the re-
action of amide proligands with organolanthanide precursors [11].
Encouraged by these results, we began to get interested in the
design and synthesis of lanthanide amidate complexes. What we
tion [2], a-alkylation [2c], allylic etherification [3], olefin oxidation
[4], Strecker reaction [5], asymmetric intermolecular boron Heck-
type reactions [6], oxygen activation and intramolecular CeH
bond activation [7], and polymerization [8,9].
The amidate group possesses two different donor atoms, namely
N and O, in its scaffold, and can adopt a variety of coordination
* Corresponding author. Fax: þ86 512 65880305.
** Corresponding author.
E-mail addresses: xlhu@suda.edu.cn (X. Hu), zhaobei@suda.edu.cn (B. Zhao).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.02.022

X. Hu et al. / Journal of Organometallic Chemistry 732 (2013) 92e101
93
CH(CH3)2), 1.16 (d, J ¼ 8 Hz, 6H, CH(CH3)2), 1.10 (d, J ¼ 8 Hz, 6H,
CH(CH3)2). Anal. Calcd for C19H23NO: C, 81.10; H, 8.24; N, 4.98.
Found C, 81.07; H, 8.28; N, 4.93. IR (KBr pellet, cmꢁ1): 3305 (m),
3062 (w), 2962 (m), 1643 (s), 1520 (s), 1489 (s), 1385 (w), 1292 (m),
798 (w), 744 (w), 698 (m).
2.3. Synthesis of Li(THF)La[C6H5C(O)NC6H3(iPr)2]4(THF)$(THF)1.5
(1)
To a THF solution of HL (2.25 g, 8.00 mmol), LiLa(NiPr2)4(THF)
(1.24 g, 2.00 mmol) in 20 mL THF was slowly added. The mixture
was stirred at room temperature for 4 h. After the reaction, the
volatile solvent was pumped off, and the residue was recrystallized
from a mixture solution of THF and hexane at room temperature to
give 1 as colorless crystals. Yield: 2.40 g (79%). Mp. 267.3e267.9 ꢀC
Fig. 1. Several possible coordination modes of amidate ligands.
focused on were as below: Would there be different coordination
modes in lanthanide amidate complexes? And what kinds of
structureereactivity relationships exist in the lanthanide amidate
complexes?
(dec.). 1H NMR (400 MHz, C6D6):
d
7.73 (d, J ¼ 7.2 Hz, 6H, aryl H),
As for their application on the ring-opening polymerization
(ROP), Zi et al. [11e,f] obtained isotactic-rich polylactides with low Pm
using amidate lanthanide amides as catalysts, while the stereo-
control ability of bridged bis(phenolate) lanthanide complexes was
far better [16]. Since ancillary ligand plays a crucial rule on the
stereoselectivity, we are eager to investigate into the characteristics,
including both activity and stereocontrol ability, of organolanthanide
amidate complexes acting as catalysts for ROP of rac-lactide.
Herein, we report the synthesis of two new series of lanthanide
amidate complexes via the convenient protonolysis reactions.
Structural characterization revealed that the amidate ligands indeed
exhibit diverse coordination modes, and the presence of an NeHeN
bond between two amidate ligands was also observed for the first
time. All the lanthanide amidates were proved to be efficient cata-
lysts for the ring-opening polymerization of rac-lactide, affording
heterotactic-rich polylactides. Here we report these results.
7.25 (t, J ¼ 8 Hz, 4H, aryl H), 7.14 (t, J ¼ 10 Hz, 10H, aryl H), 7.07 (t,
J ¼ 7.6 Hz, 8H, aryl H), 6.86 (br s, 4H, aryl H), 3.55 (s, 14H, OCH2CH2),
3.16 (septet, J ¼ 6.8 Hz, 8H, CH(CH3)2), 1.38 (s, 14H, OCH2CH2), 1.20
(d, J ¼ 6.4 Hz, 48H, CH(CH3)2). 13C NMR (75 MHz, C6D6):
d 166.4 (C]
O), 147.3, 135.4, 129.0, 127.9, 124.2 (aryl C), 68.3 (OCH2CH2), 39.9
(OCH2CH2), 29.6 (CH(CH3)2), 26.0 (CH(CH3)2), 24.4 (CH(CH3)2).
Anal. Calcd for C180H232Li2N8O15La2 (3039.44): C 71.13, H 7.69, N
3.69, La 9.14. Found: C 71.08, H 7.50, N 3.79, La 9.30. IR (KBr pellet,
cmꢁ1): 3064 (w), 2963 (m), 2868 (w), 1560 (w), 1522 (s), 1488 (s),
1384 (w), 1290 (m), 924 (w), 797 (m), 745 (m), 695 (m).
2.4. Synthesis of Li(THF)Nd[C6H5C(O)NC6H3(iPr)2]4(THF)$(THF)1.5
(2)
Following the method described for complex 1, using HL (2.25 g,
8.00 mmol) and LiNd(NiPr2)4 (1.25 g, 2.00 mmol), afforded 2 as blue
crystals. Yield: 2.17 g (71%). Mp. 214.9e215.6 ꢀC (dec.). Anal. Calcd
for C180H232Li2N8O15Nd2 (3050.10): C 70.88, H 7.67, N 3.67, Nd 9.46.
Found: C 70.78, H 7.50, N 3.94, Nd 9.73. IR (KBr pellet, cmꢁ1): 3064
(w), 2963 (m), 2869 (w), 1580 (w), 1522 (m), 1488 (m), 1389 (w),
1291 (w), 925 (w), 797 (m), 745 (m), 695 (m).
2. Experimental
2.1. General procedures
All manipulations were performed under pure argon with
rigorous exclusion of air and moisture using standard Schlenk
techniques. Solvents were distilled from Na/benzophenone ketyl
under pure argon prior to use. Metal analyses were carried out by
complexometric titration. Carbon, hydrogen, and nitrogen analyses
were performed by direct combustion on a Carlo-Erba EA-1110
instrument. Melting points were determined in sealed Ar-filled
capillary tubes and are uncorrected. The IR spectra were recorded
on a Magna-IR 550 spectrometer. Molecular weight and molecular
weight distributions were determined against a polystyrene stan-
dard by gel permeation chromatography (GPC) on a waters 1515
apparatus with three HR columns (HR-1, HR-2, and HR-4); THF was
used as an eluent at 30 ꢀC. 1H NMR spectra were measured on a
Unity Inova-400 spectrometer in C6D6 or CDCl3.
2.5. Synthesis of Li(THF)Sm[C6H5C(O)NC6H3(iPr)2]4$(n-Hex) (3)
Following the method described for complex 1, using HL (2.53 g,
9.00 mmol) and LiSm(NiPr2)4 (1.42 g, 2.25 mmol), afforded 3 as
colorless crystals. Yield: 2.30 g (71%). Mp. 213.7e215.0 ꢀC (dec.).
Anal. Calcd for C86H110LiN4O5Sm (1437.07): C 71.88, H 7.72, N 3.90,
Sm 10.46. Found: C 71.53, H 7.66, N 4.11, Sm 10.44. IR (KBr pellet,
cmꢁ1): 3064 (w), 2964 (m), 2868 (w), 1580 (w), 1522 (s), 1488 (s),
1290 (m), 797 (m), 745 (m), 695 (m).
2.6. Synthesis of Li(THF)Yb[C6H5C(O)NC6H3(iPr)2]4$(n-Hex) (4)
Following the method described for complex 1, using HL (2.25 g,
8.00 mmol) and LiYb(NiPr2)4 (1.31 g, 2.00 mmol), afforded 4 as
colorless crystals. Yield: 2.20 g (75%). Mp. 217.3e218.5 ꢀC (dec.).
Anal. Calcd for C86H110LiN4O5Yb (1459.76): C 70.76, H 7.60, N 3.84,
Yb 11.85. Found: C 70.67, H 7.30, N 3.97, Yb 11.72. IR (KBr pellet,
cmꢁ1): 3064 (w), 2963 (m), 2868 (w), 1580 (w), 1522 (s), 1488 (s),
1291 (w), 923 (w), 797 (m), 745 (m), 708 (m).
2.2. Synthesis of C6H5CONHC6H3(iPr)2 (HL)
A 250 mL round-bottomed flask was charged with a solution of
2,6-diisopropylaniline (6.66 g, 37.5 mmol) and K2CO3 (5.53 g,
40 mmol) in anhydrous ether (50 mL). The mixture was cooled to
0
ꢀC, and a ether solution (20 mL) of benzoyl chloride (5.27 g,
37.5 mmol) was added dropwise. The resulting off-white suspen-
sion was left to stir at room temperature for 2 h. After filtration and
washed by water, a white solid was obtained. The solid was
recrystallized from hot ethanol. Yield: 7.04 g (67%).1H NMR (DMSO-
2.7. Synthesis of Li(THF)Y[C6H5C(O)NC6H3(iPr)2]4(THF)$(THF) (5)
Following the method described for complex 1, using HL (2.25 g,
8.00 mmol) and LiY(NiPr2)4 (1.14 g, 2.00 mmol), afforded 5 as color-
less crystals. Yield: 2.09 g (73%). Mp. 227.7e228.3 ꢀC (dec.). 1H NMR
d6, 400 MHz)
d
9.75 (s, 1H, NH), 8.00 (d, J ¼ 8 Hz, 2H, aryl H), 7.60 (t,
J ¼ 8 Hz, 1H, aryl H), 7.54 (t, J ¼ 8 Hz, 2H, aryl H), 7.30 (t, J ¼ 8 Hz, 1H,
(400 MHz, C6D6):
d 7.75 (br m, 6H, aryl H), 7.13 (br s, 14H, aryl H),
aryl H), 7.20 (d, J ¼ 8 Hz, 2H, aryl H), 3.08 (septet, J ¼ 8 Hz, 2H,
6.92e6.68 (br m, 12H, aryl H), 3.66 (br s, 6H, CH(CH3)2), 3.48 (s, 2H,

94
X. Hu et al. / Journal of Organometallic Chemistry 732 (2013) 92e101
CH(CH3)2, 12H, OCH2CH2), 1.29 (s, 12H, CH(CH3)2, 12H, OCH2CH2),
1.20 (s,12H, CH(CH3)2), 0.98 (br s, 24H, CH(CH3)2). 13C NMR (75 MHz,
afforded 7 blue crystals. Yield: 1.27 g (60%, based on HL). Mp.
270.3e271.8 ꢀC (dec.). Anal. Calcd for C84H105N4O6Nd (1410.96): C
71.50, H 7.50, N 3.97, Nd 10.22. Found: C 71.38, H 7.32, N 3.94, Nd
10.20. IR (KBr pellet, cmꢁ1): 3299 (m), 3063 (w), 2963 (m), 2868
(w),1642 (s),1522 (m),1488 (s),1290 (m), 797 (w), 745 (w), 695 (w).
C6D6):
d 176.4 (C]O), 147.4, 140.5, 135.8, 130.6, 125.2, 124.3, 68.7
(OCH2CH2), 32.3 (OCH2CH2), 29.6 (CH(CH3)2), 28.9 (CH(CH3)2), 26.0
(CH(CH3)2), 24.3 (CH(CH3)2). Anal. Calcd for C88H112LiN4O7Y
(1437.07): C 73.72, H 7.87, N 3.91, Y 6.20. Found: C 73.82, H 7.80, N
4.12, Y 6.17. IR (KBr pellet, cmꢁ1): 3064 (w), 2963 (m), 2869 (w),1580
(w), 1522 (m), 1488 (m), 1290 (w), 797 (m), 745 (m), 695 (m).
2.10. Synthesis of {PhC(O)NC6H3(iPr)2}2Sm{OC(Ph)(C6H3(iPr)2)Ne
HeN(C6H3(iPr)2)C(Ph)O}(THF)2 (8)
2.8. Synthesis of {PhC(O)NC6H3(iPr)2}2La{OC(Ph)(C6H3(iPr)2)NeHe
N(C6H3(iPr)2)C(Ph)O}(THF)2 (6)
Following the method described for complex 6, using HL (2.53 g,
9.00 mmol) and Sm[N(SiMe3)2]3 (3.00 mmol, 20 mL of THF),
afforded 7 as colorless crystals. Yield: 2.05 g (64%, based on HL). Mp.
264.4e265.3 ꢀC (dec.). Anal. Calcd for C84H105N4O6Sm (1417.07): C
71.20, H 7.47, N 3.95, Sm 10.61. Found: C 71.39, H 7.48, N 4.03, Sm
10.59. IR (KBr pellet, cmꢁ1): 3298 (m), 3064 (w), 2964 (m), 2868
(w), 1642 (s), 1522 (m), 1488 (m), 1290 (w), 797 (w), 745 (w), 600
(w).
A Schlenk flask was charged with HL (1.69 g, 6.00 mmol), THF
(10 mL), and a stir bar. La[N(SiMe3)2]3 (2.00 mmol, 15 mL of THF)
was then added slowly, and the color of the solution gradually
changed to light yellow. After stirring overnight at room tempera-
ture, the solvent was removed under vacuo. The residue was
extracted by hexane to remove extra La[N(SiMe3)2]3, then the solid
left was dissolved in THF/hexane, and crystallized at room tem-
perature to give 6 as colorless crystals. Yield: 1.20 g (57%, based on
2.11. X-ray structure determination of complexes 1e8
HL). Mp. 259.7e261.3 ꢀC (dec.). 1H NMR (400 MHz, THF-d8):
d 8.92
Owing to air and moisture sensitivity, suitable single crystals of
(s, 1H, NH), 7.91 (d, J ¼ 8 Hz, 2H, aryl H), 7.52 (br s, 6H, aryl H), 7.39
(t, J ¼ 7.2 Hz, 1H, aryl H), 7.32 (t, J ¼ 7.2 Hz, 2H, aryl H), 7.19 (t,
J ¼ 8 Hz, 1H, aryl H), 7.10 (m, 4H, aryl H), 7.02 (m, 6H, aryl H), 6.90
(m, 7H, aryl H), 6.86 (m, 3H, aryl H), 3.27 (m, 6H, CH(CH3)2), 3.17
(septet, J ¼ 6.8 Hz, 2H, CH(CH3)2), 1.11 (d, J ¼ 6.8 Hz, 12H, CH(CH3)2),
0.90 (br s, 18H, CH(CH3)2), 0.63 (br s, 18H, CH(CH3)2). 13C NMR
complexes 1e8 were each sealed in thin-walled glass capillaries.
Intensity data were collected on a Rigaku Mercury CCD equipped
ꢀ
with graphite-monochromatized Mo K
a
(l
¼ 0.71070 A) radiation.
Details of the intensity data collection and crystal data are given in
Tables 1 and 3. The crystal structures of these complexes were
solved by direct methods and expanded by Fourier techniques.
Atomic coordinates and thermal parameters were refined by full-
matrix least-squares analysis on F2. All the non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were all generated
geometrically with assigned appropriate isotropic thermal param-
eters. The structures were solved and refined by using the SHELXL-
97 program [17].
(75 MHz, THF-d8):
d 166.8 (C]O), 147.5, 140.3, 136.1, 133.8, 131.8,
130.6, 129.9, 129.0, 128.5, 128.3, 127.9, 123.8, 123.7, 123.2 (aryl C),
29.6 (CH(CH3)2), 28.5 (CH(CH3)2), 24.6 (CH(CH3)2), 24.1 (CH(CH3)2).
Anal. Calcd for C84H105N4O6La (1405.63): C 71.78, H 7.53, N 3.99, La
9.88. Found: C 71.73, H 7.32, N 3.90, La 10.00. IR (KBr pellet, cmꢁ1):
3295 (m), 3064 (w), 2964 (m), 2868 (w), 1642 (s), 1522 (m), 1488
(s), 1290 (m), 797 (w), 745 (w), 695 (w).
2.12. A typical polymerization procedure
2.9. Synthesis of {PhC(O)NC6H3(iPr)2}2Nd{OC(Ph)(C6H3(iPr)2)Ne
HeN(C6H3(iPr)2)C(Ph)O}(THF)2 (7)
The procedures for the polymerization of rac-lactide initiated by
complexes 1e8 were similar, and a typical polymerization proce-
dure is given below. A 30 mL Schlenk flask, equipped with a mag-
netic stirring bar, was charged with the desired amount of rac-
Following the method described for complex 6, using HL (1.69 g,
6.00 mmol) and Nd[N(SiMe3)2]3 (2.00 mmol, 15 mL of THF),
Table 1
Selected crystal data and experimental parameters for complexes 1e5.
1$1.5THF
2$1.5THF
3$hexane
4$hexane
5$THF
Formula
Fw
T (K)
C90H116LiN4O7.5La
1519.72
223(2)
C90H116LiN4O7.5Nd
1525.05
223(2)
C86H110LiN4O5Sm
1437.07
223(2)
C86H110LiN4O5Yb
1459.76
223(2)
C88H112LiN4O7Y
1433.67
223(2)
Cryst syst
Space group
Crystal size (mm3)
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/c
0.50 ꢂ 0.50 ꢂ 0.25
14.2651(11)
27.5870(20)
21.6884(14)
99.849(3)
8409.1(11)
4
0.50 ꢂ 0.20 ꢂ 0.20
14.2222(10)
27.6355(18)
21.6369(16)
99.713(2)
8382.2(10)
4
0.45 ꢂ 0.40 ꢂ 0.40
14.3040(6)
25.7255(11)
21.8575(9)
93.6180(10)
8027.0(6)
4
0.44 ꢂ 0.36 ꢂ 0.20
14.1723(9)
25.8143(17)
21.8163(15)
92.640(2)
7973.0(9)
4
0.70 ꢂ 0.45 ꢂ 0.20
13.5155(9)
24.4574(17)
25.0322(18)
93.166(2)
8261.9(10)
4
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
b
(ꢀ)
3
ꢀ
V (A )
Z
Dcalc (g/cm3)
1.200
0.563
1.208
0.674
1.189
0.782
1.216
1.224
1.153
0.760
m
(mmꢁ1
)
F (000)
q
3216
3.07e27.50
76,077
3228
3.08e25.50
43,096
3036
3.02e27.50
45,947
3068
3.02e27.49
44,303
3064
3.01e25.50
41,995
range (ꢀ)
Collected
Unique reflns
19,203
15,523
18,181
18,131
15,304
R
0.0718
0.0955
0.0689
0.0654
0.0859
wR
Rint
GOF
0.1463
0.0611
1.230
1.026, ꢁ0.780
0.1759
0.0864
1.218
0.655, ꢁ0.923
0.1361
0.0542
1.177
0.693, ꢁ0.858
0.1229
0.0542
1.167
0.811, ꢁ1.078
0.1786
0.0635
1.122
0.637, ꢁ0.517
3
ꢀ
Peak/hole (e/A )

X. Hu et al. / Journal of Organometallic Chemistry 732 (2013) 92e101
95
Table 2
Selective bond lengths (A) and bond angles ( ) for complexes 1e4.
indication of the increase in electron density, as a result of coor-
dination to the metal center. The septet at 3.15 ppm is assigned to
the methine proton in the isopropyl group, while the correspond-
ing methyl protons appear at 1.20 ppm as a doublet. The signals
observed for the coordinated THF methylene protons are at 1.38
and 3.55 ppm respectively, which are close to typical residual THF
solvent signals (1.40 and 3.57 ppm) [18]. Elemental analyses
revealed that these complexes consist of four amidate ligands in the
solid state. Definitive molecular structure determination revealed
that these are anionic lanthanide-lithium amidate complexes,
Li(THF)Ln[C6H5C(O)NC6H3(iPr)2]4(THF)n$(sol)m (Ln ¼ La (1), Nd (2),
Sm (3), Yb (4) and Y (5), n ¼ 0 or 1; sol ¼ THF or n-Hex), as shown in
Scheme 1. All the complexes are air and moisture sensitive. They are
soluble in THF, toluene, and slightly soluble in hexane.
ꢀ
ꢀ
1
2
3
4
Lne
Lne
LneO(av. in
LneO(6)
LneN(av. in
Lnek-N(4)
CeO (av.)
CeN (av.)
O(4)eLneN(4)
C(58)eO(4)eLn
O(4)eC(58)eN(4)
C(58)eN(4)eLn
m
-O(1)
2. 317(3)
2. 457(3)
2.550(3)
2.603(3)
2.669(3)
2.728(3)
1.295(5)
1.302(5)
50.24(9)
100.3(2)
117.7(3)
87.7(2)
2.262(5)
2.385(5)
2.475(4)
2.551(5)
2.617(5)
2.694(5)
1.308(8)
1.307(8)
51.70(16)
101.4(4)
116.8(6)
86.7(4)
2.256(3)
2.371(3)
2.436(3)
e
2.175(3)
2.265(3)
2.328(3)
e
k-O(4)
m
-O:
k
2-L)
2-L)
m
-O:
k
2.485(3)
2.455(3)
1.306(5)
1.304(5)
54.33(11)
97.2(3)
115.8(4)
92.7(3)
2.406(4)
2.362(4)
1.305(5)
1.308(6)
56.80(13)
96.8(3)
114.8(4)
91.6(3)
Crystals of complexes 1e5 suitable for X-ray diffraction were
obtained from hexane/THF mixed solvent at room temperature.
Since complexes 1 and 2 are isostructural, and so are complexes 3
and 4, hence, only the representative molecular structures of
complexes 1, 3 and 5 are shown in Figs. 2e4, respectively. Details of
their crystallographic data are summarized in Table 1, and the
corresponding selected bond lengths and angles are provided in
Table 2.
Complexes 1 and 2 are isomorphous, and so are complexes 3 and
4. Their structures have much in common except for a tetrahy-
drofuran molecule coordinated to the lanthanide metal. Four ami-
date groups are bound to lanthanide and lithium atoms: one
lactide and toluene. Then a solution of the initiator in toluene was
added to this solution by syringe. The mixture was stirred vigor-
ously at room temperature for the desired time, during which time
an increasing viscosity was observed. The reaction mixture was
quenched by the addition of methanol and then poured into
ethanol to precipitate the polymer, which was dried under vacuum
and weighed.
3. Results and discussion
3.1. Synthesis and characterization of anionic and neutral rare earth
metal amidate complexes 1e8
bridges the two atoms (namely,
lates the lanthanide (namely,
2-amidate); another two chelate the
lanthanide and also act as bridges between metals (namely,
m-N:m-O-amidate); the other che-
k
m
-O:k2
-
-
The amide proligand, N-2,6-diisopropylphenylbenzamide,
C6H5C(O)NHC6H3(iPr)2 (HL), was synthesized through the reaction
of 2,6-diisopropylaniline and benzoyl chloride. Reaction of
4 equiv of HL with anionic lanthanide amido complexes, LiLn(-
NiPr2)4(THF) (Ln ¼ La, Nd, Sm, Yb and Y), in THF at room temper-
ature, gave the final products as crystalline samples from THF/
hexane mixed solvent in good isolated yields, after routine workup.
amidate), as those observed in the known complexes, [(C5H5)2Ln(
m
h1
:h
2-OC(N]C(NMe2)2)NPh)]2 (Ln ¼ Gd, Er) [19], [Cp2Dy(OC(Ph)
NCy)]2 [15] and [Y(tBu[O,N](CH3)2Ph)3]2 [11c]. The lanthanide
metal is eight coordinated in complexes 1 and 2, seven for 3 and 4.
The lanthanide metallocycles defined by rare earth metals and the
chelating amidate groups are essentially planar, since the sum of
the bond angles are about 360ꢀ (see Table 2). This is similar to those
Disappearance of the amido NeH signal (d
9.75) in the 1H NMR
spectrum of the lanthanum complex confirms the occurrence of
protonolysis. The chemical shifts of the aryl hydrogens moved
upfield, from 8.00e7.20 ppm to 7.73e6.86 ppm, which is an
reported in
a
related monoamidate yttrium complex
(MeC5H4)2Y(THF)(N(iPr)2[O,N]Ph) [20], and a homoleptic tris(ami-
date) complex [(THF)Y(Nap[O,N](iPr)2Ph)3]2 [11c].
ꢀ
In complex 1, the Lae
m
-O bond distance is 2.317(3) A, and
2-bonding amidate
ꢀ
2.457(3) A for the Lae
k
-O bond. For the
m-O:k
ꢀ
group, the average length of the LaeO bond is 2.550(3) A, which is
Table 3
significantly longer than either the Lae
m
-O or Lae
k
k
-O bonds.
Selected crystal data and experimental parameters for complexes 6e8.
Meanwhile, the average distance of LaeN in the
m-O:
2-bonding
6
7
8
ꢀ
mode is 2.669(3) A, which is slightly shorter than that of the pure
Formula
Fw
T (K)
C
84H105N4O6La
C84H105N4O6Nd
1410.96
223(2)
C84H105N4O6Sm
1417.07
223(2)
ꢀ
chelating ligand (2.728(3) A). These data indicate that when the
1405.63
223(2)
amidate group adopts the m-O:k
2-coordination mode, the interac-
Cryst syst
Space group
Crystal size
(mm3)
Monoclinic
C2/c
Monoclinic
C2/c
Monoclinic
C2/c
tion between La and O atoms is weakened to a certain extent, while
that between La and N atoms is somewhat strengthened. The
0.80 ꢂ 0.40
0.90 ꢂ 0.40
0.40 ꢂ 0.30
average CeO and CeN bond lengths in the k
2-amidate backbone are
ꢂ 0.40
ꢂ 0.40
ꢂ 0.25
ꢀ
very close (1.295(5) and 1.302(5) A), suggesting significant electron
delocalization. The bond parameters in complex 2 are similar to the
corresponding values in complex 1, taking into account the differ-
ence in ionic radii.
ꢀ
a (A)
24.038(4)
16.233(2)
23.040(4)
120.317(3)
7761(2)
4
23.866(4)
16.167(2)
23.070(3)
120.447(3)
7673.9(19)
4
23.850(3)
16.1262(13)
23.317(2)
121.417(2)
7653.0(13)
4
ꢀ
b (A)
ꢀ
c (A)
b
(ꢀ)
3
ꢀ
V (A )
For complex 3, the average SmeO (
m
-O:
k
2-amidate) bond length
-O
k-O (2.371(3) A). All these bond lengths are
Z
ꢀ
Dcalc (g/cm3)
1.203
0.603
2968
3.03e27.50
21687
8715
0.0509
0.0986
0.0473
1.221
0.730
2980
3.04e27.50
21649
8756
0.0448
0.0851
0.0472
1.230
0.821
2988
3.05e27.48
21773
8688
0.0714
0.1174
0.0718
is 2.436(3) A, which is also longer than those for Sme
m
(mmꢁ1
)
(2.256(3) A) and Sme
significantly shorter than that for Sme
ꢀ
ꢀ
m
ꢀ
F (000)
k-O (2.515(6) A) in the re-
q
range (ꢀ)
ported complex, (
s
OMe:
k
O:
k
N-1)2SmN(SiMe3)2 (1 ¼ (R)-2-(mesi-
Collected
Unique reflns
R
wR
Rint
GOF
toylamino)-20-methoxy-6,60-dimethyl-1,10-biphenyl) [11e]. The
ꢀ
SmeN bond distance is 2.455(3) A in
consistent with the corresponding value (2.448(8) A) in (
k
2-bonding mode, which is
ꢀ
sOMe:-
k
k
O:kN-1)2SmN(SiMe3)2. The electron delocalization through the
1.159
0.611, ꢁ0.897
1.106
0.481, ꢁ0.851
1.226
0.517, ꢁ0.949
2-amidate backbone in complex 3 is confirmed by the average CeO
3
ꢀ
Peak/hole (e/ A )
ꢀ
and CeN distances (1.306(5) and 1.304(5) A, respectively).

96
X. Hu et al. / Journal of Organometallic Chemistry 732 (2013) 92e101
Scheme 1. Synthesis of anionic rare earth metal amidate complexes 1e5.
In complex 5, the coordination modes for three of the four
amidate ligands are identical to those observed in complexes 1e4,
published by Schafer [11c]. The geometry around the yttrium atom
can be described as a pentagonal-bipyramid, with O(1) and O(6) at
the two apical positions (O(1)eYeO(6) 165.93(11)ꢀ), and O(2), O(3),
O(4), N(2) and N(3) almost coplanar with the yttrium atom (the
with the fourth amidate ligand adopting a monodentate coordi-
nation mode (namely, h
1-amidate). This difference may have arisen
as a result of the coordination of THF molecule and steric hindrance
about the yttrium atom, in view of the relatively small ionic radius
of yttrium. Such bonding mode was also observed in earlier work
sum of the central angles is 360.55ꢀ). The Ye
h
1-O(4) bond distance
-O(1)
ꢀ
is 2.132(3) A, which is slightly shorter than that for the Ye
m
ꢀ
(2.169(3) A). Nevertheless, both YeO bonds are apparently
ꢀ
shorter than that of the
m
-O:k2-amidate (2.370(3) A on average).
ꢀ
The average YeN bond length is 2.494(3) A, which is slightly longer
than that reported in the literature [11c].
Fig. 2. ORTEP diagram of complex 1 with the probability ellipsoids drawn at the 20%
level, and hydrogen atoms are omitted for clarity. Complex 2 is isomorphous with
complex 1.
Fig. 3. ORTEP diagram of complex 3 with the probability ellipsoids drawn at the 20%
level, and hydrogen atoms are omitted for clarity. Complex 4 is isomorphous with
complex 3.

X. Hu et al. / Journal of Organometallic Chemistry 732 (2013) 92e101
97
Fig. 4. ORTEP diagram of complex 5 with the probability ellipsoids drawn at the 20%
Fig. 5. ORTEP diagram of complex 6 showing the atom-numbering scheme. Thermal
ellipsoids are drawn at the 20% probability level, and partial hydrogen atoms are
omitted for clarity. Complexes 7 and 8 are isomorphous with complex 6.
ꢀ
level, and hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles
(o): Ye
2.369(3), YeN (av. in
m
-O(1) 2.169(3), Ye
h m-O:k
1-O(4) 2.132(3), YeO (av. in 2-L) 2.370(3), YeO(6)
m
-O:
k
2-L) 2.494(3), CeO (av.) 1.306(5), CeN (av.) 1.292(5); O(1)e
YeO(6) 165.93(11), O(3)eY(1)eO(2) 67.95(10), O(2)eY(1)eN(2) 53.70(10), O(4)eY(1)e
N(2) 93.99(11), O(4)eY(1)eN(3) 90.50(11), O(3)eY(1)eN(3) 54.41(11).
{PhC(O)NC6H3(iPr)2}2Ln{OC(Ph)(C6H3(iPr)2)NeHeN(C6H3(iPr)2)
C(Ph)O}(THF)2 (Ln ¼ La (6), Nd (7) and Sm (8)), which was kind of
different from the structure determined by the NMR spectrum of
complex 6 in solution (Scheme 2). Further progresses to get a
homoleptic neutral complex bearing three (not four) amidate li-
gands failed, neither at high temperature nor in toluene. Complexes
6e8 are also air and moisture sensitive. Their solubilities in organic
solvents are higher in comparison with the anionic ones.
Crystals of complexes 6e8 suitable for X-ray diffraction were
obtained from hexane/THF mixed solvent at room temperature.
Since complexes 6e8 are isomorphous, only the molecular struc-
ture of complex 6 is depicted in Fig. 5 as a representation. Details of
the crystallographic data of complexes 6e8 are given in Table 3 and
selected bond lengths and angles are listed in Table 4.
In order to obtain neutral lanthanide amidate complexes, the
neutral lanthanide amido complex, Ln[N(SiMe3)2]3, was used as
starting material instead of LiLn(NiPr2)4(THF). The protonolysis
reaction of Ln[N(SiMe3)2]3 (Ln ¼ La, Nd, Sm) with the proligand HL
in a 1:3 molar ratio in THF at room temperature, followed by
crystallization from a mixture of hexane and THF, afforded three
lanthanide amidate complexes in good isolated yields. Elemental
analyses revealed that there are also four amidate ligands in each of
these complexes. In the IR spectra, the NeH stretching vibrations
were observed as broad peaks at about 3295e3299 cmꢁ1. For the
lanthanum complex 6, a singlet resonance at 8.92 ppm was
observed in the 1H NMR spectrum, which can be attributed to the
amido NeH proton (upfield shift from 9.75 ppm of the free amide).
More comprehensive analysis showed that one amidate ligand
might coordinate to the lanthanum metal as a monodentate neutral
molecule in the THF-d8 solution, while the others adopt chelating
modes, since there were three groups of peaks assigned to the
protons of methyl groups in the isopropyl, which could be divided
into two classes according to the splitting and peak areas. However,
definitive single-crystal X-ray structural determination revealed
that complexes 6e8 in solid-state are the isomorphous neutral
lanthanide amidate complexes containing NeHeN bonding,
Complex 6 crystallizes in the monoclinic crystal system, C2/c
space group, and has C2-symmetric structure and a coordination
number of eight. As shown in Fig. 5, the lanthanum atom is coor-
dinated to two THF molecules and four amidate groups, where
there are two types of amidates: two of the amidates are bound to
the central metal in a chelating manner and the other two coor-
dinate in a monodentate fashion. The Lae
h
1-O(2) bond length is
ꢀ
ꢀ
2.387(2) A, while the Lae
k
-O(1) bond is 2.468(2) A, which are both
longer than those in anionic complex 1, but shorter than those
found in [(THF)Y(Nap[O,N](iPr)2Ph)3]2 (2.284 A on average) [11c],
ꢀ
Scheme 2. Synthesis of neutral lanthanide amidate complexes 6e8.

98
X. Hu et al. / Journal of Organometallic Chemistry 732 (2013) 92e101
Table 4
Table 5
Polymerization of rac-lactide initiated by lanthanide amidate complexes.a
ꢀ
ꢀ
Selected bond distances (A) and bond angles ( ) for complexes 6e8.
6
7
8
Entry
Cat.
[M]/[I]
t (min)
Yield (%)
Mn (ꢂ104)
PDIb
Prc
Lne
Lne
LneO(3)
Lne -N(1)
O(1)eC(1)
O(2)eC(20)
N(1)eC(1)
N(2)eC(20)
N(2)eH(2)
C(1)eO(1)eLn
O(1)eC(1)eN(1)
C(1)eN(1)eLn
O(1)eLneN(1)
k
h
-O(1)
2.468(2)
2.387(2)
2.589(2)
2.621(2)
1.286(3)
1.282(3)
1.306(4)
1.301(4)
0.8700
2.4123(18)
2.3335(19)
2.5374(18)
2.571(2)
1.285(3)
1.276(3)
1.307(3)
1.314(4)
0.8700
2.385(3)
2.303(3)
2.517(3)
2.538(3)
1.288(5)
1.282(5)
1.318(5)
1.317(6)
0.8700
1
2
3
4
5
6
7
8
1 (La)
1 (La)
2 (Nd)
2 (Nd)
3 (Sm)
3 (Sm)
4 (Yb)
4 (Yb)
5 (Y)
2500:1
3000:1
2500:1
3000:1
2000:1
2500:1
300:1
1000:1
1000:1
1500:1
250:1
300:1
500:1
1000:1
2000:1
2500:1
30
40
40
40
60
60
60
110
60
140
60
120
50
60
60
60
>99
97
96
80
98
94
99
81
96
86
83
80
97
73
94
27
21.30
25.25
12.52
18.57
10.49
6.63
3.67
8.33
8.02
12.21
2.32
3.53
9.03
10.13
8.11
3.57
1.56
1.49
1.40
1.32
1.44
1.45
1.22
1.23
1.25
1.26
1.49
1.50
1.44
1.45
1.62
1.62
0.59
0.57
0.64
0.61
0.59
0.62
0.58
0.58
0.58
0.60
0.57
0.62
0.57
0.54
0.59
0.63
1-O(2)
k
9
99.1(2)
98.7(2)
98.8(2)
116.7(4)
91.0(3)
10
11
12
13
14
15
16
5 (Y)
117.6(3)
91.50(17)
51.57(7)
117.7(2)
90. 76(16)
52.75(6)
6 (La)
6 (La)
7 (Nd)
7 (Nd)
8 (Sm)
8 (Sm)
53.5(1)
a
Conditions: 20 ꢀC, [LA] ¼ 1.0 mol/L, toluene.
taking into consideration the difference in the ionic radii. The LaeN
b
c
Measured by GPC (using polystyrene standards in THF).
ꢀ
bond length is 2.621(2) A, which is apparently shorter than the Lae
Pr is the probability of racemic enchainment of monomer units calculated ac-
cording to the methine region of the homonuclear decoupled 1H NMR spectrum in
CDCl3 at 25 ꢀC.
N(k2-L) (2.728(3) A) in complex 1. The CeO (1.286(3) A) and CeN
ꢀ
ꢀ
ꢀ
(1.306(4) A) bond lengths are indicative of electron delocalization
through the
angles in the chelating amidate metallacycle in complex 6 is 359.8ꢀ,
implying that the lanthanide metal center and the
2-amidate
k
2-amidate backbone in complex 6. The sum of the four
influence on the catalytic activity. The anionic lanthanide amidate
complexes exhibited significantly higher activities than their
neutral counterparts as expected. For example, the conversion
reached 96% in the case of [M]/[I] ¼ 2500 within 40 min using
anionic neodymium complex 2 as the initiator, whereas the poly-
merization initiated by the neutral neodymium complex 7 only
afforded 73% yield in 1 h, even upon decreasing the molar ratio of
[M]/[I] to 1000/1 (entries 3 and 14). Similar phenomenon was also
k
backbone are exactly in the same plane (see Table 4), which is
similar to the earlier examples above. It is noteworthy that there is a
special bonding situation in complex 6, where the two nitrogen
atoms of the two monodentate amidate ligands share one hydrogen
atom to form an NeHeN bridge. This result is quite different from
that in [(Nap[O,NH](iPr)2Ph)Y(Nap[O,N](iPr)2Ph)3] [11c], for which
the fourth amide coordinates to the yttrium atom in its neutral
form. This is the first time such kind of bonding is observed in
amidate coordination chemistry.
observed for
-3 caprolactone polymerization initiated by organo-
lanthanide complexes [21].
The central metal also has a great influence on the polymeri-
zation activity. For instance, using the anionic lanthanide amidate
complexes as the initiators, complete polymerization of
2500 equiv of the monomer was achieved in only 30 min for
complex 1 (entry 1), whereas for complexes 2 and 3, attaining
similar yields with the same catalyst loading required 40 min (entry
3) and 60 min (entry 6), respectively. However, high yield of 96% is
obtainable in 60 min using yttrium complex 5, even when the
catalyst loading was decreased to 1000/1 (entry 9). The observed
decreasing order of activity, La > Nd > Sm > Y > Yb, is consistent
3.2. Catalytic activity of complexes 1e8 for the polymerization of
rac-lactide
Biodegradable polymers, such as poly( -caprolactone) (PCL) and
3
poly(lactide) (PLA), have recently attracted significant attention as
replacements for conventional synthetic materials because of their
biodegradability, biocompatibility and permeability. Ring-opening
polymerization of cyclic esters initiated by organometallic com-
plexes is a convenient method for the synthesis of these high
molecular weight polymers. Zi and co-workers have demonstrated
that unbridged bis(amidate) lanthanide amides can serve as cata-
lysts for the ROP of rac-lactide, affording isotactic-rich polylactides
[11e,f]. With complexes 1e8 in hand, their performance as catalysts
for the ROP of rac-lactide was examined (Scheme 3), and the results
are listed in Table 5. It can be seen that both the anionic and neutral
lanthanide amidate complexes can initiate the polymerization of
rac-lactide in high activity under mild polymerization conditions,
to give the polylactides (PLAs) with high molecular weights and
relatively narrow molecular weight distributions (PDI ¼ 1.22e1.62).
It was found that the nature of the initiators has a profound
ꢀ
ꢀ
with the trend in ionic radii (La (1.16 A) > Nd (1.11 A) > Sm
ꢀ
ꢀ
ꢀ
(1.02 A) > Y (0.96 A) > Yb (0.93 A)). This decreasing order of activity
is generally seen for cyclic polymerizations initiated by organo-
lanthanide complexes [22]. To our surprise, in contrast to the
anionic series, the trend in activity for the neutral lanthanide
amidate complexes is La < Nd < Sm (entries 11e16), which is
opposite to the ionic radii. A similar activity order has been re-
ported previously by Shen et al. for methyl methacrylate poly-
merization [23], but the reason is still not well understood.
The microstructures of the polymers obtained were determined
from the homonuclear decoupled 1H NMR spectra in CDCl3.
The present polymerization systems yielded heterotactic-rich
Scheme 3. Catalytic reaction of complexes 1e8 for the polymerization of rac-lactide.

X. Hu et al. / Journal of Organometallic Chemistry 732 (2013) 92e101
99
a. Cat. = anionic lanthanide amidate complexes
LA
Li(THF)Ln[C6H5C(O)NC6H3(iPr)2]4(THF)n
Li(LA)Ln[C6H5C(O)NC6H3(iPr)2]4(THF)n
a1
O
N
O
(THF)n
O
O
N
O
(THF)n
O
N
O
Li
Ln
N
Li
Ln
Ring-open and initiation
N
N
O
N
N
O
O
O
O
O
O
O
O
O
(THF)n
N
O
O
O
N
O
N
Propagation
O
H+
H
LA
Ln
N
Li
O
N
n
O
O
O
O
O
O
O
O
O
a2
O
b. Cat. = neutral lanthanide amidate complexes
{PhC(O)NC6H3(iPr)2}2Ln{OC(Ph)(C6H3(iPr)2)N---H---N(C6H3(iPr)2)C(Ph)O}(THF)2
Sol.
{PhC(O)NC6H3(iPr)2}3Ln{PhC(O)NHC6H3(iPr)2}(THF)2 b1
HL
HL
Ln
(THF)2
(THF)2
N
N
O
N
O
N
O
O
Ln
Ring-open and initiation
LA
N
N
O
O
O
O
O
O
O
O
O
O
HL
(THF)2
N
O
N
O
O
O
N
O
O
LA
Ln
O
Propagation
H+
H
O
N
n
O
O
O
O
O
O
b2
O
O
O
O
N
=
N
H
HL =
N
O
Scheme 4. Proposed catalytic mechanisms for the ROP of rac-lactide.
polylactides, and the Pr ranges from 0.54 to 0.64. These results are
quite different from those initiated by the chiral lanthanide amidate
amido complexes, which gave isotactic-rich polylactides [11e,f],
suggesting that the coordination environment around the metal
center may be a major deciding factor for the stereoselectivity
during polymerization [11e]. However, there is no distinct differ-
ence in stereoselectivity between the anionic and the neutral
lanthanide amidate complexes. Further investigation of the ligand
architecture for this transformation is in progress.
To figure out the active species and mechanism for the catalytic
process, we conducted end group analysis of the oligomers of rac-
lactide, which were synthesized by the reaction of complex 1 or 8
with rac-lactide in a 1:15 molar ratio. End group analysis by 1H
NMR spectroscopy (Fig. 6) showed clearly the existence of one
amidate ligand according to the resonances between 7 and 8 ppm
for the aromatic rings, at about 3.11 and 1.19 ppm for the isopropyl
groups as well. Thus, the polymerization proceeds by a common
“coordinationeinsertion” mechanism, as shown in Scheme 4.
When using anionic lanthanide amidate complexes as catalysts,
it is believed that the cooperative effect plays an important role in
the catalytic reaction [21a], contributing to much higher activities.
First, rac-lactide (represented by “LA” in Scheme 4) is supposed to
replace THF that originally coordinated to lithium to form a1 spe-
cies. Second, rac-lactide can coordinate to both Ln and Li metals
concomitantly through its carbonyl group and ester group,
respectively, and then insert into the LneN (chelating amidate
group) bond, and the second rac-lactide can coordinate to Ln and Li,
forming the corresponding active species a2. The process repeats to

100
X. Hu et al. / Journal of Organometallic Chemistry 732 (2013) 92e101
Fig. 6. 1H NMR spectrum of the oligomer of rac-lactide initiated by complex 1 in CDCl3.
yield the polymer. In the case of neutral lanthanide amidate com-
plexes, their structures firstly alter to form b1 when dissolved in
solvent. Then, rac-lactide is coordinated to the metal center and a
sequential nucleophilic attack on the carbonyl carbon of the lactide
by one of the amidate groups forms new metalealkoxo species b2.
The propagation step is the continued monomer coordination and
insertion into the active metalealkoxo bond just like that of anionic
catalysts.
Education Institutions and the Natural Science Foundation of the
Jiangsu Higher Education Institutions (Project 10KJD150005).
Appendix A. Supplementary material
CCDC-850238 (for 1), CCDC-850239 (for 2), CCDC-850240 (for
3), CCDC-852822 (for 4), CCDC-852821 (for 5), CCDC-850237 (for
6), CCDC-850241 (for 7), and CCDC-850242 (for 8) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
4. Conclusions
In summary, two series of anionic and neutral lanthanide ami-
date complexes were successfully synthesized and well-
characterized. In these complexes, the amidate group shows great
diversity in terms of the bonding mode. The amidate ligands in
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