Zinc complexes supported by multidentate aminophenolate ligands: Synthesis, structure and catalysis in ring-opening polymerization of rac-lactide

Article abstract of DOI:10.1039/c0dt00250j

Monomeric zinc silylamido and ethyl complexes bearing tetradentate aminophenolato ligands [(DNNO)ZnR] (D = NMe₂, OMe; R = N(SiMe ₃)₂ (1-5, 8), Et (6, 7, 9, 10)), were isolated from the reaction of Zn[N(SiMe₃)₂]₂ or ZnEt₂ and one equivalent of aminophenols {aryl-CH₂N[(CH₂) ₂NMe₂]CH₂-phenol} in moderate to high yields. The monomeric nature of these complexes was further confirmed by X-ray diffraction studies of silylamido complexes 1, 3 and ethyl complexes 7, 9, 10. The methoxy or N,N-dimethylamino group of the aryl unit does not coordinate with the metal center in the solid state, only the remaining three donors of the ligand and silylamido or ethyl group interact with zinc center constructing a distorted tetrahedral coordination geometry at the metal center. All these zinc complexes efficiently initiated the ring-opening polymerization of rac-lactide, and the polymerization runs were better controlled in the presence of isopropanol, giving atactic PLAs end-capped with isopropyl ester and hydroxyl groups. The structure of the ancillary ligands showed some influence on the catalytic activity and selectivity of the corresponding zinc complexes. The introduction of bulky ortho-substituents on the phenoxy unit resulted in a decrease of the polymerization rate, whereas the isotactic dyad selectivity in the ROP of rac-lactide was enhanced.

Full text of DOI:10.1039/c0dt00250j

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PAPER
www.rsc.org/dalton | Dalton Transactions
Zinc complexes supported by multidentate aminophenolate ligands: synthesis,
structure and catalysis in ring-opening polymerization of rac-lactide†
Liying Wang and Haiyan Ma*
Received 1st April 2010, Accepted 27th May 2010
First published as an Advance Article on the web 26th July 2010
DOI: 10.1039/c0dt00250j
Monomeric zinc silylamido and ethyl complexes bearing tetradentate aminophenolato ligands
[(DNNO)ZnR] (D = NMe2, OMe; R = N(SiMe3)2 (1–5, 8), Et (6, 7, 9, 10)), were isolated
from the reaction of Zn[N(SiMe3)2]2 or ZnEt2 and one equivalent of aminophenols
{aryl-CH2N[(CH2)2NMe2]CH2-phenol} in moderate to high yields. The monomeric nature of these
complexes was further confirmed by X-ray diffraction studies of silylamido complexes 1, 3 and ethyl
complexes 7, 9, 10. The methoxy or N,N-dimethylamino group of the aryl unit does not coordinate
with the metal center in the solid state, only the remaining three donors of the ligand and silylamido or
ethyl group interact with zinc center constructing a distorted tetrahedral coordination geometry at the
metal center. All these zinc complexes efficiently initiated the ring-opening polymerization of
rac-lactide, and the polymerization runs were better controlled in the presence of isopropanol, giving
atactic PLAs end-capped with isopropyl ester and hydroxyl groups. The structure of the ancillary
ligands showed some influence on the catalytic activity and selectivity of the corresponding zinc
complexes. The introduction of bulky ortho-substituents on the phenoxy unit resulted in a decrease of
the polymerization rate, whereas the isotactic dyad selectivity in the ROP of rac-lactide was enhanced.
zinc are therefore much preferred. In general, zinc complexes
are efficient initiators for the ring-opening polymerization of
Introduction
lactide,29–32 but lacking satisfied isotactic selectivity and producing
mainly heterotactic or atactic polylactides.33–42 Among them, zinc
complexes with b-diketiminate, phenoxy-imine, phenoxy-amine
have been extensively developed (Chart 1). Coates and co-workers
synthesized zinc complexes bearing sterically demanding achiral
b-diketiminate ligands (A), which initiated rac-lactide polymer-
ization to afford heterotactic PLA via a chain-end control mech-
anism. In particular, the authors found that subtle modifications
of steric bulkiness of the N-aryl substituents of b-diketiminate
ligands resulted in dramatic effects on stereoselectivity (Pr could
be improved to 0.94).34 Chisholm reported that zinc silylamido
complex ligated with phenoxy-imine ligand B catalyzed the
polymerization of rac-lactide to give atactic polylactide.42 Lin et al.
introduced zinc alkoxide complex supported by mono-methylether
salen-type ligand C for the polymerization of rac-lactide to afford
heterotactic predominant PLA with Pr = 0.75; meanwhile, a
magnesium analogue containing the same ligand gave isotactic-
enriched PLA with Pm = 0.67.36 Further investigation showed
that zinc alkoxide complexes supported by phenoxy-imine-amine
ligands D proved highly heterotactic selective (Pr = 0.91) for
ROP of rac-lactide in CH2Cl2 at low temperature.39 Hillmyer and
Tolman reported the highly active zinc ethoxide complexes derived
from phenoxydiamine ligands E, which were observed to initiate
rapid polymerization of rac-lactide at a high initial monomer-
to-catalyst ratio of 1500, yielding PLAs with average molecular
weight as large as 130 kg mol-1.29 Very recently, Mehrkhodavandi
described some unusually stable chiral zinc ethyl complexes;
among them, complexes supported by ligands F initiated rac-
lactide polymerization to give PLA with Pm = 0.54.43
Polylactide (PLA), prepared from natural renewable resources
has recently gained much attention due to its biodegradable
and biocompatible nature, and suitable properties as a potential
alternative to polyolefins.1–4 Nowadays, methods for preparing
high molecular weigh polylactides generally rely on the controlled
ring-opening polymerization (ROP) of lactides initiated by well-
defined metal complexes. Systematic mechanistic studies have
demonstrated the influence both of the initiating group and of the
ancillary ligand architecture on polymerization control, reaction
rate and/or stereoselectivity during the polymerization process.5,6
Stereocontrolled polymerizations have been observed by us-
ing aluminium initiators with salen-type ligands, and excellent
isotactic stereospecificity can be obtained in the ROP of rac-
lactide via either enantiomorphic site control7–12 or a chain-end
control mechanism.13–20 The catalytic activities of these aluminium
complexes are generally low and the polymerization runs had
to be carried out at high temperature over a relatively long
period of time. Rare-earth metal complexes are highly active for
ROP of rac-lactide, in some cases showing significant preference
for heterotactic dyad enchainment.21–28 When regarding possible
incorporation of trace amount of metal residues in the obtained
polymer, initiators consisting of biocompatible metals such as
Laboratory of Organometallic Chemistry, East China University of Science
and Technology, 130 Meilong Road, Shanghai, 200237, People’s Republic of
China. E-mail: haiyanma@ecust.edu.cn (H. Ma); Fax: +86 21 64253519;
Tel: +86 21 64253519
† Electronic supplementary information (ESI) available: Variable-
temperature 1H NMR spectra of 10, 1H NMR spectra of active rac-lactide
oligomer by 1/iPrOH, the complex 1 and the ligand L1H, 1H NMR trace
spectra of reaction between complex 9 and isopropanol. CCDC reference
numbers 772262–772266 for 1, 3, 7, 9 and 10. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c0dt00250j
Due to the divalent nature of the zinc ion, monoanionic
ligands were utilized throughout to construct complexes of the
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Scheme 1
paraformaldehyde to give the corresponding proligands in mod-
erate yields.
Zinc complexes 1–5 were synthesized via the reaction of
corresponding aminophenol and Zn[N(SiMe3)2]2 in 1 : 1 molar
ratio in light petroleum with the concomitant formation of 1
equiv. of HN(SiMe3)2 at room temperature. Analytically pure
complexes 1–5 were isolated from toluene or hexane as colorless,
air/moisture sensitive crystalline solids in 61–75% yields after
work-up (Scheme 2). In the case of L6H or L7H, a similar
approach only acquired white powders which were very poorly
soluble in common solvents such as light petroleum, aromatic
solvents, and decomposed in methylene dichloride and THF. To
overcome the problem of dissolvability, one equiv. of L6H or
L7H was treated with diethyl zinc to afford zinc ethyl complexes
6 and 7 by ethane elimination reaction in almost quantitative
yields (Scheme 3). Zinc complex 8 containing an aryl-N,N-
dimethylamino group could be synthesized similarly as complexes
1–5 via amine elimination reaction, but analogous complexes
with either cumyl or chloro substituents could not be prepared
Chart 1
form LnZnX (where Ln represents a multidentate monoanionic
ligand, X is a group capable of initiating polymerization or can
be converted to such a group). However, structural features of an-
cillary ligands capable of governing isotactic stereocontrol during
the ROP of lactide by zinc complexes are still uncertain rather than
uncovered. Crucial factors in the polymerization process such as
activity and stereoselectivity need to be further studied for well-
defined zinc complexes. Herein, we report the synthesis and lactide
polymerization investigation of a series of zinc complexes bearing
monoanionic claw-type aminophenolate ligands with the aim to
construct an asymmetric coordination environment around the
metal center for selective monomer recognition. Nevertheless, zinc
complexes with similar bis(phenolate) ligand G hardly initiated the
polymerization of cyclic esters.44
Results and discussion
Synthesis and spectroscopic studies
The tetradentate phenol proligands (L1–10H) were prepared via
three-step reactions as illustrated in Scheme 1. The condensation
reaction of arylaldehydes with N,N-dimethylethylenediamine in
methanol afforded the corresponding Schiff-base compounds
which were sequentially reduced to amines without further
purification; the crude amines were then exposed to a modified
Mannich reaction with substituted phenols in the presence of
Scheme 2
7898 | Dalton Trans., 2010, 39, 7897–7910
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the dimethylamino group should take part in the coordination
with the zinc center; the coordination of the methoxy group is
however inconclusive. Most likely the same structure features are
maintained in solution as they are in the solid state (vide post).
The non-coordination mode of the methoxy group to the metal
center was also observed for zinc complexes bearing a mono-
methylether Salen-type ligand36 as well as ether-substituted b-
diketiminate ligands.37
The alteration of aryl-methoxy group with dimethylamino in
complex 8 does not change the coordination fashion, as similar
features mentioned above are also observed. In contrast, sharp
resonances are displayed both for aryl- and alkyl-N(CH3)2 groups
in the 1H NMR spectra of complexes 9 and 10. For complex 9 the
resonance of the alkyl-N(CH3)2 group shifts significantly upfield,
whereas that of complex 10 shifts slightly downfield. Based on the
fact that a significant upfield shift (Dd = 0.77–1 ppm) of one methyl
resonance of alkyl-N(CH3)2 groups is also observed for complexes
4 and 6 that all possess cumyl substituents, the origin of the appar-
ent upfield shift of alkyl-N(CH3)2 resonance observed for complex
9 (cumyl substituted) should be independent of the introduction
of the aryl amino group. Variable-temperature 1H NMR study of
complex 10 in toluene-d8 over the temperature range of 298 to
198 K further witnessed the gradual broadening and splitting into
two broad peaks of the sharp alkyl-N(CH3)2 signal with decrease
of temperature. Similar behavior was also observed for the aryl-
N(CH3)2 signal, which broadened and finally split into two broad
peaks at an even lower temperature of 198 K. Although these
spectroscopic features could be attributed to the restricted rotation
of the methyl groups, based on the quite similar behavior of both
amino groups as well as our unpublished work,45 a rapid exchange
process of these two types of nitrogen donors coordinating to the
zinc core alternatively might not be ruled out, which could be
frozen out at low temperature on the NMR time scale. Taking the
same ligand skeleton into consideration, a similar process might
also take place for complex 9.
Scheme 3
due to poor solubility in common hydrocarbon solvents, thus
corresponding zinc ethyl complexes 9 and 10 were obtained from
the reaction of aminophenols L9H, L10H with diethyl zinc.
The stoichiometric structures of complexes 1–10 were further
confirmed on the basis of 1H and 13C NMR spectroscopy as well
1
as elemental analysis. In the H NMR spectrum of complex 1 in
C6D6, the two protons of each methylene in the Ar–CH2–N units
are inequivalent and give rise to two doublets as compared to
the singlet in the free ligand, indicating a rigid configuration in
solution. Similar phenomena were also displayed in the proton
NMR spectra of the remaining zinc complexes except for complex
4, where two doublets at 4.33, 3.28 ppm with coupling constant of
2J = 12.8 Hz as well as one singlet accounting for two protons at
4.11 ppm are displayed. It is worth noting that the methylene
resonances of the bridging unit (NCH2CH2N) in these zinc
complexes exhibit unexpected features. Besides the unidentifiable
coupling modes, the signal of one methylene proton shifts upfield
significantly (Dd = 0.5–0.8 ppm for silylamido complexes), while
the remainder are at the same positions as those of the free ligand.
By referring the result of X-ray diffraction studies, we suggest that
it is most likely due to some specific shielding effect of the aromatic
rings.
To better understand the coordination environment around the
zinc center in complexes 1–10, chemical shifts of representative
donor groups are summarized in Table 1. It is found that
the sharp resonance assignable to Ar–OCH3 in complexes 1–
7 hardly changes when compared to that of the corresponding
free ligand. However, the resonance assignable to the six protons
of the dimethylamino group either splits into two peaks or still
displays as a singlet, but both along with significant broadening.
All these suggest that in complexes 1–7 the nitrogen atom of
Molecular structures of zinc complexes
Single crystals of 1, 3, 7, 9 and 10 suitable for X-ray diffraction
studies were obtained by slightly cooling a saturated toluene, n-
hexane solution or toluene–pentane mixture respectively. Crystal-
lographic data and results of the refinements are summarized in
Table 2, selected bond lengths and angles are listed in Tables 3 and
4. As depicted in Fig. 1, complex 1 has a monomeric structure
Table 1 Selected 1H NMR data for zinc complexes 1–10 and corresponding ligands
Complex
Ar–OMe/NMe2
Alkyl-NMe2
Ligand
Ar–OMe/NMe2
Alkyl-NMe2
Solvent
1
3.11 (s, 3H)
3.10 (s, 3H)
3.33 (s, 3H)
3.31 (s, 3H)
3.29 (s, 3H)
3.78 (s, 3H)
3.83 (s, 3H)
2.27 (s, 6H)
2.54 (s, 6H)
2.60 (s, 6H)
1.93 (br s, 6H)
1.92 (br s, 6H)
L1H
L2H
L3H
L4H
L5H
L6H
L7H
L8H
L9H
L10H
3.37 (s, 3H)
3.36 (s, 3H)
3.27 (s, 3H)
3.25 (s, 3H)
3.27 (s, 3H)
3.66 (s, 3H)
3.77 (s, 3H)
2.38 (s, 6H)
2.53 (s, 6H)
2.56 (s, 6H)
1.93 (s, 6H)
1.94 (s, 6H)
1.92 (s, 6H)
1.91 (s, 6H)
1.82 (s, 6H)
2.02 (s, 6H)
2.13 (s, 6H)
1.94 (s, 6H)
2.03 (s, 6H)
2.17 (s, 6H)
C6D6
C6D6
C6D6
C6D6
2
3
2.04 (br s, 3H), 1.74 (br s, 3H)
1.91 (br s, 3H), 1.14 (br s, 3H)
2.01 (br s, 3H), 1.71 (br s, 3H)
2.02 (br s, 3H), 1.02 (br s, 3H)
2.39 (br s, 3H), 2.15 (br s, 3H)
2.06 (br s, 3H), 1.81 (br s, 3H)
1.49 (s, 6H)a
4
5
C6D6
6
CDCl3
CDCl3
C6D6
CDCl3
CDCl3
7
8
9
10
2.26 (s, 6H)
a This signal is slightly broader than that of complex 10.
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Table 2 Crystallographic data for 1, 3, 7, 9, 10
1
3
7
9
10
Empirical formula
Mr
C30H53N3O2Si2Zn
609.30
293(2)
0.34 ¥ 0.33 ¥ 0.26
Orthorhombic
P212121
12.052(7)
15.516(9)
18.0946(10)
90
90
90
3383.5(3)
4
1.196
C35H63N3O2Si2Zn
679.43
296(2)
0.25 ¥ 0.20 ¥ 0.20
Monoclinic
P21/c
8.9250(10)
24.604(3)
18.129(2)
90
95.663(2)
90
3961.4(8)
4
1.139
0.711
C21H28Cl2N2O2Zn
476.72
293(2)
0.31 ¥ 0.16 ¥ 0.12
Monoclinic
P21/n
10.5566(12)
18.482(2)
12.2472(14)
90
108.060(2)
90
2271.8(4)
4
1.394
1.334
C41H55N3OZn
671.25
296(2)
C23H33Cl2N3OZn
503.79
293(2)
0.42 ¥ 0.37 ¥ 0.21
Monoclinic
P21/c
16.3448(17)
9.4596(10)
16.1050(16)
90
97.982(2)
90
2466.0(4)
4
1.357
1.232
T/K
Crystal size/mm
Crystal system
Space group
0.25 ¥ 0.22 ¥ 0.20
Triclinic
¯
P1
˚
a/A
8.2877(11)
13.4436(18)
18.389(2)
110.4870(10)
90.143(2)
100.628(2)
1881.3(4)
2
1.185
0.686
720
2.35–25.05
9, -13 to 16,
-21 to 20
9813/6535
0.0224
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
Dc/Mg m-3
m/mm-1
0.825
1312
1.73–27.00
15, 19, -17 to 23
F(000)
1472
992
1056
q range/◦
Range hkl
2.26–25.04
-9 to 10, -29 to
18, -20 to 21
20329/7020
0.0564
2.07–26.00
12, -22 to 20,
-14 to 15
12375/4440
0.0962
2.49–25.99
-16 to 20, 11, 19
Reflns collected/unique
Rint
20151/7318
0.0474
13064/4831
0.0940
Max., min. transmission
Data/restrains/param.
Goodness-of-fit on F2
Final R1, wR2 [I > 2s(I)]
R1, wR2 (all data)
1.0000, 0.8375
7318/0/356
1.018
0.0412, 0.0811
0.0463, 0.0829
0.443, -0.274
0.8708, 0.8422
7020/0/396
1.009
0.0467, 0.0955
0.0960, 0.1155
0.294, -0.285
1.0000, 0.7298
4440/0/257
0.856
0.0586, 0.0899
0.1341, 0.1100
0.323, -0.403
0.8749, 0.8471
6535/0/425
1.021
0.0435, 0.0933
0.0607, 0.1027
0.361, -0.318
1.0000, 0.7719
4831/2/288
0.965
0.0470, 0.1108
0.0633, 0.1171
0.566, -0.331
-3
˚
Drmax,min/e A
◦
◦
˚
˚
Table 3 Selected bond lengths (A) and angles ( ) in 1 and 3
Table 4 Selected bond lengths (A) and angles ( ) in 7, 9 and 10
[(L1)ZnN(SiMe3)2] (1)
[(L7)ZnEt] (7)
Zn–O(1)
Zn–N(1)
Zn–N(3)
Zn–O(1)
Zn–N(1)
Zn ◊ ◊ ◊ Si(1)
1.935(2)
Zn–N(2)
Si(2)–N(3)
Si(1)–N(3)
2.150(2)
1.703(2)
1.717(2)
1.936(3)
2.156(3)
Zn–C(20)
Zn–N(2)
1.950(6)
2.170(4)
1.9366(18)
2.1293(19)
2.979(8)
O(1)–Zn–C(20)
C(20)–Zn–N(1)
C(20)–Zn–N(2)
C(16)–O(1)–Zn
C(7)–N(1)–Zn
C(18)–N(2)–Zn
C(17)–N(2)–Zn
127.3(2)
121.5(2)
116.5(3)
125.1(3)
107.0(3)
113.0(3)
110.4(3)
O(1)–Zn–N(1)
O(1)–Zn–N(2)
N(1)–Zn–N(2)
C(8)–N(1)–Zn
C(10)–N(1)–Zn
C(9)–N(2)–Zn
C(21)–C(20)–Zn
94.01(13)
103.80(16)
83.88(15)
106.3(3)
107.6(3)
103.7(3)
119.9(5)
N(3)–Zn–O(1)
O(1)–Zn–N(1)
O(1)–Zn–N(2)
C(8)–N(1)–Zn
C(10)–N(1)–Zn
C(23)–N(2)–Zn
Si(2)–N(3)–Si(1)
Si(1)–N(3)–Zn
120.1(9)
95.7(7)
104.9(9)
104.32(14)
111.87(14)
113.08(18)
122.56(13)
109.17(12)
N(3)–Zn–N(1)
N(3)–Zn–N(2)
N(1)–Zn–N(2)
C(7)–N(1)–Zn
C(22)–N(2)–Zn
C(9)–N(2)–Zn
Si(2)–N(3)–Zn
C(1)–O(1)–Zn
126.6(9)
117.0(9)
85.93(8)
106.45(15)
112.02(18)
102.19(15)
127.18(13)
126.57(17)
[(L9)ZnEt] (9)
Zn(1)–O(1)
Zn(1)–N(1)
1.9205(17)
2.158(2)
Zn(1)–C(1)
Zn(1)–N(2)
1.966(3)
2.176(2)
[(L3)ZnN(SiMe3)2] (3)
Zn(1)–N(3)
Zn(1)–N(1)
Si(1)–N(3)
Zn ◊ ◊ ◊ Si(2)
1.930(3)
2.136(2)
1.708(3)
2.986(5)
Zn(1)–O(1)
Zn(1)–N(2)
Si(2)–N(3)
1.934(2)
2.164(3)
1.722(3)
O(1)–Zn(1)–C(1)
C(1)–Zn(1)–N(1)
C(1)–Zn(1)–N(2)
C(2)–C(1)–Zn(1)
C(17)–N(1)–Zn(1)
C(5)–N(2)–Zn(1)
C(6)–N(2)–Zn(1)
120.79(11)
123.81(11)
119.60(12)
113.2(3)
107.73(15)
108.97(17)
113.57(19)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(2)
C(3)–N(1)–Zn(1)
C(7)–N(1)–Zn(1)
C(4)–N(2)–Zn(1)
C(23)–O(1)–Zn(1)
94.18(7)
107.09(8)
83.46(8)
105.75(15)
104.80(14)
105.36(16)
129.95(16)
N(3)–Zn(1)–O(1)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(2)
C(26)–N(1)–Zn(1)
C(12)–N(1)–Zn(1)
C(27)–N(2)–Zn(1)
Si(1)–N(3)–Si(2)
Si(2)–N(3)–Zn(1)
118.60(11)
96.2(9)
103.77(11)
105.75(19)
104.85(18)
102.7(2)
N(3)–Zn(1)–N(1)
N(3)–Zn(1)–N(2)
N(1)–Zn(1)–N(2)
C(13)–N(1)–Zn(1)
C(28)–N(2)–Zn(1)
C(29)–N(2)–Zn(1)
Si(1)–N(3)–Zn(1)
C(1)–O(1)–Zn(1)
120.23(12)
125.27(12)
85.03(10)
110.07(18)
110.9(2)
114.5(2)
128.41(16)
127.1(2)
[(L10)ZnEt] (10)
Zn–O(1)
Zn–N(1)
1.952(2)
2.150(2)
Zn–C(20)
Zn–N(2)
1.954(4)
2.162(3)
121.79(16)
109.52(15)
O(1)–Zn–C(20)
C(20)–Zn–N(1)
C(20)–Zn–N(2)
C(16)–O(1)–Zn
C(8)–N(1)–Zn
C(18)–N(2)–Zn
C(17)–N(2)–Zn
C(21)–C(20)–Zn
122.58(17)
123.57(14)
119.28(16)
124.26(19)
107.17(16)
112.1(2)
O(1)–Zn–N(1)
O(1)–Zn–N(2)
N(1)–Zn–N(2)
C(10)–N(1)–Zn
C(7)–N(1)–Zn
C(9)–N(2)–Zn
C(21)–C(20)–Zn
94.1(9)
105.4(10)
83.3(9)
107.15(17)
104.99(16)
104.43(17)
115.0(12)
in the solid state in which the zinc atom is four-coordinate
by three heteroatom donors of the tetradentate ligand and one
bis(trimethylsilyl)amido group adopting a distorted tetrahedral
geometry. The coordination of the ether functional group to zinc
is not observed in the solid state as evidenced by the long distance
110.4(2)
126.4(6)
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Zn–O2 (122.33◦ in 3 vs. 67.36◦ in 1). In addition, the angle of
N3–Zn–N1 = 126.61(9)◦ in complex 3 is significantly more open
than that in complex 1 (120.23(12)◦), whereas the angle of N3–
Zn–N2 = 117.00(9)◦ is much smaller than that in complex 1
(125.27(15)◦). All these mentioned features are obviously related
with the introduction of the second steric demanding tert-butyl
group, which causes reasonable changes of the coordination
parameters of the ligand wrapping around the zinc center.
Similar to zinc silylamido complexes 1 and 3, the oxygen atom
of the ether functional group in complex 7 is not coordinate to
zinc core as indicated by the corresponding distance of Zn ◊ ◊ ◊ O2
˚
= 4.995(4) A (Fig. 3). The coordination of the nitrogen atom of the
N(CH3)2 functional group on phenyl to zinc atom is not observed
either in the solid state structures of complexes 9 and 10 (Zn ◊ ◊ ◊ N3
˚
distances are 4.8697(30) and 5.196(4) A, respectively) (Figs 4
and 5). All these donor groups adopt “syn” orientation towards
the NCH2CH2N(CH3)2 bridge with respect to the Zn1–N1–C13
plane, indicating a less hindered environment in complexes 7,
9, 10 in comparison with that in complex 3. Although bearing
the same chloro substituents at the ortho- and para-positions of
the phenoxide group, complex 7 possesses different coordination
Fig. 1 ORTEP diagram of the molecular structure of [(L1)ZnN(SiMe3)2]
(1). Thermal ellipsoids are drawn at the 30% probability level. Hydrogen
atoms are omitted for clarity.
˚
of Zn ◊ ◊ ◊ O2 (4.867(2) A). The bond length of the zinc to silylamido
˚
nitrogen atom (Zn–N3) in complex 1 is 1.935(2) A, which is slightly
longer than those in b-diketiminate zinc silylamido complexes
37,46,47
˚
(1.881–1.896 A).
The bond distances of Zn–N1 and Zn–
˚
N2 are 2.1293(19) and 2.150(2) A respectively, fall into the range
of Zn–N coordinated bond lengths in common zinc complexes
33,39,48–50
˚
(2.058–2.324 A).
Being attributed to the steric repulsion
between the ligand and the silylamido group, the angles of N3–
Zn–N2 = 117.00(9)◦, N3–Zn–N1 = 126.61(9)◦ and O1–Zn–N3 =
120.05(9)◦ deviate significantly from the normal value of 109.47◦.
The molecular structure of complex 3 (Fig. 2) is similar to that
described for complex 1, except that, in complex 3 the methoxy
group on the phenyl moiety and the NCH2CH2N(CH3)2 bridge
are “trans” oriented with respect to the plane constructed by Zn1,
N1, C13 atoms, whereas those in 1 are in “syn” form, which
is also clear when we look at the corresponding angles of N2–
Fig. 3 ORTEP diagram of the molecular structure of [(L7)ZnEt] (7).
Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms
are omitted for clarity.
Fig. 2 ORTEP diagram of the molecular structure of [(L3)ZnN(SiMe3)2]
(3). Thermal ellipsoids are drawn at the 30% probability level. Hydrogen
atoms are omitted for clarity.
Fig. 4 ORTEP diagram of the molecular structure of [(L9)ZnEt] (9).
Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms
are omitted for clarity.
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slightly smaller. The other structural features of complexes 7, 9,
10 are however similar.
Ring-opening polymerization of rac-lactide
As can be seen from the data compiled in Table 5, the zinc
silylamido complexes 1–5 and 8 are active initiators for the ring-
opening polymerization of rac-lactide at ambient temperature in
THF or toluene. In each case, high conversion of monomer to
PLA could be achieved within 50 min (74–95%). The polymers
produced in either solvent have high molecular weights and
relatively broad molecular weight distributions (Mw/Mn = 1.51–
1.93). The molecular weighs of polymer samples obtained in THF
are close to the theoretical values, whereas those obtained in
toluene deviate from the calculated values significantly.
The structure of the ancillary ligands also has considerable
influence on the catalytic activity. It is found that the presence
of substituents, particularly, at ortho-position of the phenox-
ide unit of the ligand, plays an important role in determining
the polymerization rate. In general, the introduction of bulky
substituents leads to a decrease of the polymerization rate.
Complex 4 with both bulky cumyl and tert-butyl groups exhibits
the lowest catalytic activity for the polymerization of rac-lactide
among complexes 1–5 and 8. Although being far away from
the metal center evidenced by the results of X-ray diffraction
Fig. 5 ORTEP diagram of the molecular structure of [(L10)ZnEt] (10).
Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms
are omitted for clarity.
parameters from those of complex 10, which are however more
similar to those of complex 9. In complex 7, the angle of C20–
Zn–O1 (127.3(2)◦) is significantly larger than those in the other
zinc complexes of this work (118.60(11)◦~122.58(17)◦), while the
angles of C20–Zn–N1 (121.5(2)◦) and C20–Zn–N2 (116.5(3)◦) are
Table 5 Ring-opening polymerization of rac-lactide initiated by zinc silylamido complexes 1–5 and 8a
[LA]0/[Zn]0/[iPrOH]0
Solvent
T/◦C
t/min
Conv. b (%)
10-4Mn,cald
10-4Mn
Mw/Mn
Pm
c
d
d
e
Run
Cat.
1
2
3
4
5
6
1
200 : 1 : 0
200 : 1 : 1
200 : 1 : 1
200 : 1 : 0
200 : 1 : 1
200 : 1 : 1
THF
THF
THF
Tol
Tol
Tol
25
25
25
24
25
25
40
4
9
50
5
9
95
84
92
87
77
98
2.72
2.42
2.66
2.50
2.22
2.84
4.14
1.51
0.51
0.48
0.48
0.45
0.43
0.43
2.69
4.03
1.89
1.48
1.86
1.53
7
8
9
10
2
3
4
200 : 1 : 0
200 : 1 : 1
200 : 1 : 0
200 : 1 : 1
THF
THF
Tol
25
25
25
25
40
4
50
5
97
98
98
98
2.79
2.82
2.81
2.84
2.61
2.48
2.18
1.98
1.53
1.40
1.86
1.44
0.50
0.49
0.46
0.44
Tol
11
12
13
14
200 : 1 : 0
200 : 1 : 1
200 : 1 : 0
200 : 1 : 1
THF
THF
Tol
26
25
24
24
50
9
50
9
89
90
84
91
2.57
2.60
2.43
2.64
2.97
2.73
4.16
1.43
1.93
1.10
1.47
1.16
0.52
0.45
0.48
0.42
Tol
15
16
17
18
19
20
200 : 1 : 0
200 : 1 : 0
200 : 1 : 1
200 : 1 : 0
200 : 1 : 1
2000 : 1 : 5
THF
THF
THF
Tol
Tol
Tol
24
-40
25
25
25
25
50
1020
10
50
9
85
10
80
74
91
71
2.46
0.29
2.31
2.13
2.63
4.08
2.34
1.76
0.60
0.54
0.54
0.57
0.49
0.50
1.00
4.17
1.60
2.31
1.24
1.59
1.17
1.09
60
21
22
23
24
5
8
200 : 1 : 0
200 : 1 : 1
200 : 1 : 0
200 : 1 : 1
THF
THF
Tol
24
24
25
25
15
5
30
4
67
95
92
95
1.94
2.73
2.66
2.74
2.87
2.61
6.42
2.09
1.71
1.22
1.57
1.45
0.41
0.37
0.33
0.35
Tol
25
26
27
28
200 : 1 : 0
200 : 1 : 1
200 : 1 : 0
200 : 1 : 1
THF
THF
Tol
24
24
25
25
40
4
50
5
95
97
84
98
2.75
2.80
2.42
2.83
2.81
1.96
3.18
1.49
1.44
1.29
1.53
1.34
0.51
0.46
0.48
0.44
Tol
c
i
a [rac-LA]0 = 1.0 M. b Determined by 1H NMR spectroscopy. Mn,calc = ([LA]0/[Zn]0) ¥ 144.13 ¥ conv.; with the presence of PrOH, Mn,calc
1H NMR spectroscopy.
=
([LA]0/[iPrOH]0) ¥ 144.13 ¥ conv. + 60. d Determined by GPC. e Pm is the probability of forming a new m-dyad, determined by homonuclear decoupled
7902 | Dalton Trans., 2010, 39, 7897–7910
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studies, the substituents on the phenyl ether moiety influence
the activity as well when comparing the polymerization runs
initiated by complexes 1 and 3. It is easy to understand that
the presence of bulky groups in the coordination sphere of
the central metal tends to block the coordination/insertion of
incoming monomer and hence is disadvantageous to the catalytic
activity. The introduction of chloro groups to phenoxide unit
of the ligand in complex 5 has a different effect; on one hand
the less-hindered chloro substituents would make the zinc core
more accessible for the incoming monomer, on the other hand
the electron withdrawing effect of chloro groups would enhance
greatly the electrophilicity of the zinc center. The increase of
activity of complex 5 towards lactide polymerization should be
a combined consequence of both aspects. A similar phenomenon
was observed by Gibson et al. in the polymerization of rac-
lactide with an aluminium complex supported by a tetradentate
aminophenoxide ligand, which involved four chloro substituents
at the ortho- and para-positions of phenoxide units.51 Nevertheless,
there was an opposite trend for lactide polymerization with zinc39
and magnesium52 complexes supported by NNO-tridentate Schiff-
base ligands which only possessed halo substituent at the para-
position of the phenoxide.
Fig. 6 1H NMR spectrum (400 MHz, C6D6) of active rac-lactide oligomer
by 1/iPrOH (*, monomer; **, free HN(SiMe3)2; [LA]0 : [Zn]0 : [iPrOH]0 =
20 : 1 : 1, at 20 ◦C).
gave PLAs with narrow molecular weight distributions (Mw/Mn =
1.08–1.20). However, the molecular weights of the obtained poly-
mer samples are much lower than the theoretical values. To gain
some insights into the structure of the assumed zinc isopropoxide
initiator, the reaction of zinc ethyl complex 9 with one equiv.
Upon addition of isopropanol, the activities of zinc amide
complexes 1–5 and 8 increase significantly, high conversion of
monomer to PLA up to 98% could be reached just within minutes
when a molar ratio of [LA]0/[Zn]0 = 200 was adopted. Even for
2000 equiv. of rac-lactide, in the presence of 5 equiv. of isopropanol
the polymerization initiated by complex 4 still proceeded smoothly
to 71% in 1 h (run 20) and produced polylactides with an average
number molecular weight of 2.31 ¥ 104 g mol-1 and a narrow
PDI value of 1.09. To acquire some information about ROP of
lactide initiated by in situ generated zinc isopropoxide, NMR-scale
polymerization was conducted with [rac-LA]0 : [Zn]0 : [iPrOH]0 =
20 : 1 : 1, the polymerization started instantaneously and active
oligomer could be identified unambiguously (Fig. 6).53 The
addition of a second equiv. of isopropanol did not decompose the
active oligomer, the polymerization rate was increased instead,
1
of isopropanol was monitored by H NMR spectroscopy. The
alcoholysis reaction occurred only at relatively high temperature
and unexpectedly proved to be quite slow; full conversion could
not be reached even after 8 h at 60 ◦C. Thus it is conceivable
that under polymerization conditions such reaction might be
accelerated to a certain degree in the presence of monomer, but
still could not reach full conversion; the residual isopropanol
then acted as a chain transfer agent and led to the decrease of
molecular weights. From the ratios of measured molecular weighs
and the calculated ones (Table 6), around 40–65% of zinc ethyl
complexes were estimated to be converted to the active metal
alkoxide initiators. Furthermore, in the presence of isopropanol,
complexes 7 and 10 with 4,6-dichloro-substitution exhibit higher
catalytic activities than complexes 6 and 9 with bulky cumyl
substituents. Complexes 9 and 10 possess a dimethylamino donor
on one of the phenyl rings in the ligand framework instead a
methoxy group, which do have some influence on the activity. In
either THF or toluene complexes 9 and 10 show higher activities
than their methoxy analogues, for which we do not have reasonable
explanation yet.
1
giving rise to an “immortal” ROP of rac-lactide. The H NMR
spectra of the isolated polylactides showed that the polymer chains
are end-capped by isopropyl ester and hydroxyl groups, indicating
a coordination-insertion mechanism.
Zinc ethyl complexes 6, 7, 9, 10 can not initiate the polymer-
ization of rac-lactide at ambient or elevated temperature through
ethyl initiation. In the presence of added isopr◦opanol, desirable
polymerization results could be achieved at 60 C (Table 6), and
Table 6 Ring-opening polymerization of rac-lactide initiated by zinc ethyl complexes 6, 7, 9, 10 in the presence of isopropanola
c
d
d
e
Run
Cat.
6
[LA]0/[Zn]0/[iPrOH]0
Solvent
T/◦C
t/min
Conv. b(%)
10-4Mn,cald
10-4Mn
Mw/Mn
Pm
1
2
3
4
5
6
7
8
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
THF
Tol
THF
Tol
THF
Tol
THF
Tol
60
60
60
60
60
60
60
60
240
100
250
60
240
100
250
60
55
74
76
72
62
79
83
78
1.60
2.13
2.20
2.07
1.78
2.27
2.41
2.25
1.02
1.09
1.21
1.04
0.53
0.84
1.17
1.39
1.08
1.08
1.07
1.09
1.17
1.12
1.20
1.09
0.53
0.53
0.44
0.42
0.54
0.54
0.44
0.43
7
9
10
a [rac-LA]0 = 1.0 M, [Zn]0 = 0.005 M. b Determined by 1H NMR spectroscopy. c Mn,calcd = ([LA]0/[iPrOH]0) ¥ 144.13 ¥ conv. + 60. d Determined by GPC.
e Pm is the probability of forming a new m-dyad, determined by homonuclear decoupled 1H NMR spectroscopy.
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Microstructure analyses of PLAs were achieved through in-
specting the methine region of homonuclear decoupled 1H NMR
spectra of the resultant polymers. Complex 4 with sterically
demanding cumyl groups at the ortho- and para-positions of
phenoxide unit shows certain preference for isotactic dyad en-
chainment during lactide polymerization (Pm = 0.60, in THF),
whereas complex 5 with less hindered chloro-substituent displays
certain preference for heterotactic dyad enchainment (Pr = 0.67, in
toluene). Gibson et al.51 found that for aluminium complexes with
Salan-type bis(phenolato) ligands, the replacement of hydrogen
atom at the ortho-position of phenoxide with a methyl led to a
dramatic decrease of Pm value from 0.79 to 0.19. An isotactic
dyad preference in rac-lactide polymerization was achieved with
Group 4 complexes bearing the same type of bis(phenolato) ligand
with smaller ortho-methyl group instead of those with bulky
ortho-group.54 Concerning this inconsistency, we think that it may
relate with the structure of the real active species. It is generally
accepted that for lactide polymerization, regardless of the type
of initiation groups, upon coordination and insertion of the first
monomer, metal alkoxide species are formed, which are known to
aggregate easily in solution.36 The presence of sterically demanding
groups in the vicinity of donor atoms such as phenoxide oxygen
atom might be likely to prevent such aggregation. Thus the
assumed asymmetric monomeric metal center might plausibly
induce isotactic selectivity for rac-lactide polymerization to a
certain degree depending on the stability of chiral environment
around the metal (the fluxionality of the ligand framework). The
aggregation of formed metal alkoxides might not be avoided in
complex 5 due to the less hindered chloro substituents, and may
enable a chain-end control to afford heterotactic-enriched PLA.
dramatically raise the activity in the polymerization process and
favor the heterotactic dyad enchainment.
Experimental
General considerations
All manipulations were carried out under a dry argon atmosphere
using standard Schlenk-line or glove-box techniques. Toluene and
n-hexane were refluxed over sodium benzophenone ketyl prior
to use. Benzene-d6, toluene-d8, chloroform-d and other reagents
were carefully dried and stored in a glove-box. [ZnN(SiMe3)2]2 was
synthesized according to the literature method.55 3-tert-Butyl-5-
methyl-2-methyoxybenzaldehyde,56,57 2-(N,N-dimethyl)amino-5-
methylbenzaldehyde,58 were prepared according to the reported
methods. rac-Lactide (Aldrich) was recrystallized with dry toluene
and then sublimed twice under vacuum at 80 ◦C. 2-Propanol
was dried over calcium hydride prior to distillation. All other
chemicals were commercially available and used after appropriate
purification. Glassware and vials used in the polymerization were
dried in an oven at 120 ◦C overnight and exposed to vacuum-argon
cycle three times.
NMR spectra were recorded on Bruker AVANCE-400 and
Bruker AVANCE-500 spectrometers at 25 ◦C (1H : 400, 500 MHz;
13C : 100 MHz) unless otherwise stated. Chemical shifts for 1H and
13C NMR spectra were referenced internally using the residual
solvent resonances and reported relative to tetramethylsilane
(TMS). Elemental analyses were performed on an EA-1106
instrument. Spectroscopic analyses of polymers were performed
in CDCl3. Gel permeation chromatography (GPC) analyses were
carried out on a Waters instrument (M1515 pump, Optilab Rex
injector) in THF at 25 ◦C, at a flow rate of 1 mL min-1. Calibration
standards were commercially available narrowly distributed linear
polystyrene samples that cover a broad range of molar masses
(103 < M < 2 ¥ 106 g mol-1.
Conclusions
In conclusion, several monomeric zinc silylamido and ethyl com-
plexes 1–10 supported by non-symmetric tetradentate aminophe-
nolate ligands were synthesized and structurally characterized.
X-Ray diffraction studies reveal that all the complexes possess a
four-coordinate zinc center. The substituent CH3O or N(CH3)2
on one phenyl moiety is not coordinated to the zinc center
in the solid state; only the other three heteroatom donors of
the tetradentate ligand and bis(trimethylsilyl)amido or ethyl
group chelate to zinc atom adopting a distorted tetrahedral
geometry. The zinc silylamido complexes 1–5 and 8 acted as
highly active single-component initiators for the ring-opening
polymerization of rac-lactide at room temperature in THF or
toluene, providing polymers with a certain degree of tacticity.
Addition of isopropanol may significantly raise the polymerization
rate. Zinc ethyl complexes 7, 9 and 10 could not initiate the
ring-opening polymerization of rac-lactide; zinc isopropoxides
formed by in situ alcoholysis of the ethyl complexes successfully
initiated the polymerization of rac-lactide at 60 ◦C in THF or
toluene and afforded the PLAs with narrow molecular weight
distributions. The activity and selectivity in the polymerization of
rac-lactide using complexes 1–10 as initiators/catalysts depend
upon the ligand substitution pattern to a certain extent. The
introduction of steric bulky substituents increases the amount of
isotactic dyad along the growing polymer chain and reduces the
polymerization rate. Notably, electron-withdrawing substituents
Syntheses
6-tert-Butyl-2-{N -(2-methoxybenzyl)-N -[2-(N,N -dimethyl)-
aminoethyl]aminomethyl}-4-methylphenol
(L1H). N,N-
Dimethylethylenediamine (2.64 g, 30.0 mmol) and a solution of
2-methoxybenzaldehyde (4.08 g, 30.0 mmol) in methanol (20
mL) were heated to reflux for 24 h. After cooling to r.t., sodium
borohydride (2.28 g, 60.0 mmol) was sequentially added to the
above yellow solution at 0 ◦C (ice-water bath) and the mixture
was stirred for 12 h. The reaction mixture was extracted with
methylene dichloride. The organic phase was dried over anhydrous
MgSO4. Removal of the solvent by rotary evaporation gave a
viscous oil, to which was added a solution of paraformaldehyde
(0.900 g, 30.0 mmol) and 2-tert-butyl-4-methylphenol (4.92 g, 30.0
◦
mmol) in methanol (20 mL) at 80 C during 12 h with magnetic
stirring. The mixture was cooled and concentrated under vacuum
to give an oil, which was purified by column chromatography
(silica gel 100 Merck, light petroleum–ethyl acetate 10 : 1) to
provide white solids after removal of all the volatiles (4.93 g,
42.8%). Anal. Calc. for C24H36N2O2: C, 74.96; H, 9.44; N, 7.28.
Found: C, 75.22; H, 9.54; N, 7.25%. 1H NMR (CDCl3, 400 MHz):
4
d 10.75 (s, 1H, OH), 7.28–7.23 (m, 2H, ArH), 6.97 (d, 1H, J =
1.8 Hz, ArH), 6.92 (td, 1H, 3J = 8.0 Hz, 4J = 1.0 Hz, ArH), 6.88
7904 | Dalton Trans., 2010, 39, 7897–7910
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(dd, 1H, 3J = 8.0 Hz, 4J = 1.0 Hz, ArH), 6.68 (d, 1H, 4J = 1.8 Hz,
ArH), 3.86 (s, 3H, CH3O–Ar), 3.74 (s, 2H, Ar–CH2–N), 3.72 (s,
solids (7.22 g, 53.0%). Anal. Calc. for C29H46N2O2: C, 76.65; H,
1
10.13; N, 6.17. Found: C, 76.61; H, 10.30; N, 6.04%. H NMR
(CDCl3, 400 MHz): d 10.62 (s, 1H, OH), 7.07 (d, 1H, 4J =
3
2H, N–CH2–Ar), 2.61 (d, 1H, J = 6.6 Hz, CH2CH2), 2.59 (d,
1H, 3J = 5.5 Hz, CH2CH2), 2.44 (d, 1H, 3J = 6.6 Hz, CH2CH2),
1.8 Hz, ArH), 7.00 (d, 1H, J = 2.2 Hz, ArH), 6.99 (d, 1H, J
4
4
3
4
2.42 (d, 1H, J = 5.5 Hz, CH2CH2), 2.24 (s, 3H, Ar–CH3), 2.12
= 2.2 Hz, ArH), 6.73 (d, 1H, J = 1.8 Hz, ArH), 3.69 (s, 2H,
1
(s, 6H, N(CH3)2), 1.43 (s, 9H, C(CH3)3). H NMR (C6D6, 400
Ar–CH2–N), 3.64 (s, 3H, CH3O–Ar), 3.62 (s, 2H, N–CH2–Ar),
3
3
3
MHz): d 10.90 (s, 1H, OH), 7.33 (d, 1H, J = 7.7 Hz, ArH),
2.54 (d, 1H, J = 6.1 Hz, CH2CH2), 2.53 (d, 1H, J = 6.6 Hz,
CH2CH2), 2.45 (d, 1H, 3J = 6.6 Hz, CH2CH2), 2.45 (d, 1H,
3J = 6.1 Hz, CH2CH2), 2.261 (s, 3H, Ar–CH3), 2.257 (s, 3H,
Ar–CH3), 2.13 (s, 6H, N(CH3)2) 1.47 (s, 9H, C(CH3)3), 1.38
3
7.17 (s, 1H, ArH), 7.05 (t, 1H, J = 7.7 Hz, ArH), 6.85 (t, 1H,
3J = 7.7 Hz, ArH), 6.67 (s, 1H, ArH), 6.51 (d, 1H, 3J = 7.7 Hz,
ArH), 3.68 (s, 2H, Ar–CH2–N), 3.58 (s, 2H, N–CH2–Ar), 3.37
3
1
(s, 3H, CH3O–Ar), 2.49 (t, 2H, J = 6.5 Hz, CH2CH2), 2.24 (t,
(s, 9H, C(CH3)3). H NMR (C6D6, 400 MHz): d 10.69 (s, 1H,
3
4
4
2H, J = 6.5 Hz, CH2CH2), 2.24 (s, 3H, Ar–CH3, overlapped
OH), 7.29 (d, 1H, J = 1.9 Hz, ArH), 7.23 (d, 1H, J = 1.9 Hz,
ArH), 7.04 (d, 1H, 4J = 1.9 Hz, ArH), 6.78 (d, 1H, 4J = 1.9 Hz,
ArH), 3.58 (s, 2H, Ar–CH2–N), 3.51 (s, 2H, N–CH2–Ar), 3.27
with CH2CH2), 1.93 (s, 6H, N(CH3)2), 1.67 (s, 9H, C(CH3)3).
1
13C{ H} NMR (CDCl3, 100 MHz): d 158.0, 154.4, 136.1, 131.4,
3
128.7, 127.5, 126.6, 126.3, 125.6, 122.6, 120.3, 110.3 (all Ar–C),
58.2 (CH3O–Ar), 56.6 (Ar–CH2–N), 55.1 (N–CH2–Ar), 53.1
(CH2CH2), 50.6 (CH2CH2), 45.6 (N(CH3)2), 34.5 (C(CH3)3), 29.5
(C(CH3)3), 20.8 (Ar–CH3).
(s, 3H, CH3O–Ar), 3.36 (t, 2H, J = 6.2 Hz, CH2CH2), 2.29 (s,
3
3H, Ar–CH3), 2.25 (s, 3H, Ar–CH3), 2.13 (t, 2H, J = 6.2 Hz,
CH2CH2), 1.92 (s, 6H, N(CH3)2), 1.72 (s, 9H, C(CH3)3), 1.42 (s,
9H, C(CH3)3). 13C{ H} NMR (CDCl3, 100 MHz): d 156.7, 154.2,
1
142.1, 136.4, 132.5, 131.4, 130.1, 128.1, 126,9, 126.6, 123.1 (all
Ar–C), 62.5 (CH3O–Ar), 57.6 (Ar–CH2–N), 56.3 (N–CH2–Ar),
52.6 (CH2CH2), 50.6 (CH2CH2), 45.2 (N(CH3)2), 34.9 (C(CH3)3),
34.7 (C(CH3)3), 31.1 (C(CH3)3), 29.6 (C(CH3)3), 21.0 (Ar–CH3),
20.8 (Ar–CH3).
4,6-Di-tert-butyl-2-{N -(2-methoxybenzyl)-N -[2-(N,N -dime-
thyl)aminoethyl]aminomethyl}phenol (L2H). The procedure was
same as that of L1H, except that 2,4-di-tert-butylphenol (6.18 g,
30.0 mmol) were used to afford ligand L2H as a viscous oil (5.28 g,
41.3%). Anal. Calc. for C27H42N2O2: C, 76.01; H, 9.92; N, 6.57.
Found: C, 75.97; H, 9.88; N, 6.48%. 1H NMR (CDCl3, 400 MHz):
d 10.82 (s, 1H, OH), 7.25 (d, 1H, 3J = 7.8 Hz, ArH, overlapped
2-{N -(3-tert-Butyl-2-methoxy-5-methylbenzyl)-N -[2-(N,N-
dimethyl)aminoethyl]aminomethyl}-4,6-dicumylphenol
(L4H).
3
4
by C6D6 signal), 7.24 (t, 1H, J = 7.8 Hz, ArH), 7.17 (d, 1H, J
N,N-Dimethylethylenediamine (2.64 g, 30.0 mmol) and
a
3
3
= 2.2 Hz, ArH), 6.9 (t, 1H, J = 7.8 Hz, ArH), 6.87 (d, 1H, J
solution of 3-tert-butyl-5-methyl-2-methoxybenzaldehyde (6.18 g,
30.0 mmol) in methanol (20 mL) were heated to reflux for
24 h. After cooling, sodium borohydride (2.28 g, 60.0 mmol)
was sequentially added to the above yellow solution at 0 ◦C
and the mixture was stirred for 12 h. The reaction mixture was
extracted to give a viscous oil, to which was added a solution of
paraformaldehyde (0.900 g, 30.0 mmol) and 2, 4-dicumylphenol
(9.90 g, 30.0 mmol) in methanol (20 mL) at 80 ◦C during 12 h to
give an oil, which was purified by column chromatography (silica
gel 100 Merck, light petroleum–ethyl acetate 10 : 1) to provide
colorless crystals (9.29 g, 48.7%). Anal. Calc. for C42H56N2O2: C,
4
= 7.8 Hz, ArH), 6.83 (d, 1H, J = 2.2 Hz, ArH), 3.86 (s, 3H,
CH3O–Ar), 3.75 (s, 2H, Ar–CH2–N), 3.74 (s, 2H, N–CH2–Ar),
3
3
2.60 (d, 1H, J = 6.6 Hz, CH2CH2), 2.58 (d, 1H, J = 7.2 Hz,
CH2CH2), 2.43 (d, 1H, 3J = 6.6 Hz, CH2CH2), 2.42 (d, 1H, 3J =
7.2 Hz, CH2CH2), 2.11 (s, 6H, N(CH3)2), 1.42 (s, 9H, C(CH3)3),
1
1.27 (s, 9H, C(CH3)3). H NMR (C6D6, 400 MHz): d 11.04 (s,
4
4
1H, OH), 7.48 (d, 1H, J = 2.3 Hz, ArH), 7.34 (dd, 1H, J =
1.4 Hz, J = 7.4 Hz, ArH), 7.05 (td, 1H, J = 1.4 Hz, J =
3
4
3
4
4
7.4 Hz, ArH), 6.97 (d, 1H, J = 2.3 Hz, ArH), 6.84 (td, 1H, J
3
3
= 1.4 Hz, J = 7.4 Hz, ArH), 6.50 (d, 1H, J = 7.4 Hz, ArH),
3.70 (s, 2H, Ar–CH2–N), 3.62 (s, 2H, N–CH2–Ar), 3.36 (s, 3H,
CH3O–Ar), 2.50 (t, 2H, 3J = 6.6 Hz, CH2CH2), 2.25 (t, 2H, 3J =
6.6 Hz, CH2CH2), 1.94 (s, 6H, N(CH3)2), 1.71 (s, 9H, C(CH3)3),
1
81.24; H, 9.09; N, 4.51. Found: C, 81.02; H, 9.49; N, 4.24%. H
NMR (CDCl3, 400 MHz): d 10.42 (s, 1H, OH), 7.25–7.13 (m,
10H, ArH), 7.09 (tt, 1H, 3J = 6.7 Hz, 4J = 1.7 Hz, ArH), 6.97 (d,
1H, 4J = 1.7 Hz, ArH), 6.80 (d, 1H, 4J = 1.7 Hz, ArH), 6.77 (d,
1.36 (s, 9H, C(CH3)3). 13C{ H} NMR (CDCl3, 100 MHz): d 158.1,
1
154.2, 140.0, 135.4, 131.4, 128.7, 125.7, 123.6, 122.5, 121.8, 120.3,
110.3 (all Ar–C), 58.5 (CH3O–Ar), 56.6 (Ar–CH2–N), 55.1 (N–
CH2–Ar), 53.1 (CH2CH2), 50.6 (CH2CH2), 45.5 (N(CH3)2), 34.8
(C(CH3)3), 34.0 (C(CH3)3), 31.7 (C(CH3)3), 29.6 (C(CH3)3).
4
1H, J = 2.2 Hz, ArH), 3.56 (s, 5H, CH3O–Ar, overlapped with
Ar–CH2–N), 3.52 (s, 2H, N–CH2–Ar), 2.38 (d, 1H, 3J = 6.4 Hz,
CH2CH2), 2.37 (d, 1H, 3J = 7.3 Hz, CH2CH2), 2.27 (d, 1H, 3J =
6.4 Hz, CH2CH2), 2.26 (d, 1H, 3J = 7.3 Hz, CH2CH2), 2.19 (s, 3H,
Ar–CH3), 1.99 (s, 6H, N(CH3)2), 1.70 (s, 6H, CMe2Ph), 1.68 (s,
6H, CMe2Ph), 1.35 (s, 9H, C(CH3)3). 1H NMR (C6D6, 400 MHz):
d 10.69 (s, 1H, OH), d 7.56 (d, 1H, 4J = 2.4 Hz, ArH), 7.46 (dd,
2H, 3J = 8.2 Hz, 4J = 1.2 Hz, ArH), 7.36 (dd, 2H, 3J = 8.2 Hz,
J = 1.0 Hz, CMe2Ph), 7.21–7.01 (m, 8H, ArH and CMe2Ph),
6.91 (d, 1H, 4J = 2.4 Hz, ArH), 3.49 (s, 2H, Ar–CH2–N), 3.27 (s,
2H, N–CH2–Ar), 3.25 (s, 3H, CH3O–Ar), 2.19 (s, 3H, Ar–CH3),
6-tert-Butyl-2-{N -(3-tert-butyl-2-methoxy-5-methylbenzyl)-
N-[2-(N,N-dimethyl)aminoethyl]aminomethyl}-4-methylphenol
(L3H). N,N-Dimethylethylenediamine (2.64 g, 30.0 mmol) and a
solution of 3-tert-butyl-5-methyl-2-methoxybenzaldehyde (6.18 g,
30.0 mmol) in methanol (20 mL) were heated to reflux for 24 h.
After cooling to r.t., sodium borohydride (2.28 g, 60.0 mmol) was
sequentially added to the above yellow solution at 0 ◦C (ice-water
bath). After 12 h, the reaction mixture was extracted to give a
viscous oil, to which was added a solution of paraformaldehyde
(0.900 g, 30.0 mmol) and 2-tert-butyl-◦4-methylphenol (4.92 g,
30.0 mmol) in methanol (20 mL) at 80 C during 12 h and give
an oil, which was purified by column chromatography (silica gel
100 Merck, light petroleum–ethyl acetate 10 : 1) to provide white
3
3
2.18 (t, 2H, J = 6.2 Hz, CH2CH2), 1.95 (t, 2H, J = 6.2 Hz,
CH2CH2), 1.91 (s, 6H, N(CH3)2), 1.78 (s, 6H, CMe2Ph), 1.73 (s,
6H, CMe2Ph), 1.42 (s, 9H, C(CH3)3). 13C{ H} NMR (CDCl3,
1
100 MHz): d 156.6, 153.7, 151.5, 142.1, 139.4, 135.2, 132.4,
130.8, 129.7, 127.8, 127.5, 126.8, 126.7, 126.4, 125.7, 125.3, 124.7,
124.6, 122.4 (all Ar–C), 62.3 (CH3O–Ar), 57.5 (Ar–CH2–N), 55.9
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©

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(N–CH2–Ar), 53.4 (CH2CH2), 50.1 (CH2CH2), 45.0 (N(CH3)2),
42.4 (CMe2Ph), 42.0 (CMe2Ph), 34.9 (C(CH3)3), 31.1 (CMe2Ph),
31.0 (C(CH3)3), 29.4 (CMe2Ph), 21.0 (Ar–CH3).
400 MHz): d 7.24 (d, 1H, 4J = 2.6 Hz, ArH), 7.23 (td, 1H, 3J =
7.8 Hz, 4J = 1.7 Hz, ArH), 7.15 (dd, 1H, 3J = 7.8 Hz, 4J = 1.7 Hz,
ArH), 6.91 (d, 1H, 4J = 2.6 Hz, ArH), 6.88 (td, 1H, 3J = 7.8 Hz,
4J = 1.0 Hz, ArH), 6.84 (d, 1H, 3J = 7.8 Hz, ArH), 3.77 (s, 3H,
CH3O–Ar), 3.64 (s, 2H, Ar–CH2–N), 3.60 (s, 2H, N–CH2–Ar),
2-{N -(3-tert-Butyl-2-methoxy-5-methylbenzyl)-N -[2-(N,N-
dimethyl)aminoethyl]aminomethyl}-4,6-dichlorophenol
(L5H).
3
3
2.57 (d, 1H, J = 6.2 Hz, CH2CH2), 2.55 (d, 1H, J = 6.2 Hz,
N,N-Dimethylethylenediamine (2.64 g, 30.0 mmol) and
a
CH2CH2), 2.48 (d, 1H, 3J = 6.2 Hz, CH2CH2), 2.46 (d, 1H, 3J =
solution of 3-tert-butyl-5-methyl-2-methoxybenzaldehyde (6.18 g,
30.0 mmol) in methanol (20 mL) were heated to reflux for 24 h.
After cooling, sodium borohydride (2.28 g, 60.0 mmol) was
sequentially added to the above yellow solution at 0 ◦C to give a
viscous oil, to which was added a solution of paraformaldehyde
(0.900 g, 30.0 mmol) and 2,4-dichlorophenol (4.89 g, 30.0 mmol)
in methanol (20 mL) at 80 ◦C during 12 h. The mixture was
cooled to provide colorless crystals (6.44 g, 45.8%). Anal. Calc.
for C24H34Cl2N2O2: C, 63.57; H, 7.56; N, 6.18. Found: C, 63.92;
H, 7.98; N, 5.84%. 1H NMR (CDCl3, 400 MHz): d 7.25 (d,
1
6.2 Hz, CH2CH2), 2.13 (s, 6H, N(CH3)2). 13C{ H} NMR (CDCl3,
100 MHz): d 158.0, 152.8, 131.5, 128.9, 128.4, 127.7, 126.0, 125.1,
122.4, 121.6, 120.1, 110.3 (all Ar–C), 55.9 (CH3O–Ar), 55.6 (Ar–
CH2–N), 55.0 (N–CH2–Ar), 52.9 (CH2CH2), 49.7 (CH2CH2), 44.9
(N(CH3)2).
6-tert-Butyl-2-{N -(2-(N,N -dimethlyamino)-5-methylbenzyl)-
N-[2-(N,N-dimethyl)aminoethyl]aminomethyl}-4-methylphenol
(L8H). N,N-Dimethylethylenediamine (2.64 g, 30.0 mmol) and
a
solution of 2-(N,N-dimethyl)amino-5-methylbenzaldehyde
4
4
(4.89 g, 30.0 mmol) in methanol (20 mL) were heated to reflux for
24 h. After cooling, sodium borohydride (2.28 g, 60.0 mmol) was
sequentially added to the above yellow solution at 0 ◦C to give a
viscous oil, to which was added a solution of paraformaldehyde
(0.900 g, 30.0 mmol) and 2-tert-butyl-4-methylphenol (4.92 g,
30.0 mmol) in methanol (20 mL) at 80 ◦C during 12 h. The
mixture was cooled to provide ligand L8H as white solids (3.74 g,
30.4%). Anal. Calc. for C26H41N3O: C, 75.87; H, 10.04; N, 10.21.
Found: C, 75.86; H, 9.96; N, 10.11. 1H NMR (CDCl3, 400 MHz):
d 7.21 (s, 1H, ArH), 6.994 (s, 1H, ArH), 6.991 (s, 1H, ArH),
6.98 (d, 1H, 4J = 1.8 Hz, ArH), 6.71 (d, 1H, 4J = 1.8 Hz, ArH),
3.72 (s, 2H, Ar–CH2–N), 3.66 (s, 2H, N–CH2–Ar), 2.61 (s, 6H,
(CH3)2N–Ar), 2.55–2.52 (m, 2H, CH2CH2), 2.46–2.42 (m, 2H,
CH2CH2), 2.26 (s, 3H, Ar–CH3), 2.24 (s, 3H, Ar–CH3), 2.13
1H, J = 2.6, ArH), 6.98 (d, 1H, J = 2.0 Hz, ArH), 6.94 (d,
4
4
1H, J = 2.6 Hz, ArH), 6.92 (d, 1H, J = 2.0 Hz, ArH), 3.59
(s, 2H, Ar–CH2–N), 3.58 (s, 5H, CH3O–Ar and N–CH2–Ar,
overlapped), 2.50 (s, 4H, CH2CH2), 2.24 (s, 3H, Ar–CH3), 2.18 (s,
6H, N(CH3)2), 1.35 (s, 9H, C(CH3)3). 1H NMR (C6D6, 400 MHz):
d 7.33 (d, 1H, 4J = 2.6 Hz, ArH), 7.014 (s, 1H, ArH), 7.011 (s, 1H,
ArH), 6.88 (d, 1H, 4J = 2.6 Hz, ArH), 3.39 (s, 2H, Ar–CH2–N),
3.27 (s, 3H, CH3O–Ar), 3.10 (s, 2H, N–CH2–Ar), 2.16 (s, 3H,
3
3
Ar–CH3), 2.13 (t, 2H, J = 6.1 Hz, CH2CH2), 1.90 (t, 2H, J =
6.1 Hz, CH2CH2), 1.82 (s, 6H, N(CH3)2), 1.40 (s, 9H, C(CH3)3).
1
13C{ H} NMR (CDCl3, 100 MHz): d 156.5, 152.8, 142.3, 132.4,
130.6, 130.0, 128.6, 128.1, 127.1, 126.2, 122.2, 120.0 (all Ar–C),
62.3 (CH3O–Ar), 55.8 (Ar–CH2–N), 54.9 (N–CH2–Ar), 53.0
(CH2CH2), 49.4 (CH2CH2), 44.7 (N(CH3)2), 34.9 (C(CH3)3), 31.0
(C(CH3)3), 21.0 (Ar–CH3).
1
(s, 6H, N(CH3)2), 1.45 (s, 9H, C(CH3)3). H NMR (C6D6, 400
MHz): d 10.89 (s, 1H, OH), 7.47 (s, 1H, ArH), 7.22 (s, 1H,
ArH), 6.92 (d, 1H, 3J = 8.1 Hz, ArH), 6.86 (d, 1H, 3J = 8.1 Hz,
ArH), 6.76 (s, 1H, ArH), 3.71 (s, 2H, Ar–CH2–N), 3.59 (s, 2H,
2 - {N - (2 - Methoxybenzyl) - N - [2 - (N,N - dimethyl)ami-
noethyl]aminomethyl}-4,6-dicumylphenol (L6H). The procedure
was same as that of L1H, except that 2, 4-dicumylphenol (9.90 g,
30.0 mmol) were used to afford ligand L6H as colorless crystals
(5.28 g, 32.0%). Anal. Calc. for C37H46N2O2: C, 80.73; H, 8.36;
3
N–CH2–Ar), 2.43 (t, 2H, J = 6.4 Hz, CH2CH2), 2.38 (s, 6H,
(CH3)2N–Ar), 2.27 (s, 3H, Ar–CH3), 2.25 (s, 3H, Ar–CH3), 2.19
3
(t, 2H, J = 6.4 Hz, CH2CH2), 1.94 (s, 6H, N(CH3)2), 1.72 (s,
1
1
9H, C(CH3)3). 13C{ H} NMR (CDCl3, 100 MHz): d 154.2, 151.0,
N, 5.09. Found: C, 80.70; H, 8.31; N, 5.01%. H NMR (CDCl3,
400 MHz): d 7.29–7.25 (m, 4H, ArH), 7.24–7.20 (m, 6H, ArH),
7.19–7.16 (m, 1H, ArH), 7.15–7.09 (m, 1H, ArH), 6.92 (dd, 1H,
136.3, 132.8, 132.5, 131.6, 128.3, 127.8, 126.5, 126.4, 123.1, 119.0
(all Ar–C), 57.8 (Ar–CH2–N), 56.4 (N–CH2–Ar), 52.8 (CH2CH2),
50.6 (CH2CH2), 45.5 ((CH3)2N–Ar), 45.3 (R–N(CH3)2), 34.6
(C(CH3)3), 29.6 (C(CH3)3), 20.8 (Ar–CH3), 20.7 (Ar–CH3).
4
3J = 7.4 Hz, J = 1.8 Hz, ArH), 6.81–6.78 (m, 2H, ArH), 6.74
4
(d, 1H, J = 2.2 Hz, ArH), 3.66 (s, 3H, CH3O–Ar), 3.62 (s, 2H,
Ar–CH2–N), 3.56 (s, 2H, N–CH2–Ar), 2.44 (d, 1H, 3J = 7.0 Hz,
2-{N -(2-(N,N -Dimethlyamino)-5-methylbenzyl)-N -[2-(N,N-
3
3
CH2CH2), 2.42 (d, 1H, J = 5.5. Hz, CH2CH2), 2.19 (d, 1H, J
dimethyl)aminoethyl]aminomethyl}-4,6-dicumylphenol
(L9H).
3
= 7.0 Hz, CH2CH2), 2.16 (d, 1H, J = 5.5 Hz, CH2CH2), 2.02
The procedure was same as that of L8H, except that 2,4-
dicumylphenol (9.90 g, 30.0 mmol) were used to provide ligand
L9H as viscous oil (4.05 g, 23.4%). Anal. Calc. for C39H51N3O: C,
(s, 6H, N(CH3)2) 1.69 (s, 6H, CMe2Ph), 1.67 (s, 6H, CMe2Ph).
13C{ H} NMR (CDCl3, 100 MHz): d 158.1, 153.8, 151.8, 151.6,
1
139.5, 135.2, 131.7, 128.7, 127.9, 127.6, 126.8, 125,9, 125.8, 125.5,
125.3, 124.6, 122.4, 120.4, 110.3 (all Ar–C), 58.2 (CH3O–Ar), 56.3
(Ar–CH2–N), 55.1 (N–CH2–Ar), 53.1 (CH2CH2), 50.5 (CH2CH2),
45.5 (N(CH3)2), 42.5 (CMe2Ph), 42.0 (CMe2Ph), 31.2 (CMe2Ph),
29.5 (CMe2Ph).
1
81.06; H, 8.90; N, 7.27. Found: C, 81.14; H, 8.95; N, 7.11%. H
NMR (CDCl3, 400 MHz): d 7.27–7.06 (m, 10H, ArH), 7.09 (tt,
1H, 3J = 6.7 Hz, 4J = 1.7 Hz, ArH), 6.98 (s, 2H, ArH), 6.94 (s, 1H,
ArH), 6.76 (d, 1H, 4J = 2.2 Hz, ArH), 3.60 (s, 2H, Ar–CH2–N),
3.58 (s, 2H, N–CH2–Ar), 2.53 (s, 6H, (CH3)2N–Ar), 2.41 (d, 1H,
3
2 - {N - (2 - Methoxybenzyl) - N - [2 - (N,N - dimethyl)ami-
noethyl]aminomethyl}-4,6-dichlorophenol (L7H). The procedure
was same as that of L1H, except that 2,4-dichlorophenol (4.89 g,
30.0 mmol) were used to afford ligand L7H as colorless crystals
(3.29 g, 28.6%). Anal. Calc. for C19H24Cl2N2O2: C, 59.53; H, 6.31;
3J = 6.6, CH2CH2), 2.39 (d, 1H, J = 5.5, CH2CH2), 2.24 (d,
1H, 3J = 5.5, CH2CH2), 2.22 (d, 1H, 3J = 6.6, CH2CH2), 2.21 (s,
3H, Ar–CH3), 2.03 (s, 6H, N(CH3)2), 1.70 (s, 6H, CMe2Ph), 1.69
1
(s, 6H, CMe2Ph). 13C{ H} NMR (CDCl3, 100 MHz): d 153.7,
151.6, 151.5, 150.9, 139.3, 135.1, 132.7, 132.1, 131.4, 128.4, 127.8,
127.4, 126.7, 126.1, 125.7, 125.3, 124.6, 124.5, 122.5, 119.1 (all
1
N, 7.31. Found: C, 59.30; H, 6.29; N, 7.31%. H NMR (CDCl3,
7906 | Dalton Trans., 2010, 39, 7897–7910
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©

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Ar–C), 58.0 (Ar–CH2–N), 56.1 (N–CH2–Ar), 53.3 (CH2CH2),
50.3 (CH2CH2), 45.3 ((CH3)2N–Ar), 45.2 (R–N(CH3)2), 42.4
(CMe2Ph), 42.0 (CMe2Ph), 31.1 (CMe2Ph), 29.4 (CMe2Ph), 20.7
(Ar–CH3).
= 2.5 Hz, ArH), 7.08–7.02 (m, 2H, ArH), 6.78 (d, 1H, 4J = 2.5 Hz,
ArH), 6.77 (t, 1H, 3J = 7.4 Hz, ArH), 6.43 (d, 1H, 3J = 8.2 Hz,
ArH), 4.43 (d, 1H, 2J = 14.0 Hz, Ar–CH2–N), 4.27 (d, 1H, 2J =
12.4 Hz, N–CH2–Ar), 4.15 (d, 1H, 2J = 14.0 Hz, Ar–CH2–N), 3.44
(d, 1H, 2J = 12.4 Hz, N–CH2–Ar), 3.10 (s, 3H, CH3O–Ar), 2.56–
2.43 (m, 2H, CH2CH2), 2.35–2.31 (m, 1H, CH2CH2), 1.92 (br s,
6H, N(CH3)2), 1.81 (s, 9H, C(CH3)3), 1.62–1.58 (m, 1H, CH2CH2),
2-{N -(2-(N,N -Dimethlyamino)-5-methylbenzyl)-N -[2-(N,N-
dimethyl)aminoethyl]aminomethyl}-4,6-dichlorophenol
(L10H).
The procedure was same as that of L8H, except that 2,4-
dichlorophenol (4.89 g, 30.0 mmol) were used to afford ligand
L10H as colorless crystals (3.80 g, 30.9%). Anal. Calc. for
C21H29Cl2N3O: C, 61.46; H, 7.07; N, 10.24. Found: C, 61.37; H,
1
1.32 (s, 9H, C(CH3)3), 0.56 (s, 18H, N(Si(CH3)3)2). 13C{ H} NMR
(C6D6, 100 MHz): d 164.8, 158.9, 138.2, 134.8, 134.5, 130.3, 126.5,
124.9, 120.9, 120.4, 111.3 (all Ar–C), 60.2 (CH3O–Ar), 57.9 (Ar–
CH2–N), 54.8 (N–CH2–Ar), 52.8 (CH2CH2), 46.0 (CH2CH2), 35.9
(C(CH3)3), 34.0 (C(CH3)3), 32.2 (C(CH3)3), 30.5 (C(CH3)3), 7.4
(Si(CH3)3).
1
7.01; N, 10.18%. H NMR (CDCl3, 400 MHz): d 7.24 (d, 1H,
4J = 2.6 Hz, ArH), 7.07 (s, 1H, ArH), 6.98 (s, 2H, ArH), 6.93
4
(d, 1H, J = 2.6 Hz, ArH), 3.63 (s, 2H, Ar–CH2–N), 3.62 (s,
2H, N–CH2–Ar), 2.56 (s, 6H, (CH3)2N–Ar), 2.54–2.47 (m, 4H,
CH2CH2), 2.17 (s, 6H, R–N(CH3)2). 1H NMR (C6D6, 400 MHz):
[(L3)ZnN(SiMe3)2] (3). Following a procedure similar to that
described for 1, L3H (0.454 g, 1.00 mmol) was treated with
Zn[N(SiMe3)2]2 (0.385 g, 1.00 mmol) in light petroleum (20 mL) at
r.t. to obtain white solids. Recrystallization with toluene afforded
colorless crystals (468 mg, 69%, two crops). Anal. Calc. for
C35H63N3O2Si2Zn: C, 61.95; H, 9.29; N, 6.19. Found: C, 61.49;
4
d 7.30 (d, 1H, J = 2.6 Hz, ArH), 7.15 (s, 1H, ArH, overlapped
with C6D6 signal), 6.7 (dd, 1H, 3J = 8.1 Hz, 4J = 1.8 Hz, ArH),
3
6.84 (s, 1H, ArH), 6.82 (d, 1H, J = 8.1 Hz, ArH overlapped),
3.50 (s, 2H, Ar–CH2–N), 3.17 (s, 2H, N–CH2–Ar), 2.38 (s,
3
6H, (CH3)2N–Ar), 2.21 (t, 2H, J = 6.1 Hz, CH2CH2), 2.16 (s,
1
H, 9.46; N, 5.77%. H NMR (C6D6, 400 MHz): d 7.29 (d, 1H,
3
3H, ArCH3), 1.97 (t, 2H, J = 6.1 Hz, CH2CH2), 1.83 (s, 6H,
4J = 2.0 Hz, ArH), 7.15 (br s, 1H, ArH, overlapped with C6D6
signal), 6.82 (d, 1H, 4J = 1.6 Hz, ArH), 6.36 (d, 1H, 4J = 1.6 Hz,
ArH), 4.28 (d, 1H, 2J = 14.0 Hz, Ar–CH2–N), 4.20 (d, 1H, 2J =
1
R–N(CH3)2). 13C{ H} NMR (CDCl3, 100 MHz): d 152.8, 151.0,
132.6, 131.8, 131.5, 128.6, 128.5, 127.9, 126,3, 122.3, 121.8, 119.1
(all Ar–C), 55.9 (Ar–CH2–N), 55.4 (N–CH2–Ar), 53.2 (CH2CH2),
49.6 (CH2CH2), 45.4 ((CH3)2N–Ar), 44.8 (R–N(CH3)2), 20.7
(Ar–CH3).
2
12.4 Hz, N–CH2–Ar), 4.11 (d, 1H, J = 14.0 Hz, Ar–CH2–N),
3.33 (s, 3H, CH3O–Ar), 3.23 (d, 1H, 2J = 12.4 Hz, N–CH2–Ar),
2.49–2.30 (m, 3H, CH2CH2), 2.16 (s, 3H, Ar–CH3), 2.15 (s, 3H,
Ar–CH3), 2.04 (br s, 3H, NCH3), 1.77 (s, 9H, C(CH3)3), 1.74 (br s,
3H, NCH3), 1.61–1.55 (m, 1H, CH2CH2), 1.36 (s, 9H, C(CH3)),
[(L1)ZnN(SiMe3)2] (1). The ligand L1H (0.384 g, 1.00 mmol)
was added slowly to a solution of Zn[N(SiMe3)2]2 (0.385 g, 1.00
mmol) in light petroleum (20 mL). The solution was stirred for
24 h at r.t. and white solids precipitated. The mixture was filtered
and the solids were dried under vacuum for several hours. The
white powder obtained was then dissolved with 10 mL of toluene
and filtered. The clear filtrate was concentrated and kept at -40 ◦C
to give colorless crystals (465 mg, 75%, two crops). Anal. Calc. for
C30H53N3O2Si2Zn: C, 59.21; H, 8.72; N, 6.91. Found: C, 59.43; H,
8.86; N, 6.95%. 1H NMR (C6D6, 400 MHz): d 7.31 (d, 1H, 4J =
2.0 Hz, ArH), 7.10 (td, 1H, 3J = 8.0 Hz, 4J = 1.6 Hz, ArH), 6.97
(dd, 1H, 3J = 7.6 Hz, 4J = 1.6 Hz, ArH), 6.80 (td, 1H, 3J = 7.6 Hz,
4J = 0.8 Hz, ArH), 6.48 (d, 1H, 3J = 8.0 Hz, ArH), 6.41 (d, 1H,
4J = 2.0 Hz, ArH), 4.40 (d, 1H, 2J = 14.0 Hz, Ar–CH2–N), 4.24
1
0.59 (s, 18H, N(Si(CH3)3)2). 13C{ H} NMR (C6D6, 100 MHz): d
164.8, 158.0, 143.4, 138.5, 133.3, 132.9, 130.7, 129.6, 128.9, 125.0,
121.1, 120.9 (all Ar–C), 63.3 (CH3O–Ar), 59.6 (Ar–CH2–N), 58.2
(N–CH2–Ar), 53.9 (CH2CH2), 45.6 (CH2CH2), 35.5 (C(CH3)3),
35.1 (C(CH3)3), 31.3 (C(CH3)3), 30.5 (C(CH3)3), 21.1 (Ar–CH3),
20.8 (Ar–CH3), 7.6 (Si(CH3)3).
[(L4)ZnN(SiMe3)2] (4). An analogous method to that of 1 was
utilized, except that L4H (0.636 g, 1.00 mmol) and Zn[N(SiMe3)2]2
(0.385 g, 1.00 mmol) were used to give colorless crystals (559 mg,
65%, two crops). Anal. Calc. for C48H73N3O2Si2Zn: C, 68.17; H,
8.70; N, 4.97. Found: C, 67.76; H, 8.75; N, 4.47%. 1H NMR (C6D6,
400 MHz): d 7.55 (d, 2H, 3J = 7.6 Hz, CMe2Ph), 7.52 (d, 1H, 4J
= 2.0 Hz, ArH), 7.29 (d, 2H, 3J = 8.0 Hz, CMe2Ph), 7.17 (t, 2H,
2
2
(d, 1H, J = 12.0 Hz, N–CH2–Ar), 4.13 (d, 1H, J = 14.0 Hz,
Ar–CH2–N), 3.31 (d, 1H, 2J = 12.0 Hz, N–CH2–Ar), 3.11 (s, 3H,
CH3O–Ar), 2.45 (m, 2H, CH2CH2), 2.23 (s, 3H, Ar–CH3), 2.21
(m, 1H, CH2CH2),1.93 (br s, 6H, N(CH3)2), 1.77 (s, 9H, C(CH3)3),
3
3J = 7.6 Hz, CMe2Ph), 7.12 (t, 2H, J = 7.6 Hz, CMe2Ph), 7.07
(s, 1H, ArH), 7.01 (m, 2H, CMe2Ph), 6.80 (s, 1H, ArH), 6.68 (d,
4
2
1H, J = 2.0 Hz, ArH), 4.33 (d, 1H, J = 12.8 Hz, Ar–CH2–
N), 4.11 (s, 2H, N–CH2–Ar), 3.31 (s, 3H, CH3O–Ar), 3.28 (d,
1H, Ar–CH2–N, partially overlapped with CH3O–Ar signal), 2.38
(m, 2H, CH2CH2), 2.18 (s, 3H, Ar–CH3), 2.09 (s, 3H, CMe2Ph),
2.07 (m, 1H, CH2CH2), 1.91 (br s, 3H, N(CH3)2), 1.73 (s, 3H,
CMe2Ph), 1.64 (br, 1H, CH2CH2), 1.61 (s, 3H, CMe2Ph), 1.59 (s,
3H, CMe2Ph), 1.33 (s, 9H, C(CH3)), 1.14, (br s, 3H, N(CH3)2),
1
1.60–1.57 (m, 1H, CH2CH2), 0.56 (s, 18H, N(Si(CH3)3)2). 13C{ H}
NMR (C6D6, 100 MHz): d 164.9, 159.0, 138.6, 134.5, 130.6, 130.4,
128.9, 120.9, 120.8, 120.4, 111.2 (all Ar–C), 59.6 (CH3O–Ar), 58.0
(Ar–CH2–N), 54.9 (N–CH2–Ar), 52.8 (CH2CH2), 47.6 (N(CH3)2),
45.6 (CH2CH2), 35.5 (C(CH3)3), 30.5 (C(CH3)3), 20.9 (Ar–CH3),
7.4 (Si(CH3)3).
[(L2)ZnN(SiMe3)2] (2). Following a procedure similar to that
described for 1, L2H (0.426 g, 1.00 mmol) was treated with
Zn[N(SiMe3)2]2 (0.385 g, 1.00 mmol) in light petroleum (20 mL) at
r.t. to obtain white solids. Recrystallization with toluene afforded
colorless crystals (403 mg, 62%, two crops). Anal. Calc. for
C33H59N3O2Si2Zn: C, 60.92; H, 9.07; N, 6.46. Found: C, 60.71;
H, 9.28; N, 6.42%. 1H NMR (C6D6, 400 MHz): d 7.60 (d, 1H, 4J
0.48 (s, 18H, N(Si(CH3)3)2). 13C{ H} NMR (C6D6, 100 MHz): d
1
164.3, 157.9, 152.4, 143.4, 137.6, 133.9, 132.9, 132.8, 129.6, 127.3,
127.1, 125.4, 125.1, 124.6, 120.4, 100.2 (all Ar–C), 63.2 (CH3O–
Ar), 60.6 (Ar–CH2–N), 58.3 (N–CH2–Ar), 54.6 (CH2CH2), 46.2
(CH2CH2), 42.8 (CMe2Ph), 42.4 (CMe2Ph), 35.0 (C(CH3)3), 33.5,
(CMe2Ph), 31.42 (CMe2Ph), 31.37 (CMe2Ph), 31.3 (C(CH3)3), 27.0
(CMe2Ph), 21.1 (Ar–CH3), 7.5 (Si(CH3)3).
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[(L5)ZnN(SiMe3)2] (5). An analogous method to that of 1 was
utilized, except that L5H (0.469 g, 1.00 mmol) and Zn[N(SiMe3)2]2
(0.385 g, 1.00 mmol) were used to give colorless crystals (413 mg,
61%). Anal. Calc. for C30H51Cl2N3O2Si2Zn·1/4(C7H8): C, 54.43;
6.97 (d, 1H, 3J = 8.2 Hz, ArH), 6.67 (d, 1H, 4J = 2.7 Hz, ArH),
4.30 (d, 1H, 2J = 14.0 Hz, Ar–CH2–N), 4.16 (d, 1H, 2J = 12.0 Hz,
N–CH2–Ar), 3.98 (d, 1H, 2J = 14.0 Hz, Ar–CH2–N), 3.83 (s, 3H,
2
CH3O–Ar), 3.32 (d, 1H, J = 12.0 Hz, N–CH2–Ar), 2.74–2.63
1
H, 7.57; N, 6.00. Found: C, 54.22; H, 7.74; N, 5.88%. HNMR
(m, 2H, CH2CH2), 2.42–2.35 (m, 1H, CH2CH2), 2.39 (br, 3H,
NCH3), 2.18–2.12 (m, 1H, CH2CH2), 2.15 (br, 3H, NCH3), 1.33
(C6D6, 400 MHz): d 7.43 (d, 1H, 4J = 2.4 Hz, ArH), 7.15 (br s, 1H,
ArH, overlapped with C6D6 signal), 6.83 (s, 1H, ArH), 6.37 (d, 1H,
4J = 2.4 Hz, ArH), 4.13 (d, 1H, 2J = 14.0 Hz, N–CH2–Ar), 3.96
(d, 1H, 2J = 14.0 Hz, N–CH2–Ar), 3.92 (d, 1H, 2J = 12.8 Hz, Ar–
CH2–N), 3.29 (s, 3H, CH3O–Ar), 2.88 (d, 1H, 2J = 12.8 Hz, Ar–
CH2–N), 2.19 (s, 3H, Ar–CH3), 2.16–2.11 (m, 2H, CH2CH2), 2.10
(s, 0.72 H, CH3–C6H5), 2.01 (br s, 3H, NCH3), 1.96–1.93 (m, 1H,
CH2CH2), 1.71 (br s, 3H, NCH3), 1.53–1.50 (m, 1H, CH2CH2),
3
3
2
(t, 3H, J = 8.0 Hz, CH2CH3), 0.29 (qd, 2H, J = 8.0 Hz, J =
1.3 Hz, CH2CH3). 13C{ H} NMR (CDCl3, 100 MHz): d 161.4,
1
158.4, 133.7, 130.4, 129.5, 129.3, 134.9, 124.8, 120.5, 120.0, 116.7,
111.1 (all Ar–C), 57.9 (CH3O–Ar), 57.6 (Ar–CH2–N), 55.3 (N–
CH2–Ar), 53.2 (CH2CH2), 46.2 (CH2CH2), 13.3 (CH2CH3), 3.60
(CH2CH3).
1
1.36 (s, 9H, C(CH3)3), 0.54 (s, 18H, N(Si(CH3)3)2). 13C{ H} NMR
[(L8)ZnN(SiMe3)2] (8). An analogous method to that of
1 was utilized, except that L8H (0.411 g, 1.00 mmol) and
Zn[N(SiMe3)2]2 (0.385 g, 1.00 mmol) were used to give colorless
crystals (426 mg, 67%, two crops from hexane). Anal. Calc. for
C32H58N4OSi2Zn·1/4(C6H14): C, 61.10; H, 9.35; N, 8.51. Found:
C, 60.93; H, 9.35; N, 8.71. 1H NMR (CDCl3, 400 MHz): d 7.30 (d,
1H, ArH), 6.97 (d, 1H, 3J = 8.0 Hz, ArH), 6.94 (s, 1H, ArH), 6.93
(d, 1H, 3J = 8.0 Hz, ArH), 6.40 (s, 1H, ArH), 4.52 (d, 1H, 2J =
13.6 Hz, Ar–CH2–N), 4.28 (br d, 1H, 2J = 11.3 Hz, N–CH2–Ar),
(C6D6, 100 MHz): d 161.8, 157.7, 143.5, 133.3, 132.4, 130.3, 129.8,
129.4, 125.7, 124.8, 123.7, 116.9, (all Ar–C), 63.1 (CH3O–Ar), 58.7
(Ar–CH2–N), 57.4 (N–CH2–Ar), 55.0 (CH2CH2), 48.2 (N(CH3)2),
47.2 (CH2CH2), 45.1 (N(CH3)2), 35.1 (C(CH3)3), 31.4 (C(CH3)3),
21.2 (Ar–CH3), 20.8 (Ar–CH3), 7.10 (Si(CH3)3).
[(L6)ZnEt] (6). L6H (0.643 g, 1.00 mmol) was dissolved in
toluene (10 mL) and cooled to -40 ◦C. Diethyl zinc (1.00 mL,
1.00 mmol, 1 M in hexane) was added to this solution and
the colorless mixture was stirred for 12 h at room temperature.
White solids were afforded by solvent evaporation under vacuum,
which were further dried under high vacuum for several hours.
The ◦solids were then recrystallized with toluene and kept at
-40 C to give colorless crystals (508 mg, 79%). Anal. Calc. for
C39H50N2O2Zn·1/2(C7H8): C, 74.02; H, 7.84; N, 4.06. Found: C,
2
2
4.06 (br d, 1H, J = 13.6 Hz, Ar–CH2–N), 3.34 (br d, 1H, J =
11.3 Hz, N–CH2–Ar), 2.54 (t, 1H, 2J = 12.8 Hz, CH2CH2), 2.44
(t, 1H, 2J = 12.8 Hz, CH2CH2), 2.37–2.32 (m, 1H, CH2CH2), 2.27
(s, 6H, Ar–N(CH3)2), 2.22 (s, 3H, Ar–CH3), 2.12 (s, 3H, Ar–CH3),
2.06 (br s, 3H, N(CH3)2), 1.81 (br s, 3H, N(CH3)2), 1.77 (s, 9H,
2
C(CH3)3), 1.63 (d, 1H, J = 10.3 Hz, CH2CH2), 1.22–1.28 [m, 2
1
73.64; H, 8.08; N, 3.79%. H NMR (CDCl3, 400 MHz): d 7.47
H, CH3(CH2)4CH3] 0.88 [t, 1.5H, 3J = 6.8, CH3(CH2)4CH3], 0.57
3
4
3
1
(dd, 2H, J = 8.4 Hz, J = 1.2 Hz, CMe2Ph), 7.35 (td, 1H, J
(s, 18H, N(Si(CH3)3)2). 13C{ H} NMR (C6D6, 100 MHz): d 164.8,
4
3
= 7.8 Hz, J = 2.0 Hz, ArH), 7.26 (d, 1H, J = 7.2 Hz, ArH,
overlapped with CDCl3 signal), 7.23–7.15 (m, 8H, CMe2Ph), 7.06
159.0, 138.3, 134.6, 133.9, 130.6, 130.5, 128.6, 121.2, 120.8, 120.6
(all Ar–C), 59.6 (Ar–CH2–N), 58.0 (N–CH2–Ar), 53.4 (CH2CH2),
45.7 (CH2CH2), 35.3 (N(CH3)2), 31.7 (C(CH3)3), 30.3 (C(CH3)3),
20.7 (Ar–CH3), 7.3 (Si(CH3)3).
3
3
4
(t, 1H, J = 7.3 Hz, CMe2Ph), 6.97 (td, 1H, J = 7.4 Hz, J =
3
4
0.8 Hz, ArH), 6.92 (d, 1H, J = 8.4 Hz, ArH), 6.51 (d, 1H, J
2
= 2.8 Hz, ArH), 4.14 (d, 1H, J = 14.0 Hz, Ar–CH2–N), 4.07
2
2
(d, 1H, J = 11.6 Hz, N–CH2–Ar), 3.92, (d, 1H, J = 14.0 Hz,
Ar–CH2–N), 3.78 (s, 3H, CH3O–Ar), 3.12 (d, 1H, 2J = 11.6 Hz,
N–CH2–Ar), 2.57–2.46 (m, 2H, CH2CH2), 2.37 (s, 1.5 H, CH3–
C6H5), 2.36–2.31 (m, 1H, CH2CH2), 2.02 (very br, 3H, NCH3),
1.95 (s, 3H, CMe2Ph), 1.93–1.88 (m, 1H, CH2CH2), 1.65 (s, 3H,
CMe2Ph), 1.63 (s, 3H, CMe2Ph), 1.62 (s, 3H, CMe2Ph), 1.32 (t, 3H,
3J = 8.1 Hz, CH2CH3), 1.02 (very br, 3H, NCH3), 0.14 (dq, 1H,
2J = 12.9 Hz, 3J = 8.1 Hz, CH2CH3), 0.05 (dq, 1H, 2J = 12.9 Hz,
[(L9)ZnEt] (9). An analogous method to that of 6 was utilized,
except that L9H (0.577 g, 1.00 mmol) and diethyl zinc (1.00 mL,
1.00 mmol, 1 M in hexane) were used to give colorless crystals
(542 mg, 80%). Anal. Calc. for C41H55N3OZn: C, 73.43; H, 8.21;
1
N, 6.27. Found: C, 73.22; H, 8.21; N, 6.07%. H NMR (CDCl3,
3
400 MHz): d 7.45 (d, 2H, J = 7.3 Hz, CMe2Ph), 7.21–7.07 (m,
11H, ArH), 7.05 (t, 1H, 3J = 7.3 Hz, CMe2Ph), 6.52 (d, 1H, 4J =
2.5 Hz, ArH), 4.27 (d, 1H, 2J = 13.6 Hz, Ar–CH2–N), 4.06 (d, 1H,
2J = 11.9 Hz, N–CH2–Ar), 3.80 (d, 1H, 2J = 13.6 Hz, Ar–CH2–N),
3.12 (d, 1H, 2J = 11.9 Hz, N–CH2–Ar), 2.54 (s, 6H, Ar–N(CH3)2),
2.54–2.43 (m, 2H, CH2CH2 overlapped with Ar–CH3), 2.32 (s, 3H,
Ar–CH3), 2.29–2.23 (m, 1H, CH2CH2), 1.94 (s, 3H, CMe2Ph),
1.84–1.80 (m, 1H, CH2CH2), 1.63 (s, 3H, CMe2Ph), 1.62 (s, 3H,
CMe2Ph), 1.61 (s, 3H, CMe2Ph), 1.49 (br s, 6H, N(CH3)2), 1.32 (t,
3H, 3J = 8.1 Hz, CH2CH3), 0.15 (dq, 1H, 2J = 12.9 Hz, 3J = 8.1 Hz,
1
3J = 8.1 Hz, CH2CH3). 13C{ H} NMR (CDCl3, 100 MHz): d
165.1, 158.5, 152.7, 150.8, 136.4, 133.9, 133.4, 129.9, 128.2, 127.5,
126.9, 126.7, 125.7, 124.9, 124.2, 122.0, 120.9, 120.3, 110.8 (all Ar–
C), 59.0 (CH3O–Ar), 57.4 (Ar–CH2–N), 55.2 (N–CH2–Ar), 52.5
(CH2CH2), 45.4 (CH2CH2), 42.1 (CMe2Ph), 41.9 (CMe2Ph), 31.2,
(CMe2Ph), 31.11 (CMe2Ph), 31.06 (CMe2Ph), 26.5 (CMe2Ph), 13.2
(CH2CH3), 3.60 (CH2CH3).
[(L7)ZnEt] (7). An analogous method to that of 6 was utilized,
except that L7H (0.383 g, 1.00 mmol) and diethyl zinc (1.00 mL,
1.00 mmol, 1 M in hexane) were used to give colorless crystals
(362 mg, 76%). Anal. Calc. for C21H28Cl2N2O2Zn: C, 52.91; H,
6.08; N, 5.88. Found: C, 52.97; H, 6.03; N, 5.71%. 1H NMR
CH2CH3), 0.06 (dq, 1H, J = 12.9 Hz, J = 8.1 Hz, CH2CH3).
2
3
1
13C{ H} NMR (CDCl3, 100 MHz): d 165.2, 152.7, 152.3, 150.8,
136.4, 134.0, 133.6, 133.3, 130.2, 128.1, 128.0, 127.5, 127.4, 126.9,
126.7, 125.9, 124.9, 124.1, 122.2, 120.7 (all Ar–C), 59.4 (Ar–CH2–
N), 57.7 (N–CH2–Ar), 53.3 (CH2CH2), 45.7 (Ar–N(CH3)2), 45.3
(R–N(CH3)2), 45.1 (CH2CH2), 42.1 (CMe2Ph), 41.9 (CMe2Ph),
31.2, (CMe2Ph), 31.1 (CMe2Ph), 31.07 (CMe2Ph), 26.6 (CMe2Ph),
20.9 (Ar–CH3), 13.3 (CH2CH3), 3.28 (CH2CH3).
3
4
(CDCl3, 400 MHz): d 7.39 (td, 1H, J = 8.2 Hz, J = 1.7 Hz,
ArH), 7.27 (dd, 1H, 3J = 7.4 Hz, 4J = 1.7 Hz, ArH), 7.24 (d, 1H,
4J = 2.7 Hz, ArH), 7.02 (td, 1H, 3J = 7.4 Hz, 4J = 1.0 Hz, ArH),
7908 | Dalton Trans., 2010, 39, 7897–7910
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[(L10)ZnEt] (10). An analogous method to that of 6 was
utilized, except that L10H (0.410 g, 1.00 mmol) and diethyl
zinc (1.00 mL, 1.00 mmol, 1 M in hexane) were used to give
colorless crystals (458 mg, 91%, two crops). Anal. Calc. for
C23H33Cl2N3OZn: C, 54.87; H, 6.56; N, 8.35. Found: C, 55.10;
H, 6.58; N, 8.31%. 1H NMR (CDCl3, 400 MHz): d 7.23 (d, 1H, 4J
= 2.7 Hz, ArH), 7.18 (s, 2H, ArH), 7.10 (s, 1H, ArH), 6.67 (d, 1H,
4J = 2.7 Hz, ArH), 4.42 (d, 1H, 2J = 13.6 Hz, Ar–CH2–N), 3.91
(d, 1H, 2J = 12.4 Hz, N–CH2–Ar), 3.98 (d, 1H, 2J = 13.6 Hz, Ar–
CH2–N), 3.34 (d, 1H, 2J = 12.4 Hz, N–CH2–Ar), 2.77 (ddd, 1H,
2J = 12.6 Hz, 3J = 5.6 Hz, 3J = 4.0 Hz, CH2CH2), 2.69–2.62 (m,
1H, CH2CH2), 2.60 (s, 6H, Ar–N(CH3)2), 2.36 (s, 3H, Ar–CH3),
2.34–2.28 (m, 1H, CH2CH2), 2.26 (s, 6H, R–N(CH3)2), 2.12 (ddd,
1H, 2J = 12.6 Hz, 3J = 5.6 Hz, 3J = 4.0 Hz, CH2CH2), 1.34 (t, 3H,
3J = 8.0 Hz, CH2CH3), 0.314 (qd, 2H, 3J = 8.0 Hz, 2J = 2.2 Hz,
were done by Bruker SAINT.61 The structure solution and
refinement were performed by SHELXS-9762 and SHELXL-9763
respectively. For further crystal data and details of measurements
see Tables 2–4. Molecular structures were generated using ORTEP
program.64
Acknowledgements
This work is subsidized by the National Basic Research Program
of China (2005CB623801), National Natural Science Foundation
of China (NNSFC, 20604009 and 20774027), the Program for
New Century Excellent Talents in University (for H. Ma, NCET-
06-0413) and the Fundamental Research Funds for the Central
Universities (WK0914042). All the financial supports are grate-
fully acknowledged. H. Ma also thanks the very kind donation of
a Braun glove-box by AvH foundation.
1
CH2CH3). 13C{ H} NMR (CDCl3, 100 MHz): d 161.5, 152.3,
133.8, 130.6, 129.5, 129.5, 129.3, 127.0, 125.1, 124.8, 121.0, 116.6
(all Ar–C), 58.1 (Ar–CH2–N), 57.9 (N–CH2–Ar), 54.0 (CH2CH2),
46.1 (Ar–N(CH3)2), 45.9 (CH2CH2), 45.7 (R–N(CH3)2), 20.9 (Ar–
CH3), 13.4 (CH2CH3), 3.49 (CH2CH3).
Notes and references
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104, 6147–6176.
2 R. Mehta, V. Kumar, H. Bhumia and S. N. Upadhyay, J. Macromol.
Sci., Part C, 2005, 45, 325–349.
Typical polymerization experiments
3 N. E. Kamber, W. Jeong and R. M. Waymouth, Chem. Rev., 2007, 107,
5813–5840.
4 R. H. Platel, L. M. Hodgson and C. Williams, Polym. Rev., 2008, 48,
11–63.
5 H. Tsuji, F. Horii, S.-H. Hyonfand and Y. Ikada, Macromolecules, 1991,
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7910 | Dalton Trans., 2010, 39, 7897–7910
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