Syntheses, characterization of N-functionalized benzyl zinc, cadmium and manganese (II) compounds

Article abstract of DOI:10.1016/j.ica.2012.02.022

Treatment of [LiL·TMEDA] (1) {L = [2-Me₂NCH ₂C₆H₄CH(SiMe₃)]^-} with half equivalent of ZnCl₂, CdCl₂ or MnCl₂ in diethyl ether gave the crystalline compound [

Full text of DOI:10.1016/j.ica.2012.02.022

Inorganica Chimica Acta 388 (2012) 127–134
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Syntheses, characterization of N-functionalized benzyl zinc, cadmium
and manganese (II) compounds
⇑
⇑
Bin Jia, Xuehong Wei , Hongbo Tong, Meisu Zhou, Diansheng Liu
Institute of Applied Chemistry, Shanxi University, Taiyuan 030006, PR China
a r t i c l e i n f o
a b s t r a c t
Treatment of [LiLꢀTMEDA] (1) {L = [2-Me2NCH2C6H4CH(SiMe3)]ꢁ} with half equivalent of ZnCl2, CdCl2 or
MnCl2 in diethyl ether gave the crystalline compound [ML2] {M = Zn (2), Cd (3) and Mn (4)}, respectively.
Article history:
Received 14 June 2011
Received in revised form 8 February 2012
Accepted 13 February 2012
Available online 23 February 2012
Reaction of
1 with one equivalent of ZnCl2 in diethyl ether afforded the crystalline compound
[Zn(Cl)LꢀTMEDA] (5) in good yield. An eight-membered cyclic homoleptic binuclear compound [ZnL0]2
(6) {L0 = [(2-Me2NCH2C6H4CH)2SiMe2]2ꢁ} was prepared from the reaction of (2-Me2NCH2C6H4CH2)2SiMe2
(B0) with two equivalents of n-BuLi and one equivalent of ZnCl2. All of the crystalline compounds 1–6
were well characterized by 1H NMR, 13C NMR spectroscopy, elemental analyses and single crystal X-
ray crystallography. In addition, moderate activity for the polymerization of rac-lactide to poly(lactic
acid) (PLA) was found in compounds 2 and 5, and all the resulting polylactides are most predominantly
heterotactic-rich.
Keywords:
Zinc
Cadmium
Manganese (II)
Benzyl
Ó 2012 Elsevier B.V. All rights reserved.
rac-Lactide
1. Introduction
were used in direct ortho-metalation of anisole or cyclic ethers
(tetrahydrofuran; tetrahydropyran) adjacent to oxygen [17] and
Transition metal alkyl compounds are well known and play an
important role in the chemistry of simple organic compounds be-
cause the properties of alkyl groups have been imparted by the
transition metals [1]. Zinc and cadmium metal alkyl adducts with
nitrogenous bases were firstly reported by Thiele in 1962 [2], then
zinc and cadmium metal(II) compounds with alkyl and amido li-
gands extensively appeared in the literature [3–15]. For organo-
manganese (II) compounds having alkyl and amido ligands,
bimetallic sodium-manganese base was a useful reagent for cleav-
age and capture chemistry of tetrahydrofuran [18,19].
Organometallic compounds based on N-functionalized benzyl
anion ligand A [20–26] or silyl-substituted benzyl anion ligand A0
have been well documented [27–30], whereas organometallic com-
pounds based on the ligand L {L = [2-Me2NCH2C6H4CH(SiMe3)]ꢁ}
are rarely reported. The sole example is the lithium compound
co-crystallized with n-BuLi to form a ladder structure [31].
NMe2
NMe2
CH2
CH2NMe2
Me2
Si
C
H
C
H
CH
CH
SiMe3
CH2NMe2
CH2NMe2
SiMe3
A
A'
L'
L
Cahiez and his co-workers compiled an authoritative review in
2009 [16]. Alkyl compounds have attracted increasing attention
due to their use in the deprotative metalation for the regioselective
functionalization of aromatic compounds, cyclic ethers or ethylene.
For example, bimetalic alkyl lithium cadmates or lithium zincates
Herein, we report the synthesis and structural characterization of a
series of lithium, zinc, cadmium and manganese compounds based
on L and the novel zinc compound with the dimethylsily group
bridged dianion ligand L0 {L0 = [(2-Me2NCH2C6H4CH)2SiMe2]2ꢁ}.
⇑
Corresponding authors. Tel.: +86 351 701 8390; fax: +86 351 701 1688 (D. Liu).
E-mail addresses: xhwei@sxu.edu.cn (X. Wei), dsliu@sxu.edu.cn (D. Liu).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2012.02.022

128
B. Jia et al. / Inorganica Chimica Acta 388 (2012) 127–134
The catalytic behaviors in ring-opening polymerization of rac-lac-
tide were also presented for the zinc compounds 2 and 5.
2.4. Synthesis of [2-Me2NCH2C6H4CH(SiMe3)LiꢀTMEDA] (1)
n-BuLi (31.7 mmol, 12.7 mL, 2.5 M in hexane) was added drop-
wise to solution of B (7.11 g, 31.7 mmol) and TMEDA (3.72 g,
31.7 mmol) in hexane (40 mL) at 0 °C. The solution became yellow
and was stirred at room temperature for 8 h. The yellow precipitate
was collected by filtration and dried in vacuo to give the yellow so-
lid which was recrystallized from a saturated hexane solution to
yield pale yellow crystals of 1 (8.20 g, 75%). Mp: 91–93 °C. Anal.
Calc. for C19H38N3SiLi: C, 66.44; H, 11.21; N, 12.13. Found: C,
66.32; H, 11.06; N, 12.31%. 1HNMR (C6D6): d 0.09 (s, 9H, SiMe3),
2.06 (s, 18H, NMe2 and Me of TMEDA), 2.11 (t, 4H, CH2 of TMEDA),
2.15 (s, 2H, CH2SiMe3), 3.34 (s, 2H, CH2NMe2), 7.04–7.37 (m, 4H,
Ar–H), 13C NMR (C6D6): d 1.73 (SiMe3), 21.2 (CH2SiMe3), 45.9
(CH3 of TMEDA), 48.1 (NMe2), 56.2 (CH2 of TMEDA), 63.2
(CH2NMe2), 126.2, 127.5, 128.7, 131.8, 135.8, 140.1 (Ar–C).
2. Experimental
2.1. General comments
All manipulations were carried out under nitrogen atmosphere
in flamed Schlenk-type glassware on a dual manifold Schlenk line.
Solvents purchased from commercial sources were distilled over
standard drying agents under nitrogen from alkali metals directly
and stored over 4 Å molecular sieves. All the chemicals used were
of reagent grade, obtained from Aldrich. N,N,N,N-tetramethylethyl-
enediamine (TMEDA) were distilled from KOH prior to use. rac-Lac-
tide was recrystallized with dry toluene and sublimed twice under
vacuum at 50 °C. Melting points were determined in sealed capil-
laries under argon on an electrothermal apparatus and are uncor-
rected. 1H and 13C NMR spectra were recorded on a Bruker DRX
300 (300.1 MHz for 1H, 75.5 MHz for 13C) instrument and refer-
enced internally to the residual solvent resonances (chemical shift
data in d). All NMR spectra (1H, 13C) were measured at 298 K and all
13C NMR spectra were proton-decoupled. The homonuclear decou-
pled 1H NMR spectrum were recorded on a Bruker AV 400 spec-
trometer at 400. Elemental analyses were performed on a Vario
EL-III instrument. X-ray single crystal structures were determined
on a Bruker Smart CCD APEX area detector. Gel permeation chro-
matography (GPC) analyses were carried out on a Waters 1515
Breeze Gel Permeation Chromatograph equipped with differential
refractive index detectors. The GPC columns were eluted with tet-
rahydrofuran with 1 mL/min rate at 25 °C and were calibrated with
monodisperse polystyrene standards.
2.5. Synthesis of [{2-Me2NCH2C6H4CH(SiMe3)}2Zn] (2)
ZnCl2 (0.21 g, 1.5 mmol) was added to a yellow solution of 1
(1.04 g, 3.0 mmol) in diethyl ether (20 mL) at ꢁ78 °C. The resulting
mixture was warmed up to room temperature slowly and stirred
for 12 h. The white precipitate was filtered off. The filtrate was con-
centrated to ca. 10 mL in vacuo and set aside yielding colorless
crystals of
2 (0.62 g, 81%). Mp: 134–136 °C. Anal. Calc. for
C
26H44N2Si2Zn: C, 61.69, H, 8.76, N, 5.53. Found: C, 61.54, H, 8.69,
N, 5.71%. 1HNMR (C6D6): d 0.09 [s, 18H, SiMe3], 1.43, 1.47 (s, 2H,
CHSiMe3), 2.55, 2.68 (s, 12H, NMe2), 3.53, 3.57 (s, 4H, CH2NMe2),
6.95–7.34 (m, 8H, Ar–H); 13CNMR (C6D6):
d 2.49 (SiMe3),
31.5(CHSiMe3), 56.3 (NMe2), 67.4 (CH2NMe2), 119.1, 125.3, 129.3,
131.8, 133.3, 138.9, 149.8, 151.4 (Ar–C).
2.6. Synthesis of [{2-Me2NCH2C6H4CH(SiMe3)}2Cd] (3)
From CdCl2 (0.27 g, 1.5 mmol) and 1 (1.03 g, 3.0 mmol), using
the procedure similar to that for 2, there were obtained colorless
crystals of 3 (0.61 g, 72%) by recrystallization from hexane/tet-
rohydrofuran (1:2). Mp: 135–137 °C. Anal. Calc. for C26H44N2Si2Cd:
C, 56.45, H, 8.02, N, 5.06. Found: C, 56.27, H, 8.15, N, 4.91%. 1HNMR
(C6D6): d 0.06 (s, 18H, SiMe3), 1.85 (s, 2H, CHSiMe3), 2.21(s, 6H,
NMe2), 2.24(s, 6H, NMe2), 2.54(s, 2H, CH2NMe2), 2.58 (s, 2H,
CH2NMe2), 6.62–7.24 (m, 8H, Ar–H); 13CNMR (C6D6): d 4.5 (SiMe3),
31.9 CH(SiMe3), 67.4 (CH2NMe2), 50.3 (NMe2), 123.7, 126.4, 129.4,
131.8, 132.9, 133.7, 134.7, 151.7, 153.8 (Ar–C).
2.2. Synthesis of 2-Me2NCH2C6H4CH2SiMe3 (B)
To a solution of 2-Me2NCH2C6H4CH3 (12.7 g, 85.2 mmol) and
TMEDA (9.9 g, 12.7 mL, 85.2 mmol) in diethyl ether (100 mL) was
added dropwise n-BuLi (2.5 M, 34.1 mL, 85.2 mmol) in hexane at
0 °C. The mixture was slowly allowed to warm to ambient temper-
ature and stirred for 8 h. ClSiMe3 (10.9 mL, 9.3 g, 85.2 mmol) was
added dropwise via a syringe at 0 °C. The reaction mixture was stir-
red overnight, and then water (10 mL) was added. The aqueous
phase was separated and extracted with diethyl ether
(15 mL ꢂ 3). The combined organic phase was dried over MgSO4
and rotary evaporated under reduced pressure. Compound B
(17.4 g, 91%) was obtained as a colorless liquid by distillation un-
der reduced pressure (bp 72ꢃ74 °C, 5 Pa). 1HNMR (CDCl3): d 2.16
(s, 6H, NMe2, 2.37 (s, 2H, CH2SiMe3), 3.34 (s, 2H, CH2NMe2), 0.07
(s, 9H, SiMe3) 7.04–7.37 (m, 4H, Ar–H), 13C NMR (CDCl3): d ꢁ1.2
(SiMe3), 21.5 (CH2SiMe3), 48.6 (NMe2), 62.2 (CH2NMe2), 123.7,
126.0, 126.5, 131.8, 135.1, 140.3 (Ar–C).
2.7. Synthesis of [{2-Me2NCH2C6H4CH(SiMe3)}2Mn] (4)
From MnCl2 (0.19 g, 1.5 mmol) and 1 (1.03 g, 3.0 mmol), using
the procedure similar to that for 2, there were obtained yellow
crystals of 4 (0.54 g, 72%) by recrystallization from hexane/tet-
rohydrofuran (1:2). Mp: 128–130 °C. Anal. Calc. for C26H44MnN2Si2:
C, 62.99, H, 8.95, N, 5.65. Found: C, 62.83; H, 8.81; N, 5.79%.
2.8. Synthesis of [2-Me2NCH2C6H4CH(SiMe3)Zn(Cl)ꢀTMEDA] (5)
2.3. Synthesis of (2-Me2NCH2C6H4CH2)2SiMe2 (B0)
From ZnCl2 (0.41 g, 3.0 mmol) and 1 (1.04 g, 3.0 mmol), using
the procedure similar to that for 2, there was obtained colorless
From 2-Me2NCH2C6H4CH3 (6.41 g, 42.6 mmol), TMEDA (6.3 mL,
42.6 mmol), n-BuLi (2.5 M, 17.1 mL, 42.6 mmol) and Cl2SiMe2
(2.6 mL, 21.3 mol), using the procedure similar to that for B, there
was obtained pale yellow liquid of B0 (5.43 g, 71%, bp 118–120 °C,
5 Pa). 1HNMR (CDCl3): d ꢁ0.03 (6H, SiMe2), 2.33 (s, 2H, CH2SiMe2),
2.37 (s, 2H, CH2SiMe2), 2.11 (s, 6H, NMe2), 2.19 (s, 6H, NMe2), 3.24
(s, 4H, CH2NMe2), 6.94–7.25 (m, 8H, Ar–H), 13C NMR (CDCl3): d
ꢁ1.57 (SiMe2), 22.7 (CH2SiMe2), 46.7 (NMe2), 63.6 (CH2NMe2),
125.1, 128.1, 130.3, 131.5, 136.5, 140.6 (Ar–C).
crystals of
5 (1.1 g, 81%). Mp: 146–148 °C, Anal. Calc. for
C19H38ClN3SiZn: C, 52.16, H, 8.76, N, 9.61. Found: C, 52.04, H,
8.63, N, 9.76%. 1HNMR (C6D6): d 0.59 (s, 9H, SiMe3), 1.88 (s, 9H,
NMe2 and NMe2 of TMEDA), 2.01 (s, 9H, NMe2 and NMe2 of TMEDA),
2.24 (t, 4H, CH2 of TMEDA), 3.43 (s, 2H, CH2NMe2), 7.09–7.42 (m,
4H, Ar–H); 13CNMR (C6D6): d ꢁ0.27 (SiMe3), 31.5 (CHSiMe3), 45.6
(NMe2), 47.7 (NMe2 of TMEDA), 53.1 (CH2 of TMEDA), 67.8
(CH2NMe2), 122.9, 127.2, 129.7, 138.9, 142.5 (Ar–C).

B. Jia et al. / Inorganica Chimica Acta 388 (2012) 127–134
129
2.9. Synthesis of [(2-Me2NCH2C6H4CH)2SiMe2Zn]2 (6)
and then directly mounted on the diffractometer under a stream
of cold nitrogen gas. The crystal data and summary of X-ray data
collection are presented in Table 1. A total of N reflections were
n-BuLi (4.1 mL, 10.3 mmol, 2.5 M, in hexane solution) was
added dropwise to a solution of (2-Me2NCH2C6H4CH2)2SiMe2 (B0)
(1.81 g, 5.1 mmol) and TMEDA (1.54 mL, 10.2 mmol) in tetrahydro-
furan (30 mL) at 0 °C. The solution became yellow and was stirred
at room temperature for 12 h, and the yellow solid was isolated via
filtration and dried under vacuum to generate lithium salt 1.78 g
(3.0 mmol), which was redissolved in tetrahydrofuran (30 mL).
ZnCl2 (0.41 g, 3.0 mmol) was added to in several portions to the
above solution at ꢁ78 °C. The resulting mixture was warmed up
to room temperature slowly and stirred for 15 h. The white precip-
itate was filtered off and the volatiles were removed in vacuo. The
residue was extracted with hexane / tetrahydrofuran (1:2) and fil-
tered. The filtrate was concentrated in vacuo to ca. 15 mL and set
aside to afford colorless crystals of 6 (0.92 g, 74%). Mp: 136–
138 °C. Anal. Calc. for C44H64N4Si2Zn2: C, 63.21; H, 7.72; N, 6.70.
Found: C, 63.09, H, 7.66, N, 6.77%. 1HNMR (C6D6): d 0.19 (s, 12H,
SiMe2), 1.81 (s, 2H, CHSiMe3), 1.87 (s, 2H, CHSiMe3), 2.38 (s, 12H,
NMe2), 2.45 (s, 12H, NMe2), 3.48 (s, 8H, CH2NMe2), 6.98–7.43 (m,
16H, Ar–H); 13CNMR (C6D6): d ꢁ0.75 (SiMe2), 30.2 (CHSiMe2),
46.3 (NMe2), 61.1 (CH2NMe2), 112.9, 114.7, 128.7, 129.4, 131.8,
133.8, 138.4, 139.9, 150.1, 151.8 (Ar–C).
collected in the
and polarization effects as well as absorption by using multiscans
SADABS) [32]. The structure was solved by direct methods (SHELXS
97) [33]. Then, the remaining non-hydrogen atoms were obtained
from the successive difference Fourier maps. All non-hydrogen
atoms were refined with anisotropic displacement parameters,
whereas hydrogen atoms were constrained to parent sites, by
using a riding mode (SHELXTL) [34].
x scan mode. Corrections were applied for Lorentz
(
-
3. Results and discussion
3.1. Synthesis and characterization of compounds 1–5
The general synthetic routes for the compounds 1–5 are illus-
trated in Scheme 1. Treatment of 2-Me2NCH2C6H4CH3 with one
equivalent of n-BuLi in the presence of TMEDA in diethyl ether,
and addition of ClSiMe3, gave compound
B (B = 2-Me2NCH2
C6H4CH2-SiMe3) as a colorless liquid in 91% yield by distillation un-
der reduced pressure (bp 72–74 °C, 5 Pa). Metalation of B by equiv-
alent n-BuLi and TMEDA in hexane gave pale yellow crystalline
lithium compound 1 in good yield as highly air and moisture
sensitive liquid.
2.10. Typical polymerization procedure
The compounds 2–5 were prepared from the reaction of 1 and
the corresponding anhydrous ZnCl2, CdCl2 or MnCl2 (Scheme 1).
Thus, treatment of 1 with anhydrous ZnCl2, CdCl2 or MnCl2 in a
2:1 M ratio in diethyl ether or tetrahydrofuran at ꢁ78 °C afforded
compound 2, 3 or 4 with the general formula [M(L)2] [M = Zn (2),
Cd (3), Mn (4)] in good yield, respectively. The single crystals
suitable for X-ray diffraction studies of compounds 2, 3 or 4 were
obtained from recrystallization in hexane/tetrahydrofuran. How-
ever compound 5 was obtained by treatment of compound 1 with
anhydrous ZnCl2 in a 1:1 M ratio and recrystallization from diethyl
ether. Attempts for the synthesis of the compound LMCl (M = Cd or
Mn) from the reaction of 1 with equal molar ratio of CdCl2 or MnCl2
via a similar procedure were failed.
A Schlenk tube previously dried at 150 °C and cooled under
nitrogen, and then the Schlenk flask was charged with 1.0 mmol
of rac-lactide in toluene (5 mL) containing a prescribed amount
of benzyl alcohol. To this solution was added a solution of
0.01 mmol of catalyst in 0.5 mL of toluene ([lactide]/[metal] = 100).
The mixture was immediately stirred with a magnetic stir bar at
room temperature or 70 °C. After the desired time, the reaction
was quenched by adding acidified methanol (ca. 1 mL of 1.2 M
CH3COOH solution) and the polymer was precipitated with excess
methanol (50 mL). The polymer was filtered and then dried under
vacuum to constant weight.
2.11. X-ray crystallography
3.2. Molecular structures of compounds 1–5
Data collection for compounds 1–6 was performed with Mo K
a
radiation (k = 0.71073 Å) by using a Bruker Smart Apex CCD
The molecular structure of the crystalline lithium compound 1
diffractometer at 298(2) or 213(2) K. Crystals were coated in oil
is illustrated in Fig. 1, and selected bond lengths and angles are
Table 1
Crystallographic data and structure refinement for compounds 1–6.
Complex
1
2
3
4
5
6
Formula
Fw
C
19H38LiN3Si
C26H44ZnN2Si2
506.18
C26H44CdN2Si2
553.21
C26H44MnN2Si2
495.75
C19H38ClN3SiZn
437.43
C44H64N4Si2Zn2
835.92
343.55
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P2(1)/n
10.136(8)
17.141(13)
13.030(8)
90.00
91.08(9)
90.00
2263(3)
4
orthorhombic
Pna2(1)
18.657(8)
9.410(4)
16.443(8)
90.00
90.00
90.00
2887(2)
4
1.165
orthorhombic
Pca2(1)
15.546(3)
10.231(2)
18.107(3)
90.00
90.00
90.00
2879.9(10)
4
1.276
orthorhombic
Pca2(1)
15.247(2)
10.1992(15)
18.139(3)
90.00
90.00
90.00
2820.7(7)
4
1.167
triclinic
P1
tetragonal
P4
16.395(4)
16.395(4)
8.452(4)
90.00
90.00)
90.00
2271.9(12)
4
1.222
ꢀ
ꢀ
9.780(4)
10.114(4)
14.050(3)
87.59(4)
74.75(4)
62.86(4)
1188.3(7)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.008
0.108
1.223
1.203
l
(mmꢁ1
)
0.949
0.856
0.568
1.141
F(000)
760
1088
1160
1068
468
888
Reflections collected
Independent reflections
Rint
9194
3975
0.0510
10128
3305
0.1056
10304
4201
0.0291
11103
4907
0.0265
4919
4099
0.0169
9337
3951
0.0289
R1, wR2 [I_2
R1, wR2 (all data)
r
(I)]
0.0995, 0.1950
0.1255, 0.2069
1.209
0.489 to ꢁ0.264
0.0556, 0.1136
0.1024, 0.1345
0.992
0.328 to ꢁ0.279
0.0382, 0.0772
0.0403, 0.0790
1.106
0.666 to ꢁ0.672
0.0385, 0.0869
0.0407, 0.0879
1.084
0.468 to ꢁ0.170
0.0374, 0.0953
0.0414, 0.0975
1.063
0.774 to ꢁ0.446
0.0531, 0.1451
0.0547, 0.1464
1.097
0.764 to ꢁ0.501
Goodness of fit
F2 Largest difference in peak and hole (e Åꢁ3
)

130
B. Jia et al. / Inorganica Chimica Acta 388 (2012) 127–134
CH2NMe2
N
Me2
N
ii)
Li
CH2
N
Me2
SiMe3
SiMe3
i)
B (91)%
1 (75%)
CH2NMe2
iii)
N
iv)
CH3
CH2NMe2
N
Me2
N
Cl
v)
2
M
Zn
N
Me2
SiMe3
SiMe3
SiMe3
2 M=Zn (81%)
3 M=Cd (72%)
5
(81%)
4
M=Mn (72%)
Scheme 1. Reagents and conditions: (i) n-BuLi, TMEDA, ClSiMe3, diethyl ether or hexane, 0 °C; (ii) n-BuLi, TMEDA, diethyl ether or hexane, 0 °C; (iii) MCl2 (0.5 equiv.), (M = Zn,
Cd, Mn), diethyl ether or tetrohydrofuran, ꢁ78 °C; (iv) ZnCl2 (1 equiv.), diethyl ether or tetrohydrofuran, ꢁ78 °C; (v) compound 1 (1 equiv.), diethyl ether, ꢁ78 °C.
Fig. 2. Molecular structure of compound 2 showing thermal ellipsoids is plotted at
20% probability level, hydrogen atoms are omitted for clarity.
Fig. 1. Molecular structure of compound 1 showing thermal ellipsoids is plotted at
20% probability level, hydrogen atoms are omitted for clarity.
Table 2
in Table 3. To the best of our knowledge, 2 is the only example for
the solvated-free neutral benzylzinc compound. The core structure
Selected bond lengths [Å] and angles [°] for 1.
of 2 is a spirocycle [6,6] built by two ligands and zinc atom with the
latter as the spiro union, of which zinc atom and each of the ligands
form a twist boat-shaped six-membered ring. The bond lengths
2.002(9) and 2.043(9) Å of Zn–C1 and Zn–C14 are shorter than
those [2.041(4) and 2.050(4) Å] of the reported benzylzinc com-
pound [Zn{CH(SiMe3)Ph}2ꢀTMEDA] [26], respectively.
Bond lengths
Li–C1
Li–N2
2.298(8)
2.130(8)
1.829(4)
Li–N1
Li–N3
N1–C8
2.139(8)
2.200(8)
1.478(6)
Si–C1
Bond angles
N2–Li–N1
N1–Li–N3
N1–Li–C1
C8–N1–Li
113.0(3)
120.7(4)
95.9(3)
N2–Li–N3
C1–Li–N2
N3–Li–C1
C2–C1–Li
86.1(3)
122.0(4)
121.3(3)
84.6(3)
The molecular structures of compounds 3 and 4 which are very
similar to compound 2 are illustrated in Figs. 3 and 4, respectively,
and selected bond lengths and angles are presented in Table 3. To
the best of our knowledge, compound 3 is the only case for the sol-
vated-free neutral benzyl cadmium compound. Cadmium atom
and two the bulky ligands form a twist boat-shaped six-membered
ring. The bond lengths 2.227(5) and 2.220(6) Å of Cd–C1 and Cd–
C14 are longer than those [2.002(9) and 2.043(9) Å] in the com-
pound 2, respectively. The bond angle 158.1° (2) of C1CdC14 is
wider than that [146.8°] in the compound 2.
103.2(3)
listed in Table 2. The TMEDA-solvated lithium compound (1)
exhibits a monomeric structure in which the lithium atom and
the ligand form a six-membered cycle.
The molecular structure of the solvated-free compound 2 is
illustrated in Fig. 2 and selected bond lengths and angles are listed

B. Jia et al. / Inorganica Chimica Acta 388 (2012) 127–134
131
Table 3
Selected bond lengths (Å) and angles (°) for 2, 3 and 4.
2
3
4
Bond lengths
Zn–C1
Zn–C14
Zn–N1
Zn–N2
N1–C8
N2–C21
2.002(9)
2.043(9)
2.235(10)
2.361(9)
1.517(16)
1.437(16)
Cd–C1
Cd–C14
Cd–N1
Cd–N2
N1–C8
N2–C21
2.227(5)
2.220(6)
2.524(5)
2.535(4)
1.486(7)
1.478(7)
Mn–C1
Mn–C14
Mn–N1
Mn–N2
N1–C8
2.185(3)
2.197(3)
2.285(2)
2.283(2)
1.501(4)
1.496(3)
N2–C21
Bond angles
C1–Zn–C14
C1–Zn–N1
C1–Zn–N2
C14–Zn–N1
C14–Zn–N2
N1–Zn–N2
C8–N1–Zn
C2–C1–Zn
146.8(3)
96.6(4)
104.1(4)
102.6(4)
95.1(4)
108.8(2)
106.9(8)
108.4(6)
103.6(8)
108.8(7)
C1–Cd–C14
C1–Cd–N1
C1–Cd–N2
C14–Cd–N1
C14–Cd–N2
N1–Cd–N2
C8–N1–Cd
C2–C1–Cd
C21–N2–Cd
C15–C14–Cd
158.1(2)
83.6(18)
109.8(19)
110.7(19)
83.8(18)
102.7(17)
109.2(3)
101.3(3)
109.0(3)
103.0(3)
C1–Mn–C14
C1–Mn–N1
C1–Mn–N2
C14–Mn–N1
C14–Mn–N2
N1–Mn–N2
C8–N1–Mn
C2–C1–Mn
C21–N2–Mn
C15–14–Mn
141.9(11)
89.0(10)
112.6(10)
112.0(9)
88.8(9)
112.0(9)
109.7(17)
97.7(16)
110.2(16)
95.8(16)
C21–N2–Zn
C15–C14–Zn
Fig. 3. Molecular structure of compound 3 showing thermal ellipsoids is plotted at
20% probability level, hydrogen atoms are omitted for clarity.
Fig. 5. Molecular structure of compound 5 showing thermal ellipsoids is plotted at
20% probability level, hydrogen atoms are omitted for clarity.
For compound 4, the four-coordinated manganese atom is
wrapped by two C atoms and two N atoms of two ligands forming
the distorted tetrahedral coordination geometry composed by two
six-membered rings, which were puckered rather than in a trans
arrangement. The bond lengths of Mn–C1[2.185(3) Å] and
Table 4
Selected bond lengths (Å) and angles (°) for 5.
Bond lengths
Zn–C(1)
Zn–N2
Si–C1
2.006(3)
2.172(2)
1.856(3)
Zn–Cl
Zn–N3
2.2497(17)
2.136(2)
Bond angles
C(1)–Zn–N3
N3–Zn–N2
Cl–Zn–N3
118.42(10)
84.04(9)
103.89(8)
111.65(16)
C(1)–Zn–N2
C(1)–Zn–Cl
Cl–Zn–N2
115.13(10)
123.62(8)
104.13(8)
111.67(13)
Fig. 4. Molecular structure of compound 4 showing thermal ellipsoids is plotted at
20% probability level, hydrogen atoms are omitted for clarity.
C(2)–C(1)–Zn
Si–C(1)–Zn

132
B. Jia et al. / Inorganica Chimica Acta 388 (2012) 127–134
Mn–C14 [2.197(3) Å] are longer than that [2.002(9) and 2.043(9) Å]
of the compound 2, respectively. The bond angle 141.94° (11) of
C1MnC14 is narrower than that [146.8°] of the compound 2.
Compound 5 was isolated by crystallization from diethyl ether
as a colorless crystalline solid in good yield. The molecular struc-
ture of compound 5 is illustrated in Fig. 5, and selected bond
lengths and angles are presented in Table 4. The TMEDA-solvated
heteroleptic zinc compound 5 is a monomer, in which zinc atom
is surrounded by one C atom of the ligand unit and two N atoms
from TMEDA molecule and one Cl atom. Unexpectedly, the amino
group on the ligand does not take part in the coordination and
the coordination mode is similar to that reported benzylzinc com-
pound [Zn(Cl)CH(SiMe3)PhꢀTMEDA] [25]. The bond lengths of Zn–
C(1) 2.006(3) Å, Zn–Cl 2.249(17) Å, Zn–N2 2.173(2) Å and Zn–N3
2.136(2) Å are close to those of the reported compound,
[2.011(4), 2.252(2), 2.170(4) and 2.130(4) Å] [25], respectively.
3.3. Synthesis and characterization of compound 6
Using a similar procedure as for B, compound B0 [B0 = (2-
Me2NCH2C6H4CH2)2SiMe2] was synthesized from the reaction of
N,N-dimethyl-o-methylbenzylamine with n-BuLi, TMEDA, and
then Cl2SiMe2. Metalation of B0 with two equivalents of n-BuLi in
tetrahydrofuran yielded the corresponding benzyl lithium com-
pound, which reacted directly with equivalent anhydrous ZnCl2
in tetrahydrofuran at ꢁ78 °C affording compound [L0Zn]2 (6). The
compound 6 was isolated by recrystallization from tetrahydrofu-
ran/hexane (2:1) as colorless crystals in 74% yield as shown in
Scheme 2. Attempts for synthesis of cadmium or manganese com-
pound based on L0 were not successful.
Fig. 6. Molecular structure of compound 6 showing thermal ellipsoids is plotted at
20% probability level, hydrogen atoms are omitted for clarity.
Table 5
Selected bond lengths (Å) and angles (°) for 6.
Bond lengths
Zn–C1
Zn–N1
C1–Si
2.027(4)
2.320(4)
1.873(5)
1.510(7
Zn–C130
Zn–N20
Si–C13
C8–N1
2.012(5)
2.339(5)
1.890(5)
1.489(8)
3.4. Molecular structure of compound 6
C2–C1
Bond angles
130–Zn–C1
C1–Zn–N1
C1–Zn–N20
Zn–Zn0–C10
C2–C1–Zn
C20–N2–Zn0
C130–Zn–N1
C130–Zn–N20
N1–Zn–N20
Zn0–Zn–C130
C8–N1–Zn
Si–C1–Zn
104.80(18)
95.53(18)
105.62(17)
82.80(1)
105.3(3)
119.1(2)
The molecular structure of 6 is illustrated in Fig. 6. Centrosym-
metric crystalline bimetallic zinc compound 6 exists as a dimer in
solid state. The central eight-membered ZnC1SiC13Zn0C10Si0C130
ring is flanked by four twist boat-shaped six-membered rings built
by two zinc atoms and four 2-(N,N-dimethylaminomethyl)benzyl
units. The average distance of Zn–C [2.0200 0.0075 Å] is slightly
shorter than that in compound 2 [2.0234 0.0205 Å]. The geome-
try of the flanked six-membered cycles is similar to that of com-
pound 2, and selected bond lengths and angles of 6 are listed in
Table 5.
143.9(2)
96.39(17)
106.57(17)
30.45(2)
106.6(3)
106.0(3)
polymerization (ROP) of lactide [35–41]. Hence, the highly hin-
dered N-functionalized benzyl zinc compounds 2 and 5 were used
as initiators for catalytic ring-opening polymerization of rac-lac-
tide. Polymerizations were carried out in Schlenk flask under nitro-
gen atmosphere strictly free of moisture and oxygen in toluene, as
well as the polymerization factors of molar ratio of [LM]/[LA](100
or 200) and reaction temperature (room temperature or 70 °C)
3.5. Polymerization reactions of rac-lactide for compounds 2 and 5
In the view of zinc initiators based on aliphatic alkyl amide
compounds have been extensively used in the ring-opening
CH2NMe2
N
N
Zn
CH3
Me2Si
SiMe2
(i)
(ii)
Zn
Me2
Si
N
N
C
C
H2
H2
CH2NMe2
CH2NMe2
6 (74%)
B' (71)%
Scheme 2. Reagents and conditions: (i) n-BuLi, TMEDA, Cl2SiMe2 (0.5 equiv.), diethyl ether or hexane, 0 °C; (ii) n-BuLi (2 equiv.), TMEDA (2 equiv.), ZnCl2, tetrohydrofuran,
ꢁ78 °C.

B. Jia et al. / Inorganica Chimica Acta 388 (2012) 127–134
133
Table 6
rac-Lactide polymerization data for the compounds 2 and 5.
Entry
Catalyst
[LA]/[C]a
Temperature (°C)
Time (h)
Yield (%)b
Mn (g/mol)c
Mw/Mnc
Prd
1
2
3
4
5
6
2
2
2
5
5
5
100:1
100:1
200:1
100:1
100:1
200:1
25
70
70
25
70
70
14
6
6
14
6
6
11
86
53
12
89
81
–
–
11497
11729
–
9531
18206
1.39
1.50
–
1.46
1.38
0.56
0.60
0.64
0 .63
a
b
c
Benzyl alcohol.
The yields were calculated according to the mass of the polymer was precipitated by the addition of MeOH and was collected by filtration and dried.
Determined by gel-permeation chromatography, calibrated with polystyrene standards in tetrahydrofuran.
d
Pr is the probability of racemic linkages between monomer units and is determined from the methine region (5.30–5.00 ppm) of the homonuclear decoupled 1H NMR
spectra in CDCl3 at 25 °C. Pr = 2I1/(I1 + I2), with I1 = 5.20–5.25 ppm, I2 = 5.13–5.20 ppm [42–47].
were tested, Compounds 2 and 5 exhibited very similar activity for
the ROP of rac-lactide .The details are summarized in Table 6.
Compound 2 initiated polymerization of rac-lactide at room
temperature in toluene in the presence of benzyl alcohol and gave
only 11% of yield (entry 1). Prolongation of the reaction time did
not improve the yield. As expected, an increase in the temperature
to 70 °C yielded 86% in 6 h with a medium broad polydispersity in-
dex [36] (Mn = 11497, Mw/Mn = 1.39, entry 2). With the molar ra-
tio of monomer: initiator from 100:1 to 200:1, molecular weight of
the polymers and the molecular weight distribution were almost
unchanged (Mn = 11729, Mw/Mn = 1.50, entry 3) while only 53%
of yield was obtained.
Compound 5 showed similar catalytic activity with compound
2. Compound 5 catalyzed rac-lactide to polylactide with 12% or
89% yield at room temperature or 70 °C (entries 4 and 5), respec-
tively. Good yield (81%), However, when the molar ratio of mono-
mer: initiator increased to 200:1, a significantly higher molecular
weight polymer (Mn = 18206) and the narrower molecular weight
distribution (Mw/Mn = 1.38, entry 6) were observed.
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
References
[1] M. Brookhart, M.L.H. Green, G. Parkin, PNAS 104 (2007) 6908.
[2] K.H. Thiele, Z. Anorg. Aug. Chem. 319 (1962) 183.
[3] M.J. Henderson, R.I. Papasergio, C.L. Raston, A.H. White, M.F. Lappert, J. Chem.
Soc., Chem. Commun. (1986) 672.
[4] N. Seidel, K. Jacob, P. Zanello, M. Fontani, J. Organomet. Chem. 620 (2001) 243.
[5] O.F.Z. Khan, D.M. Frigo, P. O’Brien, A. Howes, M.B. Hursthouse, J. Organomet.
Chem. 34 (1987) C27.
[6] T.R. Ancker, L.M. Engelhardt, M.J. Henderson, G.E. Jacobsen, C.L. Raston, B.W.
Skelton, A.H. White, J. Organomet. Chem. 689 (2004) 1991.
[7] M. Kaupp, H. Soll, H. Preuss, W. Kaim, T. Stahl, G. van Koten, E. Wissing, W.J.J.
Smeets, A.L. Spek, J. Am. Chem. Soc. 113 (1991) 5606.
[8] S. Javed, D.M. Hoffman, Inorg. Chem. 47 (2008) (1992) 11984.
[9] H.R. Barley, W. Clegg, S.H. Dale, E. Hevia, G.W. Honeyman, A.R. Kennedy, R.E.
Mulvey, Angew. Chem., Int. Ed. Engl. 44 (2005) 6018.
[10] M.J. Almond, M.P. Beer, M.G.B. Drew, D.A. Rice, Organometallics 10 (1991)
2072.
[11] M.L. Steigerwald, A.P. Alivisatos, J.M. Gibson, T.D. Harris, R. Kortan, A.J. Muller,
A.M. Thayer, T.M. Duncan, D.C. Douglass, L.E. Brus, J. Am. Chem. Soc. 110
(1988) 3046.
[12] E.K. Bryne, L. Parkanyi, K.H. Theopold, Science 241 (1988) 332.
[13] R.L. Wells, C.G. Pitt, A.T. McPhail, A.P. Purdy, S. Shafieezad, R.B. Hallock, Chem.
Mater. 1 (1989) 4.
All the resulting polylactides are most predominantly hetero-
tactic-rich under our conditions examined, as determined by the
methine region of the homonuclear decoupled 1HNMR experi-
ments in the region of 5.30–5.00 ppm [42–47].
[14] M.D. Healy, P.E. Laibinis, P.D. Stupik, A.R. Barron, J. Chem. Soc., Chem.
Commun. (1989) 359.
[15] S.M. Stuczynski, J.G. Brennan, M.L. Steigerwald, J. Organomet. Chem. 449
(1993) 167. and references therei.
[16] G. Cahiez, C. Duplais, J. Buendia, Chem. Rev. 109 (2009) 1434.
[17] A.R. Kennedy, J. Klett, R.E. Mulvey, D.S. Wright, Science 326 (2009) 706.
[18] K. Snegaroff, S. Komagawa, M. Yonehara, F. Chevallier, P.C. Gros, M. Uchiyama,
F. Mongin, J. Org. Chem. 75 (2010) 3117.
[19] R.E. Mulvey, V.L. Blair1, W. Clegg, A. Kennedy, J. Klett1, L. Russo, Nat. Chem. 2
(2010) 588.
[20] S. Harder, Organometallics 24 (2005) 373.
[21] C. Ruspic, J.R. Moss, M. Schürmann, S. Harder, Angew. Chem., Int. Ed. Engl. 47
(2008) 2121.
[22] S. Barroso, J. Cui, J.M. Carretas, A. Cruz, I.C. Santos, M.T. Duarte, J.P. Telo, N.
Marques, A.M. Martins, Organometallics 28 (2009) 3449.
[23] M.R. Crimmin, R. Mark, A.G.M. Barrett, M.S. Hill, D.J. MacDougall, M.F. Mahon,
P.A. Procopiou, Dalton Trans. (2009) 9715.
[24] M. Nishiura, T. Mashiko, Z. Hou, Chem. Commun. (2008) 2019 (and references
therein).
[25] M. Westerhausen, M. Wienekea, B.B. Rademachera, W. Schwarzb, Chem. Ber.
Recl. 130 (1997) 1499.
4. Conclusions
Six sterically hindered N-functionalized benzyl metal(II) com-
pounds [LiLꢀTMEDA] (1), [ML2] [M = Zn (2), Cd (3) or Mn (4)],
[L ZnClꢀTMEDA] (5) and [Zn L0]2 (6) were obtained. Each of the com-
pounds 1–6 has been characterized by microanalysis, multinuclear
NMR spectra at ambient temperature and X-ray single crystal
study. Compound 2 or 3 would be the only sample for solvated-free
homoleptic neutral benzylzinc or benzylcadmium compound,
respectively. Compounds ZnL2 (2) and [LZn(Cl)ꢀTMEDA] (5) exhib-
ited moderate activity for the ring-opening polymerization of rac-
lactide in toluene in the presence of benzyl alcohol at 70 °C. All the
resulting polylactides are most predominantly heterotactic-rich.
[26] M. Westerhausen, M. Wieneke, W. Schwarz, J. Organomet. Chem. 522 (1996)
137.
Acknowledgements
[27] S. Harder, Angew. Chem., Int. Ed. Engl. 43 (2004) 2714.
[28] S. Harder, F. Feil, K. Knoll, Angew. Chem., Int. Ed. Engl. 40 (2001) 4261.
[29] F. Feil, S. Harder, Organometallics 20 (2001) 4616 (and references therein).
[30] D.F.-J. Piesik, K. Habe, S. Harder, Eur. J. Inorg. Chem. (2007) 5652.
[31] P. Wijkens, J.T.B.H. Jastrzebski, N. Veldman, A.L. Spek, G. van Koten, Chem.
Commun. (1997) 2143.
We thank the NSFC (20772074), SXNSFC (2008011021;
2008012013-2) and for the Shanxi Schloship Council of China for
financial support.
[32] G.M. Sheldrick, Correction Software, University of Göttingen, Göttingen,
Germany, 1996.
[33] G.M. Sheldrick, Program for the Solution of Crystal Structures, University of
Göttingen, Göttingen, Germany, 1997.
Appendix A. Supplementary material
[34] Program for Crystal Structure Refinement, Bruker Analytical X-ray Instruments
Inc., Madison, WI, USA, 1998.
[35] L. Wang, H. Ma, Dalton Trans. 39 (2010) 7897.
[36] F.S.B. Luis, A.M. Carlos, G. Andrés, F. Mariano, F.B. Juan, O. Antonio, L.S. Agustín,
M.R. Ana, L.S. Isabel, Dalton Trans. (2009) 8054.
CCDC 797568, 797569, 797570, 797571, 797572 and 797573
contain the supplementary crystallographic data for compounds
1, 2, 3, 4, 5 and 6, respectively. These data can be obtained free

134
B. Jia et al. / Inorganica Chimica Acta 388 (2012) 127–134
[37] M.D. Jones, M.G. Davidson, C.G. Keir, L.M. Hughes, M.F. Mahon, D.C. Apperley,
Eur. J. Inorg. Chem. (2009) 635.
[42] F. Drouin, P.O. Oguadinma, T.J.J. Whitehorne, R.E. Prud’homme, F. Schaper,
Organometallics 29 (2010) 2139.
[38] H. Sun, J.S. Ritch, P.G. Hayes, Inorg. Chem. 50 (2011) 8063.
[39] C.D. Iulio, M.D. Jones, M.F. Mahon, D.C. Apperley, Inorg. Chem. 49 (2010)
10232.
[40] L. Liang, T. Tsai, C. Li, Y. Hsu, T. Lee, Eur. J. Inorg. Chem. (2011) 2948.
[41] B.M. Chamberlain, M. Cheng, D.R. Moore, T.M. Ovitt, E.B. Lobkovsky, G.W.
Coates, J. Am. Chem. Soc. 123 (2001) 3229.
[43] K. Peng, C. Chen, Dalton Trans. (2009) 9800.
[44] J.E. Kasperczyk, Macromolecules 28 (1995) 3937.
[45] K.A.M. Thakur, R.T. Kean, E.S. Hall, M.A. Doscotch, J.I. Siepmann, E.J. Munson,
Macromolecules 30 (1997) 2422.
[46] X. Pang, X. Chen, H. Du, X. Wang, X. Jing, J. Organomet. Chem. 692 (2007) 5605.
[47] J.C. Buffet, J. Okuda, P.L. Arnold, Inorg. Chem. 49 (2010) 419.