Structural and catalytic studies of lithium complexes bearing pendant aminophenolate ligands

Article abstract of DOI:10.1039/b717370a

Lithium complexes bearing mono-anionic aminophenolate ligands are described. Reactions of ligand precursors HON^MePh^OMe, HON^MePh^SMe, HON^MeC^OMe or HON ^MeC^NMe2 [HON^M

Full text of DOI:10.1039/b717370a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Structural and catalytic studies of lithium complexes bearing pendant
aminophenolate ligands†
Chi-An Huang, Chia-Lin Ho and Chi-Tien Chen*
Received 9th November 2007, Accepted 7th February 2008
First published as an Advance Article on the web 18th March 2008
DOI: 10.1039/b717370a
Lithium complexes bearing mono-anionic aminophenolate ligands are described. Reactions of ligand
precursors HONMePhOMe, HONMePhSMe, HONMeCOMe or HONMeCNMe2 [HONMePhOMe = (2-OMeC6H4-
CH2)N(Me)(CH2-2-HO-3,5-C6H2(tBu)2); HONMePhSMe= (2-SMe-C6H4CH2)N(Me)(CH2-2-HO-3,5-
C6H2(tBu)2); HONMeCOMe = (MeOCH2CH2)N(Me)(CH2-2-HO-3,5-C6H2(tBu)2); HONMeCNMe2
=
(Me2NCH2CH2)N(Me)(CH2-2-HO-3,5-C6H2(tBu)2)] with 1.1–1.3 molar equivalents of nBuLi in diethyl
ether solution afford (LiONMePhOMe)2 (3), (LiONMePhSMe)2 (4), (LiONMeCOMe)2 (5) and (LiONMeCNMe2
(6) as dinuclear lithium complexes. The BnOH adduct of 5, (BnOH)(LiONMeCOMe) (7), was prepared
)
2
from the reaction of 5 and BnOH in diethyl ether solution. The molecular structures are reported for
ligand precursor HONMePhSMe and compounds 3–5 and 7. These dinuclear lithium complexes show
excellent catalytic activities toward the ring-opening polymerization of L-lactide in the presence of
benzyl alcohol.
Introduction
Results and discussion
There is an increasing interest in the development of cata-
lysts/initiators for ring opening polymerization during the past
decades. Indeed, a large diversity of metal complexes has been
synthesized and these have been reviewed recently.1 Among these
studies, metal complexes bearing multidentate aminophenolate(s)
ligands have been a focus of interest, mainly due to their excellent
activities and great success in the preparation of the well-defined
polyesters.2–4 The steric and electronic effects of those versatile
ligands can be easily programmed through variation of the
substituents on the nitrogen atoms, many of which can be easily
achieved via the Mannich condensation reaction. Most recently,
some lithium complexes bearing bridged phenolates have been
reported to be effective catalysts/initiators in the ring opening
polymerization of cyclic esters.3r,5 Their performances on both
‘living’ and ‘immortal’ properties also encourage us to examine the
catalytic activities of lithium aminophenolate complexes toward
ring opening polymerization reaction.
Syntheses and characterization of lithium aminophenolate
complexes
Ligand precursors HONMePhOMe, HONMePhSMe, HONMeCOMe or
HONMeCNMe2 [HONMePhOMe = (2-OMe-C6H4CH2)N(Me)(CH2-
2-HO-3,5-C6H2(tBu)2); HONMePhSMe= (2-SMe-C6H4CH2)N(Me)-
(CH2-2-HO-3,5-C6H2(tBu)2); HONMeCOMe = MeOCH2CH2N-
(Me)(CH2-2-HO-3,5-C6H2(tBu)2); HONMeCNMe2 = Me2NCH2-
CH2N(Me)(CH2-2-HO-3,5-C6H2(tBu)2)] are prepared from cy-
clization of 2-methoxybenzylamine or 2-methylthiobenzylamine
with 2,4-di-tert-butylphenol and formaldehyde followed by
the reduction of C-O bond with lithium aluminium hy-
dride (for HONMePhOMe and HONMePhSMe),6 or from the
condensation reaction of N-(2-methoxyethyl)methylamine or
N,N,Nꢀ-trimethylethylenediamine with 2,4-di-tert-butylphenol
and formaldehyde (for HONMeCOMe and HONMeCNMe ),4b as shown
2
in Scheme 1.
All the ligand precursors are characterized by NMR spec-
troscopy as well as microanalyses or by comparison with data
reported in the literature.4b Crystals of HONMePhSMe suitable for
X-ray crystallographic analysis were grown from slow evaporation
of hexane solution at room temperature. The molecular structure
features a monomer without any intra- or inter- molecular hydro-
gen bonding, as shown in Fig. S1 (ESI†). This structure reveals
a tertiary amine with potential to work as pendant aminophe-
As part of our continuing interest in the development of novel
catalysts/initiators for ring opening polymerization,3b,d,r we report
here the synthesis and characterization of lithium complexes
bearing the pendant amine-phenolate ligands. Their catalytic
activities toward ring opening polymerization of L-lactide in the
presence of benzyl alcohol are also presented.
nolate ligand. Reactions of ligand precursors HONMePhOMe
,
HONMePhSMe, HONMeCOMe or HONMeCNMe2 with 1.1–1.3 molar
n
equivalents of BuLi in diethyl ether afford (LiONMePhOMe)2 (3),
(LiONMePhSMe)2 (4), (LiONMeCOMe)2 (5) and (LiONMeCNMe2)2 (6)
as dinuclear lithium complexes. Due to the good solubility, the
isolated yields (22–42%) are relatively lower for those dinuclear
lithium complexes. Compounds 3–6 are characterized by NMR
spectroscopy as well as microanalyses. Two sets of diastereotopic
signals corresponding to the methylene protons of N–CH2–aryl
Department of Chemistry, National Chung Hsing University, Taichung, 402,
Taiwan. E-mail: ctchen@dragon.nchu.edu.tw
† Electronic supplementary information (ESI) available: Fig. S1: Molecu-
lar structure of HONMePhSMe. Fig. S2: Homonuclear-decoupled methine
1H NMR spectrum (400 MHz, CDCl3) of poly(L-lactide) synthesized at
26.5 ◦C for 5 min in CH2Cl2 using 6 as initiator. CCDC reference numbers
646484–646487. see DOI: 10.1039/b717370a
3502 | Dalton Trans., 2008, 3502–3510
This journal is
The Royal Society of Chemistry 2008
©

Scheme 1
are found on the 1H NMR spectra of 3 and 4 (2.42 and 4.08 ppm
1
1
on H NMR spectrum correlate to 56.1 ppm on 13C{ H} NMR
spectrum, 2.82 and 4.37 ppm on 1H NMR spectrum correlate to
64.1 ppm on 13C{ H} NMR spectrum for 3; 2.59 and 4.15 ppm
1
1
1
on H NMR spectrum correlate to 58.4 ppm on 13C{ H} NMR
1
spectrum, 2.83 and 4.31 ppm on H NMR spectrum correlate
to 63.6 ppm on 13C{ H} NMR spectrum for 4). Due to the
1
conformational flexibility of the aliphatic pendant groups, several
sets of diastereotopic signals corresponding to the methylene
1
protons of N–CH2–aryl and N–(CH2)2–E are found on the H
NMR spectra of 5 and 6. The 7Li{ H} NMR spectra of 3–
1
6 in toluene-d8 show singlet resonances at 2.64, 2.93, 2.37 and
2.40 ppm, respectively, indicating the single Li environment in
solution. Crystals of 3–5 suitable for an X-ray determination
were grown from concentrated hexane solution. The molecular
structures of 3, 4 and 5 exist as lithium-bridged dimers with a core
planar Li–O–Li–O ring in each case and their molecular structure
diagrams are depicted in Fig. 1–3.
Compound 3 can be described as a centrosymmetric dimer
with a Li–O(1)–LiA–O(1A) planar core ring. Each of the lithium
atoms is four-coordinate, which is bonded to one nitrogen atom of
central amine, one oxygen atom of pendant functionality and two
oxygen atoms of different phenolates. The planar core features
˚
Fig. 1 Molecular structure of 3. Selected bond lengths (A) and bond
angles (◦): Li–O(1), 1.863(3); Li–O(1A), 1.910(3); Li–O(2A), 2.058(4);
Li–N(0A), 2.101(3); Li(A)–O(1), 1.910(3); Li(A)–O(2), 2.058(4); Li(A)–N,
2.101(3); O(1)–Li–O(1A), 96.09(15); Li–O(1)–Li(A), 83.91(15). Hydrogen
atoms omitted for clarity.
˚
two different Li–Ophenolates distances of 1.863(3) and 1.910(3) A
with LiOLi and OLiO angles of 83.91(15) and 96.09(15)◦. These
data are in the range of the known distances and angles for
dimeric lithium phenolate complexes.7 The bond lengths of Li–
˚
˚
2.101(3) A) are within those (2.10(2)–2.332(8) A) found in
literature.7c,9 Basically, compound 4 is quite similar to compound
3 with a different pendant group –SMe instead of –OMe for 3.
Each lithium atom is bonded to one nitrogen atom of the central
amine, one sulfur atom of pendant functionality and two oxygen
atoms of different phenolates. Similar to 3, two lithium phenolates
˚
˚
OOMe (Li–O(2A), 2.058(4) A; Li(A)–O(2), 2.058(4) A) are near
8
˚
the upper extremes of those (1.929–2.025 A) found in literature.
˚
The bond lengths of Li–Namine (Li–N(0A), 2.101(3) A; Li(A)–N,
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 3502–3510 | 3503
©

of pendant functionality beneath the planar core ring in each
molecule.
Ring-opening polymerization of L-lactide catalyzed by 3–6 in the
presence of benzyl alcohol
Several lithium phenolate complexes are known as efficient
catalysts/initiators in the ring opening polymerization (ROP)
of cyclic esters,1e,f ,3r compounds 3–6 were expected to work as
catalysts toward the ROP of L-lactide. Prescribed equivalent ratios
on the catalyst (0.05 mmol), monomers and alcohol were employed
in 10 mL solvent at 26.5 ◦C for the prescribed time. Representative
results are collected in Table 1.
The results are solvent-dependent with CH2Cl2 being the best
choice after several trials with toluene, THF and CH2Cl2 in the
presence or absence of benzyl alcohol (BnOH). For the choice of
initiator, we surveyed benzyl alcohol and isopropyl alcohol (IPA).
Finally, we found that use of CH2Cl2 and benzyl alcohol leads to
the best controlled behavior (entries 1–7). The same conditions
were applied to examine the catalytic activity of 3, 4 and 6.
After several trials (entries 8–10), compound 6 is the choice of
the best catalyst among these dinuclear lithium complexes. Linear
relationships between the number average molecular weights and
the monomer-to-initiator ratio ([M]0/[I]0) demonstrated in Fig. 4
exhibit the ‘living’ character of the polymerization process (entries
10–14), however, the PDI values increase with monomer-to-
initiator ratio. For the study of transesterification, compound 5
was chosen as candidate. Based on the data exhibited in Table 1
(entries 27–30), transesterification might occur in the later stages
of ring opening polymerization.
˚
Fig. 2 Molecular structure of 4. Selected bond lengths (A) and bond
angles (◦): Li(1)–O(1), 1.894(4); Li(1)–O(2), 1.828(3); Li(1)–N(1), 2.059(4);
Li(1)–S(1); 2.567(4); Li(2)–O(1), 1.809(3); Li(2)–O(2), 1.882(4); Li(2)–
N(2), 2.058(4); Li(2)–S(2), 2.549(3); O(2)–Li(1)–O(1), 96.88(17); O(1)–
Li(2)–O(2), 97.96(18); Li(2)–O(1)–Li(1), 82.48(16); Li(1)–O(2)–Li(2),
82.34(16). Hydrogen atoms omitted for clarity.
˚
Fig. 3 Molecular structure of 5. Selected bond lengths (A) and
bond angles (◦): Li(1)–O(1), 1.922(5); Li(1)–O(2), 2.068(5); Li(1)–O(3),
1.823(5); Li(1)–N(1), 2.064(6); Li(2)–O(1), 1.856(5); Li(2)–O(3), 1.941(5);
Li(2)–O(4), 2.022(5); Li(2)–N(2), 2.116(5); O(3)–Li(1)–O(1), 98.4(2);
O(1)–Li(2)–O(3), 96.6(2); Li(2)–O(1)–Li(1), 82.1(2); Li(1)–O(3)–Li(2),
82.4(2). Hydrogen atoms omitted for clarity.
Fig. 4 Polymerization of L-lactide initiated by 6 and BnOH in CH2Cl2 at
˚
26.5 ◦C.
are bridged via Li–Ophenolate bonds (1.828(3) and 1.809(3) A) to
form a planar core Li(1)–O(1)–Li(2)–O(2) ring with the angles
subtended at oxygen atoms (82.48(16) and 82.34(16)◦) narrower
than those (96.88(17) and 97.96(18)◦) at the lithium atoms. Unlike
3, compound 4 is formed with two nitrogen atoms of amine above
and two sulfur atoms of pendant functionality beneath the planar
core ring. Bond lengths are similar to those discussed above with
This controlled behavior is further confirmed by the resumption
experiments on 3–6 (entry 15 for 6, entry 18 for 3, entry 21
for 4, and entry 24 for 5). The ‘immortal’ character of 3–6 was
examined using two or four equiv. ratios (relative to [M]0/[Li]0)
of benzyl alcohol as the chain transfer agent (entries 16–17 for 6;
entries 19–20 for 3; entries 22–23 for 4; entries 25–26 for 5). The
number average molecular weights of the polymers created from
these polymerization reactions became half or one to fourth of
those found in the reactions with addition of one equiv. ratio
of benzyl alcohol. Polymer produced by the ‘in situ’ manner
using L-lactide, lithium complex and BnOH on the ratios of 50 :
1 : 1 was used to examine the chain-end analysis. As shown in
˚
two Li–SSMe bond lengths (2.567(4) and 2.549(3) A) instead of
˚
Li–OOMe. Bond lengths of Li–Ophenolates (1.809(3)–1.894(4) A) and
˚
Li–Namine (2.059(4) and 2.058(4) A) and bond angles of planar
core Li–O–Li–O ring (O–Li–O, 96.88(17) and 97.96(18)◦; Li–O–
Li, 82.48(16) and 82.34(16)◦) are similar to those discussed above
for 3. However, the geometric structures of 5 are similar to 4
with two nitrogen atoms of amine above and two oxygen atoms
3504 | Dalton Trans., 2008, 3502–3510
This journal is
The Royal Society of Chemistry 2008
©

Table 1 Ring-opening polymerization of L-lactides catalyzed by 3–7 at 26.5 ◦Ca
b
Entry
Catalyst
{[M]0/[Li]0} : [BnOH]
t/min
Mn (obs.)b
Mn (calc.)c
Conv. (%)d
Yield (%)e
Mw/Mn
1f
2g
5
5
5
5
5
5
5
3
4
6
6
6
6
6
6
6
6
3
3
3
4
4
4
5
5
5
5
5
5
5
7
7
7
7
7
50 : 0
50 : 0
50 : 0
50 : 1
50 : 1
50 : 1
50 : 1
50 : 1
50 : 1
15
15
15
15
15
15
15
15
20
5
5
5
5
5
5(5)
5
52000(30200)
9500(5500)
41100(23800)
10700(6200)
3300(1900)
12400(7200)
9600(5600)
11000(6400)
10100(5900)
9700(5600)
16900(9800)
21400(12400)
28000(16200)
33000(19100)
26100(15100)
10200(5900)
13600(7900)
30400(17600)
13500(7800)
14100(8200)
18000(10400)
13900(8100)
13200(7700)
23000(13300)
12900(7500)
14000(8100)
14200(8200)
23100(13400)
25100(14600)
27600(16000)
14100(8200)
22500(13050)
28600(16600)
29100(16900)
15700(9100)
5200
6100
4900
6400
6900
7000
3200
6700
6400
73
84
68
88
94
95
44
92
89
93
93
96
98
20
42
41
64
77
81
23
76
68
82
79
79
80
84
72
75
88
70
81
94
77
85
88
67
87
98
30
58
90
73
58
76
69
66
76
1.86
35.64
1.89
1.18
2.87
1.14
2.16
1.14
1.17
1.19
1.25
1.25
1.54
1.56
1.30
1.15
1.11
1.41
1.23
1.38
1.26
1.22
1.32
1.34
1.14
1.37
1.06
1.24
1.27
3.99
1.11
1.17
1.25
1.30
1.17
3
4f
5g
6
7h
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
50 : 1
75 : 1
6800
10100
13900
17800
20700
13200
6300
6600
12800
7100
7000
12500
7000
7100
13900
6900
100 : 1
125 : 1
150 : 1
50(50)i : 1
100 : 2
200 : 4
50(50)i : 1
100 : 2
200 : 4
50(50)i : 1
100 : 2
200 : 4
50(50)i : 1
100 : 2
200 : 4
100 : 1
100 : 1
100 : 1
100 : 1
50 : 0
95
94(91)
86
90
89(88)
97
98
91(86)
96
97
96(96)
95
5
15(15)
15
15
25(25)
20
20
15(15)
15
15
2
5
15
30
10
10
10
7100
6300
99
43
73
95
95
93
92
95
10600
13800
13800
6800
10100
13800
12800
7200
75 : 0
100 : 0
50(50)i : 0
100 : 1
10(10)
10
95(88)
98
a In 10 mL CH2Cl2. [Li]0= 0.01 M. b Obtained from GPC analysis and calibrated by polystyrene standard. Values in parentheses are the values obtained
from GPC × 0.58.10 c Calculated from [M(lactide) × ([M]0/[Li]0) × conversion yield/([BnOH]eq)] + M(BnOH). d Obtained from 1H NMR analysis.
e Isolated yield. f In 10 mL toluene. g In 10 mL THF. h [BnOH] was replaced with [IPA]. i The values in parentheses are the second portion of monomers
added after the polymerization of the first addition had gone to completion.
Fig. 5, peaks are almost the same as those found on the 1H NMR
spectra of polymers produced by lithium benzyl oxide initiators
bearing bulky bis-phenolate ligands,5a,c and are assignable to the
corresponding protons in the proposed structure.
Additionally, only one methine peak was found in the decoupled
1H NMR spectrum of the products, as shown in Fig. S2 of ESI,†
indicating that no significant racemization occurred during the
polymerization of L-lactide initiated by the “in situ” manner.11
Mechanistic study for lithium amino phenolate complexes
In order to study the pathway of ROP of polyesters for the system
discussed above, compound 5 and 2.2 molar equivalents of BnOH
were mixed in diethyl ether solution to afford 7 as crystalline solid
after slow evaporation of volatiles, as shown in Scheme 2.
Compound 7 is characterized by NMR spectroscopy as well as
microanalyses. Similar to 5, several sets of diastereotopic signals
corresponding to the methylene protons of N–CH2–aryl and N–
(CH2)2–OMe are found on the 1H NMR spectrum. A singlet
Fig. 5 1H NMR spectrum of PLA-50 initiated by 6 and BnOH in CDCl3.
resonance corresponding to the coordinated BnOH molecule
1
(HOCH2Ph) is found at 4.70 ppm on the H NMR spectrum;
amino phenolate ligand at room temperature. A reasonable ratio
is observed upon cooling to −60 C. Therefore low-temperature
◦
however, with lower ratio compared to the integral intensities of
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 3502–3510 | 3505
©

NMR data are reported for 7. The molecular structure of 7 is
depicted in Fig. 6.
Scheme 2
Fig. 7 Two symmetry related molecules of 7 bridged via intermolecular
hydrogen bonds to form a dinuclear structure. Only the hydrogen atom on
the oxygen atom of BnOH is shown.
those using the “in situ” route. The spectroscopic studies also
demonstrate polymers prepared from those two conditions are
capped with benzyl alkoxy groups, as shown in Fig. 8. However,
poor stereocontrol was observed by using 5/BnOH or 7 as
initiating systems in ROP of rac-lactide ([M]0/[Li]0= 50) with Pr
values equal to 0.58 (for 5/BnOH) and 0.60 (for 7).
˚
Fig. 6 Molecular structure of 7. Selected bond lengths (A) and bond
angles (◦): Li–O(1), 1.856(4); Li–O(2), 2.039(4); Li–O(3), 1.898(4); Li–N,
2.124(4); O(1)–Li–O(2), 126.6(2); O(1)–Li–O(3), 115.6(2); O(2)–Li–O(3),
110.4(2); O(1)–Li–N, 96.41(18); O(2)–Li–N, 83.05(16); O(3)–Li–N,
119.5(2). Only the hydrogen atom on the oxygen atom of BnOH is
exhibited.
Compound 7 can be described as monomer–BnOH adduct
with a four–coordinate lithium metal center bonded to one
nitrogen atom of the central amine, one oxygen atom of pendant
functionality, one oxygen atom of phenolate and one oxygen
˚
atom of BnOH. The bond distances of Li–Namine (2.124(4) A),
˚
˚
Li–OOMe (2.039(4) A) and Li–Ophenolate (1.856(4) A) are similar to
those discussed above. The bond distance of Li–OBnOH (1.898(4)
˚
˚
A) is in the range of those (1.897(4) and 1.981(8) A) found in
the literature.5c Although only a mononuclear lithium complex
is found in the unit cell, however, hydrogen bonding between
the hydrogen atom of BnOH and oxygen atom of phenolate
was expected. A dinuclear geometry is observed upon increasing
the van der Waals radius of the hydrogen atom of BnOH up to
˚
1.68 A. Two molecules of 7 from different unit cells are bridged
via intermolecular hydrogen bonds to form a dinuclear structure
with a nearly linear OBnOH–H–OPhenolate angle at 167◦, as shown in
Fig. 7.
The molecular structure of 7 reveals that neither ligand disso-
ciation nor metal alkoxide formation could occur in the presence
of added BnOH. The catalytic activity of 7 was examined and
results are given in Table 1 (entries 31–35). Compound 7 shows
both living and immortal properties in ROP. The reactivity of
7 and the properties of polymer produced by 7 are similar to
Fig. 8 1H NMR spectra of PLA-50 initiated by (A) 5/BnOH or (B) 7 in
CDCl3.
3506 | Dalton Trans., 2008, 3502–3510
This journal is
The Royal Society of Chemistry 2008
©

Scheme 3
On the basis of these results, the alcohol initiator could be
activated by the metal center first, followed by the insertion of
the benzyl alkoxy group to the carbonyl group of L-lactide leading
to ring opening polymerization, as shown in Scheme 3.
in THF at 35 ◦C with a Waters 1515 isocratic HPLC pump, a
Waters 2414 refractive index detector, and Waters Styragel column
(HR4E). Molecular weights and molecular weight distributions
were calculated using polystyrene as standard.
In conclusion, several dinuclear lithium complexes (3–6) sup-
ported by pendant aminophenolate ligands have been prepared
and fully characterized. They all demonstrate efficient activity in
catalyzing ring opening polymerization of L-lactide in the presence
of benzyl alcohol at 26.5 ◦C with both living-controlled and
immortal characters. Among them, the complex bearing amino
phenolate with pendant amino functionality seems to exhibit
better catalytic activity than those with pendant methoxy or
thioether functionalities. The solid-state and catalytic studies of
the monomer–BnOH adduct 7 reveal that the mechanism for
the preparation of polyesters can be proposed in terms of the
alcohol initiator being activated by the metal center first, followed
by insertion of benzyl alkoxy group to the carbonyl group of L-
lactide leading to ring opening polymerization for this lithium
amino phenolate system.
2,4-Di-tert-butylphenol (Acros), 2-methoxybenzylamine (98%,
Lancaster), N-(2-methoxyethyl)methylamine (TCI), formalde-
hyde (Union, 24 wt%) and anhydrous magnesium sulfate
(99%, Showa) were used as received. Benzyl alcohol was
dried over anhydrous magnesium sulfate and distilled be-
fore use. L-Lactide was recrystallized from toluene prior to
use. nBuLi (2.5 M in hexane, Acros) was used as sup-
plied. 2-Methylthiobenzylamine12 and 2,4-di-tert-butyl-6-{[(2ꢀ-
dimethylaminoethyl)methylamino]methyl}phenol (HONMeCNMe2
)
were prepared according to previously reported procedures.4b
Preparations
6,8-Di-tert-butyl-3-[2-(methoxy)benzyl]-3,4-dihydro-2H -1,3-
benzoxazine (1). 2,4-Di-tert-butylphenol (2.06 g, 10 mmol), 2-
methoxybenzylamine (1.30 ml, 10 mmol), and formaldehyde
(2.3 ml, 20 mmol) were dissolved in ethanol (30 ml). The solution
was heated at reflux for 72 h and then cooled to room temperature.
All the volatiles were removed under reduced pressure. The crude
product was washed with 15 ml ethanol to afford a white powder.
Experimental
All manipulations were carried out under an atmosphere of dini-
trogen using standard Schlenk-line or drybox techniques. Solvents
were refluxed over the appropriate drying agent and distilled prior
to use. Ethanol (95%) was used as received. Deuterated solvents
were dried over molecular sieves.
1
Yield, 3.44 g, 93.4%. H NMR (600 MHz): d 1.28 (s, 9H, Ar-C-
(CH3)3), 1.40 (s, 9H, Ar-C-(CH3)3), 3.82 (s, 3H, OCH3), 3.92, 4.06,
4.85 (three singlets, 6H, one for N(CH2)ArOMe, one for N(CH2)O,
one for N(CH2)ArOH), 6.79 (d, 1H, C6H2, J = 3.0 Hz), 6.89 (d, 1H,
CH–Ph, J = 8.4 Hz), 6.95 (t, 1H, CH–Ph, J = 7.8 Hz), 7.16 (d,
1H, C6H2, J = 2.4 Hz), 7.27 (m, 1H, CH–Ph), 7.34 (m, 1H, CH–
1
1H and 13C{ H} NMR spectra were recorded either on a
Varian Mercury-400 (400 MHz) or a Varian Inova-600 (600 MHz)
spectrometers in chloroform-d at ambient temperature unless
stated otherwise and referenced internally to the residual solvent
peak and reported as parts per million relative to tetramethylsilane.
1
Ph). 13C{ H} NMR (150 MHz): d 29.7 (s, Ar-C-(CH3)3), 31.6 (s,
Ar-C-(CH3)3), 34.2 (s, Ar-C-(CH3)3), 34.9 (s, Ar-C-(CH3)3), 50.0
(s, CH2), 51.2 (s, CH2), 55.5 (s, OCH3), 81.0 (s. CH2), 110.5, 120.3,
121.8, 122.0, 128.5, 130.8 (s, CH-Ph), 119.1, 126.5, 136.5, 141.9,
150.6, 158.0 (s, tert-C). Anal. Calc. for C24H33NO2: C, 78.43; H,
9.05; N, 3.81. Found: C, 78.19; H, 8.89; N, 3.55%.
1
7Li{ H} NMR spectra were referenced externally to LiCl in
DMSO-d6 at d 0. Elemental analyses were performed by Elementar
Vario ELIV instrument. The GPC measurements were performed
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 3502–3510 | 3507
©

6,8-Di-tert-butyl-3-[2-(methylthio)benzyl]-3,4-dihydro-2H-1,3-
benzothiazine (2). 2,4-Di-tert-butylphenol (2.06 g, 10 mmol),
2-methythiobenzylamine (1.57 g, 10 mmol), and formaldehyde
(2.3 ml, 20 mmol) were dissolved in ethanol (30 ml). The solution
was heated at reflux for 72 h and then cooled to room temperature.
All the volatiles were removed under reduced pressure. The crude
product was washed with 10 ml ethanol to afford a white powder.
2,4-Di-tert-butyl-6-{[(2-methoxyethyl)methylamino]methyl}-
phenol (HONMeCOMe). To
flask containing 2,4-di-tert-
a
butylphenol (4.12 g, 20 mmol), MgSO4 (3 g, 25 mmol), N-(2-
methoxyethyl)methylamine (2.14 ml, 20 mmol) and formaldehyde
(2.74 ml, 20 mmol), 30 ml ethanol was added. The solution was
heated at reflux for 5 days and then cooled to room temperature.
The reaction mixture was filtered and the volatiles were removed
under reduced pressure to afford a yellow oil. Yield, 5.5 g, 88%.
1H NMR (600 MHz): d 1.28 (s, 9H, Ar-C-(CH3)3), 1.42 (s, 9H, Ar-
C-(CH3)3), 2.36 (s, 3H, NCH3), 2.68 (t, 2H, N-(CH2)2-OMe, J =
5.4 Hz), 3.33 (s, 3H, OCH3), 3.54 (t, 2H, N-(CH2)2-OMe, J = 6.0
Hz), 3.71 (s, 2H, N–CH2-Ar), 6.82 (d, 2H, C6H2, J = 2.4 Hz), 7.21
1
Yield, 2.6 g, 67%. H NMR (600 MHz): d 1.29 (s, 9H, Ar-C-
(CH3)3), 1.42 (s, 9H, Ar-C-(CH3)3), 2.48 (s, 3H, SCH3), 3.98, 4.06
(two broads, 4H, one for N(CH2)O, one for N(CH2)Artert-Butyl),
4.84 (s, 2H, N(CH2)ArSMe), 6.81 (d, 1H, C6H2, J = 2.4 Hz), 7.14
(t, 1H, CH–Ph, J = 7.8 Hz), 7.19 (d, 1H, C6H2, J = 1.8 Hz),
1
7.26–7.32 (overlap, 3H, CH–Ph). 13C{ H} NMR (150 MHz): d
1
(d, 2H, C6H2, J = 2.4 Hz). 13C{ H} NMR (150 MHz): d 29.6 (s,
15.7 (s, SCH3), 29.6 (s, Ar-C-(CH3)3), 31.5 (s, Ar-C-(CH3)3), 34.2
(s, Ar-C-(CH3)3), 34.9 (s, Ar-C-(CH3)3), 50.9 (s, CH2), 53.7 (s,
CH2), 80.6 (s, N(CH2)ArSMe), 122.0, 124.5, 125.3, 128.1, 130.1 (s,
CH-Ph), 118.8, 135.9, 136.6, 139.2, 142.1, 150.5 (s, tert-C). Anal.
Calc. for C24H33NOS: C, 75.15; H, 8.67; N, 3.65. Found: C, 75.11;
H, 8.80; N, 3.69%.
Ar-C-(CH3)3), 31.7 (s, Ar-C-(CH3)3), 34.1 (s, Ar-C-(CH3)3), 34.8
(s, Ar-C-(CH3)3), 42.0 (s, NCH3), 55.5 (s, N-(CH2)2-OMe), 58.7
(s, OCH3), 62.2 (s, N-(CH2)2-OMe), 70.3 (s, N-CH2-Ar), 122.8,
123.3 (s, CH-Ph), 121.3, 135.6, 140.3, 154.3 (s, tert-C). Anal. Calc.
for C19H33NO2: C, 74.22; H, 10.82; N, 4.56. Found: C, 74.26; H,
10.92; N, 4.38%.
(LiONMePhOMe)2 (3). To a solution of HONMePhOMe (1.24 g,
3.36 mmol) in 20 ml Et2O, 1.48 ml n-BuLi (2.5 M in hexane,
3.7 mmol) was added dropwise at 0 ◦C. The reaction mixture was
warmed to room temperature and reacted for 6 h. The resulting
mixture was filtered and the filtrate was pumped to dryness. The
residue was washed with 20 ml hexane to afford a white powder.
Yield, 0.55 g, 22%. Crystals suitable for X-ray crystallographic
analysis were grown from concentrated hexane solution at −24 ◦C.
1H NMR (600 MHz): d 1.24 (s, 18H, two Ar-C-(CH3)3), 1.30 (s,
18H, two Ar-C-(CH3)3), 2.02 (s, 6H, NCH3), 2.42 (d, 2H, N–CH2-
Ar, J = 12.6 Hz), 2.82 (d, 2H, N–CH2-Ar, J = 11.4 Hz), 3.95 (s,
6H, OCH3), 4.08 (d, 2H, N–CH2-Ar, J = 12.6 Hz), 4.37 (d, 2H, N–
CH2-Ar, J = 10.8 Hz), 6.85 (d, 2H, C6H2, J = 3.0 Hz), 6.89 (t, 2H,
CH–Ph, J = 7.2 Hz), 6.94 (d, 2H, CH–Ph, J = 7.8 Hz), 7.05 (m,
2H, CH–Ph), 7.10 (d, 2H, C6H2, J = 3.0 Hz), 7.24 (m, 2H, CH–
2,4-Di-tert-butyl-6-{[(2-methoxybenzyl)methylamino]methyl}-
phenol (HONMePhOMe). To a flask containing LiAlH4 (0.38 g,
10 mmol) and 15 ml THF, a solution containing 1 (1.84 g, 5 mmol)
◦
in 15 ml THF was added dropwise at 0 C. After 7 h of stirring,
the resulting mixture was quenched with deionized water, followed
by extraction with ether to afford a yellow crystalline solid. Yield,
1.51 g, 81.6%. 1H NMR (600 MHz): d 1.28 (s, 9H, Ar-C-(CH3)3),
1.42 (s, 9H, Ar-C-(CH3)3), 2.17 (s, 3H, NCH3), 3.65, 3.72 (two
br, 4H, one for N(CH2)ArOMe, one for N(CH2)ArOH), 3.87 (s, 3H,
OCH3), 6.84 (d, 1H, C6H2, J = 2.4 Hz), 6.89 (d, 1H, CH–Ph,
J = 8.4 Hz), 6.92 (t, 1H, CH–Ph, J = 7.2 Hz), 7.19 (d, 1H, C6H2,
J = 2.4 Hz), 7.23 (m, 1H, CH–Ph), 7.27 (m, 1H, CH–Ph), 11.16
1
(br, 1H, OH). 13C{ H} NMR (150 MHz): d 29.6 (s, Ar-C-(CH3)3),
31.7 (s, Ar-C-(CH3)3), 34.1 (s, Ar-C-(CH3)3), 34.9 (s, Ar-C-(CH3)3),
40.7 (s, NCH3), 55.1 (s, OCH3), 56.2 (s, CH2), 61.8 (s, CH2), 110.4,
120.2, 122.6, 123.3, 128.9, 131.3 (s, CH-Ph), 121.6, 125.4, 135.3,
140.0, 154.5, 158.2 (s, tert-C). Anal. Calc. for C24H35NO2: C, 78.00;
H, 9.55; N, 3.79. Found: C, 77.74; H, 9.05; N, 3.77%.
1
Ph). 13C{ H} NMR (150 MHz): d 30.1 (s, Ar-C-(CH3)3), 32.0 (s,
Ar-C-(CH3)3), 33.7 (s, Ar-C-(CH3)3), 35.1 (s, Ar-C-(CH3)3), 43.0 (s,
NCH3), 56.1 (s, N-CH2-Ar), 57.34 (s, OCH3), 64.1 (s N-CH2-Ar),
113.1, 121.9, 123.2, 126.9, 128.7, 131.6 (s, CH-Ph), 123.9, 127.6,
7
1
132.5, 135.9, 156.7, 164.2 (s, tert-C). Li{ H} NMR (233 MHz,
0.3M in toluene-d8): d 2.64. Anal. Calc. for C48H68Li2N2O4: C,
76.77; H, 9.13; N, 3.73. Found: C, 76.12; H, 9.31; N, 4.25%.
2,4-Di-tert-butyl-6-{[(2-methylthiobenzyl)methylamino]methyl}-
phenol (HONMePhSMe). To a flask containing LiAlH4 (0.12 g,
3.0 mmol) and 15 ml THF, a solution containing 2 (0.57 g,
◦
1.5 mmol) in 15 ml THF was added dropwise at 0 C. After 7 h
(LiONMePhSMe)2 (4). To a solution of HONMePhSMe (1.64 g,
4.3 mmol) in 20 ml Et2O, 1.87 ml n-BuLi (2.5 M in hexane,
4.68 mmol) was added dropwise at 0 ◦C. The reaction mixture was
warmed to room temperature and reacted overnight. After 23 h of
stirring, the volatiles were removed under reduced pressure. The
residue was washed with 5 ml hexane to afford a white powder.
Yield, 0.954 g, 28.7%. Crystals suitable for X-ray crystallographic
analysis were grown from concentrated hexane solution at room
of stirring, the resulting mixture was quenched with deionized
water, followed by extraction with ether to afford a yellow
crystalline solid. Yield, 0.37 g, 65.5%. Crystals suitable for X-ray
crystallographic analysis were grown from slow evaporation of
1
hexane solution at room temperature. H NMR (600 MHz): d
1.28 (s, 9H, Ar-C-(CH3)3), 1.42 (s, 9H, Ar-C-(CH3)3), 2.22 (s,
3H, NCH3), 2.48 (s, 3H, SCH3), 3.69, 3.75 (two singlets, 4H,
one for N(CH2)ArOMe, one for N(CH2)ArOH), 6.86 (s, 1H, C6H2),
7.14 (m, 1H, CH–Ph), 7.20 (s, 1H, C6H2), 7.25 (m, 2H, CH–Ph),
1
temperature. H NMR (600 MHz): d 1.20 (s, 18H, two Ar-C-
(CH3)3), 1.24 (s, 18H, two Ar-C-(CH3)3), 2.12 (s, 6H, NCH3), 2.23
(s, 6H, SCH3), 2.59 (d, 2H, N–CH2–Ar, J = 12.6 Hz), 2.83 (d, 2H,
N–CH2-Ar, J = 11.4 Hz), 4.15 (d, 2H, N–CH2–Ar, J = 12.6 Hz),
4.31 (d, 2H, N–CH2–Ar, J = 10.8 Hz), 6.89 (d, 2H, C6H2, J = 3.0
Hz), 7.04–7.11 (m, 8H (2H for C6H2, 6H for CH–Ph)), 7.23 (m,
1
7.30 (d, 1H, CH–Ph, J = 7.2 Hz), 11.61 (br, 1H, OH). 13C{ H}
NMR (150 MHz): d 16.1 (s, SCH3), 29.6 (s, Ar-C-(CH3)3), 31.7 (s,
Ar-C-(CH3)3), 34.1 (s, Ar-C-(CH3)3), 34.8 (s, Ar-C-(CH3)3), 41.1
(s, NCH3), 58.8 (s, CH2), 62.0 (s, CH2), 122.8, 123.5, 125.0, 126.0,
128.1, 130.2 (s, CH-Ph), 121.4, 135.36, 135.38, 138.6, 140.4, 154.1
(s, tert-C). Anal. Calc. for C24H35NOS: C, 74.75; H, 9.15; N, 3.63.
Found: C, 74.77; H, 8.94; N, 3.57%.
1
2H, CH–Ph). 13C{ H} NMR (150 MHz): d 14.0 (s, SCH3), 29.4
(s, Ar-C-(CH3)3), 32.0 (s, Ar-C-(CH3)3), 33.7 (s, Ar-C-(CH3)3),
34.8 (s, Ar-C-(CH3)3), 43.6 (s, NCH3), 58.4 (s, N-CH2-Ar), 63.6
3508 | Dalton Trans., 2008, 3502–3510
This journal is
The Royal Society of Chemistry 2008
©

(s N-CH2-Ar), 123.2, 125.0, 125.3, 126.7, 128.3, 131.9 (s, CH-
N-(CH2)2-NMe2), 2.86 (d, 2H, N–CH2-Ar, J = 10.8 Hz), 4.18 (d,
2H, N–CH2-Ar, J = 10.8 Hz), 6.83 (d, 2H, C6H2, J = 3 Hz),
7
1
Ph), 123.5, 132.8, 135.6, 135.8, 136.0, 163.7 (s, tert-C). Li{ H}
NMR (233 MHz, 0.15 M in toluene-d8): d 2.93. Anal. Calc. for
C48H68Li2N2O2S2: C, 73.62; H, 8.75; N, 3.58. Found: C, 73.95; H,
8.59; N, 3.74%.
1
7.13 (d, 2H, C6H2, J = 3 Hz). 13C{ H} NMR (150 MHz): d 30.1
(s, Ar-C-(CH3)3), 32.0 (s, Ar-C-(CH3)3), 33.7 (s, Ar-C-(CH3)3),
35.4 (s, Ar-C-(CH3)3), 44.7 (s, N-CH3), 46.2 (s, N(CH3)2), 49.7
(s, N-(CH2)2-NMe2), 58.3 (s, N-(CH2)2-NMe2), 62.7 (s, N-CH2-
Ar), 123.0 (s, CH-Ph), 127.0 (s, CH-Ph), 124.6, 132.3, 136.2, 165.1
(LiONMeCOMe
)
(5). To a solution of HONMeCOMe (11.5 g,
2
37.4 mmol) in 50 ml Et2O, 19.4 ml n-BuLi (2.5 M in hexane,
48.5 mmol) was added dropwise at 0 ◦C. The reaction mixture was
warmed to room temperature and reacted overnight. After 18 h of
stirring, the volatiles were removed under reduced pressure. The
residue was washed with 30 ml hexane to afford white powder.
Yield, 8.07 g, 34.5%. Crystals suitable for X-ray crystallographic
analysis were grown from concentrated hexane solution at room
temperature. 1H NMR (600 MHz): d 1.28 (s, 18H, Ar-C-(CH3)3),
1.42 (s, 18H, Ar-C-(CH3)3), 2.34 (s, 6H, NCH3), 3.14 (s, 6H,
OCH3), 2.23, 2.74, 2.86, 2.93, 3.32, 4.13 (six br (two for N–CH2-
Ar, four for N-(CH2)2-OMe), 12H (4H for N–CH2-Ar, 8H for
N-(CH2)2-OMe)), 6.85 (d, 2H, C6H2, J = 2.4 Hz), 7.17 (d, 2H,
1
(s, tert-C). 7Li{ H} NMR (233 MHz, 0.3M in toluene-d8): d 2.40.
Anal. Calc. for C40H70Li2N4O2: C, 73.58; H, 10.81; N, 8.58. Found:
C, 73.66; H, 10.68; N, 8.72%.
(BnOH)LiONMeCOMe (7). To
a solution of 5(0.319 g,
0.509 mmol) in 15 ml Et2O, benzyl alcohol (0.110 g, 1.02 mmol)
was added at room temperature. All the volatiles were removed
under slow evaporation to afford a colorless crystalline solid.
Yield, 0.404 g, 94.0%. H NMR (600 MHz, −60 ◦C): d 1.28 (s,
1
9H, Ar-C-(CH3)3), 1.42 (s, 9H, Ar-C-(CH3)3), 2.23, 2.75, 2.83,
3.35 (four br for N-(CH2)2-OMe), 4H), 2.35 (s, 3H, NCH3), 2.93
(d, 1H, N–CH2-Ar, J = 11.4 Hz), 3.17 (s, 3H, OCH3), 4.12 (d, 1H,
N–CH2-Ar, J = 10.2 Hz), 4.72 (s, 2H, HO–CH2-Ph), 6.89 (d, 1H,
C6H2, J = 2.4 Hz), 7.16 (d, 1H, C6H2, J = 2.4 Hz), 7.35–7.44 (m,
1
C6H2, J = 2.4 Hz). 13C{ H} NMR (150 MHz): d 29.7 (s, Ar-
C-(CH3)3), 32.0 (s, Ar-C-(CH3)3), 33.7 (s, Ar-C-(CH3)3), 35.0 (s,
Ar-C-(CH3)3), 45.3 (s, NCH3), 58.8 (s, OCH3), 53.5, 63.5, 70.0 (s,
CH2), 123.1, 126.0 (s, CH-Ph), 124.7, 132.3, 136.1, 164.5 (s, tert-
◦
1
5H, HO–CH2-Ph). 13C{ H} NMR (150 MHz, −60 C): d 29.2 (s,
Ar-C-(CH3)3), 31.8 (s, Ar-C-(CH3)3), 33.6 (s, Ar-C-(CH3)3), 34.9
(s, Ar-C-(CH3)3), 45.2 (s, NCH3), 58.9 (s, OCH3), 65.0 (s, O-CH2-
Ph), 52.9, 63.1, 69.6 (s, CH2), 122.8, 125.9, 126.9, 127.5, 128.4
1
C). 7Li{ H} NMR (233 MHz, 0.3M in toluene-d8): d 2.37. Anal.
Calc. for C38H64Li2N2O4: C, 72.81; H, 10.29; N, 4.47. Found: C,
73.23; H, 9.67; N, 4.61%.
7
1
(s, CH-Ph), 124.6, 131.7, 135.4, 140.4, 164.1 (s, tert-C). Li{ H}
NMR (233 MHz, 0.3M in toluene-d8): d −2.62. Anal. Calc. for
C26H40LiNO3: C, 74.08; H, 9.56; N, 3.32. Found: C, 74.65; H, 9.51;
N, 3.25%.
(LiONMeCNMe2
)
(6). To a solution of HONMeCNMe2 (2.0 g,
2
6.24 mmol) in 30 ml Et2O, 2.75 ml n-BuLi (2.5M in hexane,
6.87 mmol) was added dropwise at 0 ◦C. The reaction mixture
was warmed to room temperature and reacted overnight. After
21 h of stirring, the reaction mixture was filtered and the volatiles
were removed under reduced pressure to afford a white powder.
Polymerization studies. Typically, to a flask containing a
prescribed amount of L-lactide and catalyst (0.05 mmol for 3–6;
0.1 mmol for 7) was added a solution (10 ml in CH2Cl2) containing
a prescribed amount of benzyl alcohol. The reaction mixture was
1
Yield, 1.71 g, 42.0%. H NMR (600 MHz): d 1.27 (s, 18H, Ar-
◦
C-(CH3)3), 1.44 (s, 18H, Ar-C-(CH3)3), 1.65 (m, 2H, N-(CH2)2-
NMe2), 1.88 (m, 14H; 12H for N-(CH3)2, 2H for N-(CH2)2-NMe2),
2.27 (s, 6H, N-CH3), 2.42 (m, 2H, N-(CH2)2-NMe2), 2.82 (m, 2H,
stirred at 26.5 C for the prescribed time. After the reaction was
quenched by the addition of 10 ml acetic acid solution (0.35 M), the
resulting mixture was poured into 50 ml n-heptane to precipitate
Table 2 Summary of crystal data for compounds HONMePhSMe, 3–5 and 7
HONMePhSMe
C24H35NOS
385.59
293(2)
Monoclinic
3
4
5
7
Formula
Mr
C48H68Li2N2O4
750.92
C48H68Li2N2O2S2
783.04
C38H64Li2N2O4
626.79
C26H40LiNO3
421.53
293(2)
T/K
293(2)
Triclinic
P1
293(2)
Triclinic
P1
293(2)
Monoclinic
P21/c
Crystal system
Space group
Triclinic
P1
¯
¯
¯
P21/c
˚
a/A
14.4226(12)
9.8356(9)
17.4956(15)
90
108.763(2)
90
2349.9(4)
4
1.090
9.6656(8)
10.6883(9)
10.9810(9)
96.694(2)
90.990(2)
92.233(2)
1125.57(16)
1
1.108
0.068
6425
253
12.726(2)
13.834(2)
18.762(3)
72.370(3)
72.813(4)
65.937(3)
2817.7(9)
2
0.923
0.125
15649
532
18.434(3)
17.666(3)
12.896(2)
90
105.790(4)
90
4041.2(12)
4
1.030
10.3335(10)
10.6740(11)
12.8376(13)
99.290(2)
90.890(2)
112.650(2)
1284.9(2)
2
1.089
0.069
7371
284
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
Dc/Mg m−3
l(Mo-Ka)/mm−1
Reflections collected
No. of parameters
0.150
12881
244
0.064
45212
455
Indep. reflns (Rint
)
4594 (0.0299)
0.0504, 0.1483
0.0766, 0.1658
1.036
4358 (0.0381)
0.0746, 0.2144
0.0892, 0.2336
0.996
10729 (0.0185)
0.0625, 0.1710
0.0924, 0.1893
1.140
7913 (0.0635)
0.0668, 0.1773
0.1381, 0.2160
1.154
4984 (0.0189)
0.0644, 0.1918
0.0969, 0.2149
1.199
a
Final R indices R1a, wR2
R indices (all data)
GoFb
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
a R1 = [ |Fo| − |Fc|]/ |Fo|]; wR2 = [ w(Fo − Fc2)2/ w(Fo2)2]1/2; w = 0.10. b GoF = [ w(Fo − Fc2)2/(Nrflns − Nparams)]1/2
.
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 3502–3510 | 3509
©

PLL (poly-L-lactide). Crude products were recrystallized from
THF–hexane and dried in vacuo up to a constant weight.
J.-F. Carpentier, Chem. Commun., 2004, 330; (f) F. M. Kerton, A. C.
Whitwood and C. E. Willans, Dalton Trans., 2004, 2237; (g) P.
Hormnirun, E. L. Marshall, V. C. Gibson, A. J. P. White and D. J.
Williams, J. Am. Chem. Soc., 2004, 126, 2688; (h) Y. Yao, M. Ma, X. Xu,
Y. Zhang, Q. Shen and W.-T. Wong, Organometallics, 2005, 24, 4014;
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Crystal structure data
Crystals were grown from slow evaporation of diluted solution
(hexane for HONMePhSMe, diethyl ether for 7) or concentrated
hexane solution (3–5), and isolated by filtration. Suitable crystals
of 3, 4, 5 or 7 were sealed in thin-walled glass capillaries under
a nitrogen atmosphere and mounted on a Bruker AXS SMART
1000 diffractometer. The absorption correction was based on the
symmetry equivalent reflections using the SADABS program. The
space group determination was based on a check of the Laue
symmetry and systematic absences and was confirmed using the
structure solution. The structure was solved by direct methods
using a SHELXTL package. All non-H atoms were located from
successive Fourier maps, and hydrogen atoms were refined using
a riding model. Anisotropic thermal parameters were used for
all non-H atoms, and fixed isotropic parameters were used for H
atoms. Some details of the data collection and refinement are given
in Table 2.
CCDC reference numbers 646484–646487
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b717370a
Acknowledgements
Financial support from the National Science Council (grant num-
ber NSC 95–2113-M-005–010-MY3) and Ministry of Education
(under the ATU plan), Taiwan, ROC, are appreciated.
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3510 | Dalton Trans., 2008, 3502–3510
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