Calcium complexes containing oxalamidinate ligands as catalysts for ε-caprolactone polymerization

Article abstract of DOI:10.1039/c2dt32300a

A series of calcium complexes containing oxalamidinate ligands is described. Reactions of oxalamidinate ligand precursors, [PhNC{NH(CH ₂)₂OMe}-C{NH(CH₂)₂OMe}NPh] (1), [PhNC{NH(CH₂)₂NMe₂}-C{NH(CH₂) ₂NMe₂}NPh] (2), [Ph^TriMeNC{NH(CH ₂)₂OMe}-C{NH(CH₂)₂OMe}NPh ^TriMe] (3), [Ph^TriMeNC{NH(CH₂) ₂SMe}-C{NH(CH₂)₂SMe}NPh^TriMe] (4), [Ph^TriMeNC{NHCH₂Py}-C{NHCH₂Py}NPh ^TriMe] (5), with two molar equivalents of Ca[N(SiMe₃) ₂]₂(THF)₂ gave calcium oxalamidinate complexes, [Ca{N(SiMe₃)₂}(THF)(PhN)C{N(CH₂) ₂OMe}-]₂ (6), [Ca{N(SiMe₃)₂}(THF) (PhN)C{N(CH₂)₂NMe₂}-]₂ (7), [Ca{N(SiMe₃)₂}(THF)(Ph^TriMeN)C{N(CH ₂)₂OMe}-]₂ (8), [Ca{N(SiMe₃) ₂}(THF)(Ph^TriMeN)C{N(CH₂)₂SMe}-] ₂ (9), [Ca{N(SiMe₃)₂}(THF)(Ph ^TriMeN)C{NCH₂Py}-]₂ (10), respectively. The molecular structure of complex 7 was further characterized by the single crystal X-ray diffraction technique. The catalytic activities of complexes 6-10 toward the ring opening polymerization of ε-caprolactone were studied. Complex 8 exhibited excellent activity for the polymerization of ε-caprolactone with controlled molecular weights and polydispersities.

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Calcium complexes containing oxalamidinate ligands
as catalysts for ε-caprolactone polymerization†
Cite this: Dalton Trans., 2013, 42, 9255
Tzu-Lun Huang and Chi-Tien Chen*
A series of calcium complexes containing oxalamidinate ligands is described. Reactions of oxalamidinate
ligand precursors, [PhNvC{NH(CH2)2OMe}–C{NH(CH2)2OMe}vNPh] (1), [PhNvC{NH(CH2)2NMe2}–C{NH-
(CH2)2NMe2}vNPh] (2), [PhTriMeNvC{NH(CH2)2OMe}–C{NH(CH2)2OMe}vNPhTriMe] (3), [PhTriMeNvC{NH-
] ] (5), with
(CH2)2SMe}–C{NH(CH2)2SMe}vNPhTriMe (4), [PhTriMeNvC{NHCH2Py}–C{NHCH2Py}vNPhTriMe
two molar equivalents of Ca[N(SiMe3)2]2(THF)2 gave calcium oxalamidinate complexes, [Ca{N(SiMe3)2}-
(THF)(PhN)C{N(CH2)2OMe}–]2 (6), [Ca{N(SiMe3)2}(THF)(PhN)C{N(CH2)2NMe2}–]2 (7), [Ca{N(SiMe3)2}(THF)-
(PhTriMeN)C{N(CH2)2OMe}–]2 (8), [Ca{N(SiMe3)2}(THF)(PhTriMeN)C{N(CH2)2SMe}–]2 (9), [Ca{N(SiMe3)2}(THF)-
(PhTriMeN)C{NCH2Py}–]2 (10), respectively. The molecular structure of complex 7 was further characterized
by the single crystal X-ray diffraction technique. The catalytic activities of complexes 6–10 toward the
ring opening polymerization of ε-caprolactone were studied. Complex 8 exhibited excellent activity for
the polymerization of ε-caprolactone with controlled molecular weights and polydispersities.
Received 1st October 2012,
Accepted 6th November 2012
DOI: 10.1039/c2dt32300a
www.rsc.org/dalton
rates and very good stereocontrol.6e Darensbourg also reported
calcium complexes with tridentate Schiff base ligands that
Introduction
Interest in producing environmentally friendly polymers which show excellent catalytic activity for ring opening polymeriz-
can be widely used in various applications has been attractive ation of trimethylene carbonate or lactide to produce high
mainly due to their biocompatible and biodegradable proper- molecular weight polymers with narrow polydispersities.6g
ties.1 One route for synthesizing biodegradable polymers using
Amidinate ligands, which have been reported for several
metal-based initiators/catalysts for ring opening polymeriz- decades and widely applied in the coordination chemistry of a
ation has proven to be an effective pathway.2 Although bio- diversity of metal complexes, can be easily tuned by variation
degradable polymers can easily be produced by using tin(II) of the substituents on either or both the N and C atoms. Many
octanoate as catalyst,3 however, the toxicity of the metal center amidinate ligands with various substituents have been syn-
and the poor control of the molecular weight of the polymers thesized and some of them have been applied in catalytic reac-
produced resulting from side reactions such as trans-esterifica- tions.10 Oxalamidinate ligands, which have similar coordination
tion encouraged researchers to develop new human-friendly type to amidinate ligands, have been attractive owing to the dis-
metal catalysts with a growing interest. Various metal com- covery of their versatile bonding modes and their application in
plexes have been applied in polymerizing cyclic esters and catalytic reactions for some metal complexes. They show the
these containing Zn,4 Mg,5 Ca,6 Na7 or Fe8 metal centers are potential to work as diimine,11 diimine–diamide,12 or amidi-
more attractive due to their participation in the human meta- nate13 ligands. Once the pendant functionality has been intro-
bolism. Among these, calcium metal is hard, inexpensive, bio- duced, the oxalamidinate ligands can act as ligands up to three-
compatible, and kinetically labile ion with a larger ionic radius coordinate; six-electron-donor on each side. Following our pre-
and Lewis acidity than Mg2+ or Zn2+ ions,9 some highly reactive vious studies on the aluminium and magnesium oxalamidinate
calcium complexes containing nitrogen-based auxiliary complexes,12e we report here some calcium complexes contain-
ligands have received increasing attention recently for their ing oxalamidinate ligands which can work as catalysts in cata-
successful application in ring opening polymerization reac- lyzing ring opening polymerization of ε-caprolactone.
tions.2 For example, Chisholm and co-workers reported a
series of calcium complexes that show excellent polymerization
Results and discussion
Department of Chemistry, National Chung Hsing University, Taichung 402, Taiwan.
Synthesis and characterization
E-mail: ctchen@dragon.nchu.edu.tw
Preparations of ligand precursors [PhNvC{NH(CH2)2OMe}–
C{NH(CH2)2OMe}vNPh] (1), [PhNvC{NH(CH2)2NMe2}–C{NH-
†CCDC 900478 for 7. For crystallographic data in CIF or other electronic format
see DOI: 10.1039/c2dt32300a
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Scheme 1 Preparation of ligand precursors.
(CH2)2NMe2}vNPh] (2) have been reported by the reactions of temperature. This indicates complexes are highly symmetric
bis(imidoyl)chloride with the relevant amines.12e Following species in solution. The elemental analysis data are also consist-
the previous established procedures, similar ligand precursors ent with a complex containing one coordinated THF on each
[PhTriMeNvC{NH(CH2)2OMe}–C{NH(CH2)2OMe}vNPhTriMe] (3), side.6c–e,k Suitable crystals for the structural determination of 7
[PhTriMeNvC{NH(CH2)2SMe}–C{NH(CH2)2SMe}vNPhTriMe
[PhTriMeNvC{NHCH2Py}–C{NHCH2Py}vNPhTriMe
]
(4), were obtained from concentrated hexane solution. The molecular
]
(5) were structure is depicted in Fig. 1. The structure also confirmed a
prepared straightforwardly by treatment of N1,N2-bis(2,4,6-tri- symmetric penta-coordinated calcium center with a planar amidi-
methylphenyl) oxaldiimidoyl dichloride with suitable amine or nate moiety on each side. Similar to the magnesium complexes
hydrochloride salts of amine in the presence of triethylamine discussed previously,12e deprotonated ligand precursor 2 acts as a
in refluxed THF, in high yield.14 All of these ligand precursors tridentate ligand. Each metal center is coordinated with two
are characterized by NMR spectroscopy as well as elemental nitrogen atoms from different amidinate units, one nitrogen
analyses. Syntheses and the proposed structures are summar- atom from pendant arm and one oxygen atom from coordinated
ized in Scheme 1. Treatment of these ligand precursors with THF. The geometry around the calcium center of 7 can be
two molar equivalents of Ca[N(SiMe3)2]2(THF)2 in THF affords described as distorted trigonal bipyramid with O and N(4) occu-
calcium complexes, [Ca{N(SiMe3)2}(THF)(PhN)C{N(CH2)2OMe}–]2 pying the axial positions (O–Ca–N(4) 143.94(6)°). The N(1), N(2)
(6), [Ca{N(SiMe3)2}(THF)(PhN)C{N(CH2)2NMe2}–]2 (7), [Ca{N- and N(3) atoms reside equatorially, however with different angles
(SiMe3)2}(THF)(PhTriMeN)C{N(CH2)2OMe}–]2 (8), [Ca{N(SiMe3)2}- (67.95(5)°, 90.66(5)°, 138.27(5)°) subtended by calcium.15 The
(THF)(PhTriMeN)C{N(CH2)2SMe}–]2
(9),
[Ca{N(SiMe3)2}(THF)- bond lengths of CNN units (N(1)–C(7A) = 1.342(2) Å) and N(2)–
(PhTriMeN)C{NCH2Py}–]2 (10), as shown in Scheme 2. The NMR C(7) = 1.315(2) Å) are similar, which might result from the deloca-
spectroscopy showed one singlet corresponding to the SiMe3 lization of π-electrons within the amidinate moiety.12e,13 The
group (δ 0.33 ppm for 6; δ 0.41 ppm for 7; δ 0.31 ppm for 8; δ bond lengths between calcium and nitrogen atoms of the oxala-
0.38 ppm for 9; δ 0.33 ppm for 10) and two multiplets corres- midinate ligand are relatively similar (2.3620(16) and 2.3736(16)
ponding to the coordinated THF (δ 1.07 and 3.25 ppm for 6; δ Å). The bond lengths of calcium amide (Ca–N(4) = 2.3358(16) Å)
1.14 and 3.28 ppm for 7; δ 1.25 and 3.35 ppm for 8; δ 1.16 and are close to those (2.512(2)–2.2863(12) Å) found in the litera-
3.27 ppm for 9; δ 1.10 and 3.28 ppm for 10) in each case at room ture.6a,c,d,i–k,n Moreover, this bond length is significantly shorter
Scheme 2 Preparation of calcium complexes.
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of ROP in this system. This might result from the interaction
between the calcium metal and dative atoms. We also exam-
ined the catalytic activity of Ca{N(SiMe3)2}2(THF)2 as catalyst in
the presence of benzyl alcohol (entry 10). It is worth noting
that introduction of oxalamidinate ligands could efficiently
enhance the catalytic activity. Complex 8 in the presence of
alcohol even demonstrates better activities than the [tmhd]/
iPrOH system6d and other calcium alkoxide systems.6a The
poor conversions demonstrated by 6 and 7 might result from
the solubility caused by the less bulky phenyl group. Therefore
the catalytic activities of complex 6 in the presence of benzyl
alcohol were examined in toluene, CH2Cl2 or THF within
1 min at 30 °C (entries 11–13). The conversion enhanced up to
99% in toluene whereas poor conversions were observed upon
using CH2Cl2 or THF as solvents. Due to the ease of prep-
aration and better controlled character, complex 8 was intro-
duced to examine the living and immortal characters under
optimized conditions. Experimental results exhibited that
complex 8 can work as a catalyst to initiate high monomer-to-
initiator ratios in the presence of benzyl alcohol accompanied
by increasing temperature and volume, with high conversions
of CL even up to [CL]0/[Ca]0 ratios of 1000, yielding PCLs with
a molecular weight as large as 114 000 in 240 min (entries
14–18). The linear relationship between the number-average
molecular weight (Mn) and the monomer-to-initiator ratio
([M]0/[I]0) demonstrated in Fig. 2 (entries 2, 14–18) implies the
“living” character of the polymerization process. In order to
examine the ‘immortal’ character, an increasing amount of
benzyl alcohol up to 40 equivalents has been investigated. The
produced polymers still exhibited good control of the polymer-
ization in terms of the agreement with experimental molecular
Fig. 1 Molecular structure of 7. Selected bond lengths (Å) and bond angles (°):
Ca–N(1) 2.3620(16), Ca–N(2) 2.3736(16), Ca–N(3) 2.5565(17), Ca–O 2.4348(14),
Ca–N(4) 2.3358(16), C(7)–C(7A) 1.540(14), N(1)–C(7A) 1.342(2), N(1)–C(1)
1.398(2), N(2)–C(7) 1.315(2), N(2)–C(8) 1.452(2); O–Ca–N(2) 90.66(5), N(2)–Ca–
N(4) 125.34(6), O–Ca–N(4) 143.94(6), N(2)–Ca–N(1) 67.95(5), N(1)–Ca–N(3)
138.27(5), N(2)–C(7)–N(1A) 130.68(17), N(2)–C(7)–C(7A) 115.1(2), N(1A)–C(7)–
C(7A) 114.1(2). Hydrogen atoms on carbon atoms omitted for clarity.
than that of calcium amine (Ca–N(3) = 2.5565(17) Å) due to
different electronic donating properties between the nitrogen
atom of the amidinate group and the nitrogen atom of the
pendant arm. The Ca–O bond length of coordinated THF (Ca–O
= 2.4348(14) Å) is longer than those found in the lierature.6c,d,i,k
Polymerization studies
Several calcium complexes are known as efficient catalysts/ weights (Mn) and the ratio of monomer to alcohol (entries
initiators in the ring opening polymerization of cyclic esters,6 19–22). The dependence of the experimental molecular
complexes 6–10 were introduced to examine the catalytic activi- weights (Mn) on the amount of added benzyl alcohol, for a
ties toward the ROP of ε-caprolactone. Representative results given [CL]0/[Ca]0 ratio of 600 (Fig. 3), evidences that [Ca]0/
are collected in Table 1. As usual polymerization of ε-caprolac- [BnOH] transfer takes place efficiently, since the molecular
tone was examined in toluene at 0 °C in the absence of benzyl weights of resulting polymers decrease with increasing quan-
alcohol for 1 min using 8 as catalyst (entry 1). Although the tities of alcohol, assuming that all the added alcohol mo-
isolated polycaprolactone demonstrated a narrow weight distri- lecules contribute to the “immortal” polymerization.16
bution, however, the molecular weight determined by GPC
The end group analysis is demonstrated by the 1H NMR
deviated largely from the theoretical value. A similar obser- spectrum of the polymer produced from ε-caprolactone and 8
vation was also reported by Feijen,6a,b indicating the amide with the ratio of [M]0 : [BnOH] = 30 (Table 1, entry 21), as
group was not a good initiator for the propagation step. Opti- shown in Fig. 4. Peaks are assignable to the corresponding
mized conditions were found to be toluene at 0 °C in the pres- protons in the proposed structure, indicating the ROP might
ence of benzyl alcohol after several trials on running be initiated with metal benzyl oxide complex first, followed by
polymerization of ε-caprolactone in dichloromethane, tetra- the ring cleavage of the acyl-oxygen bond to form a metal alk-
hydrofuran and toluene using 8 as catalyst (entries 2, 4–5). We oxide intermediate, which further reacts with excess lactones
also used 9-anthracenemethanol (9-AnOH) as an initiator to yield polyesters. The MALDI-TOF-MS analysis of a low mo-
(entry 3), however, with poor controlled behaviour. The same lecular weights PCLs (Mn(obsd) = 2200, Table 1, entry 22)
conditions were applied to examine the catalytic activities of clearly revealed a major population of PCLs unequivocally con-
the other four catalysts. Based on the experimental results, firmed as Na+·H{O(CH2)5C(O)}nOBn (Fig. 5). The degree of
complex 9 demonstrated similar activity to 8 within the same polymerization indicated by this spectrum (n = 16, Mn(ms) =
period, whereas complexes 6, 7 and 10 exhibited poor conver- 1958 g mol−1) is in good agreement with the experimental
sion within 1 min at 0 °C (entries 6–9). Based on the good con- value and the mass spectrum shows a cluster of homologous
versions demonstrated by 8 and 9, ligands with chalcogenide peaks separated by a molecular mass of ∼114 Da correspond-
pendant functionalities could enhance the catalytic activities ing to one ε-caprolactone repeating unit. No evidence for cyclic
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Table 1 Polymerization of ε-caprolactone using complexes 6–10 as catalysts in toluene if not otherwise stateda
Conv.d (%)
Yielde (%)
Mw/Mn
b
Entry
Catalyst
[M]0 : [Ca]0 : [BnOH]
T (°C)
t (min)
Mnb (obsd)
Mnc (calcd)
1
8
8
8
8
8
6
7
9
200 : 1 : 0
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
400 : 1 : 2
200 : 1 : 1
200 : 1 : 1
200 : 1 : 1
400 : 1 : 1
600 : 1 : 1
600 : 1 : 1
800 : 1 : 1
1000 : 1 : 1
600 : 1 : 5
600 : 1 : 10
600 : 1 : 20
600 : 1 : 40
0
0
0
0
0
0
0
0
0
0
30
30
30
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
30
5
180
240
5
140 000
39 000
21 500
36 800
—
18 400
23 000
23 000
19 300
—
80
99
99
84
30
12
Trace
99
56
86
99
Trace
Trace
97
35
94
99
99
80
82
95
84
—
—
—
88
—
73
83
—
—
97
—
94
99
99
99
95
88
99
1.13
1.32
1.92
1.24
—
2
3f
4g
5h
6
—
—
—
—
—
—
7
8
9
37 800
—
21 500
37 600
—
—
65 000
—
89 400
104 000
112 000
20 000
9600
5000
2200
23 000
—
18 900
23 000
—
—
44 400
—
64 500
91 500
114 000
13 800
7000
3500
1800
1.93
—
1.12
1.42
—
—
1.19
—
1.22
1.16
1.20
1.56
1.33
1.49
1.47
10
10
11
12g
13h
14
15
16
17i
18i
19
20
21
22
Ca{N(SiMe3)2}2(THF)2
6
6
6
8
8
8
8
8
8
8
8
8
0
30
30
30
30
30
30
30
99
99
99
99
15
30
40
a In 7.5 mL. b Obtained from GPC analysis times 0.56. c Calculated from [M(monomer) × [M]0/[Ca]0 × conversion yield/([BnOH]eq)] + M(BnOH).
d Obtained from 1H NMR analysis. e Isolated yield. f [BnOH] was replaced with [9-AnOH]. g In 7.5 mL CH2Cl2. h In 7.5 mL THF. i In 15 mL.
Fig. 2 Dependence of the experimental molar mass determined by MnGPC, on
the [ε-CL]0/[8]0 ratio for the ROP of ε-CL with [8]0/[BnOH]0 = 1/1 (Table 1).
Fig. 4 1H NMR spectrum of PCL-30 initiated by 8 in toluene at 30 °C (Table 1,
entry 21).
polymers was found, indicating that the side reactions did not
happen during polymerization.17
In conclusion, a family of calcium complexes bearing oxala-
midinate ligands have been prepared and fully characterized.
Under optimized conditions, complexes 8 and 9 demonstrate
efficient catalytic activities, and productivities for the con-
trolled “living” and “immortal” ROP of ε-caprolactone in the
presence of benzyl alcohol. The poor conversion demonstrated
by 6, 7 and 10 might result from the solubility caused by the
less bulky phenyl group and the interaction between the
Fig. 3 Dependence of the experimental molar mass determined by GPC,
MnGPC, of PCLs on the amount of added benzyl alcohol for the ROP of ε-capro-
lactone initiated by the 8/BnOH system at [ε-CL]0/[8]0 = 600/1 (Table 1).
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Fig. 5 MALDI-TOF mass spectrum of H-PCL-OBn (Mn = 2200 g mol−1, Table 1, entry 22).
pendant functionality and the metal center. To the best of our with a Bruker Autoflex III TOF/TOF equipped with an MCP
knowledge, this is the first example of calcium complexes con- detector. The sample was dissolved in THF, and the matrix was
taining oxalamidinate ligands applied in ROP of ε-caprolac- 2,5-dihydroxybenzoic acid (HABA). Ions formed by a pulsed UV
tone. Preliminary studies on fine-tuning of ligand precursors laser beam with 3 ns bandwidth (nitrogen laser λ was 337 nm)
and further application of metal complexes to the catalytic were accelerated through 20 kV, and the detection voltage was
reactions are currently underway.
set at 1.7 kV.
PCl5 (RDH), oxalyl chloride (Acros), 2-methoxyethylamine
(Acros), unsym-dimethyl-ethylenediamine (Acros), 2,4,6-tri-
methylaniline (Alfa-Aesar), 2-(aminoethyl)pyridine (Acros), oxa-
nilide (Acros), 2-aminoethanethiol hydrochloride (Alfa-Aesar),
calcium iodide (Alfa-Aesar), sodium bis(trimethylsilyl)amide
(Acros) and 9-anthracenemethanol (Acros) were used as sup-
plied. Benzyl alcohol (TEDIA) and triethylamine (TEDIA) were
dried over magnesium sulfate and distilled before use.
ε-Caprolactone (Acros) was dried over magnesium sulfate and
distilled under reduced pressure before use. HCl·H2N-
Experimental
All manipulations were carried out under an atmosphere of di-
nitrogen using standard Schlenk-line or drybox techniques. Sol-
vents were refluxed over the appropriate drying agent and distilled
prior to use. Deuterated solvents were dried over molecular sieves.
1H and 13C{1H} NMR spectra were recorded either on
Varian Mercury-400 (400 MHz) or 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 tetra-
methylsilane. Elemental analyses were performed with an Ele-
mentar Vario ELIV instrument. The GPC measurements were
performed in THF at 35 °C with a Waters 1515 isocratic HPLC
pump, a Waters 2414 refractive index detector, and a Waters
styragel column (HR4E). Molecular weights and molecular
weight distributions were calculated using polystyrene as stan-
(CH2)2SMe,18
[PhNvC{NH(CH2)2OMe}–C{NH(CH2)2OMe}v
NPh] (1),12e [PhNvC{NH(CH2)2NMe2}–C{NH(CH2)2NMe2}v
NPh] (2),12e N1,N2-bis(2,4,6-trimethylphenyl) oxaldiimidoyl
dichloride,14
[PhTriMeNvC{NHCH2Py}–C{NHCH2Py}v
NPhTriMe] (5)14 and Ca{N(SiMe3)2}2(THF)2 were prepared by
6f
literature methods.
Preparations
[PhTriMeNvC{NH(CH2)2OMe}–C{NH(CH2)2OMe}vNPhTriMe] (3).
dard. Matrix-assisted laser desorption ionization-time-of-flight To a flask containing N1,N2-bis(2,4,6-trimethylphenyl) oxaldi-
mass spectrometry (MALDI-TOF-MS) analyses were carried out imidoyl dichloride (2.67 g, 7.2 mmol), 2-methoxyethylamine
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(1.25 mL, 4.4 mmol) and triethylamine (2.20 mL, 16.2 mmol), (m, CH2, 4H), 2.87(m, CH2, 4H), 3.06(s, O-CH3, 6H), 3.35(m,
30 mL THF were added. The reaction mixture was refluxed for THF, 8H), 6.89(s, Ar-CH, 4H). 13C{1H} NMR (150 MHz, C6D6): δ
48 h. After cooling, the suspension was filtered and all the 5.9(SiMe3), 20.8(2- and 6-CH3), 20.9(4-CH3), 25.1(THF), 46.8
volatiles were removed in vacuo. The residue was washed with (CH2), 59.7(O-CH3), 68.9(THF), 74.9(CH2), 128.6(Ar-CH), 128.3,
20 mL hexane to afford a white solid. Yield, 2.60 g, 81%. 1H 129.6, 130.2, 147.4, 163.0(C). Anal. Calc. for C46H88Ca2N6O4Si4:
NMR (400 MHz): δ 2.16(s, 2- and 6-CH3, 12H), 2.24(s, 4-CH3, C, 56.28; H, 9.03; N, 8.56. Found: C, 56.18; H, 8.83; N, 8.53%.
6H), 2.78(br, CH2, 4H), 3.23(br, CH2-O-CH3, 10H), 6.78(s, Ar-
[Ca{N(SiMe3)2}(THF)(PhTriMeN)C{N(CH2)2SMe}–]2
(9). The
CH, 4H). 13C{1H} NMR (100 MHz): δ 18.4(2- and 6-CH3), 20.7(4- procedure for the preparation of 9 was similar to that used for
CH3), 41.7(CH2), 58.6(O-CH3), 71.2(CH2), 127.8(Ar-CH), 127.9, 6 but with Ca{N(SiMe3)2}2(THF)2 (1.01 g, 2.0 mmol) and 4
130.8, 144.0(C). Anal. Calc. for C26H38N4O2: C, 71.20; H, 8.73; (0.47 g, 1.0 mmol). A brown solid was obtained. Yield, 0.46 g,
1
N, 12.77. Found: C, 70.99; H, 8.52; N, 12.90%.
[PhTriMeNvC{NH(CH2)2SMe}–C{NH(CH2)2SMe}vNPhTriMe
45%. H NMR (600 MHz, C6D6): δ 0.38(s, SiMe3, 36H), 1.17(m,
(4). THF, 8H), 1.82(s, S-CH3, 6H), 2.21(s, 4-CH3, 6H), 2.32(m, CH2,
]
The procedure for the preparation of 4 was similar to that used 4H), 2.42(s, 2- and 6-CH3, 12H), 2.79(m, CH2, 4H), 3.27(m,
for 3 but with N1,N2-bis(2,4,6-trimethylphenyl) oxaldiimidoyl THF, 8H), 6.81(s, Ar-CH, 4H). 13C{1H} NMR (150 MHz, C6D6): δ
dichloride (2.00 g, 5.5 mmol), HCl·H2N(CH2)2SMe (1.50 g, 6.1(SiMe3), 15.4(S-CH3), 20.8(4-CH3), 21.3(2- and 6-CH3), 25.0
11.6 mmol) and triethylamine (3.20 mL, 23.3 mmol). A white (THF), 36.3(CH2), 46.7(CH2), 68.9(THF), 128.5(Ar-CH), 128.8,
1
solid was obtained. Yield, 1.60 g, 61%. H NMR (400 MHz): δ 129.4, 129.6, 147.6, 164.9 (C). Anal. Calc. for C46H88Ca2-
1.84(s, S-CH3, 6H), 2.13(s, 2- and 6-CH3, 12H), 2.23(s, 4-CH3, N6O2S2Si4: C, 54.49; H, 8.75; N, 8.29. Found: C, 53.96; H, 8.55;
6H), 2.33(br, CH2, 4H), 2.86(br, CH2, 4H), 6.79(s, Ar-CH, 4H). N, 8.04%.
13C{1H} NMR (100 MHz): δ 14.8(S-CH3), 18.4(2- and 6-CH3),
[Ca{N(SiMe3)2}(THF)(PhTriMeN)C{NCH2Py}–]2 (10). The pro-
20.6(4-CH3), 34.1(CH2), 40.8(CH2), 128.0(Ar-CH), 131.2, 143.6, cedure for the preparation of 10 was similar to that used for 6
144.4(C). Anal. Calc. for C26H38N4S2: C, 66.34; H, 8.14; N, but with Ca{N(SiMe3)2}2(THF)2 (1.01 g, 2.0 mmol) and 5
11.90. Found: C, 65.90; H, 8.16; N, 12.08%.
(0.50 g, 1.0 mmol). A dark blue solid was obtained. A crystal-
[Ca{N(SiMe3)2}(THF)(PhN)C{N(CH2)2OMe}–]2 (6). To a solu- line solid was recrystallized from concentrated hexane solution
1
tion of Ca{N(SiMe3)2}2(THF)2 (1.01 g, 2.0 mmol) in 10 mL after a couple of hours. Yield, 0.28 g, 27%. H NMR (600 MHz,
toluene, a solution of 1 (0.35 g, 1.0 mmol) in 10 mL toluene C6D6): δ 0.33(s, SiMe3, 36H), 1.10(m, THF, 8H), 2.34(s, 4-CH3,
was added over 10 min at 0 °C. The resulting colorless solution 6H), 2.56(s, 2- and 6-CH3, 12H), 3.28(m, THF, 8H), 4.28(s, CH2,
was warmed to room temperature and stirred overnight. After 4H), 6.24(d, Ar-CH, 2H, J = 7.8 Hz), 6.49(t, Ar-CH, 2H, J = 6.6
12 h of stirring, all the volatiles were removed in vacuo and the Hz), 6.68(t, Ar-CH, 2H, J = 7.8 Hz), 6.97(s, Ar-CH, 4H), 8.69(d,
residue was washed with hexane to afford a brown solid. Yield, Ar-CH, 2H, J = 4.8 Hz). 13C{1H} NMR (150 MHz, C6D6): δ 5.8
1
0.40 g, 44%. H NMR (600 MHz, C6D6): δ 0.33(s, SiMe3, 36H), (SiMe3), 20.9(2- and 6-CH3) 21.0(4-CH3), 25.0 (THF), 54.7(CH2-
1.08(m, THF, 8H), 2.82(br, CH2, 4H), 2.94(br, CH2, 4H), 3.05(s, Py), 68.8(THF), 121.0, 122.6, 129.7, 130.4, 137.4, 148.2(Ar-CH),
O-CH3, 6H), 3.26(m, THF, 8H), 6.74(t, Ar-CH, 2H, J = 7.8 Hz), 128.3, 128.7, 147.3, 163.5, 164.0(C). Anal. Calc. for
7.06(br, Ar-CH, 4H), 7.24(t, Ar-CH, 4H, J = 6.0 Hz). 13C{1H} C52H86Ca2N8O4Si4: C, 59.61; H, 8.27; N, 10.69. Found: C, 59.16;
NMR (150 MHz, C6D6): δ 5.9(SiMe3), 25.2(THF), 49.7(CH2), 59.6 H, 8.26; N, 10.49%.
(O-CH3), 68.7(THF), 75.1(CH2), 118.6, 121.6, 128.9(Ar-CH),
128.5, 152.1, 165.3(C). Anal. Calc. for C40H76Ca2N6O4Si4: C, flask containing the prescribed amount of catalyst
53.53; H, 8.53; N, 9.36. Found: C, 51.74; H, 8.92; N, 9.72%. (0.03125 mmol) was added 7.5 mL THF (containing
POLYMERIZATION PROCEDURE OF ε-CAPROLACTONE. Typically, to a
[Ca{N(SiMe3)2}(THF)(PhN)C{N(CH2)2NMe2}–]2 (7). The pro- 0.0625 mmol benzyl alcohol). After 3 min, the ε-caprolactone
cedure for the preparation of 7 was similar to that used for 6 was added. The reaction mixture was stirred at 0 °C or 30 °C
but with Ca{N(SiMe3)2}2(THF)2 (1.01 g, 2.0 mmol) and 2 for the prescribed time. After the reaction was quenched by
(0.38 g, 1.0 mmol). A brown solid was obtained. Yield, 0.45 g, the addition of acetic acid solution (5 mL, 0.35 N), the result-
1
49%. H NMR (600 MHz, C6D6): δ 0.42(s, SiMe3, 36H), 1.14(m, ing mixture was poured into n-heptane (25 mL) to precipitate
THF, 8H), 1.84(br, CH2, 4H), 2.00(br, NMe2, 12H), 3.09(br, CH2, polymers. Crude products were recrystallized from THF/hexane
4H), 3.28(m, THF, 8H), 6.78(t, Ar-CH, 2H, J = 7.2 Hz), 7.15(br, and dried in vacuo to a constant weight.
Ar-CH, 4H), 7.29(t, Ar-CH, 4H, J = 7.8 Hz). 13C{1H} NMR
Crystal structure data
(150 MHz, C6D6): δ 6.1(SiMe3), 25.1(THF), 45.0(NMe2), 48.4
(CH2), 61.2(CH2), 69.2(THF), 118.5, 128.3, 128.7(Ar-CH), 121.6, Crystals 7 were grown from concentrated hexane solution and
151.9, 164.8(C). Anal. Calc. for C42H82Ca2N8O2Si4: C, 54.61; H, isolated by filtration. A suitable crystal of 7 was mounted onto
8.95; N, 12.13. Found: C, 53.99; H, 9.00; N, 12.60%.
a glass fiber using perfluoropolyether oil and cooled rapidly in
[Ca{N(SiMe3)2}(THF)(PhTriMeN)C{N(CH2)2OMe}–]2 (8). The a stream of cold nitrogen gas using an Oxford Cryosystems
procedure for the preparation of 8 was similar to that used for Cryostream unit. Diffraction data were collected at 100 K using
6 but with Ca{N(SiMe3)2}2(THF)2 (1.01 g, 2.0 mmol) and 3 Oxford Gemini S diffractometer. The absorption correction
(0.44 g, 1.0 mmol). A brown solid was obtained. Yield, 0.48 g, was based on the symmetry equivalent reflections using the
1
40%. H NMR (600 MHz, C6D6): δ 0.31(s, SiMe3, 36H), 1.25(m, SADABS program.19 The space group determination was based
THF, 8H), 2.27(s, 4-CH3, 6H), 2.46(s, 2- and 6-CH3, 12H), 2.76 on a check of the Laue symmetry and systematic absences and
9260 | Dalton Trans., 2013, 42, 9255–9262
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Paper
3 R. E. Drumright, P. R. Gruber and D. E. Henton, Adv.
Mater., 2000, 12, 1841.
Table 2 Summary of crystal data for complex 7
7
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1396.
Formula
Fw
T (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C
42H82Ca2N8O2Si4
923.68
100(2)
Orthorhombic
Pbcn
15.3218(2)
15.5131(2)
23.0555(3)
90
90
90
γ (°)
V (Å3)
Z
5480.03(12)
4
1.120
0.334
29 787
ρcalc (Mg m−3
)
μ(Mo Kα) (mm−1
)
Reflections collected
No. of parameters
262
Indep. reflns (Rint
)
6728(0.0286)
0.0442, 0.1353
0.0624, 0.1429
1.005
Final R indices R1a, wR2
R indices (all data)
GoFb
a
a R1 = [Σ|Fo| − |Fc|]/Σ|Fo|]; wR2 = [Σw(Fo − Fc2)2/Σw(Fo2)2]1/2; w = 0.10.
b GoF = [Σw(Fo2 − Fc2)2/(Nrflns − Nparams)]1/2
2
.
6 (a) Z. Zhong, P. J. Dijkstra, C. Birg, M. Westerhausen and
J.
Feijen,
Macromolecules,
2001,
34,
3863;
was confirmed using the structure solution. The structure was
solved by direct methods using a SHELXTL package.20 All non-
H atoms were located from successive Fourier maps, and
hydrogen atoms were refined using a riding model. Anisotro-
pic 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 number 900478 for 7.
(b) M. Westerhausen, S. Schneiderbauer, A. N. Kneifel,
Y. Söltl, P. Mayer, H. Nöth, Z. Zhong, P. J. Dijkstra and
J. Feijen, Eur. J. Inorg. Chem., 2003, 3432;
(c) M. H. Chisholm, J. Gallucci and K. Phomphrai, Chem.
Commun., 2003, 48; (d) Z. Zhong, S. Schneiderbauer,
P. J. Dijkstra, M. Westerhausen and J. Feijen, Polym. Bull.,
2003, 51, 175; (e) M. H. Chisholm, J. C. Gallucci and
K. Phomphrai, Inorg. Chem., 2004, 43, 6717; (f) Y. Sarazin,
R. H. Howard, D. L. Hughes, S. M. Humphrey and
M.
Bochmann,
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Trans.,
2006,
340;
(g) D. J. Darensbourg, W. Choi and C. P. Richers, Macro-
molecules, 2007, 40, 3521; (h) H.-Y. Chen, H.-Y. Tang and
C.-C. Lin, Polymer, 2007, 48, 2257; (i) D. J. Darensbourg,
W. Choi, O. Karroonnirun and N. Bhuvanesh, Macromol-
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T.-Y. Lee and J.-H. Huang, Inorg. Chem., 2009, 48, 8004;
(l) M. Helou, O. Miserque, J.-M. Brusson, J.-F. Carpentier
and S. M. Guillaume, ChemCatChem, 2010, 2, 306;
(m) Y. Sarazin, D. Roşca, V. Poirier, T. Roisnel, A. Silvestru,
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Acknowledgements
We would like to thank the National Science Council of the
Republic of China for financial support (grant number NSC
98-2113-M-005-002-MY3).
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