CO2/ethylene oxide copolymerization and ligand variation for a highly active salen-cobalt(iii) complex tethering 4 quaternary ammonium salts

Article abstract of DOI:10.1039/c2dt31854g

A cobalt(iii) complex (1) of a salcy-type ligand tethering 4 quaternary ammonium salts, which is thought to act as a highly active catalyst for CO ₂/propylene oxide (PO) copolymerization, also shows high activity (TOF, 25900 h^-1; TON, 518000; 2.72 kg polymer per g cat) and selectivity (>98%) for CO₂/ethylene oxide (EO) copolymerization that results in high-molecular-weight polymers (M_n, 200000-300000) that have strictly alternating repeating units. The related cobalt(iii) complexes 11-14 were prepared through variations of the ligand framework of 1 by replacing the trans-1,2-diaminocyclohexane unit with 2,2-dimethyl-1,3- propanediamine, trans-1,2-diaminocyclopentane, or 1,1′-binaphthyl-2, 2′-diamine or by replacing the aldimine bond with ketimine. These ligand frameworks are thought to favour the formation of the cis-β configuration in complexation, and the formation of the cis-β configuration in 11-14 was confirmed through NMR studies or X-ray crystallographic studies of model complexes not bearing the quaternary ammonium salts. Complexes 11, 13, and 14, which adopt the cis-β configuration even in DMSO did not show any activity for CO₂/PO copolymerization. Complex 12, which was constructed with trans-1,2-diaminocyclopentane and fluctuated in DMSO between the coordination and de-coordination of the acetate ligand as observed for 1, showed fairly high activity (TOF, 12400 h^-1). This fluctuating behaviour may play a role in polymerization. However, complex 12 did not compete with 1 in terms of activity, selectivity, and the catalyst cost.

Full text of DOI:10.1039/c2dt31854g

Dynamic Article Links
Dalton
Transactions
Cite this: DOI: 10.1039/c2dt31854g
www.rsc.org/dalton
PAPER
View Article Online
View Journal
CO2/ethylene oxide copolymerization and ligand variation for a highly active
salen–cobalt(III) complex tethering 4 quaternary ammonium salts†
Jong Yeob Jeon,a Jung Jae Lee,a Jobi Kodiyan Varghese,a Sung Jae Na,b S. Sujith,b Min Jeong Go,c
Junseong Lee,c Myung-Ahn Okb and Bun Yeoul Lee*a
Received 14th August 2012, Accepted 2nd October 2012
DOI: 10.1039/c2dt31854g
A cobalt(III) complex (1) of a salcy-type ligand tethering 4 quaternary ammonium salts, which is thought
to act as a highly active catalyst for CO2/propylene oxide (PO) copolymerization, also shows high activity
(TOF, 25 900 h−1; TON, 518 000; 2.72 kg polymer per g cat) and selectivity (>98%) for CO2/ethylene
oxide (EO) copolymerization that results in high-molecular-weight polymers (Mn, 200 000–300 000) that
have strictly alternating repeating units. The related cobalt(III) complexes 11–14 were prepared through
variations of the ligand framework of 1 by replacing the trans-1,2-diaminocyclohexane unit with 2,2-
dimethyl-1,3-propanediamine, trans-1,2-diaminocyclopentane, or 1,1′-binaphthyl-2,2′-diamine or by
replacing the aldimine bond with ketimine. These ligand frameworks are thought to favour the formation
of the cis-β configuration in complexation, and the formation of the cis-β configuration in 11–14 was
confirmed through NMR studies or X-ray crystallographic studies of model complexes not bearing the
quaternary ammonium salts. Complexes 11, 13, and 14, which adopt the cis-β configuration even in
DMSO did not show any activity for CO2/PO copolymerization. Complex 12, which was constructed with
trans-1,2-diaminocyclopentane and fluctuated in DMSO between the coordination and de-coordination of
the acetate ligand as observed for 1, showed fairly high activity (TOF, 12 400 h−1). This fluctuating
behaviour may play a role in polymerization. However, complex 12 did not compete with 1 in terms of
activity, selectivity, and the catalyst cost.
an alternative material to polystyrene-based acrylonitrile–buta-
diene–styrene (ABS) plastic made from a blend of polyhydroxy-
Introduction
Carbon dioxide/propylene oxide (CO2/PO) copolymers, i.e.,
poly(propylene carbonate) (PPC), are in an early stage of
commercialization.1–3 PPC is an attractive material not only
because it is composed of 44% CO2 by weight but also because
it has some advantageous properties. Commodity polymers such
as PVC and PS emit large amounts of toxic materials and tar
when burning, which can cause injuries during fires, but PPC
burns without emitting any toxic materials, and it may, thus, be
utilized for formation of interior materials. It is adhesive toward
cellulosic and metal substrates and is therefore suitable as a
coating material. It displays good barrier properties for oxygen
and water, making it suitable as food packaging material. One of
its most fascinating properties is its biodegradability. Currently,
the demand for biodegradable polymers is increasing. German
companies such as Siemens and BASF have recently developed
butyrate and PPC.
In spite of those merits, the commercialization of PPC has
lagged because of the lack of efficient catalysts.4–6 Hetero-
geneous zinc catalysts are capable of producing high-molecular-
weight PPC (Mn > 100 000) with fairly high activity.7 However,
the rate of polymerization is not high, and the process thus
requires a long polymerization time (>12 h) in a batch-type
reactor. Furthermore, it is costly to remove the catalyst residue
after polymerization. The catalyst residue should be thoroughly
washed out to ensure resin stability. In the presence of the cata-
lyst residue, the resin is easily degraded during thermal proces-
sing and even during storage at room temperature.8 Thus, the
initial commercialization using the heterogeneous zinc catalyst
has been limited to small-scale processes for special applications
such as sacrificial binders because of the high resin price.9
During the last decade, several studies have addressed the
development of homogeneous catalysts,10–13 and, eventually, a
highly active catalyst (salcy–cobalt(III) complex tethering 4 qua-
ternary ammonium salts) was reported in 2008.14 The initially
reported catalyst was modified by the exchange of 2,4-dinitro-
phenolate anions for nitrate to eliminate the safety concerns and
reduce the cost in a large-scale preparation (1 in eqn (1)).15,16
The rate of polymerization using catalyst 1 was extraordinarily
higher (turnover frequency (TOF) > 20 000 h−1) in CO2/PO
aDepartment of Molecular Science and Technology, Ajou University,
Suwon 443-749, South Korea
bInstitute of Technology, SK Innovation, 140-1 Wonchon-dong,
Yuseong-gu, Daejeon 305-712, Korea
cDepartment of Chemistry, Chonnam National University, 77 Yongbong-ro,
Buk-gu, Gwangju 500-757, Korea. E-mail: bunyeoul@ajou.ac.kr;
Fax: +82-31-219-2394; Tel: +82-31-219-1844
†CCDC 894114, 894115 and 894116. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2dt31854g
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.

View Article Online
copolymerization than that of any other catalysts reported, and a
high activity of up to 2.0 kg per g cat (57 kg per g Co: 32 900
TON) was attained by polymerization for just 2 h, thus permit-
ting the polymerization process to proceed in a more efficient
and continuous fashion. By employing 1 as a catalyst, a high-
molecular-weight polymer (Mn up to 300 000) can be generated;
moreover, the molecular weight can be controlled across a very
large range of Mn 2000–600 000 by feeding a certain amount of
chain transfer agents or chain extenders to the reaction.17–19
Another advantage of 1 is that the catalyst can be efficiently
removed simply by filtration through a thin pad of silica gel.
After filtration, the resin contains a negligible amount of cobalt;
hence, it is thermally stable up to 190 °C, which permits thermal
processing without degradation and provides lasting mechanical
stability.20 The captured catalyst on the silica surface can be
extracted for reuse, and 1 can be prepared in a large scale
(100 kg per batch) with a minimal cost.21,22 In this study, we
report the CO2/ethylene oxide (EO) copolymerization reactivity
of 1 and some results related to our effort to find an efficient
catalyst based on 1.
copolymerization in an industrial laboratory and investigated the
reactivity of 1 in CO2/EO copolymerization. As shown in
Table 1, catalyst 1 functions equally well for both CO2/EO co-
polymerization and CO2/PO copolymerization. Extremely high
activity of TOF up to 25 900 h−1 was achieved, corresponding to
2.72 kg polymer per g cat (entry 8). Polymers with high molecu-
lar weights of up to Mn = 272 000 were generated (entry 7), and
a negligible amount of cyclic carbonate was formed during the
polymerization (selectivity > 98%). In the 1H NMR spectra, only
1 signal was observed at 4.4 ppm in CDCl3, which indicates a
perfect alternating structure that does not contain any ether
linkage. The optimum polymerization temperature was approxi-
mately 70 °C in terms of activity and selectivity (entries 1–5),
which was in accord with the optimum temperature for CO2/PO
copolymerization. As the CO2 pressure increases, the activity
increases gradually (entries 4, 6–8). At a low pressure of 20 bar,
the selectivity decreases to 96%. After polymerization, the cata-
lyst can be removed almost completely by passing the reaction
mixture through a thin pad of silica gel to provide colourless
polymers that contain a negligible amount of cobalt.
Cobalt(III) complexes of cis-β configuration
Recently, it has been reported that the capability to adopt the
cis-β configuration (Fig. 1) may be related to high catalytic perform-
ance in CO2/epoxide copolymerization.28–30 Some ligand frame-
works are known to be favourable for the formation of the cis-β
configuration in complexation.31 Typical examples are illustrated
in Fig. 1. The cis-β configuration was found in a cobalt(III)
acetate complex prepared from a flexible 1,3-diaminopropane-
based compound such as 2.32,33 Compound 3 may favourably
form the cis-β configuration because severe torsional strains are
expected in the cyclopentane unit under the normal trans
configuration. An X-ray crystallographic study of a single crystal
of a ruthenium complex constructed with a binaphthyl Schiff
base (4 [R = Cl]) revealed the structure of the cis-β configu-
ration.34 Compound 5 constructed with 1,2-diaminocyclohexane
and a 2′-hydroxyacetophenone derivative was also reported to be
favourable for the formation of the cis-β configuration because
of repulsion between the methyl and cyclohexane units. The cis-β
structure of the TiCl2 complex ligated by 5 (RvH) was revealed
by X-ray crystallography.35
Cobalt complexes ligated by 3–5 have not been reported in
the literature. Compound 3 (R = Me) can be easily constructed
by reacting the corresponding salicylaldehyde and diamine in
CH2Cl2 for 1 day. Compound 4 (R = Me) can be constructed by
a condensation reaction in ethanol–acetic acid (7 : 1) at 60 °C.
Construction of 5 (R = Me), which is prepared from a relatively
less reactive ketone, requires more severe conditions (refluxing
in 1-butanol for 2 days). Metallation of 3 (R = Me) was success-
fully performed by a well-established routine method: stirring
the ligand with Co(OAc)2 in CH2Cl2. The resulting cobalt(II)
complex was converted to the corresponding cobalt(III) acetate
complex 6 by using silver acetate as an oxidant (eqn (2)).36 In
the cases of 4 (R = Me) and 5 (R = Me), the corresponding
cobalt complexes were not generated by the reaction with Co-
(OAc)2. However, the desired cobalt(II) complexes were gene-
rated when the ligands were reacted with Co[N(SiMe3)2]2 in
ð1Þ
Result and discussion
CO2/EO copolymerization
CO2 copolymerization using other epoxides, such as cyclo-
hexene oxide, 1-hexene oxide, 1-butene oxide, styrene oxide,
indene oxide, and epichlorohydrin, either alone or in combi-
nation with PO, has been previously reported.23–27 However, the
epoxides (except epichlorohydrin) are not currently produced on
a bulk scale, and hence, polymers prepared using the epoxides
are rarely relevant to commercialization on a large scale. One of
the most attractive epoxides is EO, which is a bulk chemical that
is annually produced on a scale of 15 million tons. Its production
from ethylene using O2 as an oxidant is more economical than
PO, as the production of PO requires expensive oxidants such as
H2O2 or Cl2.
The CO2/EO copolymer poly(ethylene carbonate) (PEC) is
also a biodegradable material and has a slightly lower glass tran-
sition temperature (∼20 °C) than PPC (∼40 °C). However,
studies on CO2/EO copolymerization have rarely been reported.
EO is a hazardous gas (b.p. 11 °C), and its handling requires
specialized safety equipment. Its availability is also very limited
in academic laboratories. We equipped an apparatus for CO2/EO
Dalton Trans.
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 1 CO2/EO polymerization resultsa
Entry
T (°C)
Pb (bar)
Yield (g)
TOF (h−1
)
Mn c × 10−3
Mw/Mn
Selectivityd (%)
1
2
3
4
5
6
7
8
40
50
60
70
80
70
70
70
30
30
30
30
30
20
40
50
40
50
5040
6310
121
137
177
225
230
218
272
213
1.45
1.42
2.02
2.50
2.58
2.35
1.81
2.18
98
98
>99
>99
98
96
98
111
146
139
144
178
205
14 000
18 400
17 500
18 200
22 400
25 900
98
a Polymerization conditions: EO (800 g, 18.2 mol) [EO]/[1] = 400 000, 1 (0.075 g, 0.045 mmol), 2.0 h after initiation. b Total pressure of CO2 and EO
at the polymerization temperature. c Determined on GPC using a polystyrene standard in methylene chloride. d Selectivity of the polycarbonate over
cyclic carbonate as determined by 1H NMR spectroscopic analysis of the crude product.
CH3CN overnight. The resulting cobalt(II) complexes were also
converted to cobalt(III) acetate 7 and 8 by oxidation with silver
acetate (eqn (2)).
ð2Þ
Fig. 1 Three possible configurations of the octahedral complexes
formed by the tetradentate [NOON] ligand and the ligand frameworks
1
In the H NMR spectrum of 6 in CD2Cl2, very broad signals
were observed, which did not provide any useful information
about the binding mode, but the signal pattern in DMSO-d6 was
the same as that observed for the diaminocyclohexane analogue
(Me-salcy)Co(III)OAc (Me-salcy = N,N’-bis(3,5-dimethylsalicyl-
idene)-1,2-trans-diaminocyclohexane). Although these signals
were broad, they could be assigned as 2 sets of signals in the
ratio of approximately 4 : 1. The ratio was much higher than that
observed for (Me-salcy)Co(III)OAc (10 : 1). In a previous report,
this spectrum was assigned as an equilibrium between 2 species
(eqn (3)).28 The minor set was tentatively assigned to the sym-
metric structure of the acetate de-coordinated complex [(Me-
salcy)Co(DMSO)2]+AcO− because it exhibited only 3 signals in
the aromatic region. This assumption was further supported in
this study by the addition of tetrabutylammonium acetate (0.5
equiv.), which resulted in the reduction of the minor set of
signals. Six signals were observed in the aromatic region for the
major set, indicating that the 2 salicylidene units were not equi-
valent. This observation can be assigned to (Me-salcy)Co(κ2-OAc)
of the cis-β configuration or to (Me-salcy)Co(κ1-OAc)(DMSO)
of the conventional trans configuration. The 2 salicylidene units
favourable for the cis-β configuration.
are not magnetically equivalent, even in the trans configuration,
for the complex constructed with a chiral diamine, whose axial
sites are occupied by different ligands.37 However, in the trans
configuration, the signal separation for each corresponding sali-
cylidene proton is not as severe as in that in the cis-β structure.
The signal separation was small in the major set, and hence, it
could preferably be assigned to (Me-salcy)Co(κ1-OAc)(DMSO)
of the conventional trans configuration.
ð3Þ
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.

View Article Online
1
In the H and 13C NMR spectra of 7 and 8, sharp signals are
conditions. Such an easy reduction was also observed for the
cobalt(III) acetate complex constructed from the N,N′-bis(3,5-
dimethylsalicylidene)-1,2-cis-diaminocyclohexane.28 In a single
crystal, 2 enantiomers are randomly packed.
observed in the normal range, indicating a diamagnetic low-spin
state, and the signals can be assignable to the binding mode of
the cis-β configuration. Some cobalt(III) complexes of the tra-
ditional trans-binding mode are in paramagnetic high-spin state,
but all the cobalt(III) complexes adopting the cis-β configuration
reported up to now are in diamagnetic low-spin state. In the
1H NMR spectrum of 7 in CD2Cl2, 4 methyl signals were
observed at 2.38, 2.25, 2.14, and 2.10 ppm, which indicated that
the 2 dimethylsalicylidene units were not magnetically equi-
valent to each other. The signals in the aromatic region
(8–6.5 ppm) also indicated that the 2 salicylidene units were not
equivalent. The signal separation for each unit was fairly large,
and 6 singlet signals were observed at 7.47, 7.01, 6.94, 6.82,
6.73, and 6.65 ppm for the salicylidene protons. Hence, the
1H NMR spectrum of 7 could preferably be assigned to the cis-β
configuration. In DMSO-d6, complex 7 gave rise to a set of
signals, which was contrary to the observation of 2 sets of
signals for 6 and 1. The signal pattern generated was the same as
that observed in CD2Cl2, which implies the cis-β configuration,
even in DMSO. In CD3OD, the same signal pattern was
observed, which indicates that 7 persistently adopts the cis-β
configuration in CD3OD.
A solution of 7 in CD3OD was evaporated to recover the
sample that was redissolved in CH2Cl2. The solution in CH2Cl2
was layer-diffused with hexane to deposit brown crystals. The
X-ray crystallographic studies revealed the structure of a cobalt(III)
complex 7, which was additionally coordinated by CD3OD
(Fig. 3). In the case of [NOON] cobalt(III) complexes, the cis-β
configuration has been observed with a chelating ligand such as
acetate, but in this binaphthyl Schiff base ligand, the cis-β
configuration was preserved, even with monodentate ligands. In
the trans configuration, the phenoxyimine ligand forms a stable
coplanar structure with cobalt, but, in this cis-β configuration,
both phenoxyimine ligands were found to be deviated from the
formation of a strict plane with cobalt. The angle between the
NvCCC–O plane and the N–Co–O plane was 32.70(6)° or
31.83(6)° for each phenoxyimine cobalt binding. The corres-
ponding angles observed for the reduced cobalt(II) complex of 6
were 3.1(3)°. The angle between the 2 naphthyl rings was
65.13(7)°. The neutral methanol ligand was located opposite to
the neutral imine ligand, whereas the anionic acetate ligand was
opposite to the anionic phenoxy ligand. This binding trend was
similar to that observed in the structure of (Me-salcy)Co(κ2-OAc),
where the Co-O(κ2-OAc) distance opposite to the neutral imine
ligand is longer (1.989(2) Å) than that opposite to the anionic
phenoxy ligand (1.963(2) Å), whereas the C–O distance
(1.265(6) Å) in the κ2-OAc ligand is shorter for the oxygen
opposite to the neutral imine ligand and is preferably assignable
as a carbonyl oxygen.28
1
In the H NMR spectrum of 8 in CD2Cl2, both the halves of
the ligand were also observed separately. Six singlet methyl
signals were observed at 2.77, 2.62, 2.33, 2.25, 2.10, and
1.65 ppm. The 2 NCH signals were widely separated, as they
were observed at 5.0 (very broad) and 3.60 ppm (broad triplet).
These features strongly supported the cis-β configuration. In
DMSO-d6, a set of clear signals was observed with the same
feature as observed in CD2Cl2, which implies that 8 also persist-
ently adopts the cis-β configuration in DMSO.
When hexane was layer-diffused onto a solution of 8 in
CH2Cl2, brown crystals were deposited. The X-ray crystallo-
graphic studies revealed the cis-β configuration (Fig. 4). Both
phenoxyimine ligands were found to be deviated from the
X-ray crystallographic studies
When hexane is layer-diffused onto a brown solution of 6 in
CH2Cl2 for several days, red crystals are deposited. The X-ray
crystallographic studies of the single crystal revealed the struc-
ture of an unexpected cobalt(II) complex (Fig. 2). During the
crystallization, the brown cobalt(III) complex was reduced to
the corresponding cobalt(II) complex, which has a red colour.
Most of the deposited crystals were red rather than brown, which
indicates that 6 is readily reduced under the crystallization
Fig. 2 Thermal ellipsoid plot (30% probability level) of the reduced
cobalt(II) complex of 6.
Fig. 3 Thermal ellipsoid plot (30% probability level) of 7 adducted by
methanol.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2012

View Article Online
with 9 in CH2Cl2 result in clean formation of the corresponding
Schiff base ligands. From the ligand prepared using 2,2-dimethyl-
1,3-propanediamine and trans-1,2-diaminocyclopentane, cobalt(III)
complexes 11 and 12 were synthesized according to the routine
procedure and conditions (metallation using Co(OAc)2 and then
oxidation using AgOAc). From the ligand prepared using 1,1′-
binaphthyl-2,2′-diamine, metallation using Co[N(SiMe3)2]2, but
not Co(OAc)2, was successful. Oxidation of the resulting cobalt(II)
complex to cobalt(III) acetate 13 was cleanly performed using
AgOAc as an oxidant. The imine-bond formation by conden-
sation between 10 and trans-1,2-diaminocyclohexane was
sluggish under the conditions used for aldimine bond formation,
and rather severe conditions were required (refluxing 1-butanol
for 2 days). Metallation of the ligand was also not successful
when using Co(OAc)2, but it could be successfully achieved by
reacting the ligand with Co[N(SiMe3)2]2 in CH3CN. The result-
ing paramagnetic cobalt(II) complex was cleanly converted to
the diamagnetic cobalt(III) complex 14 by oxidation using
AgOAc.
Fig. 4 Thermal ellipsoid plot (30% probability level) of 8.
formation of a plane with cobalt. The angles between the
NvCCC–O plane and the N–Co–O plane were 28.23(5)° and
44.13(5)° for each phenoxyimine cobalt binding. The phenoxy-
imine situated in a fac-arrangement deviated more severely than
the phenoxyimine situated in a mer-arrangement. In the structure
of (Me-salcy)Co(κ2-OAc), a phenoxyimine situated in a mer-
arrangement formed a fairly strict plane with cobalt (the angle
between the NvCCC–O plane and the N–Co–O plane, 8.8(1)°)
whereas the other phenoxyimine situated in a fac-arrangement
deviated from the stable coplanar structure (the angle between
the NvCCC–O plane and the N–Co–O plane, 38.5(1)°). The
trans-diaminocyclohexane unit was situated in an unstrained
chair conformation. The average CCCC torsional angle (59.3°)
on the cyclohexane ring was very close to the ideal value of 60°.
The signal patterns of the 1H NMR spectra of 12–14 observed
in CD2Cl2 were identical to those of model complexes 6–8. Each
half of the ligand framework was magnetically nonequivalent,
giving rise to different signals. Two N–CH signals were found to
1
be widely separated at 5.15 and 3.55 ppm in the H NMR spec-
trum of 14. The signal pattern of 11 constructed using flexible
2,2-dimethyl-1,3-propanediamine was similar to those of 12–14.
These observations indicate that 11–14 adopt the cis-β configur-
1
ation in CD2Cl2. The signal patterns observed in the H NMR
spectra in DMSO-d6 were also similar to those observed for
1
model complexes 6–8. In the H NMR spectra of 11, 13, and 14
in DMSO-d6, a set of characteristic signals assignable to the
cis-β configuration was observed. The signal pattern of 12 con-
structed from trans-1,2-diaminopentane was the same as that
observed for 1 constructed from trans-1,2-diaminohexane, even
though the signals of 12 were broad. Two sets of signals were
observed, a set of symmetric complexes that can be assigned as
acetate de-coordinated and another major set of dissymmetric
complexes where acetate is coordinated.
Salen–Co(III) complexes tethering quaternary ammonium salts
Inexpensive and large-scale synthesis of salicylaldehyde deriva-
tive 9 bearing 2 quaternary ammonium salts was achieved
(100 kg per batch).21,22 A 2′-hydroxyacetophenone derivative
bearing 2 quaternary ammonium nitrate salts (10) can be pre-
pared by simply replacing the formylation step in the synthetic
route of 9 with an acetylation step (eqn (4)). Acetylation was
successfully performed using acetyl chloride (1.5 equiv.) and
TiCl4 (1.0 equiv.) in a neat condition at 120 °C for 1 h.
Complexes 11, 13, and 14 were not active at all in the CO2/PO
copolymerization even at a low [PO]/[Cat] ratio of 10 000.
Complex 12 showed activity in CO2/PO copolymerization under
our standard polymerization conditions ([PO]/[Cat] = 100 000,
70 °C, 25 bar CO2, 1.0 h). The activity (TOF, 12 400 h−1) and
selectivity (93%) were both inferior to those attained with 1. In a
previous report, we suggested that the capability to adopt the cis-
β configuration was related to high activity in CO2/epoxide
copolymerization;28 however, in this study, cobalt complexes
prepared from ligand frameworks that likely adopt the cis-β
configuration did not show any activity, though these complexes
indeed adopted the cis-β configuration, even in DMSO-d6. Thus,
the results suggested that the cis-β binding mode does not ensure
high catalytic activity. In the DMSO-d6 1H NMR spectra of
active catalysts such as 1, 12, and others previously reported,
two sets of signals were observed, one of which was assigned to
the acetate de-coordinated state. In CO2/epoxide, a key step may
be the nucleophilic attack of the terminal carbonate anion onto a
coordinating epoxide. A facile back-side attack easily occurs
once the carbonate anion is de-coordinated from the cobalt
centre. Thus, it is reasonable to observe the activity for the
ð4Þ
Condensation reactions of 2,2-dimethyl-1,3-propanediamine,
trans-1,2-diaminocyclopentane, and 1,1′-binaphthyl-2,2′-diamine
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.

View Article Online
complexes that show an acetate de-coordination equilibrium
structure in DMSO-d6. The exceptional high activity observed
for 1 remains to be elucidated. As shown in this study and pre-
vious reports, variation of the ligand framework results in con-
siderable deterioration of the catalytic performance.38,39 We
proposed that unusual binding underlies the exceptional high
activity of 1, i.e., the coordination of carbonate anions instead of
the imine ligand.16,38
started to decrease. After polymerization was initiated, CO2 gas
was continuously fed with a mass flow controller (MFC) at
30 bar to compensate for the consumed CO2. The polymerization
was performed for 2 h, and the resulting thick-viscous polymer
solution was then transferred to a 5 L reservoir equipped with a
mechanical stirrer. The polymer solution was diluted with
methylene chloride (3 L). After the CO2 pressure was released,
the polymer solution in methylene chloride was filtered through
a silica pad (70 g) that had been wetted with methylene chloride.
After removal of the methylene chloride, the residue was dried
in a vacuum oven at 60 °C overnight. The isolated polymer
weighed 146 g (entry 4 in Table 1).
Preparation
(500 mg, 3.33 mmol) was weighed into a round bottom flask in
glove box, and then ( )-trans-1,2-diaminocyclopentane
of
3. 2-Hydroxy-3,5-dimethylbenzaldehyde
a
(167 mg, 1.66 mmol) and methylene chloride (7 mL) were
added. The reaction mixture was stirred overnight at room temp-
erature. The solution was filtered through Celite, and the solvent
was removed under reduced pressure. A yellow solid was
obtained in a quantitative yield that was sufficiently pure for use
in the next reaction without further purification (580 mg, 96%).
1
IR (KBr): 3209 (OH), 1627 (CvN) cm−1. H NMR (CDCl3):
δ 13.32 (s, 2H, OH), 8.21 (s, 2H, NvCH), 6.99 (s, 2H, m-H),
6.83 (s, 2H, m-H), 3.72 (s, 2H, N–CH), 2.25 (s, 6H, CH3), 2.22
(s, 6H, CH3), 1.96 (br, 6H, CH2) ppm. 13C{1H} NMR (CDCl3):
δ 164.68, 156.85, 134.28, 129.07, 127.19, 125.44, 117.58,
65.95, 33.36, 22.26, 20.55, 15.67 ppm. Anal. calc. (C23H28-
N2O2): C, 75.79; H, 7.74; N, 7.69%. Found: C, 75.47; H, 7.39;
N, 7.95%.
Preparation
of
4. 2-Hydroxy-3,5-dimethylbenzaldehyde
(500 mg, 3.33 mmol) and 1,1′-binaphthyl-2,2′-diamine (473 mg,
1.66 mmol) were dissolved in ethanol–acetic acid (7 : 1 v/v,
10 mL) and stirred overnight at 60 °C. After removal of the
solvent under vacuum, the residue was subsequently triturated in
hexane (2 mL). A yellow solid was obtained in 97% yield
Experimental section
General procedure and materials
All manipulations were performed under an inert atmosphere
using standard glove box and Schlenk techniques. CH2Cl2,
CD2Cl2 and CDCl3 were dried by stirring over CaH2, and they
were subsequently vacuum-transferred to reservoirs. DMSO-d6
1
(885 mg). IR (KBr): 3565 (OH), 1623 (CvN) cm−1. H NMR
(CDCl3): δ 11.97 (s, 2H, OH), 8.51 (s, 2H, NvCH), 8.04 (d, J =
8.4 Hz, 2H, CH), 7.93 (d, J = 8.4 Hz, 2H, CH), 7.53 (d, J =
8.4 Hz, 2H, CH), 7.43 (t, J = 8.0 Hz, 2H, CH), 7.25 (m, 4H,
CH), 6.90 (s, 2H, m-H), 6.77 (s, 2H, m-H), 2.17 (s, 6H, CH3),
2.04 (s, 6H, CH3) ppm. 13C{1H} NMR (CDCl3): δ 162.97,
156.95, 144.70, 135.00, 133.27, 132.34, 129.90, 129.86, 128.40,
128.22, 127.01, 126.83, 126.51, 125.70, 125.57, 118.21, 117.91,
20.47, 15.67 ppm. Anal. calc. (C38H32N2O2): C, 83.18; H, 5.88;
N, 5.11%. Found: C, 82.84; H, 5.65; N, 5.40%.
1
was dried over molecular sieves 3 Å. The H NMR (400 MHz)
and 13C NMR (100 MHz) spectra were recorded on a Varian
Mercury Plus 400. Elemental analyses were performed at the
Analytical Centre, Kyunghee University. Gel permeation
chromatograms (GPC) were obtained at room temperature in
CHCl3 using a Waters Millennium apparatus with polystyrene
standards. 2-Hydroxy-3,5-dimethylbenzaldehyde,40 2-hydroxy-
3,5-dimethylacetophenone,41 trans-1,2-diaminocyclopentane,42
43
and Co[N(SiMe3)2]2 were prepared according to the reported
Preparation
of
5. 2-Hydroxy-3,5-dimethylacetophenone
method.
(1.04 g, 6.33 mmol) and ( )-trans-1,2-diaminocyclohexane
(361 mg, 3.17 mmol) were weighed into a round bottom flask,
and then 1-butanol (10 mL) was added. The solution was
refluxed for 2 days under a N2 atmosphere. After the solution
was cooled to room temperature, the solvent was removed under
reduced pressure. The resulting yellow powder was subsequently
triturated in hexane (5 mL). The yield was 97% (1.25 g). IR
CO2/EO copolymerization
A 3 L bomb reactor equipped with a mechanical stirrer was
charged with EO (790 g). A solution of catalyst 1 (0.075 g,
0.045 mmol, [EO]/[cat] = 400 000) in EO (10 g) was charged in
the reactor. The CO2 gas was pressurized up to 12 bar, and then
the temperature was increased to 70 °C. The pressure was
increased with increasing temperature to reach a steady pressure
of 30 bar. After 1.5 h from the initial heating, the pressure
(KBr): 3502 (OH), 1615 (CvN) cm−1 1H NMR (CDCl3): δ
.
16.55 (s, 2H, OH), 7.04 (s, 2H, m-H), 6.97 (s, 2H, m-H), 3.88
(m, 2H, N–CH), 2.26 (s, 6H, CH3), 2.22 (s, 6H, CH3), 2.21 (s,
6H, CH3), 1.94 (br, 4H, CH2), 1.97 (br, 2H, CH2), 1.89 (m, 2H,
Dalton Trans.
This journal is © The Royal Society of Chemistry 2012

View Article Online
CH2), 1.73 (m, 2H, CH2), 1.48 (m, 2H, CH2) ppm. 13C{1H}
NMR (CDCl3): δ 170.76, 159.92, 134.17, 126.67, 125.92,
124.99, 117.88, 63.00, 32.78, 24.51, 20.87, 16.16, 14.74 ppm.
Anal. calc. (C26H34N2O2): C, 76.81; H, 8.43; N, 6.89%. Found:
C, 76.44; H, 8.32; N, 7.24%.
(s, 1H, m-H), 6.93 (s, 1H, m-H), 6.59 (s, 1H, m-H), 3.77 (br, 1H,
N–CH), 3.03 (br, 1H, N–CH), 2.78 (s, 3H, CH3), 2.62 (s, 3H,
CH3), 2.36 (br, 2H, CH2), 2.25 (s, 3H, CH3), 2.20 (s, 3H, CH3),
2.06 (s, 3H, CH3), 1.69 (s, 3H, acetate-CH3), 1.57 (s, 3H, CH3),
1.38 (br, 2H, CH2), 1.26 (br, 2H, CH2) ppm. 13C{1H} NMR
(CD2Cl2): δ 190.57, 176.84, 170.47, 164.53, 162.01, 134.97,
134.10, 133.58, 132.38, 131.65, 126.67, 126.16, 124.24, 122.07,
74.25, 72.41, 34.19, 33.66, 26.77, 25.18, 23.49, 21.05, 20.90,
20.03, 19.85, 17.80, 16.61 ppm. Anal. calc. (C28H35CoN2O4):
C, 64.36; H, 6.75; N, 5.36%. Found: C, 63.99; H, 6.39; N,
5.57%.
Preparation of complex 6. To a flask containing 3 (200 mg,
0.548 mmol) and Co(OAc)2 (97.0 mg, 0.548 mmol), methylene
chloride (3 mL) was added under a N2 atmosphere. The solution
was stirred at room temperature for 12 h to give a reddish solu-
tion, to which AgOAc (91.6 mg, 0.548 mmol) was added. The
color of the solution changed to dark brown upon addition of
AgOAc. After the solution was stirred for 12 h, it was filtered
through Celite. The solvent was removed under reduced pressure
Preparation of 10. TiCl4 (1.81 g, 9.55 mmol) was slowly
added to 2-Me-4-[{Cl(CH2)3}2CMe]-C6H3OH (2.51 g, 8.68 mmol)
placed in a flask under a N2 atmosphere at room temperature.
The resulting dark red solution was stirred until gas evolution
ceased. CH3COCl (1.02 g, 13.0 mmol) was added to the result-
ing solid. After the resulting thick solution was stirred at room
temperature for 15 min, it was warmed to 120 °C and stirred for
an additional 1 h. The reaction mixture was cooled to room
temperature, diluted with CH2Cl2 (30 mL), and quenched with
H2O (30 mL). The organic phase was collected and washed with
H2O (20 mL) twice. After CH2Cl2 was dried over anhydrous
MgSO4, the solvent was removed using a rotary evaporator. The
crude product was purified by column chromatography on a
silica gel eluting with hexane and diethyl ether (v/v, 20 : 1). The
yield was 65% (1.85 g). From the isolated 2-Me-4-[{Cl(CH2)3}2-
CMe]-6-(CH3CO)–C6H2OH, the desired compound 10 was pre-
pared according to the same procedure and conditions employed
for the synthesis of salicylaldehyde derivative 9 via 3 steps:
exchange of chloride with iodide using NaI, nucleophilic attack
1
to give a dark-brown solid (250 mg, 95%). H NMR (DMSO-
d6) data for the major set: δ 7.57 (s, 1H, NvCH), 7.53 (s, 1H,
CHvN), 7.10–6.92 (br s, 4H, m-H), 4.49 (br, 1H, N–CH), 4.25
(br, 1H, N–CH), 2.55 (s, 3H, CH3), 2.49 (s, 3H, CH3), 2.39 (br,
2H, CH2), 2.35 (br, 2H, CH2), 2.19 (s, 6H, CH3), 1.74 (br, 2H,
CH2), 1.66 (s, 3H, acetate-CH3) ppm. Data for the minor set:
δ 7.72 (s, 2H, NvCH), 7.17 (s, 2H, m-H), 7.13 (s, 2H, m-H),
4.28 (br, 2H, NCH), 2.60 (s, 6H, CH3), 2.24 (s, 6H, CH3),
2.40–1.70 (br, 6H, CH2), 1.66 (s, 3H, acetate-CH3) ppm. 13C
{1H} NMR (CDCl3): δ 165.00, 157.19, 139.20, 134.36, 132.36,
131.68, 129.26, 127.39, 125.56, 117.92, 76.85, 33.39, 20.46,
20.25, 17.10, 15.64 ppm. Anal. calc. (C25H29CoN2O4): C,
62.50; H, 6.08; N, 5.83%. Found: C, 62.14; H, 5.96; N, 5.64%.
Preparation of complex 7. Compound
4
(200 mg,
0.364 mmol) and Co[N(SiMe3)2]2 (138 mg, 0.364 mmol) were
dissolved in acetonitrile (4 mL), and the solution was then stirred
overnight at room temperature to obtain a reddish solution. After
the solvent was removed under vacuum, the residue was tritu-
rated in diethyl ether. To a flask containing the obtained red
powder, AgOAc (60.8 mg, 0.364 mmol) was added with methyl-
ene chloride (3 mL). The solution changed to a dark-brown
colour, and it was then stirred for an additional 12 h. The solu-
tion was filtered through Celite, and the solvent was removed
under reduced pressure to obtain the desired complex (228 mg,
−
of tributylamine, and I− exchange with NO3 using AgNO3.21
1
IR (KBr): 3447 (OH), 1633 (CvO) cm−1. H NMR (CDCl3):
δ 12.57 (s, 1H, OH), 7.63 (s, 1H, m-H), 7.38 (s, 1H, m-H),
3.39–3.10 (br, 16H, NCH2), 2.73 (s, 3H, CH3), 2.23 (s, 3H,
CH3), 1.83–1.45 (br, 18H, CH2), (r, 14H, CH2), 1.36 (s, 3H,
CH3), 1.35 (br, 14H, CH2), 0.90 (t, J = 7.2 Hz, 18H, CH3) ppm.
13C{1H} NMR (CDCl3): δ 205.78, 158.99, 136.66, 135.08,
127.15, 125.99, 118.19, 60.36, 59.15, 53.61, 40.26, 36.30,
28.82, 26.83, 24.30, 19.90, 18.75, 15.98, 13.89 ppm. Anal. calc.
(C41H78N4O8): C, 65.22; H, 10.41; N, 7.42%. Found: C, 64.88;
H, 10.10; N, 7.20%.
1
94%). H NMR (DMSO-d6): δ 8.11 (d, J = 8.8 Hz, 2H, CH),
7.91 (d, J = 8.0 Hz, 1H, CH), 7.86 (d, J = 8.8 Hz, 1H, CH), 7.79
(s, 1H, NvCH), 7.69 (d, J = 8.0 Hz, 1H, CH), 7.58 (t, J = 7.6
Hz, 1H, CH), 7.49 (t, J = 7.6 Hz, 1H, CH), 7.39 (t, J = 7.6 Hz,
1H, CH), 7.29 (t, J = 7.6 Hz, 1H, CH), 7.22 (s, 1H, NvCH),
7.15 (d, J = 8.0 Hz, 1H, CH), 7.00 (d, J = 11.6 Hz, 1H, CH),
6.97 (d, J = 11.6 Hz, 1H, CH), 6.96 (s, 1H, m-H), 6.92 (s, 1H,
m-H), 6.78 (s, 1H, m-H), 6.77 (s, 1H, m-H), 2.22 (s, 3H, CH3),
2.08 (s, 3H, CH3), 2.07 (s, 3H, CH3), 2.02 (s, 3H, CH3), 1.61 (s,
3H, acetate-CH3) ppm. 13C{1H} NMR (CD2Cl2): δ 192.76,
169.13, 167.91, 165.95, 163.66, 147.92, 146.65, 137.80, 137.24,
133.03, 132.97, 132.88, 132.69, 132.61, 131.66, 130.92, 130.20,
129.97, 129.43, 128.78, 128.65, 128.00, 127.38, 127.28, 127.08,
126.87, 126.59, 126.38, 126.25, 126.08, 124.15, 124.09, 123.49,
121.97, 119.75, 23.48, 20.29, 20.04, 17.80, 17.68 ppm. Anal.
calc. (C40H33CoN2O4): C, 72.28; H, 5.00; N, 4.21%. Found: C,
71.90; H, 4.78; N, 4.60%.
Preparation of complex 11. Compound
9
(400 mg,
0.540 mmol) was weighed into a round-bottom flask in a glove
box, and then, 2,2-dimethyl-1,3-propanediamine (27.6 mg,
0.270 mmol) and methylene chloride (5 mL) were added. The
reaction mixture was stirred overnight at room temperature. The
solution was filtered through Celite and the solvent was removed
under reduced pressure. The yield for the formation of the ligand
was 98% (408 mg), and the obtained yellow solid was suffi-
ciently pure for use without further purification. To the flask con-
taining the ligand, Co(OAc)2 (47.8 mg, 0.270 mmol) and
methylene chloride (5 mL) were added. The solution was stirred
at room temperature for 12 h to give a reddish solution, to which
AgOAc (45 mg, 0.27 mmol) was added. The color of the solu-
tion immediately changed to dark brown. After the solution was
stirred for 12 h, it was filtered through Celite. The solvent was
removed under reduced pressure to obtain a dark-brown solid in
Preparation of complex 8. This compound was prepared by
the same procedure and conditions as that of complex 7 using
1
compound 5. H NMR (DMSO-d6): δ 7.23 (s, 1H, m-H), 7.02
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.

View Article Online
a quantitative yield. 1H NMR (DMSO-d6): δ 7.88 (br s, 1H,
m-H), 7.46 (br s, 1H, m-H), 7.15 (br s, 1H, m-H), 7.07 (s, 2H,
NvCH), 6.88 (br s, 1H, m-H), 4.34 (br, 2H, N–CH2), 3.57 (br,
2H, N–CH2), 3.25–2.92 (br, 32H, NCH2), 1.63 (s, 6H, CH3),
1.60–1.36 (br, 32H, CH2), 1.36–1.13(br m, 35H), 1.06 (s, 6H,
CH3), 0.98–0.77(br m, 36H, CH3) ppm.
and an exposure time of 10 s per frame. Cell parameters were
determined and refined by the SMART program. Data reduction
was performed using SAINT software. The data were corrected
for Lorentz and polarization effects. An empirical absorption
correction was applied using the SADABS program. The struc-
tures of the compounds were solved by direct methods and
refined by full matrix least-squares methods using the
SHELXTL program package with anisotropic thermal para-
meters for all non-hydrogen atoms. Hydrogen atoms were calcu-
lated at idealized positions and refined riding on the
corresponding carbon atoms with isotropic thermal parameters.
Crystallographic data for the reduced cobalt(II) complex of 6
(CCDC 894116): C23H26CoN2O2, M = 421.39, monoclinic,
a = 24.891(5), b = 11.215(2), c = 7.3326(15) Å, β = 104.80(3)°,
V = 1979.1(7) Å3, T = 293 (2) K, space group C2/c, Z = 4, 4416
reflections measured, 1740 unique (R(int) = 0.0680) which
were used in all calculations. The final wR2 was 0.1088 (I >
2σ(I)). Crystallographic data for 7·CH3OH·(CH2Cl2) (CCDC
894115): C42H39Cl2CoN2O5, M = 781.58, triclinic, a =
9.8572(2), b = 12.4423(9), c = 17.1598(12) Å, α = 111.160(2),
β = 102.001(3), γ = 91.009(3)°, V = 1909.9(2) Å3, T = 100 (2)
Preparation of complex 12. The ligand of this compound was
prepared by the same procedure as that of 11 using trans-1,2-di-
aminocyclopentane. A yellow solid was obtained in a quanti-
tative yield and was sufficiently pure enough for use without
further purification. The metallation and oxidation processes
1
were the same as those of 11. H NMR (DMSO-d6) data for the
major set: δ 7.65 (s, 1H, NvCH), 7.63 (s, 1H, CHvN),
7.30–7.16 (br s, 4H, m-H), 4.51 (br, H, N–CH), 4.26 (br, H,
N–CH), 3.33–2.92 (br, 32H, NCH2), 2.65–2.32 (br, 6H, CH3),
2.08–1.82 (br, 4H, cyclopentyl-CH2), 1.70–1.12 (br m, 75H),
1.05–0.77 (br, 36H, CH3) ppm. Data for the minor set: δ 7.82 (s,
2H, NvCH), 7.39 (s, 2H, m-H), 7.33 (s, 2H, m-H), 4.26 (br,
2H, N–CH), 3.33–2.92 (br, 32H, NCH2), 2.65–2.32 (br, 6H,
CH3), 2.08–1.82 (br, 4H, cyclopentyl-CH2), 1.70–1.12 (br m,
75H), 1.05–0.77 (br, 36H, CH3) ppm.
ˉ
K, space group P1, Z = 2, 27 710 reflections measured,
6689 unique (R(int) = 0.0156) which were used in all calcu-
lations. The final wR2 was 0.0915 (I > 2σ(I)). Crystallographic
data for 8·(CH2Cl2) (CCDC 894114): C29H37Cl2CoN2O4, M =
607.44, triclinic, a = 10.0530(3), b = 11.5924(3), c = 12.9469(4)
Å, α = 111.8210(10), β = 94.2400(10), γ = 101.0300(10)°, V =
Preparation of complex 13. The ligand of this compound
was prepared by the same procedure as that of 4, using 9 instead
of 2-hydroxy-3,5-dimethylbenzaldehyde. A yellow solid was
obtained in a quantitative yield and was sufficiently pure for use
without further purification. The metallation and oxidation pro-
cesses were same as those of 7. 1H NMR (DMSO-d6): δ 8.13 (d,
J = 8.8 Hz, 1H, CH), 8.12 (d, J = 8.0 Hz, 1H, CH), 7.95 (d, J =
8.4 Hz, 1H, CH), 7.89 (d, J = 8.8 Hz, 1H, CH), 7.88 (s, 1H,
m-H), 7.62 (d, J = 8.4 Hz, 1H, CH), 7.60 (t, J = 7.6 Hz, 1H,
CH), 7.52 (t, J = 7.6 Hz, 1H, CH), 7.40 (t, J = 7.6 Hz, 1H, CH),
7.34 (s, 1H, m-H), 7.32 (t, J = 8.0 Hz, 1H, CH), 7.16 (s, 1H,
NvCH), 7.11 (s, 1H, NvCH), 7.11 (d, J = 6.8 Hz, 1H, CH),
6.97 (s, 2H, m-H), 6.96 (d, J = 8.4 Hz, 1H, CH), 6.92 (d, J =
8.8 Hz, 1H, CH), 3.26–2.90 (br, 32H, NCH2), 2.25 (s, 3H,
CH3), 2.09 (s, 3H, CH3), 1.57 (s, 3H, CH3), 1.57–1.33 (br, 32H,
CH2), 1.33–1.09 (br m, 35H), 1.70–1.05 (br m, 73H), 1.00–0.76
(br m, 36H, CH3) ppm.
3
ˉ
1357.30(7) Å , T = 100 (2) K, space group P1, Z = 2, 16
948 reflections measured, 5000 unique (R(int) = 0.0230)
which were used in all calculations. The final wR2 was 0.0779
(I > 2σ(I)).
Conclusions
Cobalt(III) complex (1) of the salcy-type ligand tethering 4 qua-
ternary ammonium salts is as highly active in CO2/EO copoly-
merization as it is in CO2/PO copolymerization. A TOF of up to
25 900 h−1 (TON, 518 000; 2.72 kg polymer per g cat) was
achieved with the formation of a negligible amount of ethylene
carbonate. High-molecular-weight polymers (Mn, 200 000–
300 000) with strictly alternating repeating units were gener-
ated. We attempted to prepare effective catalysts based on 1 by
altering the ligand structure, especially aiming at cobalt com-
plexes favourable for formation of the cis-β configuration.
Complexes 11, 13, and 14 consistently adopted a single
binding mode of the cis-β configuration. The binding mode of
the cis-β configuration was unambiguously confirmed by X-ray
crystallography studies and NMR studies of model complexes
not bearing quaternary ammonium salt units. Complexes that
take on the cis-β configuration do not show any activity in
CO2/PO copolymerization, whereas complex 12, which fluctu-
ates in DMSO between coordination and de-coordination of the
acetate ligand, shows fairly high activity (TOF, 12 400 h−1).
This fluxional behaviour may be critical for the catalyst cycle
because a facile back-side attack easily occurs from the
de-coordinated carbonate anion. However, complex 12 still
does not compete with 1 in terms of activity, selectivity, and
the catalyst cost.
Preparation of complex 14. The ligand of this compound
was prepared by the same procedure as that of 5 using 10
instead of 3,5-dimethyl-2-hydroxybenzaldehyde.
A yellow
solid was obtained in a quantitative yield and was sufficiently
pure for use without further purification. The metallation
and oxidation processes were the same as those of complex 8.
1H NMR (DMSO-d6): δ 7.27 (s, 1H, m-H), 7.11 (s, 1H, m-H),
7.08 (s, 1H, m-H), 6.77 (s, 1H, m-H), 4.94 (br, 1H, N–CH),
3.76 (br, 1H, N–CH), 3.34–2.92 (br, 32H, NCH2), 2.83 (s, 3H,
CH3), 2.66 (s, 3H, CH3), 2.30 (s, 3H, CH3), 1.96 (br, 2H,
cyclohexyl-CH2) 1.80–1.12 (br m, 82H), 1.00–0.76(br m, 36H,
CH3) ppm.
X-ray structural determination
The crystallographic measurements were performed at 100 K
using a Bruker APEX II CCD-based diffractometer with graph-
ite-monochromated Mo Kα radiation (λ = 0.7107 Å). The reflec-
tion data were collected as multi-scan frames with 0.5° per frame
Dalton Trans.
This journal is © The Royal Society of Chemistry 2012

View Article Online
20 J. K. Varghese, S. J. Na, J. H. Park, D. Woo, I. Yang and B. Y. Lee,
Polym. Degrad. Stab., 2010, 95, 1039–1044.
Acknowledgements
21 J. Min, J. E. Seong, S. J. Na, A. Cyriac and B. Y. Lee, Bull. Korean
Chem. Soc., 2009, 30, 745–748.
22 J. Y. Jeon, J. K. Varghese, J. H. Park, S. H. Lee and B. Y. Lee,
Eur. J. Org. Chem., 2012, 3566–3569.
23 J. E. Seong, S. J. Na, A. Cyriac, B.-W. Kim and B. Y. Lee, Macromol-
ecules, 2010, 43, 903–908.
24 W.-M. Ren, X. Zhang, Y. Liu, J.-F. Li, H. Wang and X.-B. Lu, Macromol-
ecules, 2010, 43, 1396–1402.
This research was supported by a grant from the Fundamental
R&D Program for Integrated Technology of Industrial Materials
funded by the Ministry of Knowledge Economy and by Inter-
Metropolitan Cooperation Development funded by the Presiden-
tial Committee on Regional Development of Korea.
25 G.-P. Wu, S.-H. Wei, X.-B. Lu, W.-M. Ren and D. J. Darensbourg,
Macromolecules, 2010, 43, 9202–9204.
26 D. J. Darensbourg and S. J. Wilson, J. Am. Chem. Soc., 2011, 133,
18610–18613.
27 G.-P. Wu, S.-H. Wei, W.-M. Ren, X.-B. Lu, T.-Q. Xu and
D. J. Darensbourg, J. Am. Chem. Soc., 2011, 133, 15191–15199.
28 A. Cyriac, J. Y. Jeon, J. K. Varghese, J. H. Park, S. Y. Choi, Y. K. Chung
and B. Y. Lee, Dalton Trans., 2012, 41, 1444–1447.
29 D. J. Darensbourg, M. Ulusoy, O. Karroonnirum, R. R. Poland,
J. H. Reibenspies and B. Çetinkaya, Macromolecules, 2009, 42,
6992–6998.
Notes and references
1 G. A. Luinstra and E. Borchardt, Adv. Polym. Sci., 2012, 245, 29–48.
2 M. A. Ok and M. Jeon, ANTEC (Conf. Proc.), 2011, 3, 2134–2139.
3 B. Y. Lee and A. Cyriac, Nat. Chem., 2011, 3, 505–507.
4 D. J. Darensbourg, Inorg. Chem., 2010, 49, 10765–10780.
5 S. Klaus, M. W. Lehenmeier, C. E. Anderson and B. Rieger, Coord.
Chem. Rev., 2011, 255, 1460–1479.
6 M. R. Kember, A. Buchard and C. K. Williams, Chem. Commun., 2011,
47, 141–163.
7 G. A. Luinstra, Polym. Rev., 2008, 48, 192–219.
8 B. Liu, L. Chen, M. Zhang and A. Yu, Macromol. Rapid Commun.,
2002, 23, 881–884.
9 G. W. Coates and D. R. Moore, Angew. Chem., Int. Ed., 2004, 43,
6618–6639.
30 K. Nakano, M. Nakamura and K. Nozaki, Macromolecules, 2009, 42,
6972–6980.
31 T. Katsuki, Chem. Soc. Rev., 2004, 33, 437–444.
32 S. Chattopadhyay, M. G. B. Drew and A. Ghosh, Eur. J. Inorg. Chem.,
2008, 1693–1701.
10 C. T. Cohen, T. Chu and G. W. Coates, J. Am. Chem. Soc., 2005, 127,
10869–10878.
33 Y. Niu, H. Li, X. Chen, W. Zhang, X. Zhuang and X. Jing, Macromol.
Chem. Phys., 2009, 210, 1224–1229.
11 X. B. Lu, L. Shi, Y. M. Wang, R. Zhang, Y. J. Zhang, X. J. Peng,
Z. C. Zhang and B. Li, J. Am. Chem. Soc., 2006, 128, 1664–1674.
12 K. Nakano, T. Kamada and K. Nozaki, Angew. Chem., Int. Ed., 2006, 45,
7274–7277.
34 X. G. Zhou, J. S. Huang, P. H. Ko, K. K. Cheung and C. M. Che, Dalton
Trans., 1999, 3303–3309.
35 J. P. Corden, W. Errington, P. Moore and M. G. H. Wallbridge, Chem.
Commun., 1999, 323–324.
13 S. I. Vagin, R. Reichardt, S. Klaus and B. Rieger, J. Am. Chem. Soc.,
2010, 132, 14367–14369.
14 S. Sujith, J. Min, J. Seong, S. Na and B. Lee, Angew. Chem., Int. Ed.,
2008, 47, 7306–7309.
15 A. Cyriac, S. H. Lee, J. K. Varghese, E. S. Park, J. H. Park and B. Y. Lee,
Macromolecules, 2010, 43, 7398–7401.
16 J. Yoo, S. J. Na, H. C. Park, A. Cyriac and B. Y. Lee, Dalton Trans.,
2010, 39, 2622–2630.
36 R. L. Paddock and S. T. Nguyen, Macromolecules, 2005, 38, 6251–6253.
37 S. Kemper, P. Hrobárik, M. Kaupp and N. E. Schlörer, J. Am. Chem.
Soc., 2009, 131, 4172–4173.
38 S. J. Na, S. Sujith, A. Cyriac, B. E. Kim, J. Yoo, Y. K. Kang, S. J. Han,
C. Lee and B. Y. Lee, Inorg. Chem., 2009, 48, 10455–10465.
39 B. E. Kim, J. K. Varghese, Y. Han and B. Y. Lee, Bull. Korean Chem.
Soc., 2010, 31, 829–834.
40 P. D. Knight, P. N. O’Shaughnessy, I. J. Munslow, B. S. Kimberley and
P. Scott, J. Organomet. Chem., 2003, 683, 103–113.
41 B. Ahlem, Synthesis, 2003, 0267–0271.
17 A. Cyriac, S. H. Lee, J. K. Varghese, J. H. Park, J. Y. Jeon, S. J. Kim and
B. Y. Lee, Green Chem., 2011, 13, 3469–3475.
18 S. H. Lee, A. Cyriac, J. Y. Jeon and B. Y. Lee, Polym. Chem., 2012, 3,
1215–1220.
19 A. Cyriac, S. H. Lee and B. Y. Lee, Polym. Chem., 2011, 2, 950–956.
42 S. G. Gouin, J.-F. Gestin, K. Joly, A. Loussouarn, A. Reliquet, J. Claude
Meslin and D. Deniaud, Tetrahedron, 2002, 58, 1131–1136.
43 H. Bürger and U. Wannagat, Monatsh. Chem., 1963, 94, 1007–1012.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.