Aluminium salabza complexes for fixation of CO2 to organic carbonates

Article abstract of DOI:10.1039/c6dt01069e

A highly stable and easy to synthesize aluminium complex bearing a flexible N₂O₂-donor salabza ligand (N,N′-bis(salicylene)-2-aminobenzylamine) in combination with tetrabutylammonium bromide forms an active binary catalytic system for the cycloaddition of CO₂ to epoxides (TOFs 120-3434 h^-1) under mild conditions (10 bar, 80 °C) and low catalyst loadings (0.05-0.2 mol%). Kinetic experiments have shown that the cycloaddition of CO₂ to styrene oxide catalyzed by 1/TBAB is first order in 1, TBAB, CO₂ and epoxide. A reaction mechanism is proposed based on these observations. Fe(iii) and Co(iii) related complexes are less active catalysts for this reaction.

Full text of DOI:10.1039/c6dt01069e

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Aluminium salabza complexes for fixation of CO2 to organic
carbonates
L. Cuesta-Aluja,a,* J. Castillaa and A. M. Masdeu-Bultóa,*
Received 00th January 20xx,
Accepted 00th January 20xx
A higly stable and easy to synthesize aluminium complex bearing a flexible N2O2-donor salabza ligand (N,N’-bis(salicylene)-
2-aminobenzylamine) in combination with tetrabutylammonim bromide forms an active binary catalytic systems for the
cycloaddition of CO2 to epoxides (TOFs 120-3434 h-1) at mild conditions (10 bar, 80 ºC) and low catalyst loadings (0.05-0.2
mol %). Kinetic experiments have shown that the cycloaddition of CO2 to styrene oxide catalyzed by 1/TBAB is first order in
1, TBAB, CO2 and epoxide. A reaction mechanism is proposed based on these observations. Fe(III) and Co(III) related
complexes are less active catalysts for this reaction.
DOI: 10.1039/x0xx00000x
www.rsc.org/
catalysts and processes which operate at mild reaction
conditions.10
Introduction
Catalysts for the coupling of CO2 and epoxides include halide,
The metal-catalysed coupling of CO2 and epoxides has become
one of most studied topic in CO2 activation, as it is an atom-
efficient reaction to selectively obtain highly value-added cyclic
carbonates or polycarbonates from inexpensive and ready
available starting materials (Scheme 1). Cyclic carbonates are
valuable synthetic targets that are widely used as raw
materials for the synthesis of small molecules1,2 and
polymers.3,4 They are also used as electrolytes in lithium-ion
secondary batteries5 and have applications in the chemical
industries as excellent polar aprotic solvents.6,7,8
Polycarbonates are high performance and eco-efficient
materials with high transparency, durability, safety, heat and
shatter resistance, good electrical insulation, strength,
lightness and biodegradability with application in many areas
of industry.9 The increasing demand of these compounds
implies the development of new, commercially viable,
quaternary alkyl ammonium or phosphonium salts, as well as
,
ionic liquids and metal complexes.11 12 Halide, quaternary salts
and ionic liquids are known to produce the most stable
thermodynamic product, the cyclic carbonate.11 This can be
explained because in the absence of a Lewis acid the reaction
requires higher temperatures.13 On the other hand, metal
complexes can catalyse the formation of polymer and/or cyclic
carbonate products depending on the co-catalyst, substrate
and reaction conditions used. In this context, N-heterocyclic
amines, phosphines or anions derived from PPN+ (PPN+
=
[Ph3P=N=PPh3]+) and ammonium salts,14 which act as
nucleophiles, have been employed as co-catalysts.15 In most
cases, such binary catalytic systems, Lewis acid/nucleophile,
lead to an enhanced activity at milder reaction
,
conditions.16
17 18
Recently, it has been an increased interest in developing new
catalytic systems based on earth-abundant and widely
distributed metals such as aluminium and iron. Early studies by
Inoue and co-workers showed the possibility of CO2 activation
using Al(III) porphyrin complexes in the presence of imidazole,
quaternary ammonium or phosphonium salts.19 At room
temperature
and
atmospheric
pressures
of
CO2
tetraphenylporphyrinatoaluminium(III) methoxy derivative
[(TPP)AlOMe] in the presence of 1-methylimidazole catalysed
the formation of propylene carbonate from CO2 and propylene
oxide. The formation of polycarbonates from CO2 and epoxides
was also achieved using [(TPP)AlCl]/R4NBr or R4PBr under CO2
pressure.20
Scheme 1 a) Cycloaddition and b) copolymerization of CO2 and epoxides
A recent outstanding example of highly active catalysts at mild
reaction conditions is the hexachlorinated aluminum(III)-
aminetriphenolate
A (Chart 1) combined with tetrabutyl-
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selectivity towards the desired product. Taking this into
account we were interested N,N’-bis(salicylene)-2-
tBu
aminobenzylamine (salabza) derivatives as ligands for metal
complexes. These complexes would have a more flexible
structure than salen derivatives and an open active site, which
may provide higher reactivity maintaining the high stability of
the tetradentate coordination (Scheme 2). For this reason, we
decided to prepare Al(III) complexes with the tetradentate-
tBu
Cl
O
N
N
O
O
Cl
O
Cl
Al
Cl
O
Al
N
O
2
O
tBu
Cl
Cl
N2O2
ligand
N,N’-bis(3,5-di-tert-butylsalicylene)-2-
tBu
aminobenzyl-amine derivative (H2L, Scheme 2), which is easily
synthesised in one step.30 Iron(III), chromium(III) and cobalt(III)
complexes were also prepared. The activity of these metal-
salabza complexes in the coupling of CO2 and epoxides is
presented. The synthesis of other Cu, Ti, Mn, Co, Zn and Al
complexes with similar salabza-type ligands have already been
A
B
Chart 1
ammonium iodide. This catalytic system gave an initial TOF of
24000 h-1 in the cycloaddition of CO2 to 1,2-epoxyhexane at 90
°C and 10 bar of initial CO2 pressure at very low catalyst
loading. However, the molar ratio catalyst:co-catalyst was high
(100).21
,
, ,
reported.31 32 33 34
A
Co(III) complex with
a
2,2-
dimethylpropyldiamine related skeleton was reported to
produce low conversion in the copolymerisation of CO2 with
cyclohexene oxide.35
Some of the most widely employed catalysts in the literature
for these reactions are metal-salen type complexes (salen =
N,N'-ethylenebis(salicylimine)) mainly as
pioneering work of Darensbourg with chromium(salen) based
catalysts.22 These catalysts are easily prepared, with
a result of the
Results and discussion
a
Syntheses of complexes
possibility to perform a large-scale synthesis. Moreover, they
are high stable and robust. Their reactivity properties can be
easily fine-tuned changing the diimine skeleton or the
substituents in the phenolate moiety. Dimeric Al(III) salen
Ligand H2L was prepared following the general procedure
described by Lin and co-workers by the reaction of 3,5-di-tert-
butyl salicylaldehyde and 2-aminobenzylamine in ethanol.30
Treatment of H2L with different metal halide precursors MCl3
(M = Al(III), Fe(III)) afforded the corresponding metal(III)
complex [Al(salen)2(
al.23
ꢀ
-O)] (
B
, Chart 1) reported by Meléndez et
conditions and using
under solvent-free
tetrabutylammonium bromide (TBAB) as co-catalyst displayed
a unique activity at atmospheric pressures of CO2 and at 25
ºC.24 Mononuclear analogous Al(III) salen based catalytic
systems require higher pressure and temperature. Thus, Lu et
al. have reported an Al(salen)Cl/TBAB catalytic system for the
complexes
1 and 2 in good to moderate yield (Scheme 2).
Cr(III) and Co(III) complexes were prepared in moderate yields
from M(II) salts (CrCl2 and Co(OAc)2·H2O) by addition of H2L
and subsequent oxidation with air (Scheme 2). Compounds
1-4
were isolated as stable solids except in the case of 4, which
synthesis of ethylene carbonate, which gave
a rapidly
decomposed under air at room temperature. They were
characterized by mass spectrometry, elemental analysis, 1H
and 13C NMR, IR, UV-visible spectroscopy, magnetic
formation of ethylene carbonate at supercritical carbon
dioxide conditions,25 however, the rate of conversion was
reduced to a half when the reaction was carried out at less
than 40 bar pressure. Bifunctional aluminum(salen) complexes
with appended pyridinium salt substituents,26 imidazolium-
based ionic liquid moiety27 or N-methylhomopiperazine
moieties28 in the substituents of the phenolate moieties were
efficient catalysts for propylene carbonate formation (TOF up
susceptibility (2-4) and X-ray diffraction analysis (2-4).
to 297 h-1). However, the introduction of
a second
functionality in the skeleton of the catalyst required additional
synthesis steps.
Aluminum(salen) complexes together with a series of anionic
and neutral co-catalysts were active for the copolymerization
of CO2 and CHO. Darensbourg and co-workers showed that a
more electron-withdrawing salen framework was necessary to
produce significant quantities of copolymer with a high CO2
content in absence of cyclic carbonate by-product.
Nevertheless, the TOF’s obtained, ranged from 5.2 to 35.4 h-1,
while chromium(salen) systems under similar conditions
provided TOF’s as high as 1150 h-1.29
Scheme 2 Syntheses of complexes 1-4
To sum up, aluminum complexes are indeed efficient for the
activation of CO2, however, they provide low activities and
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Fig. 2 ORTEP drawing of complex of 3. All hydrogen atoms and solvent molecules are
omitted for clarity. Thermal ellipsoids are drawn at the 50 % probability level. Selected
bond lengths (Å) and angles (°): Co1a-O1a 1.866(8), Co1a-O4a 1.867(6), Co1a-N1a
1.894(7), Co1a-N2a 1.898(6), Co1a-O2 1.975(5), Co1a-O3 2.053(5), O(1A)-Co(1A)-O(3)
166.5(4)°, angle of, equatorial O(4A)-Co(1A)-N(2A) 94.2(3)°, N(2A)-Co(1A)-N(1A)
90.8(5)°, , O(1A)-Co(1A)-O(2) 101.7(3)°, O(2)-Co(1A)-O(4A) 85.9(3)° and O(2)-Co(1A)-
O(3) 64.8(18)°
Fig. 1 ORTEP drawing of complex of 2. All hydrogen atoms and solvent molecules are
omitted for clarity. Thermal ellipsoids are drawn at the 50 % probability level. Selected
bond lengths (Å) and angles (°):Cr1-O1 1.916(5), Cr1-O2 1.923(5), Cr1-N2 2.012(6), Cr1-
N1 2.059(6), Cr1-Cl1 2.299(3), Cr1-O3 2.052(5), O1-Cr1-O2 91.8(2), O1-Cr1-N2 178.0(2),
O2-Cr1-N2 90.2(2), O1-Cr1-N1 88.3(2), N2-Cr1-N1 89.8(3), O3-Cr1-Cl1 177.13(18)
According to mass spectra (
1-4) and X-ray diffraction data (2-
cm-1
(νa(COO) and (νs(COO) respectively) with a Δν value
4
), they all formed monometallic species and no evidences of
between 116-46 cm-1.42 The geometry around the cobalt atom
(Fig. 2) was a distorted octahedral as analogous Co(III) salen
complexes in the literature.35,43 Bond distances Co-N (imino),
Co-O (phenolate) and Co-O (acetate) (Fig. 2) are in the average
range as corresponding values in similar octahedral Co(III)
systems.43
bimetallic species were found. Probably, the tert-butyl
substituents together with the more hindered six membered
diamine ring prevent the formation of dinuclear species.
The molecular structures of
X-ray diffraction analysis (Fig. 1-3). Purple crystals of
obtained by slow evaporation of a diluted solution of the
complex in diethyl ether/hexane. presented a 5-coordinated
2-4
were obtained by single-crystal
2
were
2
Complex
4 adopted also an octahedral geometry around the
chromium metal centre where the anionic ligand L2- was
coordinated in the equatorial plane with a tetradentate
fashion through the imine and phenolate O atoms (Fig. 3). One
chloride anion and a water molecule, coming from wet air in
the oxidation step, were located at the axial positions. The
equatorial donor atoms presented a nearly planar geometry
(Fig. 3). The chloride anion and the water molecule were
located with an almost linear disposition (O(3)-Cr(1)-Cl(1) bond
angle of 177.13(18)°). The Cr-N(imine), Cr-O(phenolate) as well
environment (Fig. 1) with geometry around the iron center
intermediate between trigonal bipyramidal and square-
pyramidal.36 This geometry differed from those reported for
[Fe(salenR)Cl].C6H6,37 [Fe(salphen)Cl],38 and other iron salen-
type complexes,39 which had perfectly square-pyramidal
geometry. The length of the diimine ligand could be
considered to influence the iron environment producing this
change in the geometry. The Fe-N(imine) (2.139(2) and
2.0858(19) Å), Fe-O(phenolate) (1.8659(16) and (1.8995(16) Å)
and Fe(Cl) (2.2466(7) Å) bond distances are in agreement with
reported data from other salen-type iron complexes.37,38,40 The
Fe-N(imine) distance has been suggested as an indicator of the
spin state for Fe(III) in salen iron complexes, with the distance
of 2.00-2.10 Å for the high-spin state, and 1.93-1.96 Å for the
low-spin state.40 The mean bond distance in the structure
reported here suggests that the metal ion in
2 is in the high-
spin state, which is consistent with the results of room
temperature magnetic susceptibility (μeff = 5.90 μB).40
Brown crystals of
diluted solution of the complex in
ether/hexane. As shown in Fig. 2 the molecular structure of
3
were obtained by slow evaporation of a
a
mixture diethyl
3
was also monomeric with a six-coordinated central cobalt
atom. In this case L2- acted also as a tetradentated anionic
ligand and one acetate ion as bidentate chelate. Evidences of
the chelate acetate were also obtained from IR spectra41,42 by
the presence of one strong band at 1525 cm-1 and another
Fig. 3 ORTEP drawing of complex of 4. All hydrogen atoms and solvent molecules are
omitted for clarity. Thermal ellipsoids are drawn at the 50 % probability level. Selected
bond lengths (Å) and angles (°):Cr1-O1 1.916(5), Cr1-O2 1.923(5), Cr1-N2 2.012(6), Cr1-
N1 2.059(6), Cr1-Cl1 2.299(3), Cr1-O3 2.052(5)O(1)-Cr(1)-O(2) 91.8(2)°, O(1)-Cr(1)-N(1)
88.3(2)°, O(2)-Cr(1)-N(2) 90.2(2)°, N(1)-Cr(1)-N(2) 89.8(3)°.
presumably in the overcrowded ν(C=C) range of 1478-1409
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as Cr-Cl bond lengths observed were in concordance with the
chromium(III) salen-type complexes reported in the
literature.44,45
94
94
89
94
100
80
60
40
20
0
64
75
68
54
Cycloaddition of CO2 to monosubstituted epoxides
49
Initially, complexes 1-4 were tested as catalysts, in conjunction
with TBAB, for the coupling reaction of CO2 and 1,2-
epoxyhexane as a benchmark substrate. Complexes were
soluble in net substrate; therefore no additional solvent was
required. The initial reaction conditions were 10 bar CO2
using 0.2 mol % complex and 0.2 mol % TBAB during 18 h.
Catalysts /TBAB catalysed the coupling of CO2 and 1,2-
epoxyhexane to produce selectively the cyclic carbonate (Table
1). In the case of catalyst /TBAB we obtained non
reproducible results probably due to decomposition. At these
conditions, the best result was achieved with /TBAB catalytic
, 45 ºC
45
Temperature (ºC)
10 bar 30 bar
60
80
2-4
50 bar
4
Fig. 4 Effect of CO2 pressure and temperature on the coupling of 1,2-epoxyhexane and
CO2 using 1/TBAB catalyst system. Reaction conditions: catalyst 0.2 mol%, TBAB 0.2
mol%, 18h. Reactions were run in duplicate.
1
system with almost 50 % of conversion and total selectivity
towards cyclic carbonate (entries 1-3, Table 1). The higher
Lewis acidity of the Al(III) centre compared to Fe(III) and Co(III)
80 ºC, no positive effect was observed by increasing the
pressure from 10 to 50 bar.
may explain the higher conversion obtained with
1/TBAB
although other factors related with the stability of the
intermediates should also be taken into account. With this
catalytic system, an increase of the catalyst/co-catalyst ratio to
1/5 (1.0 mol % co-catalyst loading) produced an enhancement
in the catalytic activity up to 100 % conversion (entry 4, Table
1). However, in the absence of a co-catalyst almost no cyclic
carbonate was formed even running the reaction at 80 ºC
(entry 5, Table 1). It is important to note that TBAB alone
showed very low conversion under the employed catalytic
conditions (entry 6, Table 1). This synergistic effect between
At the optimized temperature (80 ºC), pressure (10 bar) and
catalyst/co-catalyst ratio of 5 we proceeded to optimize the
catalyst loading and reaction time to obtain the initial
maximum TOF at low conversion. With reduced amounts of
catalyst and co-catalyst and also decreasing the reaction time
to 1 h it was found that significant conversion could still be
achieved (up to 53 % ,initial TOF up to 531 h-1, entry 1, Table
2).
To assess if the catalytic activity was maintained under milder
reaction conditions the same reaction was done at 45 ºC (entry
2, Table 2) and at atmospheric pressure of CO2 (entry 3, Table
2). In both cases a decrease in the catalytic activity was
observed (TOF 90 and 267 h-1respectively), but the initial TOF
at atmospheric pressure was still encouraging. A maximum
TOF of 800 h-1 was obtained at a catalyst loading of 0.05 mol %
in 0.5 h of reaction time (entry 4, Table 2). This value is slightly
lower than the one reported using the hexachloro Al(III)(amine
the aluminium complex
1 and TBAB is in concordance with
analogous behaviour observed with other catalytic systems for
the same reaction. 21,46
The effect of pressure (10, 30 and 50 bar) and temperature
(45, 60, 80 ºC) was also evaluated at 18 h of reaction time with
1/TBAB (catalyst-co-catalyst = 1) (Fig. 4). As expected the
temperature has a beneficial effect in the conversion even
when the CO2 pressure increases up to 50 bar. On the other
hand, raising the pressure produced an increase of conversion
when working at 45 and 60 ºC. When the reaction was run at
triphenolate)/TBAI
catalytic
system
at
similar
catalyst/cocatalyst ratio (0.05/0.25 mol %) at 90 ºC and 10 bar
CO2 initial pressure (TOF 900 h-1).21 However, it is higher than
he one obtained with the dimeric aluminium(salen)
Table 1 Effect of the nature of the catalyst and the catalyst/co-catalyst ratio in the
cycloaddition of 1,2-epoxyhexane to CO2 using 1-3.a
([Al(salen)2(ꢀ-O)]/TBAI, (B, Chart 1) at the same conditions
(0.05/0.25 mol %) at 90 ºC and 10 bar CO2 initial pressure).21
Compared to these two catalytic systems, the advantages of
Co-
cat
Cat/TBAB
(mol %)b
Conv
(%)c,d
Y
Entry
Cat
T (ºC)
(%)f
1
/TBAB are that it does not require the introduction of
1
2
3
4
5
6
1
2
3
1
1
-
TBAB
TBAB
TBAB
TBAB
-
45
45
45
45
80
80
0.2/0.2
0.2/0.2
0.2/0.2
0.2/1.0
0.2/-
49
17
31
100
1
n.d.
16
31
73
1
chlorinated groups in the complex skeleton and can be used at
lower co-catalyst/catalyst ratio. Nevertheless, hexachloro
Al(III)(amine triphenolate)/TBAI can be used at much lower
complex concentration21 and [Al(salen)2(
1 bar CO2 and room temperature.23
ꢀ-O)]/TBAI is active at
TBAB
-/0.2
11
8
aReaction conditions: time = 18 h, PCO2 = 10 bar, 1,2-epoxyhexane: 33.15 mmol
(4 mL), reactions were run in duplicate; bmol % respect to the substrate;
cmeasured by 1H NMR; dSelectivity for the cyclic carbonate product > 99 %
eaveraged TOF (mol substrate converted·(mol catalyst)-1·h-1; fYield of carbonate
product determined by 1H NMR using mesitylene as internal standard.
The catalytic activity of
1/TBAB was studied in the
cycloaddition of CO2 to a variety of terminal and functionalized
epoxides providing the corresponding cyclic carbonates (Fig.
5). All of these selected substrates were converted into the
corresponding carbonates with total selectivity in the cyclic
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Table 2 Optimization of TOF (h-1) using catalytic system 1/TBAB in the cycloaddition of
1,2-epoxyhexane to CO2.a
of equimolar amount of PPNCl without the addition of solvent
(entry 1, Table 3). The 1H NMR of the crude of the reaction
showed a peak at
carbonate) (PCHC)22 together with signals at
δ
4.6 ppm characteristic of poly(cyclohexene
4.5 and 4.0
1/TBAB
T
(ºC)
P
(bar)
Conv
(%)c,d
TOF
Y
t
(h)
Entry
(mol %)b
(h-1)e
(%)f
δ
δ
1
2
3
4
0.1/0.5
0.1/0.5
80
45
80
80
10
10
1
1
1
53
9
531
90
50
9
ppm attributed to the cis- and trans-cyclohexene carbonate
(CHC)48,49 respectively (ratio cis/trans 75/25, ratio PCHC/CHC
71/29). The formation of mixtures of polycarbonate and cyclic
carbonate in the reaction of CHO and CO2 is consistent with
the fact that the activation energy for the formation of PCHC is
0.1/0.5
1
27
20
267
800
21
19
0.05/0.25
10
0.5
aReaction conditions: 1,2-epoxyhexane: 24.86 mmol (3 ml), reactions were run in
duplicate.; bmol % respect to the substrate; cmeasured by 1H NMR; dSelectivity for lower compared to other substrates; nevertheless, the cyclic
product is still the most stable thermodynamically.50 Indeed,
the cyclic carbonate product >99 % averaged TOF (mol substrate converted·(mol
catalyst)-1·h-1; fYield of carbonate product determined by 1H NMR using
Darensbourg and co-workers observed almost total selectivity
towards cyclic carbonate by-product using PPNCl with similar
aluminum-salen complexes.29 The polymer was isolated by
mesitylene as the internal standard.
product at turn over frequency between 120 and 3434 h-1 (Fig.
extraction of the cyclic product with hexane obtaining a
5). This information indicated the high tolerance of the
polycarbonate with high degree of incorporation of CO2 (92 %)
measured by 1H NMR spectroscopy. The number-average
as 1-chloro-2,3-epoxypropane, which presented the highest
molecular weight (Mn) of the alternating copolymer and
catalytic system especially with alkyl halide functionalities such
catalytic activity. It is remarcable that catalyst system 1/TBAB
polydispersity (Mw/Mn), estimated by gel permeation
chromatography (GPC), was 1700 and 1.3, respectively (entry
1, Table 3). Polycarbonate oligomers with diol functionalities
are interesting materials for the synthesis of polyurethanes.51
The selectivity towards de polycarbonate increased up to 84 %
by decreasing the temperature reaction to 25 ºC at longer
reaction time (entries 2 and 3, Table 3). At this temperature
the Mn of the poly(cyclohexene carbonate) increased up to
2900. Similarly, when the CO2 pressure decreased to 10 bar at
45 ºC the reaction proceeded at 63 % conversion although the
% CO2 incorporation decreased to 85 % and the cyclic
carbonate increased due to decrease of the CO2 insertion29
was also active for internal hindered substrates, such as
methyl epoxyoleate derived from a natural product, although
higher concentration of catalyst was required (Fig. 5). Leitner
and co-workers found that TBAB alone (2 mol %) gave very low
conversion of 11 % with a cis/trans ratio of 71/29 at 100 ºC,
125 bar during 6 h.47
Polymerization of CO2 with cyclohexene oxide
The reaction of CO2 and cyclohexene oxide (CHO) was then
investigated using catalyst
1 and changing the co-catalyst to a
most effective Lewis base co-catalysts for this reaction such as
(bis(triphenylphosphine)iminium chloride (PPNCl).29 The
copolymerization reaction was carried out initially at 80 ºC and
(entry 4, Table 3). The conversions obtained with
1/PPNCl
were higher than the ones reported for Al(III) Schiff base
ligands with similar propyl diamine skeleton when NEt4OAc
was used as cocatalyst.52 Instead, the polymers obtained by
50 bar during 18 h with 1 complex (0.2 mol %) in the presence
1/PPNCl catalytic system possessed lower molecular weight
than the one reported by Inoue and coworkers with salophen
aluminum Schiff base complexes. Still, the polydispersity
obtained was higher (2.47, 20 bar, 80 ºC) compared with
1/PPNCl catalytic system (1.3, 10 bar, 45 ºC). It is also
remarkable the use of solvent-free conditions.
Analyses of the polycarbonates by matrix-assisted laser
desorption/ionization time-of-flight mass spectrometry
(MALDI-TOF) revealed two distributions in the polycarbonates
formed (Fig. 6). The major distribution was attributed to a
chain with the presence of -Cl as well as –OH as end groups (a
+ K in Fig. 6) and the second distribution fitted with chains with
two –OH terminal groups (b + K in Fig. 6). This observation
suggests that chain a (Fig. 6) was formed by an initiation step
involving the opening of the epoxide by a nucleophilic attack
of chloride anion, which, presumably, comes from PPNCl co-
catalyst, to the coordinated epoxide. On the other hand, chain
b (Fig. 6), which contains two terminal –OH, suggests that the
initiation step involves the opening of the epoxide by a
nucleophilic attack with –OH originated from traces of water
present in the reactor. The termination step for both polymer
chains may proceed by hydrolysis.
Fig. 5 Cycloaddition of different epoxides to CO2 with catalytic system 1/TBAB. Reaction
conditions: T = 80 ºC, time = 0.5 h, PCO2 = 10 bar, substrate: 3 ml; 1: 0.05 mol %, TBAB:
0.25 mol %; a1: 0.03 mol %; TBAB: 0.15 mol; b1: 2 mol %, TBAB: 2 mol %; T = 100 ºC;
PCO2 = 100 bar. Reactions were run in duplicate.
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Table 3 Copolymerization of cyclohexene oxide (CHO) and CO2 using catalytic system
1/PPNCl.a
(a)
(b)
Y (%)c,
PCHC/
CHC
T.
P.
Time Conv
% CO2
Entry
(Mw·103,
(ºC) (bar)
(h)
18
24
90
24
(%)b
contentb
Mw/Mn)d
(%)c
41
1
2
3
4
80
45
25
45
50
50
50
10
66
92
96
92
85
71/29
82/18
84/16
79/21
(1700, 1.3)
50
(2100, 1.2)
45
(2900, 1.3)
46
(2100, 1.3)
63
58
63
Fig. 7 27Al NMR spectra of complex 1 (a) and a mixture 1/styrene oxide (1:1) (b) in
CDCl3.
aReaction conditions: Cyclohexene oxide: 29.70 mmol (3 ml); 1: 0.2 mol % respect
to the substrate: PPNCl: 0.2 mol % respect to the substrate, reactions were run in
duplicate.; bmeasured by 1H NMR; cYield of PCHC determined by 1H NMR using
mesitylene as the internal standard; ddetermined by GPC using polystyrene as
standard; fSelectivity determined by 1H NMR.
between the pentacoordinated
1 and hexacoordinated 1-SO
takes place (Scheme 3).To continue with the investigation of
the role of the aluminium complex, the co-catalyst and the CO2
pressure in the reaction mechanism, a kinetic study of the
Mechanistic studies for the cycloaddition of CO2 to styrene oxide
formation of cyclic styrene carbonate catalyzed by
1/TBAB
In order to elucidate the mechanism of the cycloaddition of
CO2 to styrene oxide 27Al NMR spectra and kinetic studies were
system was undertaken. Solvent-free conditions were chosen
using neat substrate to work at a similar environment that in
the catalytic studies. The reaction kinetics was monitored by
undertaken. 27Al NMR spectrum in CDCl3 of
1
exhibited a single
broad and strong resonance centred at δ 50 ppm with a width
of 65-35 ppm ( , Fig. 7), which probably collapses with the
probe background53 and can be attributed to
pentacoordinated species.54,55,56 When an equimolar amount
of styrene oxide was added in the NMR tube containing two
defined signals appeared at 40.01 ppm and 3.70 ppm (b,
Fig. 7). According to literature data we assigned the downfield
broad signal to the pentacoordinate complex , whereas the
1
sampling and subsequently analyses by H NMR spectroscopy
a
to determine the conversion of epoxide to cyclic carbonate.
The approximations taken into consideration were those
reported in the literature for similar studies.60,61,62,63 It was
a
1
assumed that the concentration of
1 and TBAB does not
δ
δ
change during the reaction since they both act as catalysts,
and CO2 is present in large excess due to the semi-batch
operation. Thus, the general rate law (Eq. 1) can be
transformed in Eq. 2.
1
up field signal could be ascribed to a hexacoordinated
complex: This compound formed by the coordination of
styrene oxide to the aluminium metal center.,57,58,59 At this
point it was proposed that in an initial step an equilibrium
Eq. 1
Eq. 2
rate = k[SO]a[CO2]b[
1
]c[TBAB]d
rate = kobs[SO]a where kobs = [CO2]b[
1
]c[TBAB]d
The representation of styrene oxide (SO) in front of time
suggested a pseudo-first order dependence respect to the
substrate since there is a lineal dependence of ln[SO] as a
function of time (a = 1, Eq 2) (Figure S28). Contrary to the
observations by North and co-workers using catalyst
(Chart 1) in the synthesis of styrene carbonate, no induction
period was detected using catalytic system
/TBAB.64 The
B/TBAI
1
same authors showed that the reaction under solvent-free
conditions was pseudo-zero order whereas in solvent it was
first order with respect to the starting material.65
To determine the order with respect to the catalyst
1 and the
co-catalyst TBAB, the reactions were performed maintaining
constant the reaction temperature and working in the presen-
O
O
n
O
n
HO
O
Cl
O
O
OH
OH
b
a
Scheme 3 Equilibrium between five and six-coordinated aluminium species.
Fig. 6 MALDI-TOF mass spectrum of polycarbonate from entry 4, Table 3
6 | J. Name., 2012, 00, 1-3
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ce of an excess of CO2. At these conditions its concentration observed, which may be related with low solubility of the
may be considered pseudo constant at the initial stage of the catalytic system in a more dense solvent.47
reaction. Thus, the natural logarithm of the rate law (kobs
k[CO2]b[ ]c[TBAB]d) results in ln kobs = ln k + b ln [CO2] + c ln [
=
The activation energy (Ea) of the formation of styrene
carbonate using catalytic system /TBAB was calculated using
1
1
]
1
+ d ln [TBAB], from which is possible to afford the orders b-d the Arrhenius equation from the relationship between the
with respect to the catalyst, co-catalyst and CO2 concentration observed rate constant (kobs) and the reaction temperature
by examination the double logarithmic plot for each case. (Fig.
Thus, initially, the pressure of CO2 and the amount of TBAB 10 bar pressure CO2. The activation energy was calculated to
was fixed at 0.2 mol % while the concentration of was varied be 38.0 kJ·mol-1. Styring and co-workers obtained a lower
between 0.1-0.4 mol %. Similarly, the pressure of CO2 and the energetic activation barrier of 23 kJ·mol-1 using
concentration of were maintained at 0.2 mol % and TBAB [Al(salacen)]/TBAB and a similar value using [Al(salacen)]
8 S39). The temperature range analysed was 40-100 ºC at
1
1
concentration was changed from 0.2-1.0 mol %. Fig. 9 and Fig. catalyst alone when they studied the synthesis of styrene
61
10 show tThe double logarithmic plot of the initial rates carbonate. Higher values (up to 78 kJ·mol-1) were reported
against catalyst or co-catalyst concentration (see also Fig. S29- using Mg-Al mixed metal oxides.66
S34 in Supplementary Information) show a linear dependence According with 27Al NMR experiments and the kinetic studies
observed with a slope of 0.6618 and 1.1127, respectively, we propose a catalytic cycle (Scheme 4), which initiates with
suggesting that the reaction was first order in the the activation of the epoxide by coordination to the metal
concentration of catalyst
1 and TBAB. This pointed to a center forming a hexacoordinated aluminum complex. The
mechanism in which only one molecule of monometallic Al second step is the formation of a reactive aluminum-alkoxide
complex and also one molecule of TBAB were involved, before species through a nucleophilic attack of the bromide anion
or during the rate-determining step of the catalytic cycle. from TBAB to the epoxide. This metal-alkoxide bond is known
Comparing with the previously reported kinetic analysis of to react easily with CO2 forming a carbonate Al(III) species. This
cyclic carbonate synthesis, similar results were reported by intermediate can either form a polycarbonate through further
Castro-Osma et al. and co-workers, with
a bimetallic alternating insertions of epoxide and CO2 or a cyclic carbonate
aluminium complex,65 and by Kleij and co-workers with a monomer via intramolecular rearrangement and leaving group
binary zinc(salen)-based complex.63 It is then assumed that the liberation.
role of the ammonium halide is to ring-open the coordinated
epoxide to form a halo-alkoxide species. However a second
Conclusion
order respect to the concentration of TBAB was found for the
dinuclear catalytic system B
/TBAI (Chart 1).64 In this case it was
In this work we reported new catalytic systems based on
tetradentate N2O2 salabza metal catalysts. In particular,
attributed to a formation of NBu3, which reacted to CO2 in a
bimetallic mechanism.
aluminium complex 1, was found to be very stable and easy to
The role of the CO2 pressure in the catalytic cycle was analysed
at four different CO2 pressures between 10-40 bar, maintaining
synthesize from simple aluminium trichloride salt. This
mononuclear aluminium complex, combined with TBAB,
formed an active binary catalytic system for cycloaddition of
1/TBAB concentration and temperature constant (80 ºC). It
was observed a first-order dependence at low CO2 pressures,
between 10-30 bar, (slope of 0.6049 including points between
10-30 bar, Fig. 8) suggesting that one CO2 molecule is involved
in the catalytic cycle as reported by North.64 However, at a
higher pressure (40 bar) a decrease of the rate constant was
Cl
N
O
N
O
Al
O
Ph
ln PCO2
NBu4Br
Cl
Al
N
O
N
O
1.5
2.0
2.5
3.0
3.5
4.0
Cl
Al
N
O
N
O
-5.3
-5.4
-5.5
-5.6
-5.7
-5.8
-5.9
-6
O
Ph
O
Br
O
NBu4
y = 0.6049x - 7.4453
R² = 0.9757
O
Ph
Cl
N
N
Al
O
O
CO2
O
O
O
-6.1
-6.2
NBu4
Ph
Br
Scheme 4 Proposed reaction mechanism for the cycloaddition of epoxides into CO2
with catalyst system 1/TBAB.
Fig. 8 Styrene carbonate synthesis at four different CO2 pressures (10-40 bar). Reaction
conditions: T = 80 ºC, 1 0.2 mol %, TBAB 0.2 mol %.
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CO2 and epoxides. This catalytic system provides cyclic concentred to one-third of the original volume. The filtrate
carbonates selectively with excellent conversions even at low was dissolved with CH2Cl2, filtered again over celite and the
pressures of CO2 (up to 94 % at 10 bar). Higher catalytic volatiles removed. The solid was further washed with hexane
activities were obtained with functionalized terminal epoxides and dried under vacuum. Black solid, 302 mg, (Yield 85 %). UV-
such 1-chloro-2,3-epoxypropane with a maximum TOF of 3434 vis (CH3CN, 2.5·10-5 M):
h-1. Even though, more sterical hindered substrate such as (86576), 240.0 (31304), 276.0 (23496), 332.0 (11528), 532.0
methyl epoxyoleate was also transformed selectively in the (3948). ꢀeff (25 ºC) = 5.90 ꢀB Anal. Calcd. for C37H48ClFeN2O2:
cyclic carbonate product although at harsher reaction C, 69.00; H, 7.51; N 4.35. Found: C, 69.29; H, 7.99; N, 4.40.
conditions. Also
detailed kinetic analysis of styrene HRMS (ESI, THF, m/z) calculated for [M-Cl]+: 608.3065, found:
carbonate synthesis catalysed by /TBAB system was carried 608.3038.
λ(nm) (ε, L mol-1 cm-1): 220.0
.
a
1
out. As a result of the observed first order dependence of the
reaction rate on catalyst, co-catalyst and CO2 concentration,
we propose a catalytic cycle, which explains the role of each
Synthesis of (acetato-κ2O,O)[N,N’-bis(3,5-di-tert-butylsalicylene)-
2-aminobenzyl-amino]chloridocobalt(III) (3)
component. Furthermore, using the catalytic system 1/PPNCl To a stirred solution of H2L (300 mg, 0.54 mmol) in THF (10 mL)
in the reaction of cyclohexene oxide and CO2 produces at room temperature under inert atmosphere, an ethanol
poly(cyclohexene carbonate) as a main product. The polymer solution (10 mL) containing 1.0 equiv. of Co(OAc)2·2H2O (134.7
formed contains high chain incorporation of CO2 and mg, 0.54 mmol) was added. The reaction mixture was refluxed
molecular weight up to 2900 g/mol and low polidispersity for 1 h under inert atmosphere, cooled down to room
(1.3). MALDI-TOF analysis of the polycarbonates obtained temperature and was further stirred under air stream for 6 h.
indicated that the initiating step involved the opening of the The resultant solution was concentrated and hexane was
epoxide by Cl- anion and OH- (from water traces).
added to precipitate the product, which was filtered off,
washed with diethyl ether and hexane, and dried under
1
vacuum. Dark red solid, 180.3 mg, (Yield: 49 %). H NMR (400
Experimental
MHz, CDCl3, ppm):
δ 1.16 (br, 9H, tBu), 1.25 (br, 9H, tBu), 1.30
(br, 9H, tBu), 1.45 (br, 9H, tBu), 1.59 (br, 3H, CH3-OAc), 4.17 (d,
1H, ArCH2N, J = 13.6 Hz), 4.54 (d, 1H, ArCH2N, J = 12.4 Hz), 6.99
(br, 1H, ArH), 7.08 (br, 1H, ArH), 7.16 (br, 1H, ArH), 7.34-7.36
(br, 2H, ArH), 7.44 (br, 1H, ArH), 7.75 (br, 1H, CH=N), 7.85 (br,
Synthesis of [N,N’-bis(3,5-di-tert-butylsalicylene)-2-aminobenzyl-
amino]chloridoaluminium(III) (1)
Anhydrous AlCl3 (144.1 mg, 1.08 mmol) was added to a
solution of H2L (400 mg, 0.72 mmol) in 15 mL of dry THF. The
yellow solution was stirred for 4 h at room temperature under
inert atmosphere, filtered over celite and the filtrate was
evaporated under vacuum. The resulting solid was washed
1H, CH=N). UV-vis (CH3CN, 2.5·10-5 M):
1): 217.0 (78980), 230.0 (35624), 258.0 (36144), 416.0 (6088).
ꢀeff (25 ºC) 0.05 ꢀB Anal. Calcd. for
λ(nm) (ε, L mol-1 cm-
=
.
C37H48CoN2O2·H2O·CH3CH2OH: C, 68.36; H, 8.02; N 3.99. Found:
C, 68.42; H, 7.83; N, 3.79. HRMS (ESI, THF, m/z) calculated for
[M-OAc]+: 611.3048, found: 611.3060.
with acetonitrile, pentane and dried again. Bright yellow solid,
1
377.4 mg, (Yield 85 %). H NMR (400 MHz, CDCl3, ppm):
δ 1.28
(s, 9H, tBu), 1.33 (s, 9H, tBu), 1.52 (s, 9H, tBu), 1.57 (s, 9H, tBu),
4.80 (br, 2H, ArCH2N), 7.04 (d, 1H, CH-phenol, J= 2.4 Hz), 7.20
(d, 1H, CH-phenol, J= 2.4 Hz), 7.22-7.27 (m, 3H, ArH), 7.38 (m,
1H, ArH), 7.54 (d, 1H, CH-phenol, J= 2.4 Hz), 7.66 (d, 1H, CH-
phenol, J= 2.4 Hz), 8.35 (s, 1H, CH=N), 8.42 (s, 1H, CH=N); 13C
Synthesis of aqua[N,N’-bis(3,5-di-tert-butylsalicylene)-2-
aminobenzyl-amino]chloridochromium(III) (4)
To a stirred solution of H2L (300.0 mg, 0.5407 mmol) in THF (15
mL) anhydrous CrCl2 (66.5 mg, 0.5407 mmol) was added. The
resulting mixture was stirred under nitrogen at room
temperature for 3 h. Then, was further stirred under air for 3
h. The solution was filtered over celite and the filtrate was
evaporated under vacuum. Cold hexane was added to the
brown mixture. The suspension was filtered off and the solid
was washed with hexane and dried under vacuum. Brown
solid, 193.7 mg, (Yield 55 %). Anal. Calcd. for
C37H50ClCrN2O3·H2O·OC4H8: C, 65.80; H, 8.08; N 3.74. Found: C,
65.99; H, 8.02; N, 3.86. HRMS (ESI, THF, m/z) calculated for
[M-Cl-H2O]+: 604.3121, found: 604.3206.
NMR (75.43 MHz, CDCl3, ppm):
δ
29.78, 29.83 (CH3, tBu), 31.37,
Bu), 35.56, 35.67 (C, tBu),
31.40 (CH3, Bu), 34.09, 34.20 (C,
t
t
62.63 (CH2), 118.08, 119.25, 123.15, 126.78, 127.41, 127.57,
128.51, 130.08, 131.57, 131.68, 132.95, 138.96, 139.55,
140.94, 141.44, 148.28, 162.84, 164.02, 171.63, 171.87. UV-vis
λ(nm) (ε
(CH3CN, 2.5·10-5 M): , L mol-1 cm-1): 226.0 (116100),
282.0 (41884), 369.0 (18752). Anal. Calcd. for
C37H48AlClN2O2·2H2O: C, 68.24; H, 8.05; N, 4.30. Found: C,
68.11; H, 8.21; N, 4.03. HRMS (ESI, m/z) calculated for [M-Cl]+:
579.3531, found 579.3503.
Synthesis of [N,N’-bis(3,5-di-tert-butylsalicylene)-2-aminobenzyl-
X-ray crystallography
amino]chloridoiron(III) (2)
Diffraction data for the structures reported were collected on
a Smart CCD 1000 Bruker diffractometer system with Mo Kα
radiation (λ = 0.71073 Å). Cell refinement, indexing and scaling
of the data sets were carried out using programs Bruker Smart
and Bruker Saint. All the structures were solved by SIR9767 and
refined by Shelxl968 and the molecular graphics with ORTEP-3
A 10 mL MeOH solution of FeCl3 (90.5 mg, 0.56 mmol) was
added dropwise to a 10 mL CH3CN suspension containing H2L
(309.4 mg, 0.56 mmol) and Et3N (0.15 ml, 1.12 mmol). The
resulting solution changed color to dark purple and was gently
refluxed for 2 h. Then the solution was filtered while warm and
8 | J. Name., 2012, 00, 1-3
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for Windows.69 All the calculations were performed using the
WinGX publication routines.70 Crystallographic data are
collected in Table S1 (Supplementary Information).
Standard procedure for the synthesis of cyclic carbonates
The catalytic tests were carried out in a 100 mL Berghof
reactor, which was previously kept for 4 hours under vacuum
at 100 ºC. After cooling, a solution under inert atmosphere
containing the catalyst dissolved in neat distilled substrate and
the co-catalyst, when indicated, was injected into the reactor.
The autoclave was pressurized with CO2, and then heated to
the specific temperature to reach the desired pressure. After
the reaction time, the reactor was cooled with an ice bath and
slowly depressurized (With PO a dichloromethane trap was
used). The conversion was determined by 1H NMR of the crude
mixture by integral ratio between alkene oxide and cyclic
carbonate. The yield was determined by 1H NMR using
mesitylene as internal standard.
1 Y. Li, K. Junge and M. Beller, ChemCatChem, 2013, 5, 1072.
2 Z.-M. Cui, Z. Chen, C.-Y. Cao, W.-G. Song and L. Jiang, Chem.
Commun., 2013, 49, 6093.
3 M. Fleischer, H. Blattmann and R. Mülhaupt, Green Chem.,
2013, 15, 934.
4 B. Nohra, L. Candy, J.-F.Blanco, C. Guerin, Y. Raoul and Z.
Mouloungui, Macromolecules, 2013, 46, 3771.
5 V. Etacheri, R. Marom, R. Elazari, G. Salitra and D. Aurbach,
Standard procedure for copolymerization with cyclohexene oxide
Energy Environ. Sci., 2011, 4, 3243.
Using the same procedure for the synthesis of cyclic
1
carbonates the conversion was also determined by H NMR of
6 C. Beattie, M. North and P. Villuendas, Molecules, 2011, 16
,
3420.
the crude mixture by integral ratio between alkene oxide with
copolymer and cyclic carbonate. The yield was determined by
1H NMR using mesitylene as internal standard. The final
mixture was dissolved in dichloromethane, the solvent was
evaporated and the residue dried in vacuum at 100 ° C for 3
hours to remove excess of cyclohexene oxide. The final residue
was washed several times with hexane to purify the
poly(carbonate) and was analysed by 1H NMR spectroscopy.
The CO2 content was calculated from 1H NMR data by the
7 B. Schäffner, F. Schäffner, S. P. Verevkin and A. Börner,
Chem. Rev, 2010, 110, 4554.
8 A.-A. G. Shaikh and S. Sivaram, Chem. Rev., 1996, 96, 951.
9 G. W. Coates, R. C. Jeske, Anastas, P. T. (Ed.) and R. H.
Crabtree (Ed.) Handbook of Green Chemistry-Green
Catalysis Vol. 1: Homogeneous Catalysis, Weinheim
(Deutschland), WILEY-VCH, 2009, 343.
10 M. Aresta,; Carbon Dioxide as Chemical Feedstock, Wiley-
VCH, 2010, Weinheim.
integral ratio between copolymer carbonate linkages (δ = 4.65
ppm) respect to ether linkage signals (δ = 3.45 ppm).
11 D. J. Darensbourg and M. W. Holtcamp, Coord. Chem. Rev.
1996, 153, 155.
Standard kinetic experiment procedure
12 M. North, R. Pasquale and C. Young, Green Chem. 2010, 12
,
1514.
A Parr 477 autoclave equipped with a proportional-integral-
derivative (PID) temperature controller and gas reservoir was
used for kinetic experiments in the reaction of styrene oxide
with CO2. In a typical experiment, the autoclave was charged
with the catalyst and co-catalyst in neat distilled styrene oxide,
heated and pressurized with CO2. Samples were taken at
determined time and the conversion of the product was
13 P. P. Pescarmona and M. Taherimehr, Catal.Sci. Technol.,
2012, , 2169.
2
14 D. J. Darensbourg, Chem. Rev., 2007, 107, 2388.
15 S. Klaus, M. W. Lehenmeier, C. E. Anderson and B. Rieger,
Coord. Chem. Rev., 2011, 255, 1460.
16 W. J. Kruper, D. V. Dellar, J. Org. Chem. 1995, 60, 725.
1
17 H. V. Babu and K. Muralidharan, Dalton Trans. 2013, 42
,
determined by H NMR spectroscopy. After the reaction time
1238.
the autoclave was then depressurized.
18 S. Iksi, A. Aghmiz, R. Rivas, M. D. González, L. Cuesta-Aluja,
J. Castilla, A. Orejón, F. El Guemmout, A. M. Masdeu-Bultó,
J. Mol. Catal. A: Chem., 2014, 383-384, 143.
19 (a) N. Takeda and S. Inoue, Bull. Chem. Soc. Jpn., 1978, 51
3564; (b) T. Aida and S. Inoue, J. Am. Chem. Soc., 1983, 105
1304.
,
,
Acknowledgements
We gratefully acknowledge the Ministerio de Economia y
Competitividad (CTQ2013-43438-R) and the Departament
20 (a) T. Aida and S. Inoue, Macromolecules, 1982, 15, 682; (b)
T. Aida, M. Ishikawa and S. Inoue, Macromolecules, 1986,
19, 8; (c) S. Inoue, J. Polym. Sci. Part A, Polym. Chem., 2000,
38, 2861.
d'Economia
i
Coneixement (Generalitat de Catalunya,
2014SGR670) for financial support.
21 (a) C. J. Whiteoak, N. Kielland, V. Laserna, E. C. Escudero-
Adán, E. Martin and A. W. Kleij, J. Am. Chem. Soc., 2013,
135, 1228; (b) C. J. Whiteoak, N. Kielland, V. Laserna, V.
Notes and references
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Castro-Gómez, E. Martin, E. C. Escudero-Adán, C. Bo and A. 41 K. M. Szécsényi, V. M. Leovac, Z. K. Jacimovic, V. I. Cesljevic,
W. Kleij, Chem. Eur. J., 2014, 20, 2264.
A. M. Kovacs, G. Pokol and S. Gal, J. Therm. Anal. Calorim.,
2001, 63, 723.
22 (a) D. J. Darensbourg and J. C. Yarbrough, J. Am. Chem. Soc.,
2002, 124, 6335; (b) D. J. Darensbourg and A. I. Moncada, 42 (a) K. Nakamoto, Infrared and Raman spectra of inorganic
Macromolecules, 2010, 43, 5996.
23 J. Meléndez, M. North and R. Pasquale, Eur. J. Inorg. Chem.,
2007, 3323.
and coordination compounds, Wiley & Sons, New York,
1998; (b) G. B. Deacon and R. J. Phillips, Coord. Chem. Rev.,
1980, 33, 227.
24 W. Clegg, R. Harrington, M. North and R. Pasquale, Chem. 43 X. Zhuang, K. Oyaizu, Y. Niu, K. Koshika, X. Chen and H.
Eur. J., 2010, 16, 6828. Nishide, Macromol. Chem. Phys., 2010, 211, 669.
25 X.-B. Lu, X.-J. Feng and R. He, Appl. Catal. A: General, 2002, 44 S. Elmas, M. Subhani, M. Harrer, W. Leitner, J.
234, 25.
Sundermeyer and T. E. Müller, Catal. Sci. Technol., 2014, 4,
26 D. Tian, B. Liu, Q. Gan, H. Li and D. J. Darensbourg, ACS
1652.
Catal. 2012,
2
, 2029.
45 D. J. Darensbourg, A. I. Moncada and S.-H. Wei, Macromol.
2011, 44, 2568.
27 R. Luo, X. Zhou, S. Chen, Y. Li, L. Zhou and H. Ji, Green
Chem., 2014, 16, 1496.
46 X.-B. Lu, Y.-J. Zhang, B. Liang, X. Li and H. Wang, J. Mol.
Catal. A: Chem., 2004, 210, 31.
28 Y. Ren, O. Jiang, H. Zeng, Q. Mao and H. Jiang, RSC
Advances, 2016, 3243.
47 J. Langanke, L. Greiner and W. Leitner, Green Chem., 2013,
15, 1173.
29 D. J. Darensbourg and D. R. Billodeaux, Inorg. Chem., 2005,
44, 1433.
48 A. Buchard, M. R. Kember, K. G. Sandeman and C. K.
Williams, Chem. Commun., 2011, 47, 212.
49 K. Matsumoto, Y. Sato, M. Shimojo and M. Hatanaka,
Tetrahedron: Asymmetr., 2000, 11, 1965.
30 H.-L. Chen, S. Dutta, P.-Y. Huang and C.-C. Lin,
Organometallics, 2012, 31, 2016.
31 M. Sasaki, K. Manseki, H. Horiuchi, M. Kumagai, M.
Sakamoto, H. Sakiyama, Y. Nishida, M. Sakai, Y. Sadaoka, 50 D. J. Darensbourg, J. C. Yarbrough, C. Ortiz and C. C. Fang, J.
M. Ohbad and H. Okawa, J. Chem. Soc. Dalton Trans., 2000,
259.
Am. Chem. Soc., 2003, 125, 7586.
51 Y. Qin, X. Sheng, S. Liu, G. Ren, X. Wang and F. Wang, J. CO2
Util., 2015, 11, 3.
32 G. J. Clarkson, V. C. Gibson, P. K. Y. Goh, M. L. Hammond, P.
D. Knight, P. Scott, T. M. Smit, A. J. P. White and D. 52 H. Sugimoto, H. Ohtsuka and S. Inoue, J. Polym. Sci., Part A:
J.Williams, Dalton Trans. 2006, 5484. Polym. Chem., 2005, 43, 4172.
33 L. Salmon, P. Thuery, E. Riviere, M. Ephritikhine, Inorg. 53 S. N. Azizi and S. Ehsani-Tilami, J. Chin. Chem. Soc., 2009,
Chem., 2006, 45, 83. 56, 898.
34 M. Asadi, M. Mohammadikish, K. Mohammadi, Cent. Eur. J. 54 N. Ropson, P. Dubois, R. Jerome and P. Teyssie,
Chem., 2010,
8, 291.
Macromolecules, 1993, 26, 6378.
35 Y. Niu and H. Li, Colloid. Polym. Sci., 2013, 291, 2181.
36 A. W. Addison, T. N. Rao, J. Reedijk, J. V. Rijn and G. C.
Verschoor, J. Chem. Soc. Dalton Trans., 1984, 1349.
55 A. Dhammani, R. Bohra and R. C. Mehrotra, Polyhedron,
1998, 17, 163.
56 D. A. Atwood and M. J. Harvey, Chem. Rev., 2001, 101, 37.
37 R. A. Pascal Junior, R. P. L'Esperance and D. Van Engen, 57 D. Tian, B. Liu, L. Zhang, X. Wang, W. Zhang, L. Han and D.-
private communication, 2014, CCDC990458.
38 K. Oyaizu and E. Tsuchida, Inorg. Chim. Acta, 2003, 355
414.
W. Park, J. Ind. Eng. Chem., 2012, 18, 1332.
58 H. Haraguchi and S. Fujiwara, J. Phys. Chem., 1969, 10
3467.
,
,
39 L. Jr. Dyers, S. Y. Que, D. VanDerveer and X. R. Bu, Inorg. 59 D. Tian, B. Liu, Q. Gan, H. Li and D. J. Darensbourg, ACS
Chim. Acta, 2006, 359, 197. Catal., 2012, , 2029.
40 H. L. Shyu, H. H. Wei, G. H. Lee and Y. Wang, J. Chem. Soc., 60 J. E. Dengler, M. W. Lehenmeier, S. Klaus, C. E. Anderson, E.
2
Dalton Trans., 2000, 915.
Herdtweck and B. Rieger, Eur. J. Inorg. Chem., 2011, 336.
61 S. Supasitmongkol and P. Styring, Catal. Sci. Technol., 2014,
4, 1622.
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ARTICLE
62 R. Luo, X. Zhou, W. Zhang, Z. Liang, J. Jiang and H. Ji, Green
Chem., 2014, 16, 4179.
63 C. Martín and A. W. Kleij, Beilstein J. Org. Chem., 2014, 10
,
1817.
64 M. North and R. Pasquale, Angew. Chem., Int. Ed., 2009,
48, 2946.
65 J. A. Castro-Osma, A. Lara-Sánchez, M. North, A. Otero and
P. Villuendas, Catal. Sci. Technol., 2012, 2, 1021.
66 K. Yamaguchi, K. Ebitani, T. Yoshida, H. Yoshida and K.
Kaneda, J. Am. Chem. Soc., 1999, 121, 4526.
[67] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori
and R. Spagna, J. Appl. Cryst., 1999, 32, 115.
[68] G. M. Sheldrick, 1997. SHELXS97 and SHELXL97.University
of Göttingen, Germany.
[69] Ortep-3 for Windows - A Version of ORTEP-III with a
Graphical User Interface (GUI). L. J. Farrugia, J. Appl.
Crystallogr., 1997, 30, 565.
[70] WinGX Suite for Single Crystal Small Molecule
Crystallography. L. J. Farrugia, J. Appl. Cryst., 1999, 32, 837.
This journal is © The Royal Society of Chemistry 20xx
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