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Mechanistic Insights into the Carbon Dioxide-Cyclohexene Oxide
Copolymerization reaction: Is one Metal Center enough?
Joan González-Fabra,[a] Fernando Castro-Gómez,[a] Arjan W. Kleij[a,b] and Carles Bo*,[a,c]

Abstract: A detailed study on the mechanism for the alternating
copolymerization of cyclohexene oxide (CHO) and CO2 mediated by
a [Al{amino‐tri(phenolate)}]/NBu4I binary catalyst system has been
carried out using density functional theory (DFT) based methods. Four
potential mechanisms (one monometallic and three bimetallic) were
considered for the first propagation cycle of the CHO/CO2
copolymerization. The obtained Gibbs free-energies provide a rational
for the relative high activity of a non-covalent dimeric structure formed
in situ and thus the feasibility of a bimetallic mechanism to obtain
polycarbonates quantitatively. Gibbs free energies also indicate that
the alternating copolymerization was favoured over the cyclic
carbonate formation.

Introduction
Climate change is one of the main societal challenges that we
face nowadays. Aiming to build up a more sustainable and
environmentally friendly chemical industry, the use of natural
resources is a main route towards the realization of this important
goal. [1] Therefore it is necessary to substitute chemical production
based on crude oil, natural gas and coal by finding renewable
carbon sources and improving the sustainability of chemical
synthesis. One of the most interesting carbon-based alternatives
to fossil sources is carbon dioxide, which constitutes the main byproduct of many chemical processes such as the combustion of
organic fuels, the aerobic metabolic processes of living organisms,
the decay of organic materials and the fermentation of sugars. All
these chemical reactions release a significant amount of CO2 to
the atmosphere, aggravating the greenhouse effect and
consequently climate change.
Carbon dioxide is a renewable, non-toxic and inexpensive
one-carbon building block that can be used for many synthetic
applications in chemistry.[2] However, carbon dioxide conversion
is not straightforward and requires appropriate and efficient
technologies for its activation and conversion because of its
kinetic and thermodynamic stability. A successful approach to
overcome this high stability is to react CO2 with relatively high free
energy compounds, such as epoxides, in the presence of a

[a]

[b]

[c]

J. González-Fabra, Dr. Fernando Castro-Gómez, Prof. Dr. A. W.
Kleij, Prof. Dr. C. Bo Institute of Chemical Research of Catalonia
(ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain
E-mail: cbo@iciq.cat
Prof. Dr. A. W. Kleij
Catalan Institute of Research and Advanced Studies (ICREA), Pg.
Lluís Companys 23, 08010 Barcelona, Spain
Prof. Dr. C. Bo
Departament de Química Física i Inorgànica, Universitat Rovira i
Virgili, Marcel•lí Domingo s/n, 43007 Tarragona, Spain
Supporting information for this article is given via a link at the end of
the document.

suitable catalyst to gain both a thermodynamic and kinetic driving
force. This successful process is interesting from an industrial
point of view because it generates minimal waste, can be carried
out under relatively mild temperature/pressure conditions and
represents high atom economy.
From a chemo-selective point of view, this approach can lead
to the formation of two commercially relevant products: cyclic
carbonates[3] and polycarbonates (Figure 1). Cyclic carbonates
are interesting products that can be used for many direct
applications or as intermediates to synthesize high added-value
products.[4] Despite the massive attention for the formation of
cyclic carbonates, polycarbonate synthesis has also received
extensive attention as these polymers are valuable products from
an industrial point of view. Aliphatic polycarbonates are
biodegradable with useful properties that might become a
potential alternative for conventional polymers based on
phosgene.
Polycarbonates can be synthesized from dienes [5] or
epoxides[6] including propylene oxide[7] or cyclohexene oxide
(CHO).[8] In this context, Williams et al. have made important
contributions towards a better mechanistic understanding of
CHO/CO2 copolymerization (and related processes) catalysed by
a dinuclear Zn complex, in which both metallic centers are
involved in the reaction mechanism.[9] Such bimetallic
mechanisms have also been reported by other groups using most
often salen-based catalyst systems.[10] Moreover, the
copolymerization (and use) of renewable oxiranes such as
limonene oxide have also been studied by the groups of Coates
and Kleij to obtain completely renewable polycarbonates.[11] The
latter group reported on a detailed DFT study that showed that a
bimetallic catalysis pathway is energetically most favourable.[11b]
Additionally, a number of different catalysts have been designed
and applied in the copolymerization reaction of epoxides and CO2
using a large variety of metals.[12]

Figure 1. The reaction between CHO and CO2 to produce either polycarbonates
or cyclic carbonates. Below, an [Al{amino‐tri(phenolate)}] complex and its
dimerization potential.

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Following our previous studies on the mechanism of both
cyclic carbonate[3d-e] and polycarbonate[11b] formation reactions,
herein we report a comprehensive computational study on the
mechanism for the copolymerization reaction between CHO and
CO2 mediated by the binary catalyst system illustrated in Figure 1
composed of [AlCl] and NBu4I. Moreover, we have focused on the
origin of the chemo-selectivity by comparing the rate of cyclic
carbonate formation versus the copolymerization rate.
This reaction is mediated by the binary system that acts as a
highly efficient catalytic system for CO2/epoxide copolymerization.
Three separate aspects of this CHO/CO2 coupling process have
been studied in detail, i.e. (i) determining the most plausible
mechanism for CO2 copolymerization with epoxides, (ii)
elucidating the chemo-selective nature of this process, and (iii)
explore computationally catalyst modifications to improve the
performance of this reaction. The results disclosed herein have
further led to a mechanistic proposal that is based on the noncovalent and reversible formation of a bimetallic Al-complex. This
dimeric species showed improved reactive intermediate
stabilization potential resulting in a smaller energetic span of the
epoxide/CO2 copolymerization process. This attractive
dimerization feature has great potential to be further developed in
the area of copolymerization of CO2 and epoxide monomers.

The key step that allows for copolymerization is the
nucleophilic attack of the carbonate moiety in Int3 onto a second
CHO monomer. This process could take place directly from Int3
involving only one (Monometallic Co-Poly) or two aluminium metal
centres (Bimetallic Co-Poly). Furthermore, in the case of a
bimetallic mechanism, each oxygen atom of the carbonate may
be involved in the attack onto the second epoxide monomer. On
the other hand, an alternative dimeric species that arises from the
dimerization of two individual Al(aminotriphenolate) complexes
through two -oxo bridges previously described by Kleij et al. [3d]
can also be catalytically active. Hence, we have computed the
Gibbs free energy profiles of all these mono- and bimetallic
pathways.

Results and Discussion
Initiation and Carbon Dioxide Insertion. In our previous studies
concerning the [AlCl]-mediated conversion of carbon dioxide and
epoxides into cyclic carbonates, we proposed a reaction
mechanism using DFT-based methods.[3d] The first mechanistic
steps of the cyclic carbonate formation and the copolymerization
reaction have found to be the same. Therefore, these steps
related to the epoxide ring-opening process and the carbon
dioxide insertion, have been depicted jointly (Scheme 1).
These first steps start with the coordination of CHO to the
aluminium complex leading to a stable intermediate (IC) with a
relative free-energy of 16.5 kcal·mol-1. After initial formation of
this coordination complex IC, the nucleophilic co-catalyst (NBu4I)
attacks one electrophilic carbon centre of the epoxide through a
ring-opening step, which leads to a metal alkoxide (Int1), which is
more stable than the previous intermediate (IC) by 1.8 kcal·mol-1.
This process is the initiation step, which has to overcome a
transition state (TS1) with a Gibbs free energy barrier of 7.7
kcal·mol-1.
After the initiation step, a CO2 molecule is inserted into the
AlO bond forming a chelating carbonate (Int2) bonded to the Al
center with a relative free energy of 0.8 kcal·mol-1. This step has
a relative barrier of 21.1 kcal·mol-1, since TS2 has a relative Gibbs
free energy of 2.8 kcal·mol-1. The second part of the CO2 insertion
is an isomerization process to form a linear hemi-carbonate (Int3)
through a relatively high energy demanding (at 11.3 kcal·mol-1)
transition state (TS3). From this Int3 intermediate (-2.2 kcal·mol1
), different reaction pathways emerge (see Scheme 1), to
produce either cyclic carbonate in which the O[2] atom attacks the
electrophilic carbon bonded to the iodide, or propagation towards
a polycarbonate product occurs.

Scheme 1. Schematic representation of the initial CHO coordination, epoxide
ring-opening, carbon dioxide insertion and isomerization steps. Calculated
relative free energy values for each intermediate are presented under each
structure in italics (kcal·mol-1). Transition state energy values for each step are
also shown (in boldface) under each reaction arrow. Al stands here for [AlCl].

Ring Closing versus Propagation Cycle. In Figure 2, we
present the free energy profiles for all studied reaction pathways,
and in Figure 3 the bimetallic and the dimeric copolymerization
reaction mechanisms are compared in detail. As we explained
above, the reaction pathway related to the formation of the cyclic
carbonate (purple) starts with the nucleophilic attack of O[2] to the
electrophilic carbon centre bonded to the iodide. This step has to
overcome a relative barrier of 11.0 kcal·mol-1 associated to the
difference between Int3 (2.2 kcal·mol-1) and TS-cc (8.8 kcal·mol1
). Hereafter, a stable intermediate designated CC is formed
(11.0 kcal·mol-1), which has the cyclic carbonate product still
bonded to the Al-complex through O[1]. Finally, the cyclic
carbonate is released and a new CHO molecule coordinates to
the aluminium. This final step has a relative free energy of 16.5
kcal·mol-1, which is effectively the Gibbs free energy of the
formation of the cyclic carbonate (ΔGr).
Int3 is the starting point for the propagation cycle relevant for
the copolymerization process, so we considered the four different
mechanisms outlined in Scheme 1. The least favorable one is the
monometallic mechanism (red profile in Figure 2) that has to
overcome an absolute barrier of 46.8 kcal·mol -1. This mechanism
starts with the coordination of CHO to a penta-coordinated Al
species (IC-p) occupying an equatorial coordination site leading

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Figure 2. Free-energy profiles for the four copolymerization mechanisms and the cyclic carbonate formation (purple trace). The copolymerization reaction mediated
by one [AlCl]-complex is depicted in red after Int3. The dark and light blue traces refer to the free energy changes related to the propagation steps for the different
bimetallic mechanisms with O[1] and O[2] acting as nucleophilic centres. The green profile represents the energy profile for the dimeric [AlCl]-catalyst.

Figure 3. Catalytic cycles showing the energy profiles for the bimetallic and dimer-mediated copolymerization pathways up to second propagation step. The relative
free energies (kcal·mol-1) of the intermediates are shown in italics beside each structure. The energetic span of both the bimetallic (O[2] attack) and dimer-mediated
pathway is shown in boldface. The formation energy of the dimer is shown at the top.

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Figure 4. Schematic representation of the transition states for the bimetallic mechanism (O[2] attack) and the dimer-mediated pathway. The relative freeenergies (kcal·mol-1) are given in boldface (black color), and the relative barrier (in grey-scale) was calculated as the free energy difference between the
respective TS and the previous intermediate for each step.

to an octahedral structure with a relative energy of 0.8 kcal·mol -1.
Subsequently, the coordinated linear carbonate attacks the CHO
through a transition state (TS-p), with a relative barrier of 27.7
kcal·mol-1 with respect to the intermediate IC-p. Once passing
through TS-p, the obtained alkoxide coordinated to the equatorial
position of the catalyst (Int-p) has a relative free-energy of 3.8
kcal·mol-1. The next step is a barrierless and exergonic
isomerization through TS-p’ (2.9 kcal·mol-1) to obtain an alkoxide
coordinated to the axial position of the Al-complex (1.8 kcal·mol1
) that can continue propagation towards a polycarbonate by
alternating CHO/CO2 insertions.
Alternatively, the second CHO monomer could stay
coordinated to an Al-complex, as in IC, instead of entering the
copolymerization reaction by intramolecular coupling. This would
then imply the need for two aluminum complexes to be involved,
one in the form of IC, which activates a second CHO molecule,
and the other stabilizing the growing chain. This combination of
events is pertinent to a bimetallic mechanism. The first step of
each bimetallic mechanism is the formation of a stable ensemble
between Int3 and IC, which has a relative low free-energy (23.8
kcal·mol-1). Once this ensemble is formed, both carbonate oxygen
atoms (O[1] and O[2], Figure 1) can ring-open the CHO monomer
coordinating to the Al-complex. In case of O[1] attack, the TS-p is
2.0 kcal·mol-1 higher in energy (at 2.4 kcal·mol-1) than the
transition state obtained O[2] attack (at 4.4 kcal·mol-1). After this,
a new alkoxide species is formed (Int-p) having a relative free
energy of 7.4 kcal·mol-1 and 12.4 kcal·mol-1 for the attack by
O[1] and O[2], respectively.
The origin of the difference in stability between the
nucleophilic attack through O[1] and O[2] relies in the larger steric
hindrance generated by the ligands of the Al-complexes in the
pathway through O[1] attack. The decoordination of the Alcomplex is a barrierless process that gives rise to an alkoxide
bonded to a single Al-complex, P in Figure 2, and enables

continuation of the propagation cycle by insertion of a new CO2
molecule forming a carbonate-ligated Al-complex which then
attacks as a nucleophilic species onto an activated CHO
coordinating a second Al-complex. The difference in stability
between the P intermediates of the two bimetallic pathways
becomes even larger compared to the energy difference
observed for Int-p since the free energy associated to P for the
O[2] pathway is 7.3 kcal·mol-1 lower than that calculated for O[1].
In addition to these bimetallic pathways, there is yet another
mechanistic description available to describe the CHO/CO2
copolymerization process. This alternative is made feasible as a
result of the potential formation of a non-covalent dimeric Alcomplex (Figure 1). This dimerization process occurs in situ and
has been previously experimentally studied for Al- and related Fecomplexes having different peripheral substituents (Figure 1, R =
H, Me and Cl).[3d,13] The dimerization process was calculated to
be an exergonic process by 20.4 kcal·mol-1 (Figure 3) thus
providing high stabilization with respect to two monomeric Alcomplexes. Therefore, the energy reference of the dimeric profile
is 20.4 kcal·mol-1 lower than the zero set for the previous profiles.
The spontaneous though reversible formation of this dimer can be
a huge advantage in new catalyst design if it allows for an
energetically more favourable copolymerization pathway.
Therefore, we also computed the free energy profile of this latter
pathway represented in green (Figure 2). The basic steps for this
dimer-mediated pathway look very similar to those presented
above for the bimetallic mechanism. First, a CHO molecule is
bonded to the axial position of one of the two aluminum centers
of the dimer forming an IC intermediate with a relative free energy
of 24.5 kcal·mol-1. The epoxide ring-opening step is also similar
represented by TS1 and has a low relative barrier of 3.5 kcal·mol1
. The structure of TS1 evolves into Int1, which is the most stable
intermediate (at 31.2 kcal·mol-1) of the entire reaction pathway.
Once this alkoxide is generated, the CO2 insertion takes place

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through TS2 having a relative free energy of 21.5 kcal·mol-1 with
a relative barrier of 9.7 kcal·mol-1. This barrier for the CO2
insertion step is 11.4 kcal·mol-1 lower than that computed in the
bimetallic mechanism (black trace in Figure 2). Hence, the
insertion process seems to be much faster when considering the
non-covalent dimer.
The next intermediate formed in the energy profile of the
dimeric catalyst is a chelated carbonate, whose structure shows
a slight structural difference with those of the other mechanisms.
In these latter cases, the chelated carbonate that forms comprises
two AlO bonds involving the same Al center. However, in the
dimermediated mechanism Int2 has one oxygen atom bonded
to each Al center (Int2 in Figure 3). After Int2, an isomerization
process takes place with a relative free-energy (TS3) of -14.6
kcal·mol-1 resulting in linear hemi-carbonate species (Int3) with a
free energy of 26.7 kcal·mol-1. The coordination of a new CHO
monomer to the free Al center is endergonic (IC-p at 23.6
kcal·mol-1) with respect to Int3. This pre-organization then allows
for the carbonate to attack the coordinated CHO unit through
transition state TS-p related to propagation step of the process
(TS-p, see Figure 5) which is the rate-determining step in this
mechanism with a barrier located at -8.3 kcal·mol-1. The
intermediate formed after TS-p (Int-p) has a relative free energy
of 27.3 kcal·mol-1.
Afterward, the alkoxide (P: at ‒27.0 kcal·mol-1) is finally
generated and the propagation cycle can continue through
repeating CO2 insertion, the coordination of a new CHO monomer
to the other Al center and attack of the linear carbonate onto the
activated CHO monomer.
35

DG‡ Barriers (kcal·mol-1)

Bimetallic

lower relative barriers (Figure 5). The absolute barrier up to
formation of the intermediate P that is the starting point for further
propagation by insertion of a second molecule of CO2, is 6.7
kcal·mol-1 lower and thus the copolymerization catalysed by the
dimeric Al-complex is favoured over the bimetallic pathway.

(a)

*
*

(b)

*

*

Dimeric

30
25
Figure 6. Optimized transition states structures related to the propagation step
(TS-p) for the (a) dimer-mediated (top) and (b) the bimetallic pathways (below)
together with schematic representations. The asterisks denote the carbon
center of the CHO unit being attacked by the carbonate species produced
initially.

20
15
10
5
0
Initiation Step

Insertion Step

Isomerization
Step

Propagation
Step

Global

Figure 5. Relative and absolute Gibbs free-energy barriers for the bimetallic
(blue) and dimer-mediated (grey) mechanisms, energies are in kcal·mol-1.

The lowest absolute barrier is found in the dimeric mechanism
with a value of 22.9 kcal·mol-1, and the only mechanism that
seems unlikely is the monometallic one since the absolute barrier
is too high (46.8 kcal·mol-1). The key transition states, their
relative energies and relative barriers with respect to the
preceding intermediates are collected in Figure 4 for both the
bimetallic
(O[2]
pathway)
and
the
dimer-mediated
copolymerization mechanisms. These mechanisms appear to be
very similar, but the dimer-mediated pathway shows significantly

In silico tuning of the catalytic activity. After having determined
that the dimeric species enables the copolymerization of CHO and
CO2 most efficiently, we further explored the effect of variations in
the structure of the binary catalytic system. Our efforts focused on
two variables: the peripheral substituents of the aminotriphenolate ligand scaffold and the type of halide used as
nucleophilic agent. We chose different aromatic substituents and
nucleophiles which were used before by Kleij et al. [3d, 12d, 13]
including the ones mentioned in Figure 1 (R = H, Me and Cl) and
comparing iodide and chloride as halides. The obtained reaction
free energy profiles are collected in Figure 7, in which the results
for the system already calculated ([AlCl]/NBu4I) are shown in dark
green, the reference profile. Note that the results for the reference
profile in Figure 7 are different from the results presented in Figure
2 since for these calculations solvent effects were included during
geometry optimization of the structures.

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Figure 7. Free energy profiles for the copolymerization reaction of CHO and CO2 catalyzed by binary catalysts derived from [AlR] and either using NBu4Cl or NBu4I as nucleophilic
additive. Schematic representations of the TS structures related to all steps of the mechanism are shown below.

The highest free-energy profile depicted in purple corresponds to
the pathway using a [AlMe]/NBu4I binary catalyst, where both the
most stable intermediate (Int1) and the highest transition state
structures (TS-p) are similar to those computed for the reference
profile. The copolymerization pathway mediated by [AlMe]/NBu4I
is endergonic by 12.5 kcal·mol-1 (non-spontaneous) and the
absolute barrier of this pathway is the highest observed (34.1
kcal·mol-1) being 14.0 kcal·mol-1 higher than observed for the
binary system [AlCl]/NBu4I (20.1 kcal·mol-1). This means that the
catalyst [AlMe]/NBu4I is the least efficient among the five
considered binary systems.
For the binary system composed of [AlMe]/NBu4Cl similar
trends are observed but with lower relative free energies for the

intermediates. The absolute barrier compared to the reference
system [AlCl]/NBu4I is moderately higher by 5.4 kcal·mol-1, but
much lower than for the [AlMe]/NBu4I catalyst (25.5 versus 34.1
kcal·mol-1). The reaction free energy also decreases with respect
to the [AlMe]/NBu4I by 13.6 kcal·mol-1 but higher than noted for the
reference catalyst by 7.9 kcal·mol-1. Hence, the presence of
electron-donating methyl groups in the Al-complex [AlR] seems to
lower the copolymerization efficiency of the binary catalyst.
Replacing the Me-groups for hydrogen atoms (i.e., [AlH])
maintaining iodide as nucleophile (NBu4I) gives a binary system
with slightly higher absolute barrier (2.3 kcal·mol-1 lower) and with
a reaction free-energy 4.9 kcal·mol-1 higher than computed for the
reference system [AlCl]/NBu4I.

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The [AlCl]/NBu4Cl catalyst system shows the lowest relative
energy values, which suggests that it should be the most efficient
binary combination. However, the absolute barrier is slightly
higher than the reference system by 1.8 kcal·mol-1 but on the
other hand the reaction free-energy (at ‒16.0 kcal·mol-1) is 7.0
kcal·mol-1 lower. Hence, while the kinetic resistance observed for
the catalyst [AlCl]/NBu4Cl is comparable, the thermodynamic
driving force is more significant, making this combination of Alcomplex and onium salt the most efficient binary catalyst for
CHO/CO2 copolymerization among the series computationally
investigated.
Electron-withdrawing groups in the aminotriphenolate ligand
(AlR: R = Cl) increase the Lewis acidity of the Al-complex and the
potential to activate the epoxide. On the other hand, when using
nucleophiles with poorer leaving group ability, the stability of the
formed carbonate species (IC-p) increases thereby enhancing the
probability of attack onto a coordinated CHO monomer at a
second Al center, and the stability of the resultant alkoxide. The
use of a chloride based nucleophile also decreases the probability
of cyclic carbonate formation. The intramolecular back-biting of
the carbonate group onto the alkyl-halide is suppressed in line
with the general excellent chemo-selectivity towards the
copolymer observed in the presence of Cl-based additives.

Conclusions
In this study we have theoretically analyzed several possible
reaction mechanisms for the copolymerization reaction of CHO
and CO2, mediated by binary [AlR]/NBu4X catalyst systems. The
mechanism involving a dimeric [AlR]2 species that is able to form
in situ in the reaction media, was found to give the most efficient
copolymerization route among all the mono-metallic and
bimetallic mechanistic manifolds. This complex represents the
first non-covalently assembled bimetallic complex for the
copolymerization reaction between epoxides and carbon dioxide.
This dimeric complex facilitates the formation of an initial
carbonate complex through relative low energetic barriers and
faster overall reaction rates compared to various other bimetallic
scenarios. The computed mechanism involving this dimer species
is compatible with the chemoselectivity of the process towards
polycarbonate, since this manifold is kinetically and
thermodynamically favored over the cyclic carbonate pathway.
The effects of the substituents in the ligand and of the
nucleophile on the catalytic activity were analysed in silico and
show that the efficiency of the binary catalyst [AlR]/NBu4X can be
fine-tuned by the peripheral substituents of the ligand and the type
of nucleophile, as long as the intermediate carbonate species (cf.,
IC-p) is not too high in energy and the energetic span of the
process enables the propagation cycle. Complexes such as [AlR]
with built-in dimerization potential may give access to new types
of efficient epoxide/CO2 copolymerization catalysts, and studies
along this line are part of our ongoing activities.

Computational Details
All calculations in this study were performed by using the Gaussian 09
package.[14] The B97-D3 dispersion-corrected functional[15] was employed.
The standard 6-311G(d,p) basis set[16] was used to describe the H, C, N
and O atoms. The LANL2DZ[17] basis sets and associated relativistic
effective core pseudopotential were used for Al, Cl, and I atoms. Full
geometry optimizations were performed without constrains. The nature of
the encountered stationary points was characterized either as minima or
transition states by means of harmonic vibrational frequencies analysis.
Gibbs free energies were calculated at standard conditions (T = 298.15 K,
P = 1 atm).
Solvent effects were accounted for the gas-phase optimized structures by
using the polarizable continuum model (PCM). Solvent effects in the “In
silico tuning of the catalytic activity” part, have been included during the
optimization of the structures using the PCM model also. The dielectric
constant (ε) of the polarizable medium was set to the value reported for
the simplest epoxide, ethylene oxide (ε = 12.42),[18] as the reaction takes
place in epoxide rich phase. Parameters for 1-hexanol were used for this
purpose (ε = 12.51), as implemented in the Gaussian09 package. A data
set collection of computational results is available in the ioChem-BD
repository [19] and can be accessed via http://dx.doi.org/10.19061/iochembd-1-17.

Acknowledgements
We thank the ICIQ Foundation, ICREA, Generalitat de Catalunya
(2014SGR409) and the Spanish Ministerio de Economía y
Competitividad (MINECO) through projects CTQ2014-52824-R
and CTQ-2014-60419-R, and the Severo Ochoa Excellence
Accreditation 2014-2018 (SEV-2013-0319).
Keywords: carbon dioxide • copolymerization • cyclohexene
oxide • DFT analysis • homogeneous catalysis
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Entry for the Table of Contents

FULL PAPER
Joan González-Fabra, Fernando CastroGómez, Arjan W. Kleij and Carles Bo*
1–8

Two better than one: A computational study of several reaction mechanisms for
CO2/cyclohexene oxide copolymerization mediated by an [Al{amino‐
tri(phenolate)}]/NBu4X binary catalyst suggest that a new non-covalent dimeric
complex formed in situ in the reaction media is indeed the catalytic active species
since it presents the most favourable free energy pathway.

Mechanistic Insights into the Carbon
Dioxide-Cyclohexene Oxide
Copolymerization reaction: Is one
Metal Center enough?