Influence of the Counterion on the Synthesis of Cyclic Carbonates Catalyzed by Bifunctional Aluminum Complexes

Article abstract of DOI:10.1021/acs.inorgchem.8b03475

New bifunctional aluminum complexes have been prepared with the aim of studying the effect of a counterion on the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO₂). Neutral ligand 1 was used as a precursor to obtain four nov

Full text of DOI:10.1021/acs.inorgchem.8b03475

Article
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Influence of the Counterion on the Synthesis of Cyclic Carbonates
Catalyzed by Bifunctional Aluminum Complexes
†,‡
Javier Martínez,†,‡,§ Felipe de la Cruz-Martínez,†,‡ Miguel A. Gaona,†,‡,†E,‡sther Pinilla-Penalver,
̃
†,‡
Juan Fernandez-Baeza,
Ana M. Rodríguez,†,‡ Jose A. Castro-Osma,*
Antonio Otero,*,†,‡
́
́
,†,‡
́
and Agustín Lara-Sanchez*
†
́
́
́
Departamento de Química Inorganica, Organica y Bioquímica-Centro de Innovacion en Química Avanzada (ORFEO−CINQA),
Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla−La Mancha, 13071 Ciudad Real, Spain
Departamento de Quımica Inorganica, Organica y Bioquımica-Centro de Innovacion en Quımica Avanzada (ORFEO−CINQA),
Facultad de Farmacia, Universidad de Castilla−La Mancha, 02071 Albacete, Spain
‡
́
́
́
́
́
́
§
́
́
Laboratorio de Química Inorganica, Facultad de Química, Universidad Catolica de Chile, Casilla 306, Santiago-22 6094411, Chile
S
* Supporting Information
ABSTRACT: New bifunctional aluminum complexes have been
prepared with the aim of studying the effect of a counterion on the
synthesis of cyclic carbonates from epoxides and carbon dioxide
(CO2). Neutral ligand 1 was used as a precursor to obtain four novel
mesylate, chloride, bromide, and iodide zwitterionic NNO ligands
(2−5). The reaction of these ligands with 1 or 2 equiv of AlR3 (R =
Me, Et) allowed the synthesis of mono- and bimetallic bifunctional
aluminum complexes [AlR2(κ2-mbpzappe)]X [X = Cl, R = Me (6),
Et (7); X = Br, R = Me (8), Et (9); X = I, R = Me (10), Et (11)]
and [{AlR2(κ2-mbpzappe)}(μ-O){AlR3}]X [X = MeSO3, R = Me
(12), Et (13); X = Cl, R = Me (14), Et (15); X = Br, R = Me (16),
Et (17); X = I, R = Me (18), Et (19)] via alkane elimination. These
complexes were studied as catalysts for the synthesis of cyclic
carbonates from epoxides and CO2. Iodide complex 11 showed to be the most active catalyst for terminal epoxides, whereas
bromide complex 9 was found to be the optimal catalyst when internal epoxides were used, showing the importance of the
nucleophile cocatalyst on the catalytic activity.
Scheme 1. Reaction of CO2 and Epoxides for the Synthesis
of Cyclic Carbonates
INTRODUCTION
■
A steady increase of carbon dioxide (CO2) emissions from
fossil fuels has been responsible for the excessive accumulation
of CO2 in the atmosphere, which is triggering severe climate
problems and has become an important concern for a
sustainable society.1−4 Although large-scale processes would
barely have an influence on the global concentration of CO2 in
the atmosphere, the growth of effective technologies for the
chemical transformation and utilization of CO2 into high-
value-added products could be one of the most important
processes to preserve fossil resources and to achieve the
balance of the carbon cycle on Earth.5−8 It is worth
highlighting that CO2 is an abundant, inexpensive, nonflam-
mable, and safe substrate that is considered to be a renewable
C1 building block for organic synthesis. However, new catalyst
systems for CO2 utilization need to be developed because of its
thermodynamics.9−11
solvents in chemical processes,17−19 electrolytes in lithium-ion
batteries,20,21 and useful intermediates in organic syn-
thesis.22−25
Over the last 2 decades, several research groups have focused
their attention on the preparation of efficient homogeneous
metal-based catalytic systems supported by salen,26−29
porphyrin,30−33 aminophenolate,34 and other ligands35−38 or
organocatalysts39−43 that have shown high catalytic activity and
selectivity for cyclic carbonate synthesis. Bifunctional metal
systems,44−47 which contain both the metal center and
nucleophile cocatalyst within the same molecular structure,
The reaction of CO2 and epoxides to produce cyclic
carbonates (Scheme 1) is a promising process because of its
high atom economy and the considerable industrial potential
of cyclic carbonates.12−16 For example, cyclic carbonates
already have interesting applications such as polar aprotic
Received: December 17, 2018
© XXXX American Chemical Society
A
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Scheme 2. Synthesis of Zwitterionic Ligands 2−5
have been far less studied for the synthesis of cyclic carbonates,
although these types of catalysts could display greater catalytic
activity for this transformation than the two-component
catalyst systems.44,48−50
[2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-hydroxy-1-phenyleth-
yl]-N,N,N-trimethylbenzenaminium bromide [4,
(mbpzappeH)Br] and 4-[2,2-bis(3,5-dimethyl-1H-pyrazol-1-
yl)-1-hydroxy-1-phenylethyl]-N,N,N-trimethylbenzenaminium
iodide [5, (mbpzappeH)I] as yellow solids (Scheme 2). All
zwitterionic ligand precursors 2−5 were isolated as racemic
mixtures.
In recent years, our research group has developed a range of
heteroscorpionate complexes that have displayed high catalytic
activity in different catalytic applications such as the ring-
opening polymerization (ROP) of cyclic esters,51−53 ring-
opening copolymerization (ROCOP) of epoxides and cyclic
anhydrides,54,55 hydroamination of aminoalkenes,56 and hydro-
alkoxylation/cyclization of alkynyl alcohols.57 However, we
have recently focused our attention on CO2 fixation into cyclic
carbonates catalyzed by organoaluminum heteroscorpionate
complexes, which have displayed high catalytic activity for this
transformation.58−60 Thus, in this work we aim to study the
influence of a counterion on the catalytic activity of
bifunctional aluminum heteroscorpionate complexes for the
synthesis of cyclic carbonates from terminal and internal
epoxides.
The solution-state structures of compounds 2−5 were
characterized by spectroscopic methods (see the Experimental
1
Section). H and 13C{1H}NMR of these compounds showed
two sets of signals for the pyrazole rings, which indicated that
1
the pyrazole rings are not equivalent. The H and 13C{1H}-
NMR spectra of compound 2 show the signal for the methyl
group from the mesylate anion. This resonance disappears in
1
the H and 13C{1H}NMR spectra of compounds 3−5 (Figure
1
1), confirming exchange of the counterions. H one-dimen-
sional nuclear Overhauser spectroscopy (1D NOESY) NMR
experiments allowed assignment of the signals corresponding
to the Ph, NPh, Me3, Me5, H4, and MeSO3 groups, and
−
1H−13C heteronuclear correlation (g-HSQC) NMR experi-
ments allowed assignment of the carbon resonances.
RESULTS AND DISCUSSION
■
The reaction of zwitterionic heteroscorpionate ligand
precursors 2−5 with 1 or 2 equiv of AlR3 (R = Me, Et) in
dry acetonitrile afforded the desired bifunctional mono- and
dinuclear alkylaluminum complexes [AlR2(κ2-mbpzappe)]X [X
= Cl, R = Me (6), Et (7); X = Br, R = Me (8), Et (9); X = I, R
= Me (10), Et (11)] and [{AlR2(κ2-mbpzappe)}(μ-O)-
{AlR3}]X [X = MeSO3, R = Me (12), Et (13); X = Cl, R =
Me (14), Et (15); X = Br, R = Me (16), Et (17); X = I, R =
Me (18), Et (19)] (Scheme 3) in yields higher than 80%. In
bimetallic complexes 12−19, the second aluminum center is
coordinated through a dative bond to the oxygen atom of the
alkoxide moiety (Scheme 3). These complexes are stable in the
solid state at room temperature for weeks.
Synthesis and Structural Characterization. The syn-
theses of zwitterionic ligands 2−5 are presented in Scheme 2.
The compound 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-
(dimethylamino)phenyl]-1-phenylethanol (1, bpzappeH) was
synthesized as previously reported60 and used as the starting
material for synthesis of the zwitterionic ligand precursor 4-
[2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-hydroxy-1-phenyleth-
yl]-N,N,N-trimethylbenzenaminium methanesulfonate [2,
(mbpzappeH)MeSO3], which was synthesized by the reaction
of 1 with an excess of methylmethanesulfonate in dry
acetonitrile under reflux. After the appropriate workup,
compound 2 was obtained as a yellow solid in 80% yield
(Scheme 2).
1
Complexes 6−19 were characterized spectroscopically. H
The reaction of 2 with an excess of potassium chloride in
CH2Cl2/H2O (1:1) provided 4-[2,2-bis(3,5-dimethyl-1H-pyr-
azol-1-yl)-1-hydroxy-1-phenylethyl]-N,N,N-trimethylbenzena-
minium chloride [3, (mbpzappeH)Cl] as a yellow solid
(Scheme 2). On the other hand, the treatment of 2 with an
excess of sodium bromide or sodium iodide in dry CH2Cl2 at
room temperature for 4 h afforded the desired compounds 4-
and 13C{1H}NMR spectra of these complexes showed the
resonances for the pyrazole rings, the methyl groups from the
ammonium moiety, and the aromatic rings and one set of
resonances for the alkyl ligands (Figure 2). It is worth
highlighting that a fluxional behavior due to a quick exchange
process between the two pyrazole rings is possible for these
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1
Figure 1. H NMR spectra of (a) 2 and (b) 4 in CDCl3.
complexes. This behavior has already been observed in other
aluminum heteroscorpionate complexes.58−60
To study the dynamic behavior of complexes 6−19, a
variable-temperature (VT) NMR study for complex 11 was
carried out (Figure 3). VT NMR analysis showed that the
signals of the pyrazole rings broaden and become resolved,
which indicates the presence of two diastereoisomers (Scheme
4) at −95 °C (Figure 3). Therefore, a fast exchange process
between the coordinated and noncoordinated pyrazole rings is
observed, which involves interconversion from one diaster-
eoisomer to the other. Notably, because of the coordination
mode of the heteroscorpionate ligands, the methine carbon
atom between the two pyrazole rings is a chiral center. Thus,
1D NOESY NMR experiments afforded unequivocal
1
assignments for most H NMR resonances, and the 13C{1H}
NMR signals were assigned by 1H−13C g-HSQC NMR
experiments (see the Experimental Section). The NMR results
are consistent with a tetrahedral environment for each
aluminum center, in which the heteroscorpionate ligand is
coordinated to the aluminum center in a κ2-NO coordination
mode for monometallic compounds 6−11 or in a κ2-NO-μ-O
coordination mode for bimetallic complexes 12−19, bridging
the two aluminum atoms (Scheme 3).
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Scheme 3. Synthesis of Aluminum Complexes 6−19
1
Figure 2. H NMR spectrum of 18 in CD3CN.
because the heteroscorpionate ligand is racemic, there are four
possible stereoisomers for complexes 6−19 (Scheme 4).
The solid-state structure of complex 11 was confirmed by
single-crystal X-ray diffraction analysis. The corresponding
ORTEP diagram is represented in Figure 4. The crystallo-
graphic data and selected interatomic distances and angles are
given in Tables S1 and S2. In complex 11, the hetero-
scorpionate ligand is coordinated in a κ2-NO coordination
mode to the aluminum center through the O1 and N1 atoms
(Figure 4). The dihedral angle between the N1−Al−O1 and
C28−Al−C30 planes has a value of 92.4(2)°, which is
consistent with a distorted tetrahedral geometry. The Al1−
N1 and Al1−O1 distances are 1.978(5) and 1.751(4) Å,
respectively. Moreover, the Al−C distances [1.965(6) and
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●
●
Figure 3. VT NMR study for compound 11 in CD2Cl2: (light-blue ) major isomer; (red ) minor isomer.
Scheme 4. Structure for the Four Stereoisomers of Complex
11
Figure 4. ORTEP diagram for compound 11. Hydrogen atoms are
omitted. Thermal ellipsoids are shown at 30%.
Scheme 5. Synthesis of 21a Catalyzed by Compounds 6−19
1.960(6) Å] are in good agreement with the previously
reported aluminum scorpionate complexes.58−60
Synthesis of Cyclic Carbonates. With the aim of
studying the influence of an anion on the synthesis of cyclic
carbonates, complexes 6−19 were screened as catalysts for the
synthesis of styrenecarbonate (21a) from styrene oxide (20a)
and CO2 at 25 °C and 0.1 MPa CO2 pressure under solvent-
free conditions (Scheme 5), and the reactions were monitored
by H NMR spectroscopy. In order to keep the aluminum
loading constant, reactions were carried out using 5 mol %
monometallic complexes 6−11 and 2.5 mol % bimetallic
complexes 12−19. The results obtained are presented in Table
1 (see the Supporting Information for further details).
Polycarbonate formation was not observed under the
aforementioned reaction conditions, and the selectivity toward
the cyclic carbonates was always higher than 99%. This
suggests that the nucleophile is not close enough to the
aluminum atom to carry out the copolymerization of terminal
epoxides and CO2.61,62
1
E
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a
bimetallic complexes 16−19 (Table 1, entries 15−18). This
resulted in a slight increase of the catalytic activity displayed by
complexes 16−19, although their performances were still lower
than those displayed by monometallic complexes 8−11.
Among the catalysts screened for the synthesis of 21a from
20a and CO2, complex 11 showed to be the most active
catalyst and was chosen for further optimization. It is
important to note that the influence of the counterion on
the reaction of CO2 with 20a is clear, with the order of the
catalytic activity being I > Br > Cl.
Table 1. Synthesis of 21a Catalyzed by 6−19
conversion (%)
b
b
entry
catalyst
cocatalyst
25 °C
50 °C
1
2
3
4
5
6
6
7
8
9
10
15
35
38
42
56
1
50
60
95
98
97
99
5
10
11
12
13
14
15
16
17
18
19
16
17
18
19
c
7
Then, the effect of the catalyst loading of complex 11 and
reaction temperature was studied (Table 2). Reactions were
c
8
c
2
5
7
9
43
55
79
82
85
90
89
84
92
94
c
10
11
12
13
10
27
30
33
42
33
38
37
48
Table 2. Optimization of Reaction Conditions for the
c
a
Synthesis of 21a Catalyzed by 11
c
c
conversion (%)
b
b
b
c
entry
11 (mol %)
25 °C
50 °C
85 °C
14
c
c
c
c
,
,
,
,
d
d
e
15
16
17
18
Bu4NBr
Bu4NBr
Bu4NI
1
2
3
4
5
0.5
1.0
1.5
2.5
5.0
6
45
78
89
96
99
98
98
98
99
99
14
20
29
79
e
Bu4NI
a
Reactions were carried out at 0.1 MPa CO2 pressure for 18 h using 5
b
a
mol % complex unless specified otherwise. Conversion of the crude
Reactions were carried out at 1.0 MPa CO2 pressure for 18 h.
Conversion of the crude mixture was determined by 1H NMR
mixture was determined by 1H NMR spectroscopy after 18 h.
b
c
d
e
Complex: 2.5 mol %. Bu4NBr: 2.5 mol %. Bu4NI: 2.5 mol %.
spectroscopy after 18 h.
As can be seen in Table 1, monometallic complexes 6−11
carried at 1.0 MPa CO2 pressure using 20a as the substrate to
avoid epoxide loss during the reaction due to its volatility,
which would result in low isolated yields.58,60 As can be seen in
Table 2, low-to-moderate conversions were obtained at any
catalyst loading for reactions carried out at 25 °C. However,
when the reaction temperature was increased at 50 °C, almost
quantitative conversions were achieved with catalyst loadings
higher than 1.5 mol % (Table 2, entries 3−5). In an attempt to
further reduce the catalyst loading and get quantitative
conversion, reactions were performed at 85 °C, and as can
be seen in Table 2, 98% conversion was achieved at 1.0 MPa
CO2 pressure after 18 h using 0.5 mol % catalyst loading.
Once the reaction conditions for the preparation of 21a
were optimized, the transformation of a variety of terminal
epoxides 20a−20m into their corresponding cyclic carbonates
21a−21m using 0.5−1.0 mol % complex 11 at 85 °C and 1.0
MPa CO2 pressure for 18 h was investigated, and the results
are collected in Figure 5. Generally, good-to-excellent yields
were obtained for the synthesis of cyclic carbonates 21a−21m
from their corresponding terminal epoxides 20a−20m under
these reaction conditions. It is worth highlighting that catalyst
11 was tolerant to aryl and alkyl epoxides and those
functionalized with halide, alcohol, ether, ester, and alkene
groups, which indicates that this catalyst is highly versatile and
selective because no polycarbonate was observed during the
reactions.
and bimetallic complexes 14−19 showed moderate catalytic
activity at 25 °C after 18 h using a catalyst loadings of 5 and
2.5 mol %, respectively (Table 1, entries 1−6 and 9−14).
However, aluminum mesylate complexes 12 and 13 displayed
very low catalytic activity for the synthesis of 21a under these
reaction conditions (Table 1, entries 7 and 8) because of the
low nucleophilicity of the mesylate anion. Moreover, aluminum
iodide complexes 10, 11, 18, and 19 displayed higher catalytic
activity than their corresponding aluminum bromide com-
plexes 8, 9, 16, and 17 and aluminum chloride complexes 6, 7,
14, and 15 for the synthesis of 21a (Table 1, entries 1−6 and
9−14). These results may be due to the higher nucleophilicity
and leaving group ability of the iodide anion compared to the
chloride and bromide anions. The order of the catalytic activity
I > Br > Cl could also be explained by the electrostatic
interaction between the halide anion and ammonium cation
(ion-pairing effect). A stronger interaction between the
ammonium cation and halide anion will result in a less active
catalyst. Therefore, the higher catalytic activity of iodide with
respect to bromide and chloride may be explained by a weaker
electrostatic interaction between the iodide anion and
ammonium cation that makes iodide to move away from the
organometallic complex, and therefore the nucleophilic attack
on the epoxide is accelerated.63−66
In order to improve the catalytic activity of complexes 6−19,
the effect of increasing the reaction temperature to 50 °C was
studied while keeping the CO2 pressure constant at 0.1 MPa
(Table 1). As expected, the catalytic activity of these
complexes increased and almost quantitative conversion of
20a was achieved after 18 h when monometallic aluminum
bromide and iodide catalysts 8−11 were used (Table 1, entries
3−6). In order to keep the concentration of the counterion
constant at 5 mol % in complexes 8−11 and 16−19, 2.5 mol %
tetrabutylammonium bromide (Bu4NBr) and tetrabutylammo-
nium iodide (Bu4NI) was added to the reaction catalyzed by
In order to further extend the substrate scope, the synthesis
of disubstituted cyclic carbonates from their corresponding
internal epoxides was studied. First, we optimized the reaction
conditions for the synthesis of cyclohexene carbonate (23a)
from cyclohexene oxide (22a) and CO2 (Scheme 6) using the
mono- and dinuclear aluminum chloride, bromide, and iodide
complexes 6−11 and 14−19, and the results are shown in
Table 3. The reactions were performed in a sealed reactor at 85
°C and 1.0 MPa CO2 pressure for 24 h under solvent-free
conditions.
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Figure 5. Synthesis of cyclic carbonates 21a−21m from epoxides 20a−20m and CO2 catalyzed by complex 11.
complexes 8, 9, 16, and 17 were more active than the iodide
ones 10, 11, 18, and 19 (Table 3, entries 3−6 and 9−12),
indicating the importance of the anion for the synthesis of
cyclic carbonates. As previously mentioned, aluminum iodide
complexes 10, 11, 18, and 19 displayed higher catalytic activity
when terminal epoxides were used as substrates (Table 1).
However, bromide complexes 8, 9, 16, and 17 showed to be
more efficient when using internal epoxides (Table 3). The
effect of adding Bu4NBr or Bu4NI into reactions catalyzed by
bimetallic complexes 16−19 to have a bromide or iodide
concentration of 1.5 mol % was studied (Table 3, entries 13−
16). The addition of more nucleophiles slightly improved their
catalytic activity, but complex 9 showed the highest catalytic
activity for the synthesis of 23a (Table 3, entry 4). According
to these results, the order of the catalytic activity for internal
epoxides was Br > I > Cl, showing that not only is the balance
between the nucleophilicity, leaving group ability, and
electrostatic interactions between the cation and anion
important but also the steric hindrance of the epoxide is
crucial, and a smaller nucleophile is needed in order to obtain
good yields of disubstituted cyclic carbonates.
After the reaction conditions were optimized, the formation
of six disubstituted cyclic carbonates 23a−23f from their
corresponding internal epoxides 22a−22f and CO2 was
studied (Figure 6). The reactions were performed using 1.5−
2.5 mol % complex 9 at 85 °C and 1.0 MPa CO2 pressure for
24 h. Cyclic carbonates 23a−23d were obtained in good yields
(65−86%) in the presence of 1.5 mol % catalyst 9. However,
2.5 mol % complex 9 was required to obtain reasonable yields
of cyclic carbonates 23e and 23f possibly because of the
greater steric hindrance of their corresponding epoxides. cis-
and trans-epoxides 22c and 22d were used for synthesis of
their corresponding cyclic carbonates 23c and 23d. The cyclic
carbonate product 23c was isolated as a 94:6 mixture of cis/
trans-cyclic carbonate (see the Supporting Information). In a
similar way, the trans-cyclic carbonate 23d was obtained as a
5:95 mixture of cis/trans-cyclic carbonate, which confirmed
Scheme 6. Synthesis of 23a
Table 3. Synthesis of 23a Catalyzed by Complexes 6−11 and
a
14−19
b
entry
catalyst
cocatalyst
conversion (%)
1
2
3
4
5
6
6
7
8
9
7
14
70
85
52
63
10
23
60
65
50
58
58
66
69
73
10
11
14
15
16
17
18
19
16
17
18
19
c
7
c
8
c
9
c
10
11
12
13
14
15
16
c
c
c
c
c
c
,
,
,
,
d
d
e
Bu4NBr
Bu4NBr
Bu4NI
e
Bu4NI
a
Reactions were carried out at 85 °C and 1.0 MPa CO2 pressure for
b
24 h using 1.5 mol % complex unless specified otherwise. Conversion
1
of the crude mixture was determined by H NMR spectroscopy after
c
d
e
24 h. Complex: 0.75 mol %. Bu4NBr: 0.75 mol %. Bu4NI: 0.75 mol
%.
As can be seen in Table 3, chloride complexes 6, 7, 14, and
15 showed very low catalytic activity for the synthesis of 23a
(Table 3, entries 1, 2, 7, and 8), whereas aluminum bromide
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for the monometallic complexes and a κ2-NO-μ-O coordina-
tion mode for the bimetallic complexes, in which the second
aluminum center is coordinated through a dative bond to the
oxygen atom of the alkoxide moiety.
These complexes were able to promote cyclic carbonate
formation from epoxides and CO2 without the need for the
addition of an external nucleophile cocatalyst. The catalysts
showed to be very selective toward cyclic carbonate synthesis,
and no polycarbonate was observed during the reaction. This
study has allowed us to conclude that iodide bifunctional
aluminum complex 11 is the optimal catalyst for the synthesis
of a wide variety of monosubstituted cyclic carbonates from
terminal epoxides and CO2 in good-to-excellent yields. On the
other hand, bifunctional aluminum bromide complex 9 was the
optimal catalyst for disubstituted cyclic carbonate synthesis
from CO2 and internal epoxides.
EXPERIMENTAL SECTION
■
All manipulations were performed under nitrogen, using standard
Schlenk techniques. Solvents were predried over sodium wire (n-
hexane or THF) or over CaCl2 (acetonitrile) and distilled under
nitrogen from sodium (toluene), a sodium−potassium alloy (n-
hexane), or CaCl2 (acetonitrile). Deuterated solvents were stored over
activated 4 Å molecular sieves and degassed by several freeze−thaw
cycles. Microanalyses were carried out with a PerkinElmer 2400 CHN
Figure 6. Synthesis of cyclic carbonates 23a−23f from epoxides 22a−
22f and CO2 catalyzed by complex 9. [a]95 °C.
that the reactions occurred with retention of the epoxide
stereochemistry. Therefore, two inversions of stereochemistry
at the less-hindered carbon atom of the epoxide take place
during the catalytic cyclic carbonate synthesis. As previously
observed for monosubstituted cyclic carbonates, no polycar-
bonate formation was observed.
Considering that the synthesis of disubstituted cyclic
carbonates takes place with retention of the epoxide stereo-
chemistry, a plausible mechanism for the cyclic carbonate
formation catalyzed by complex 9 is shown in Scheme 7, which
is consistent with the catalytic cycle previously reported for
cyclic carbonate formation using other aluminum com-
plexes.58−60
1
analyzer. H and 13C NMR spectra were recorded on a Varian Inova
FT-500 spectrometer and referenced to the residual deuterated
solvent. 1D NOESY NMR spectra were recorded using standard
VARIAN-FT software with the following acquisition parameters:
irradiation time = 2 s and number of scans = 256. 2D NMR spectra
were acquired using standard VARIAN-FT software and processed
using an IPC-Sun computer. Commercially available chemicals (Alfa,
Aldrich, and Fluka) were used as received.
Synthesis of (mbpzappeH)MeSO3 (2). In a 250 mL Schlenk
tube, compound 1 (1.00 g, 2.33 mmol) was dissolved in dry
acetonitrile (70 mL). Methylmethanesulfonate (0.59 mL, 6.99 mmol)
was added, and the mixture was heated to acetonitrile under reflux
and stirred for 16 h. Then, the solvent was removed under vacuum,
and the crude residue was washed with hexane (3 × 25 mL) to
remove excess methylmethanesulfonate. The resulting solid was dried,
and compound 2 was isolated as a yellow solid. Yield: 77% (0.97 g,
1.80 mmol). 1H NMR (500 MHz, CD3CN, 297 K): δ 7.73−7.20 (m,
9H, NPh, Ph), 7.01 (s, 1H, CH), 5.75 (s, 1H, H4′), 5.74 (s, 1H, H4),
3.56 (s, 9H, NMe3), 2.49 (s, 3H, MeSO3), 2.04 (s, 3H, Me3′), 2.01 (s,
3H, Me3′), 1.99 (s, 6H, Me5,5′). 13C{1H} NMR (125 MHz, CD3CN,
297 K): δ 147.4, 147.3, 146.7, 146.0, 143.6, 141.4, 141.1, 139.8
(Cipso,p-NPh, C3,3′, C5,5′, Cipso-Ph), 128.4−119.5 (NPh, Ph), 106.0
(C4′), 105.6 (C4), 81.3 (Ca), 71.7 (CH), 56.8 (NMe3), 39.0 (CSO3),
12.6 (Me3′), 12.5 (Me3), 10.2 (Me5′), 10.0 (Me5). Elem anal. Calcd
for C28H37N5O4S (539.06): C, 62.33; H, 6.86; N, 12.99. Found: C,
62.43; H, 6.97; N, 12.78.
CONCLUSIONS
■
New bifunctional alkylaluminum heteroscorpionate complexes
supported by zwitterionic ligands containing a mesylate,
chloride, bromide, or iodide anion have been developed.
Single-crystal X-ray studies and NMR spectroscopy confirmed
a κ2-NO coordination mode of the heteroscorpionate ligand
Scheme 7. Proposed Mechanism for the Synthesis of Cyclic
Carbonates from Epoxides and CO2 Catalyzed by Complex
9
Synthesis of (mbpzappeH)Cl (3). Compound 2 (1.00 g, 1.86
mmol) was dissolved in 1:1 CH2Cl2/H2O (25 mL), and then an
excess of KCl (1.39 g, 16.60 mmol) was added. The reaction mixture
was stirred at room temperature for 4 h. Then, the organic layer was
extracted and dried over MgSO4. The mixture was filtered and the
solvent removed under reduced pressure to give the product 3 as a
1
white solid. Yield: 79% (0.70 g, 1.46 mmol). H NMR (500 MHz,
CDCl3, 297 K): δ 8.09 (s, 1H, OH), 7.74−7.15 (m, 9H, NPh, Ph),
6.98 (s, 1H, CH), 5.70 (s, 2H, H4′,4), 3.96 (s, 9H, NMe3), 2.04 (s,
6H, Me3′,3), 2.00 (s, 3H, Me5′), 1.95 (s, 3H, Me5). 13C{1H} NMR
(125 MHz, CDCl3, 297 K): δ 147.4, 147.1, 147.0, 146.0, 143.0, 140.9,
140.8 (Cipso,p-NPh,C3,3′, C5,5′, Cipso-Ph), 128.8−119.0 (NPh, Ph),
107.2 (C4′), 106.3 (C4), 81.4 (Ca), 74.1 (CH), 57.2 (NMe3), 13.3
(Me3′,3), 11.3 (Me5′), 10.9 (Me5). Elem anal. Calcd for C27H34ClN5O
(479.45): C, 67.58; H, 7.09; N, 14.60. Found: C, 67.95; H, 7.32; N,
14.17.
H
DOI: 10.1021/acs.inorgchem.8b03475
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Synthesis of (mbpzappeH)Br (4). Compound 2 (1.00 g, 1.86
mmol) was dissolved in dry dichloromethane (25 mL), and then an
excess of NaBr (1.90 g, 18.60 mmol) was added. The reaction mixture
was stirred at room temperature for 4 h. Then, the reaction mixture
was filtered, and the solvent was removed under vacuum to give
NMR (125 MHz, CD3CN, 297 K): δ 149.3, 149.2, 148.8, 145.9,
145.5, 143.1, 141.8 (Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.2−119.1
(NPh, Ph), 106.4 (C4′), 105.9 (C4), 81.2 (Ca), 69.8 (CH), 56.9
(NMe3), 12.5 (Me3′), 12.3 (Me3), 10.3 (Me5′), 10.1 (Me5), −7.7
[Al(CH3)2]. Elem anal. Calcd for C29H39AlBrN5O (579.11): C,
60.09; H, 6.73; N, 12.09. Found: C, 60.30; H, 6.91; N, 11.94.
Synthesis of [AlEt2{κ2-mbpzappe}]Br (9). The synthesis of 9
was carried out in a manner identical with that for 6, using compound
4 (1.00 g, 1.91 mmol) and a solution of AlEt3 (1 M in hexane, 1.91
mL, 1.91 mmol). Compound 9 was isolated as a yellow solid. Yield:
1
compound 4 as a white solid. Yield: 87% (0.85 g, 1.62 mmol). H
NMR (500 MHz, CDCl3, 297 K): δ 8.07 (s, 1H, OH), 7.76−7.15 (m,
9H, NPh, Ph), 6.95 (s, 1H, CH), 5.68 (s, 1H, H4′), 5.28 (s, 1H, H4),
3.95 (s, 9H, NMe3), 2.02 (s, 3H, Me3′), 2.00 (s, 3H, Me3), 1.97 (s,
3H, Me5′), 1.94 (s, 3H, Me5). 13C{1H} NMR (125 MHz, CDCl3, 297
K): δ 147.5, 147.0, 146.9, 145.9, 143.0, 141.0, 140.9 (Cipso,p-NPh,
C3,3′, C5,5′, Cipso-Ph), 129.0−119.1 (NPh, Ph), 107.2 (C4′), 106.3
(C4), 82.4 (Ca), 74.0 (CH), 57.4 (NMe3), 13.3 (Me3′), 13.2 (Me3),
11.4 (Me5′), 10.9 (Me5). Elem anal. Calcd for C27H34BrN5O
(523.11): C, 61.93; H, 6.50; N, 13.38. Found: C, 62.43; H, 6.81;
N, 13.17.
1
88% (1.03 g). H NMR (500 MHz, CD3CN, 297 K): δ 7.66−7.21
(m, 9H, NPh, Ph), 6.90 (s, 1H, CH), 5.89 (s, 1H, H4′), 5.76 (s, 1H,
H4), 3.58 (s, 9H, NMe3), 2.18 (s, 3H, Me3′), 2.16 (s, 3H, Me3), 2.10
3
(s, 3H, Me5′), 1.93 (s, 3H, Me5), 0.94 (t, JH−H = 8.0 Hz, 6H,
AlCH2CH3), −0.14 (m, 4H, AlCH2CH3). 13C{1H} NMR (125 MHz,
CD3CN, 297 K): δ 149.8, 149.4, 149.0, 148.9, 145.9, 145.6, 143.1
(Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.1−119.0 (NPh, Ph), 106.4
(C4′), 105.9 (C4), 81.1 (Ca), 69.6 (CH), 56.9 (NMe3), 12.4 (Me3′),
12.3 (Me3), 10.3 (Me5′), 10.2 (Me5), 8.8 (AlCH2CH3), 6.0
(AlCH2CH3). Elem anal. Calcd for C31H43AlBrN5O (607.11): C,
61.27; H, 7.08; N, 11.53. Found: C, 61.52; H, 7.27; N, 11.37.
Synthesis of [AlMe2{κ2-mbpzappe}]I (10). The synthesis of 10
was carried out in a manner identical with that for 6, using compound
5 (1.00 g, 1.75 mmol) and a solution of AlMe3 (2 M in toluene, 0.88
mL, 1.75 mmol). Compound 10 was isolated as a yellow solid. Yield:
91% (1.0 g). 1H NMR (500 MHz, CD3CN, 297 K): δ 7.62−7.22 (m,
9H, NPh, Ph), 6.90 (s, 1H, CH), 5.90 (s, 1H, H4′), 5.78 (s, 1H, H4),
3.54 (s, 9H, NMe3), 2.18 (s, 3H, Me3′), 2.15 (s, 3H, Me3), 2.09 (s,
3H, Me5′), 1.93 (s, 3H, Me5), −0.85 (s, 9H, [Al(CH3)3]. 13C{1H}
NMR (125 MHz, CD3CN, 297 K): δ 149.3, 149.2, 148.8, 145.7,
145.5, 143.1, 141.8 (Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.2−119.0
(NPh, Ph), 106.4 (C4′), 105.9 (C4), 81.2 (Ca), 69.8 (CH), 57.0
(NMe3), 12.5 (Me3′), 12.3 (Me3), 10.3 (Me5′), 10.1 (Me5), −7.7
[Al(CH3)3]. Elem anal. Calcd for C29H39AlIN5O (626.90): C, 55.51;
H, 6.22; N, 11.17. Found: C, 55.80; H, 6.71; N, 10.84.
Synthesis of (mbpzappeH)I (5). The synthesis of compound 5
was carried out in a manner identical with that for 4, using compound
2 (1.0 g, 1.86 mmol) and an excess of NaI (2.79 g, 18.60 mmol).
1
Yield: 85% (0.90 g, 1.58 mmol). H NMR (500 MHz, CD3CN, 297
K): δ 7.68−7.23 (m, 9H, NPh, Ph), 6.96 (s, 1H, CH), 5.74 (s, 1H,
H4′), 5.72 (s, 1H, H4), 3.55 (s, 3H, NMe3), 2.03 (s, 3H, Me5′), 2.00
(s, 3H, Me3′), 1.98 (s, 3H, Me3), 1.96 (s, 3H, Me5). 13C{1H} NMR
(125 MHz, CD3CN, 297 K): δ 147.4, 147.3, 146.8, 145.9, 143.6,
141.3, 140.9 (Cipso,p-NPh, C3,3′, C5,5′, Cipso-Ph), 128.5−119.4 (NPh,
Ph), 105.9 (C4′), 105.5 (C4), 81.3 (Ca), 71.6 (CH), 57.1 (NMe3),
12.6 (Me3′,3), 10.3 (Me5′), 10.1 (Me5). Elem anal. Calcd for
C27H34IN5O (570.9): C, 56.75; H, 5.95; N, 12.26. Found: C, 56.81;
H, 5.99; N, 12.09.
Synthesis of [AlMe2{κ2-mbpzappe}]Cl (6). A solution of
compound 3 (1.00 g, 2.08 mmol) was dissolved in dry acetonitrile
(50 mL) and heated to 60 °C. Then, a solution of AlMe3 (2 M in
toluene, 0.88 mL, 2.08 mmol) was added, and the reaction mixture
was stirred at this temperature for 2 h. Then, the solvent was
evaporated under reduced pressure to give a yellow solid. The product
was then washed with n-hexane (25 mL) and recrystallized from
toluene at −26 °C to give compound 6 as a yellow solid. Yield: 91%
(1.02 g). 1H NMR (500 MHz, CDCl3, 297 K): δ 7.83−7.11 (m, 9H,
NPh, Ph), 6.74 (s, 1H, CH), 5.77 (s, 1H, H4′), 5.71 (s, 1H, H4), 3.98
(s, 9H, NMe3), 2.18 (s, 3H, Me3′), 2.17 (s, 3H, Me3), 2.03 (s, 3H,
Me5′), 1.94 (s, 3H, Me5), −0.88 [s, 6H, Al(CH3)2]. 13C{1H} NMR
(125 MHz, CD3CN, 297 K): δ 149.6, 149.1, 146.0, 145.1, 141.6,
141.5, 140.9 (Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.7−118.0 (NPh,
Ph), 107.0 (C4′), 106.3 (C4), 81.4 (Ca), 70.8 (CH), 57.2 (NMe3),
13.2 (Me3′), 13.1 (Me3), 11.2 (Me5′), 10.7 (Me5), −7.6 [Al(CH3)2].
Elem anal. Calcd for C29H39AlClN5O (535.43): C, 64.99; H, 7.28; N,
13.07. Found: C, 65.23; H, 7.71; N, 12.84.
Synthesis of [AlEt2{κ2-mbpzappe}]I (11). The synthesis of 11
was carried out in a manner identical with that for 6, using compound
5 (1.00 g, 1.75 mmol) and a solution of AlEt3 (1 M in hexane, 1.75
mL, 1.75 mmol). Compound 11 was isolated as a yellow solid. Yield:
1
90% (1.03 g). H NMR (500 MHz, CD3CN, 297 K): δ 7.64−7.21
(m, 9H, NPh, Ph), 6.89 (s, 1H, CH), 5.90 (s, 1H, H4′), 5.77 (s, 1H,
H4), 3.58 (s, 9H, NMe3), 2.17 (s, 3H, Me3′), 2.16 (s, 3H, Me3), 2.11
3
(s, 3H, Me5′), 1.94 (s, 3H, Me5), 0.97 (t, JH−H = 8.4 Hz, 6H,
AlCH2CH3), −0.14 (m, 4H, AlCH2CH3). 13C{1H} NMR (125 MHz,
CD3CN, 297 K): δ 149.8, 149.4, 149.0, 146.0, 145.8, 143.1, 141.8
(Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.1−119.0 (NPh, Ph), 106.4
(C4′), 105.9 (C4), 81.1 (Ca), 69.5 (CH), 57.1 (NMe3), 12.4 (Me3′),
12.3 (Me3), 10.4 (Me5′), 10.3 (Me5), 8.8 (AlCH2CH3), 6.0
(AlCH2CH3). Elem anal. Calcd for C31H43AlIN5O (654.90): C,
56.80; H, 6.57; N, 10.75. Found: C, 56.93; H, 6.94; N, 10.41.
Synthesis of [{AlMe2(κ2-mbpzappe)}(μ-O){AlMe3}]MeSO3
(12). The synthesis of 12 was carried out in a manner identical
with that for 6, using compound 2 (1.00 g, 1.86 mmol) and a solution
of AlMe3 (2 M in toluene, 1.86 mL, 3.72 mmol). Compound 12 was
Synthesis of [AlEt2{κ2-mbpzappe}]Cl (7). The synthesis of 7
was carried out in a manner identical with that for 6, using compound
3 (1.00 g, 2.08 mmol) and a solution of AlEt3 (1 M in hexane, 2.08
mL, 2.08 mmol). Compound 7 was isolated as a yellow solid. Yield:
1
91% (1.07 g). H NMR (500 MHz, CD3CN, 297 K): δ 7.61−7.21
(m, 9H, NPh, Ph), 6.88 (s, 1H, CH), 5.89 (s, 1H, H4′), 5.76 (s, 1H,
H4), 3.53 (s, 9H, NMe3), 2.19 (s, 3H, Me3′), 2.16 (s, 3H, Me3), 2.09
(s, 3H, Me5′), 1.93 (s, 3H, Me5), 0.92−1.02 (m, 6H, AlCH2CH3),
−0.14 (m, 4H, AlCH2CH3). 13C{1H} NMR (125 MHz, CD3CN, 297
K): δ 150.3, 150.0, 149.6, 146.6, 146.5, 143.7, 142.4 (Cipso,p-NPh,
C3,3′, C5,5, Cipso-Ph), 129.7−119.6 (NPh, Ph), 107.0 (C4′), 106.4
(C4), 81.7 (Ca), 70.1 (CH), 57.4 (NMe3), 13.0 (Me3′), 12.9 (Me3),
10.8 (Me5′), 10.7 (Me5), 9.3 (AlCH2CH3), 6.6 (AlCH2CH3). Elem
anal. Calcd for C31H43AlClN5O (563.43): C, 66.02; H, 7.63; N, 12.43.
Found: C, 66.23; H, 7.85; N, 12.24.
1
isolated as a yellow solid. Yield: 86% (1.07 g). H NMR (500 MHz,
CD3CN, 297 K): δ 7.61−7.23 (m, 9H, NPh, Ph), 6.91 (s, 1H, CH),
5.90 (s, 1H, H4′), 5.79 (s, 1H, H4), 3.52 (s, 9H, NMe3), 2.52 (brs,
3H, MeSO3), 2.19 (s, 3H, Me3′), 2.17 (s, 3H, Me3), 2.09 (s, 3H,
Me5′), 1.94 (s, 3H, Me5), −0.84 [s, 9H, Al(CH3)3], −1.07 [s, 6H,
Al(CH3)2]. 13C{1H} NMR (125 MHz, CD3CN, 297 K): δ 149.4,
149.2, 148.9, 145.8, 145.5, 143.0, 141.9 (Cipso,p-NPh, C3,3′, C5,5, Cipso
-
Ph), 129.2−119.2 (NPh, Ph), 106.4 (C4′), 105.9 (C4), 81.2 (Ca), 69.8
(CH), 56.9 (NMe3), 39.0 (MeSO3), 12.4 (Me3′), 12.3 (Me3), 10.1
(Me5′), 10.0 (Me5), −5.5 [Al(CH3)2], −7.8 [Al(CH3)3]. Elem anal.
Calcd for C33H51Al2N5O4S (667.06): C, 59.36; H, 7.64; N, 10.49.
Found: C, 59.42; H, 7.89; N, 10.12.
Synthesis of [AlMe2{κ2-mbpzappe}]Br (8). The synthesis of 8
was carried out in a manner identical with that for 6, using compound
4 (1.00 g, 1.91 mmol) and a solution of AlMe3 (2 M in toluene, 0.95
mL, 1.91 mmol). Compound 8 was isolated as a yellow solid. Yield:
1
90% (1.00 g). H NMR (500 MHz, CD3CN, 297 K): δ 7.62−7.20
Synthesis of [{AlEt2(κ2-mbpzappe)}(μ-O){AlEt3}]MeSO3 (13).
The synthesis of 13 was carried out in a manner identical with that for
6, using compound 2 (1.00 g, 1.86 mmol) and a solution of AlEt3 (1
M in hexane, 3.72 mL, 3.72 mmol). Compound 13 was isolated as a
(m, 9H, NPh, Ph), 6.90 (s, 1H, CH), 5.90 (s, 1H, H4′), 5.77 (s, 1H,
H4), 3.54 (s, 9H, NMe3), 2.18 (s, 3H, Me3′), 2.15 (s, 3H, Me3), 2.09
(s, 3H, Me5′), 1.93 (s, 3H, Me5), −0.85 (s, 6H, [Al(CH3)2]. 13C{1H}
I
DOI: 10.1021/acs.inorgchem.8b03475
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
yellow solid. Yield: 88% (1.20 g). 1H NMR (500 MHz, CD3CN, 297
K): δ 7.54−7.23 (m, 9H, NPh, Ph), 6.86 (s, 1H, CH), 5.90 (s, 1H,
H4′), 5.77 (s, 1H, H4), 3.47 (s, 9H, NMe3), 2.67 (brs, 3H, MeSO3),
2.19 (s, 3H, Me3′), 2.17 (s, 3H, Me3), 2.09 (s, 3H, Me5′), 1.94 (s, 3H,
Me5), 0.90−1.30 (m, 15H, AlCH2CH3), −0.10 to −0.40 (m, 10H,
AlCH2CH3). 13C{1H} NMR (125 MHz, CD3CN, 297 K): δ 149.9,
(NMe3), 12.4 (Me3′), 12.3 (Me3), 10.3 (Me5′), 10.1 (Me5), 9.6
(AlCH2CH3), 8.8, 8.0 (AlCH2CH3). Elem anal. Calcd for
C37H58Al2BrN5O (722.76): C, 61.49; H, 8.09; N, 9.70. Found: C,
61.83; H, 8.24; N, 9.52.
Synthesis of [{AlMe2(κ2-mbpzappe)}(μ-O){AlMe3}]I (18). The
synthesis of 18 was carried out in a manner identical with that for 6,
using compound 5 (1.00 g, 1.75 mmol) and a solution of AlMe3 (2 M
in toluene, 1.75 mL, 3.50 mmol). Compound 18 was isolated as a
yellow solid. Yield: 92% (1.13 g). 1H NMR (500 MHz, CD3CN, 297
K): δ 7.64−7.21 (m, 9H, NPh, Ph), 6.90 (s, 1H, CH), 5.90 (s, 1H,
H4′), 5.78 (s, 1H, H4), 3.55 (s, 9H, NMe3), 2.18 (s, 3H, Me3′), 2.15
(s, 3H, Me3), 2.10 (s, 3H, Me5′), 1.94 (s, 3H, Me5), −0.85 [s, 9H,
Al(CH3)3], −0.97 [s, 6H, Al(CH3)2]. 13C{1H} NMR (125 MHz,
CD3CN, 297 K): δ 149.3, 149.2, 148.8, 145.8, 145.5, 143.1, 141.8
(Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.2−119.1 (NPh, Ph), 106.4
(C4′), 105.9 (C4), 81.3 (Ca), 69.8 (CH), 57.1 (NMe3), 12.5 (Me3′),
12.3 (Me3), 10.3 (Me5′), 10.2 (Me5), −7.71 (AlCH3). Elem anal.
Calcd for C32H48Al2IN5O (699.62): C, 54.94; H, 6.92; N, 10.01.
Found: C, 55.12; H, 7.23; N, 9.74.
149.8, 149.4, 146.3, 146.1, 143.3, 142.4 (Cipso,p-NPh, C3,3′, C5,5, Cipso
-
Ph), 129.7−119.4 (NPh, Ph), 106.9 (C4′), 106.5 (C4), 81.8 (Ca), 70.3
(CH), 57.3 (NMe3), 39.5 (MeSO3), 13.1 (Me3′), 12.9 (Me3), 10.7
(Me5′), 10.6 (Me5), 12.3−10.1 (AlCH2CH3), 9.6−8.8 (AlCH2CH3).
Elem anal. Calcd for C38H61Al2N5O4S (737.06): C, 61.86; H, 8.28; N,
9.50. Found: C, 62.03; H, 8.71; N, 9.21.
Synthesis of [{AlMe2(κ2-mbpzappe)}(μ-O){AlMe3}]Cl (14).
The synthesis of 14 was carried out in a manner identical with that
for 6 using compound 3 (1.00 g, 2.08 mmol) and a solution of AlMe3
(2 M in toluene, 2.08 mL, 4.16 mmol). Compound 14 was isolated as
1
a yellow solid. Yield: 91% (1.15 g). H NMR (500 MHz, CD3CN,
297 K): δ 7.68−7.22 (m, 9H, NPh, Ph), 6.94 (s, 1H, CH), 5.91 (s,
1H, H4′), 5.79 (s, 1H, H4), 3.58 (s, 9H, NMe3), 2.20 (s, 3H, Me3′),
2.17 (s, 3H, Me3), 2.11 (s, 3H, Me5′), 1.96 (s, 3H, Me5), −0.83 [s,
9H, Al(CH3)3], −1.03 [s, 6H, Al(CH3)2]. 13C{1H} NMR (125 MHz,
C6D6, 297 K): δ 149.4, 149.3, 148.9, 145.8, 145.5, 143.1, 141.8,
(Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.2−119.1 (NPh, Ph), 106.5
(C4′), 106.0 (C4), 81.1 (Ca), 69.8 (CH), 57.1 (NMe3), 12.6 (Me3′),
12.4 (Me3), 10.3 (Me5′), 10.2 (Me5), −5.6 [Al(CH3)2], −7.8
[Al(CH3)3]. Elem anal. Calcd for C32H48Al2ClN5O (608.17): C,
63.21; H, 7.96; N, 11.52. Found: C, 63.43; H, 8.05; N, 11.27.
Synthesis of [{AlEt2(κ2-mbpzappe)}(μ-O){AlEt3}]Cl (15). The
synthesis of 15 was carried out in a manner identical with that for 6,
using compound 3 (1.00 g, 2.08 mmol) and a solution of AlEt3 (1 M
in hexane, 4.16 mL, 4.16 mmol). Compound 15 was isolated as a
yellow solid. Yield: 87% (1.23 g). 1H NMR (500 MHz, CD3CN, 297
K): δ 7.60−7.20 (m, 9H, NPh, Ph), 6.88 (s, 1H, CH), 5.90 (s, 1H,
H4′), 5.76 (s, 1H, H4), 3.52 (s, 9H, NMe3), 2.19 (s, 3H, Me3′), 2.17
(s, 3H, Me3), 2.10 (s, 3H, Me5′), 1.93 (s, 3H, Me5), 0.90−1.40 (m,
15H, AlCH2CH3), −0.07 to −0.43 (m, 10H, AlCH2CH3). 13C{1H}
NMR (125 MHz, CD3CN, 297 K): δ 149.5, 149.0, 148.6, 146.0,
145.7, 143.1, 141.8 (Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.1−118.8
(NPh, Ph), 106.4 (C4′), 105.8 (C4), 81.1 (Ca), 69.5 (CH), 56.8
(NMe3), 12.4 (Me3′), 12.3 (Me3), 10.2 (Me5′), 10.1 (Me5), 8.6, 6.0
(AlCH2CH3), 1.5 (AlCH2CH3). Elem anal. Calcd for
C37H58Al2ClN5O (678.31): C, 65.54; H, 8.62; N, 10.32. Found: C,
65.82; H, 8.74; N, 10.09.
Synthesis of [{AlEt2(κ2-mbpzappe)}(μ-O){AlEt3}]I (19). The
synthesis of 19 was carried out in a manner identical with that for 6,
using compound 5 (1.00 g, 1.75 mmol) and a solution of AlEt3 (1 M
in hexane, 3.50 mL, 3.50 mmol). Compound 19 was isolated as a
yellow solid. Yield: 89% (1.20 g). 1H NMR (500 MHz, CD3CN, 297
K): δ 7.61−7.22 (m, 9H, NPh, Ph), 6.88 (s, 1H, CH), 5.90 (s, 1H,
H4′), 5.77 (s, 1H, H4), 3.53 (s, 9H, NMe3), 2.19 (s, 3H, Me3′), 2.16
(s, 3H, Me3), 2.10 (s, 3H, Me5′), 1.93 (s, 3H, Me5), 0.90−1.32 (m,
15H, AlCH2CH3), −0.07 to −0.33 (m, 10H, AlCH2CH3). 13C{1H}
NMR (125 MHz, CD3CN, 297 K): δ 150.1, 149.7, 149.3, 146.3,
146.1, 143.4, 142.1 (Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.4 (mCPh),
128.0−119.2 (NPh, Ph), 106.7 (C4′), 106.2 (C4), 81.3 (Ca), 69.8
(CH), 57.2 (NMe3), 12.7 (Me3′), 12.6 (Me3), 10.6 (Me5′), 10.4
(Me5), 9.0 (AlCH2CH3), 5.6 (AlCH2CH3). Elem anal. Calcd for
C37H58Al2IN5O (769.76): C, 57.73; H, 7.59; N, 9.10. Found: C,
57.88; H, 7.81; N, 8.93.
X-ray Crystallographic Structure Determination. Colorless
crystals for 11 were obtained by the diffusion of acetonitrile/hexane.
X-ray data for 11 were collected on a Bruker X8 APEX II CCD area
detector diffractometer at T = 290 K using graphite-monochromated
Mo Kα radiation (λ = 0.710 73 Å, sealed X-ray tube). Data were
integrated using SAINT,67 and an absorption correction was
performed with the program SADABS.68 The structures were solved
by direct methods using the WINGX package69 and refined by full-
matrix least-squares methods based on F2. Non-hydrogen atoms were
refined anisotropically. All hydrogen atoms were placed in calculated
positions and thereafter treated as riding atoms. Compound 11
crystallizes with two acetonitrile molecules disordered over four
positions. These positions have been refined with occupancies of 0.25
for each one, and RIGU instruction has been necessary. Salient
crystallographic data are summarized in Table S1, and further details
can be found in the Supporting Information. Selected bond lengths
and angles are given in Table S2. CCDC 1881272 is for the structure
of 11.
Synthesis of [{AlMe2(κ2-mbpzappe)}(μ-O){AlMe3}]Br (16).
The synthesis of 16 was carried out in a manner identical with that
for 6, using compound 4 (1.00 g, 1.91 mmol) and a solution of AlMe3
(2 M in toluene, 1.91 mL, 3.82 mmol). Compound 16 was isolated as
1
a yellow solid. Yield: 82% (1.02 g). H NMR (500 MHz, C6D6, 297
K): δ 7.55−7.20 (m, 9H, NPh, Ph), 6.88 (s, 1H, CH), 5.90 (s, 1H,
H4′), 5.77 (s, 1H, H4), 3.48 (s, 9H, NMe3), 2.18 (s, 3H, Me3′), 2.16
(s, 3H, Me3), 2.08 (s, 3H, Me5′), 1.91 (s, 3H, Me5), −0.85 [s, 9H,
Al(CH3)3], −0.96 [s, 6H, Al(CH3)2]. 13C{1H} NMR (125 MHz,
CD3CN, 297 K): δ 149.7, 149.3, 148.9, 145.6, 145.5, 143.1, 141.7
(Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.2−118.9 (NPh, Ph), 106.4
(C4′), 105.9 (C4), 81.2 (Ca), 69.8 (CH), 57.0 (NMe3), 12.5 (Me3′),
12.3 (Me3), 10.2 (Me5′), 10.1 (Me5), −7.69 (AlCH3). Elem anal.
Calcd for C32H48Al2BrN5O (652.62): C, 58.90; H, 7.41; N, 10.73.
Found: C, 59.14; H, 7.54; N, 10.52.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b03475.
Synthesis of [{AlEt2(κ2-mbpzappe)}(μ-O){AlEt3}]Br (17). The
synthesis of 17 was carried out in a manner identical with that for 6,
using compound 4 (1.00 g, 1.91 mmol) and a solution of AlEt3 (1 M
in hexane, 3.82 mL, 3.82 mmol). Compound 17 was isolated as a
yellow solid. Yield: 87% (1.20 g). 1H NMR (500 MHz, CD3CN, 297
K): δ 7.55−7.20 (m, 9H, NPh, Ph), 6.86 (s, 1H, CH), 5.90 (s, 1H,
H4′), 5.76 (s, 1H, H4), 3.51 (s, 9H, NMe3), 2.19 (s, 3H, Me3′), 2.17
(s, 3H, Me3), 2.09 (s, 3H, Me5′), 1.92 (s, 3H, Me5), 0.84−1.29 (m,
15H, AlCH2CH3), −0.08 to −0.33 (m, 10H, AlCH2CH3). 13C{1H}
NMR (125 MHz, CD3CN, 297 K): δ 149.9, 149.5, 149.1, 148.9,
146.0, 145.6, 143.2 (Cipso,p-NPh, C3,3′, C5,5, Cipso-Ph), 129.2−118.8
(NPh, Ph), 106.4 (C4′), 105.9 (C4), 81.1 (Ca), 69.5 (CH), 57.0
Experimental data, workup for catalytic reactions, X-ray
1
crystallographic data for compound 11, and H and 13C
NMR spectra for cyclic carbonates (PDF)
Accession Codes
CCDC 1881272 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
J
DOI: 10.1021/acs.inorgchem.8b03475
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(12) Alves, M.; Grignard, B.; Mereau, R.; Jerome, C.; Tassaing, T.;
Detrembleur, C. Organocatalyzed coupling of carbon dioxide with
epoxides for the synthesis of cyclic carbonates: catalyst design and
mechanistic studies. Catal. Sci. Technol. 2017, 7, 2651−2684.
(13) Martín, C.; Fiorani, G.; Kleij, A. W. Recent Advances in the
Catalytic Preparation of Cyclic Organic Carbonates. ACS Catal. 2015,
5, 1353−1370.
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: JoseAntonio.Castro@uclm.es (J.A.C.-O.).
*E-mail: Antonio.Otero@uclm.es (A.O.). Tel.:
+34926295300. Fax: +34926295318.
*E-mail: Agustin.Lara@uclm.es (A.L.-S.).
ORCID
(14) Cokoja, M.; Wilhelm, M. E.; Anthofer, M. H.; Herrmann, W.
A.; Kuhn, F. E. Synthesis of cyclic carbonates from epoxides and
̈
carbon dioxide by using organocatalysts. ChemSusChem 2015, 8,
2436−2454.
(15) Comerford, J. W.; Ingram, I. D. V.; North, M.; Wu, X.
Sustainable metal-based catalysts for the synthesis of cyclic carbonates
containing five-membered rings. Green Chem. 2015, 17, 1966−1987.
(16) Zhu, M. Q.; Carreon, M. A. Porous crystals as active catalysts
for the synthesis of cyclic carbonates. J. Appl. Polym. Sci. 2014, 131,
39738−39750.
Javier Martínez: 0000-0002-1538-0689
́
Juan Fernandez-Baeza: 0000-0002-4332-9266
́
Jose A. Castro-Osma: 0000-0002-5029-0507
Antonio Otero: 0000-0002-2921-2184
́
Agustín Lara-Sanchez: 0000-0001-6547-4862
(17) Lawrenson, S. B.; Arav, R.; North, M. The greening of peptide
synthesis. Green Chem. 2017, 19, 1685−1691.
Author Contributions
(18) Alder, C. M.; Hayler, J. D.; Henderson, R. K.; Redman, A. M.;
Shukla, L.; Shuster, L. E.; Sneddon, H. F. Updating and further
expanding GSK’s solvent sustainability guide. Green Chem. 2016, 18,
3879−3890.
(19) Sathish, M.; Sreeram, K. J.; Raghava Rao, J.; Unni Nair, B.
Cyclic Carbonate: A Recyclable Medium for Zero Discharge Tanning.
ACS Sustainable Chem. Eng. 2016, 4, 1032−1040.
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
(20) Vivek, J. P.; Berry, N.; Papageorgiou, G.; Nichols, R. J.;
Hardwick, L. J. Mechanistic Insight into the Superoxide Induced Ring
Opening in Propylene Carbonate Based Electrolytes using in Situ
Surface-Enhanced Infrared Spectroscopy. J. Am. Chem. Soc. 2016, 138,
3745−3751.
(21) Wei, X. L.; Xu, W.; Vijayakumar, M.; Cosimbescu, L.; Liu, T.
B.; Sprenkle, V.; Wang, W. TEMPO-based catholyte for high-energy
density nonaqueous redox flow batteries. Adv. Mater. 2014, 26, 7649−
7653.
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support from the
́
Ministerio de Economia y Competitividad, Spain (Grants
CTQ2017-84131-R and CTQ2016-81797-REDC; Programa
Redes Consolider). J.M. acknowledges funding to the
CONICYT/FONDECYT Project (Grant 3180073). F.d.l.C.-
M. acknowledges the Ministerio de Educacion, Cultura y
Deporte for a FPU Fellowship.
́
(22) Yang, L.-C.; Rong, Z.-Q.; Wang, Y.-N.; Tan, Z. Y.; Wang, M.;
Zhao, Y. Construction of Nine-Membered Heterocycles through
Palladium-Catalyzed Formal [5 + 4] Cycloaddition. Angew. Chem., Int.
Ed. 2017, 56, 2927−2931.
REFERENCES
■
(1) Li, Y.; Cui, X.; Dong, K.; Junge, K.; Beller, M. Utilization of CO2
as a C1 building block for catalytic methylation reactions. ACS Catal.
2017, 7, 1077−1086.
(2) Song, Q.-W.; Zhou, Z.-H.; He, L.-N. Efficient, Selective and
Sustainable Catalysis of Carbon Dioxide. Green Chem. 2017, 19,
3707−3728.
(3) Aresta, M.; Dibenedetto, A.; Angelini, A. Catalysis for the
valorization of exhaust carbon: from CO2 to chemicals, materials, and
fuels. Technological use of CO2. Chem. Rev. 2014, 114, 1709−1742.
(4) Sakakura, T.; Choi, J.-C.; Yasuda, H. Transformation of Carbon
Dioxide. Chem. Rev. 2007, 107, 2365−2387.
(5) Elgrishi, N.; Chambers, M. B.; Wang, X.; Fontecave, M.
Molecular polypyridine-based metal complexes as catalysts for the
reduction of CO2. Chem. Soc. Rev. 2017, 46, 761−796.
(6) Seo, H.; Katcher, M. H.; Jamison, T. F. Photoredox activation of
carbon dioxide for amino acid synthesis in continuous flow. Nat.
Chem. 2016, 9, 453−456.
(7) Lanzafame, P.; Centi, G.; Perathoner, S. Catalysis for biomass
and CO2 use through solar energy: opening new scenarios for a
sustainable and low-carbon chemical production. Chem. Soc. Rev.
2014, 43, 7562−7580.
(8) Sternberg, A.; Jens, C. M.; Bardow, A. Life cycle assessment of
CO2-based C1-chemicals. Green Chem. 2017, 19, 2244−2259.
(9) Kleij, A. W.; North, M.; Urakawa, A. CO2 Catalysis.
ChemSusChem 2017, 10, 1036−1038.
(10) Maeda, C.; Miyazaki, Y.; Ema, T. Recent Progress in Catalytic
Conversions of Carbon Dioxide. Catal. Sci. Technol. 2014, 4, 1482−
1497.
(23) Hara, Y.; Onodera, S.; Kochi, T.; Kakiuchi, F. Catalytic
Formation of α-Aryl Ketones by C−H Functionalization with Cyclic
Alkenyl Carbonates and One-Pot Synthesis of Isocoumarins. Org. Lett.
2015, 17, 4850−4853.
́
(24) Guo, W. S.; Gonzalez-Fabra, J.; Bandeira, N. A. G.; Bo, C.;
Kleij, A. W. A Metal-free Synthesis of N-Aryl Carbamates under
Ambient Conditions. Angew. Chem., Int. Ed. 2015, 54, 11686−11690.
(25) Kumar, P.; Srivastava, V. C.; Mishra, I. M. Synthesis and
characterization of Ce−La oxides for the formation of dimethyl
carbonate by transesterification of propylene carbonate. Catal.
Commun. 2015, 60, 27−31.
(26) Kuznetsova, S. A.; Rulev, Y. A.; Larionov, V. A.; Smol’yakov, A.
F.; Zubavichus, Y. V.; Maleev, V. I.; Li, H.; North, M.; Saghyan, A. S.;
Belokon, Y. N. Self-Assembled Ionic Composites of Negatively
Charged Zn(salen) Complexes and Triphenylmethane Derived
Polycations as Recyclable Catalysts for the Addition of Carbon
Dioxide to Epoxides. ChemCatChem 2019, 11, 511−519.
(27) Wu, X.; North, M. A Bimetallic Aluminium(Salphen) Complex
for the Synthesis of Cyclic Carbonates from Epoxides and Carbon
Dioxide. ChemSusChem 2017, 10, 74−78.
(28) Luo, R. C.; Zhou, X. T.; Chen, S. Y.; Li, Y.; Zhou, L.; Ji, H. B.
Highly Efficient Synthesis of Cyclic Carbonates from Epoxides
Catalyzed by Salen Aluminum Complexes with Built-in “CO2
Capture” Capability under Mild Conditions. Green Chem. 2014, 16,
1496−1506.
(29) Wu, G.-P.; Darensbourg, D. J.; Lu, X.-B. Tandem metal-
coordination copolymerization and organocatalytic ring-opening
polymerization via water to synthesize diblock copolymers of styrene
oxide/CO2 and lactide. J. Am. Chem. Soc. 2012, 134, 17739−17745.
(11) Fiorani, G.; Guo, W.; Kleij, A. W. Sustainable conversion of
carbon dioxide: the advent of organocatalysis. Green Chem. 2015, 17,
1375−1389.
K
DOI: 10.1021/acs.inorgchem.8b03475
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(30) Jayakumar, S.; Li, H.; Tao, L.; Li, C.; Liu, L.; Chen, J.; Yang, Q.
Cationic Zn-Porphyrin Immobilized in Mesoporous Silicas as
Bifunctional Catalyst for CO2 Cycloaddition Reaction under
Cocatalyst Free Conditions. ACS Sustainable Chem. Eng. 2018, 6,
9237−9245.
(31) Hu, X.-M.; Rønne, M. H.; Pedersen, S. U.; Skrydstrup, T.;
Daasbjerg, K. Enhanced catalytic activity of cobalt porphyrin in CO2
electroreduction upon immobilization on carbon materials. Angew.
Chem., Int. Ed. 2017, 56, 6468−6472.
(32) Qin, Y. S.; Guo, H. C.; Sheng, X. H.; Wang, X. H.; Wang, F. S.
An Aluminum Porphyrin Complex with High Activity and Selectivity
for Cyclic Carbonate Synthesis. Green Chem. 2015, 17, 2853−2858.
(33) Ema, T.; Miyazaki, Y.; Shimonishi, J.; Maeda, C.; Hasegawa, J.-
Y. Bifunctional Porphyrin Catalysts for the Synthesis of Cyclic
Carbonates from Epoxides and CO2: Structural Optimization and
Mechanistic study. J. Am. Chem. Soc. 2014, 136, 15270−15279.
(34) Laserna, V.; Fiorani, G.; Whiteoak, C. J.; Martin, E.; Escudero-
(48) Ren, Y.; Chen, J.; Qi, C.; Jiang, H. A New Type of Lewis Acid−
Base Bifunctional M(salphen) (M = Zn, Cu and Ni) Catalysts for
CO2 Fixation. ChemCatChem 2015, 7, 1535−1538.
(49) Ren, Y.; Jiang, O.; Zeng, H.; Mao, Q.; Jiang, H. Lewis acid−
base bifunctional aluminum−salen catalysts: synthesis of cyclic
carbonates from carbon dioxide and epoxides. RSC Adv. 2016, 6,
3243−3249.
(50) Luo, R.; Zhou, X.; Zhang, W.; Liang, Z.; Jiang, J.; Ji, H. New bi-
functional zinc catalysts based on robust and easy-to-handle N-
chelating ligands for the synthesis of cyclic carbonates from epoxides
and CO2 under mild conditions. Green Chem. 2014, 16, 4179−4189.
́
́
(51) Otero, A.; Fernandez-Baeza, J.; Sanchez-Barba, L. F.; Sobrino,
́
́
S.; Garces, A.; Lara-Sanchez, A.; Rodríguez, A. M. Mono- and
binuclear chiral N,N,O-scorpionate zinc alkyls as efficient initiators for
the ROP of rac-lactide. Dalton Trans. 2017, 46, 15107−15117.
́
(52) Castro-Osma, J. A.; Alonso-Moreno, C.; Lara-Sanchez, A.;
́
́
Otero, A.; Fernandez- Baeza, J.; Sanchez-Barba, L. F.; Rodríguez, A.
M. Catalytic behaviour in the ring-opening polymerisation of
organoaluminiums supported by bulky heteroscorpionate ligands.
Dalton Trans. 2015, 44, 12388−12400.
(53) Castro-Osma, J. A.; Alonso-Moreno, C.; Marquez-Segovia, I.;
Otero, A.; Lara-Sanchez, A.; Fernandez-Baeza, J.; Rodríguez, A. M.;
́
Adan, E.; Kleij, A. W. Carbon dioxide as a protecting group: highly
efficient and selective catalytic access to cycliccis-diol scaffolds. Angew.
Chem., Int. Ed. 2014, 53, 10416−10419.
́
́
(35) Martínez, J.; Fernandez-Baeza, J.; Sanchez-Barba, L. F.; Castro-
́
́
Osma, J. A.; Lara-Sanchez, A.; Otero, A. An Efficient and Versatile
́
́
Lanthanum Heteroscorpionate Catalyst for Carbon Dioxide Fixation
into Cyclic Carbonates. ChemSusChem 2017, 10, 2886−2890.
(36) Zhao, Z.; Qin, J.; Zhang, C.; Wang, Y.; Yuan, D.; Yao, Y.
Recyclable Single-Component Rare-Earth Metal Catalysts for Cyclo-
addition of CO2 and Epoxides at Atmospheric Pressure. Inorg. Chem.
2017, 56, 4568−4575.
(37) Ma, R.; He, L.-N.; Zhou, Y.-B. An efficient and recyclable
tetraoxo-coordinated zinc catalyst for the cycloaddition of epoxides
with carbon dioxide at atmospheric pressure. Green Chem. 2016, 18,
226−231.
(38) Kim, S. H.; Ahn, D.; Go, M. J.; Park, M. H.; Kim, M.; Lee, J.;
Kim, Y. Dinuclear Aluminum Complexes as Catalysts for Cyclo-
addition of CO2 to Epoxides. Organometallics 2014, 33, 2770−2775.
(39) Steinbauer, J.; Kubis, C.; Ludwig, R.; Werner, T. Mechanistic
Study on the Addition of CO2 to Epoxides Catalyzed by Ammonium
and Phosphonium Salts: A Combined Spectroscopic and Kinetic
Approach. ACS Sustainable Chem. Eng. 2018, 6, 10778−10788.
(40) Castro-Osma, J. A.; Martínez, J.; de la Cruz-Martínez, F.;
́
Sanchez-Barba, L. F.; García-Martínez, J. C. Synthesis, structural
characterization and catalytic evaluation of the ring-opening polymer-
ization of discrete five-coordinate alkyl aluminium complexes. Dalton
Trans. 2013, 42, 9325−9337.
(54) Martínez, J.; Martinez de Sarasa Buchaca, M.; de la Cruz-
́
́
Martínez, F.; Alonso-Moreno, C.; Sanchez-Barba, L. F.; Fernandez-
́
Baeza, J.; Rodríguez, A. M.; Rodríguez-Dieguez, A.; Castro-Osma, J.
́
A.; Otero, A.; Lara-Sanchez, A. Versatile organoaluminium catalysts
based on heteroscorpionate ligands for the preparation of polyesters.
Dalton Trans. 2018, 47, 7471−7479.
(55) Martínez de Sarasa Buchaca, M.; de la Cruz-Martínez, F.;
́
Martínez, J.; Alonso-Moreno, C.; Fernandez-Baeza, J.; Tejeda, J.;
́
Niza, E.; Castro-Osma, J. A.; Otero, A.; Lara-Sanchez, A. Alternating
Copolymerization of Epoxides and Anhydrides Catalyzed by
Aluminum Complexes. ACS Omega 2018, 3, 17581−17589.
́
́
́
(56) Otero, A.; Lara-Sanchez, A.; Najera, C.; Fernandez-Baeza, J.;
́
́
Marquez-Segovia, I.; Castro-Osma, J. A.; Martínez, J.; Sanchez-Barba,
L. F.; Rodríguez, A. M. New Highly Active Heteroscorpionate-
Containing Lutetium Catalysts for the Hydroamination of Amino-
alkenes: Isolation and Structural Characterization of a Dipyrrolidi-
nide−Lutetium Complex. Organometallics 2012, 31, 2244−2255.
́
́
Caballero, M. P.; Fernandez-Baeza, J.; Rodríguez-Lopez, J.; Otero, A.;
́
Lara-Sanchez, A.; Tejeda, J. Development of hydroxy-containing
imidazole organocatalysts for CO2 fixation into cyclic carbonates.
Catal. Sci. Technol. 2018, 8, 1981−1987.
́
(57) Martínez, J.; Otero, A.; Lara-Sanchez, A.; Castro-Osma, J. A.;
́
(41) Sopena, S.; Martin, E.; Escudero-Adan, E. C.; Kleij, A. W.
̃
́
́
Fernandez-Baeza, J.; Sanchez-Barba, L. F.; Rodríguez, A. M.
Heteroscorpionate Rare-Earth Catalysts for the Hydroalkoxylation/
Cyclization of Alkynyl Alcohols. Organometallics 2016, 35, 1802−
1812.
Pushing the Limits with Squaramide-Based Organocatalysts in Cyclic
Carbonate Synthesis. ACS Catal. 2017, 7, 3532−3539.
̈
(42) Buttner, H.; Steinbauer, J.; Wulf, C.; Dindaroglu, M.; Schmalz,
H.-G.; Werner, T. Organocatalyzed Synthesis of Oleochemical
Carbonates from CO2 and Renewables. ChemSusChem 2017, 10,
1076−1079.
(43) Stewart, J. A.; Drexel, R.; Arstad, B.; Reubsaet, E.; Weckhuysen,
B. M.; Bruijnincx, P. C. A. Homogeneous and heterogenised masked
N-heterocyclic carbenes for bio-based cyclic carbonate synthesis.
Green Chem. 2016, 18, 1605−1618.
(44) Zhao, Z.; Qin, J.; Zhang, C.; Wang, Y.; Yuan, D.; Yao, Y.
Recyclable Single-Component Rare-Earth Metal Catalysts for Cyclo-
addition of CO2 and Epoxides at Atmospheric Pressure. Inorg. Chem.
2017, 56, 4568−4575.
(45) Dixon, D. J. Bifunctional catalysis. Beilstein J. Org. Chem. 2016,
12, 1079−1080.
(58) Martínez, J.; Castro-Osma, J. A.; Earlam, A.; Alonso-Moreno,
́
́
C.; Otero, A.; Lara-Sanchez, A.; North, M.; Rodríguez-Dieguez, A.
Synthesis of Cyclic Carbonates Catalysed by Aluminium Hetero-
scorpionate Complexes. Chem. - Eur. J. 2015, 21, 9850−9862.
́
(59) de la Cruz-Martínez, F.; Martínez, J.; Gaona, M. A.; Fernandez-
Baeza, J.; Sanchez-Barba, L. F.; Rodríguez, A. M.; Castro-Osma, J. A.;
Otero, A.; Lara-Sanchez, A. Bifunctional Aluminum Catalysts for the
́
́
Chemical Fixation of Carbon Dioxide into Cyclic Carbonates. ACS
Sustainable Chem. Eng. 2018, 6, 5322−5332.
(60) Martínez, J.; Castro-Osma, J. A.; Alonso-Moreno, C.;
́
́
Rodríguez-Dieguez, A.; North, M.; Otero, A.; Lara-Sanchez, A.
One-Component Aluminum(heteroscorpionate) Catalysts for the
Formation of Cyclic Carbonates from Epoxides and Carbon Dioxide.
ChemSusChem 2017, 10, 1175−1185.
(46) Maeda, C.; Taniguchi, T.; Ogawa, K.; Ema, T. Bifunctional
catalysts based on m-phenylene-bridged porphyrin dimer and trimer
platforms: synthesis of cyclic carbonates from carbon dioxide and
epoxides. Angew. Chem., Int. Ed. 2015, 54, 134−138.
(47) Martin, C.; Whiteoak, C. J.; Martin, E.; Martínez-Belmonte, M.;
(61) Wu, G.-P.; Wei, S.-H.; Lu, X.-B.; Ren, W.-M.; Darensbourg, D.
J. Highly Selective Synthesis of CO2 Copolymer from Styrene Oxide.
Macromolecules 2010, 43, 9202−9204.
(62) Darensbourg, D. J.; Yeung, A. D. A concise review of
computational studies of the carbon dioxide−epoxide copolymeriza-
tion reactions. Polym. Chem. 2014, 5, 3949−3962.
́
Escudero-Adan, E. C.; Kleij, A. W. Easily accessible bifunctional
Zn(salpyr) catalysts for the formation of organic carbonates. Catal.
Sci. Technol. 2014, 4, 1615−1621.
L
DOI: 10.1021/acs.inorgchem.8b03475
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
́
(63) Calo, V.; Nacci, A.; Monopoli, A.; Fanizzi, A. Cyclic Carbonate
Formation from Carbon Dioxide and Oxiranes in Tetrabutylammo-
nium Halides as Solvents and Catalysts. Org. Lett. 2002, 4, 2561−
2563.
(64) Sun, J.; Wang, L.; Zhang, S.; Li, Z.; Zhang, X.; Dai, W.; Mori, R.
ZnCl2/phosphonium halide: An efficient Lewis acid/base catalyst for
the synthesis of cyclic carbonate. J. Mol. Catal. A: Chem. 2006, 256,
295−300.
(65) Chang, T.; Jing, H.; Jin, L.; Qiu, W. Quaternary onium
tribromide catalyzed cyclic carbonate synthesis from carbon dioxide
and epoxides. J. Mol. Catal. A: Chem. 2007, 264, 241−247.
(66) Duan, S.; Jing, X.; Li, D.; Jing, H. Catalytic asymmetric
cycloaddition of CO2 to epoxides via chiral bifunctional ionic liquids.
J. Mol. Catal. A: Chem. 2016, 411, 34−39.
(67) SAINT, version 8.37; and APEX3, version 2016.1.0; Bruker
AXS; Madison, WI, 2016.
(68) SADABS: Krause, L.; Herbst-Irmer, R.; Sheldrick, G. M.; Stalke,
D. Comparison of silver and molybdenum microfocus X-ray sources
for single-crystal structure determination. J. Appl. Crystallogr. 2015,
48, 3−10.
(69) (a) Farrugia, L. J. J. Appl. Crystallogr. 2012, 45, 849.
(b) Sheldrick, G. M. SHELX-2014, Program for Crystal Structure
̈
̈
Refinement; University of Gottingen: Gottingen, Germany, 2014.
M
DOI: 10.1021/acs.inorgchem.8b03475
Inorg. Chem. XXXX, XXX, XXX−XXX