A Bimetallic Aluminium(Salphen) Complex for the Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide

Article abstract of DOI:10.1002/cssc.201601131

A bimetallic aluminium(salphen) complex is reported as a sustainable, efficient and inexpensive catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide. In the presence of this complex and tetrabutylammonium bromide, terminal and internal epoxides reacted at 50 °C and 10 bar carbon dioxide pressure to afford their corresponding cyclic carbonates in yields of 50–94 % and 30–71 % for terminal and internal cyclic carbonates, respectively. Mechanistic studies using deuterated epoxides and an analogous monometallic aluminium(salphen) chloride complex support a mechanism for catalysis by the bimetallic complex, which involves intramolecular cooperative catalysis between the two aluminium centres.

Full text of DOI:10.1002/cssc.201601131

DOI: 10.1002/cssc.201601131
Communications
A Bimetallic Aluminium(Salphen) Complex for the
Synthesis of Cyclic Carbonates from Epoxides and Carbon
Dioxide
Xiao Wu and Michael North*[a]
A bimetallic aluminium(salphen) complex is reported as a sus-
tainable, efficient and inexpensive catalyst for the synthesis of
cyclic carbonates from epoxides and carbon dioxide. In the
presence of this complex and tetrabutylammonium bromide,
terminal and internal epoxides reacted at 508C and 10 bar
carbon dioxide pressure to afford their corresponding cyclic
carbonates in yields of 50–94% and 30–71% for terminal and
internal cyclic carbonates, respectively. Mechanistic studies
using deuterated epoxides and an analogous monometallic
aluminium(salphen) chloride complex support a mechanism
for catalysis by the bimetallic complex, which involves intramo-
lecular cooperative catalysis between the two aluminium cen-
tres.
have been reported for their synthesis and, in some cases, ex-
tremely high reactivity and selectivity were observed.[7] These
include complexes of aluminium,[8,9] cobalt,[10] chromium,[8d,11]
zinc[12] and iron,[13] amongst other metals. Nevertheless, there is
still a need for the development of sustainable catalysts that
have high activity under mild reaction conditions and, in par-
ticular, that will accept internal epoxides as substrates. Aliphat-
ic polycarbonates are being developed as replacements for
petrochemical and phosgene derived aromatic poly-
carbonates,[14] which are widely used as the basis of transpar-
ent and impact resistant plastics.
Over the last ten years, we have developed bimetallic alumi-
nium(salen) complex 1 (Figure 1) as a highly effective catalyst
for the synthesis of cyclic carbonates from epoxides and
carbon dioxide.[8a,b] In the presence of aluminium(salen) com-
plex 1 and tetrabutylammonium bromide (TBAB), a range of
terminal epoxides were converted into their corresponding
cyclic carbonates at 258C and 1 bar carbon dioxide pressure.
The conversion of carbon dioxide into value-added chemicals
is an area that is currently receiving much attention,[1,2] and
the development of metal-based catalysts for such transforma-
tions has become an important area of research. The synthesis
of cyclic- or aliphatic poly-carbonates from epoxides and
carbon dioxide (Scheme 1) are often regarded as benchmark
reactions for new catalyst development in carbon dioxide cou-
pling processes. Polycarbonates[3,4] are the kinetic product of
this 100% atom economical reaction, whilst cyclic carbo-
nates[4,5] are the thermodynamic product.
Figure 1. Structure of catalysts 1–3.
Scheme 1. Reaction between epoxides and carbon dioxide.
Subsequently, one-component and immobilised analogues of
catalyst 1 have also been developed.[15] Using the immobilised
catalyst, it was shown that both ethylene and propylene car-
bonate could be produced in a gas-phase reactor, and the re-
action was also compatible with both simulated and real flue
gas. Further development of bimetallic aluminium complexes
led to the development of aluminium(salphen) complex 2,
which was shown to be a more efficient catalyst for the forma-
tion of cyclic carbonates from both terminal and internal epox-
ides.[8d]
Cyclic carbonates are useful reaction intermediates in organ-
ic synthesis, polar aprotic solvents and electrolytes in lithium-
ion batteries.[6] A number of highly active metal-based catalysts
[a] Dr. X. Wu, Prof. M. North
Green Chemistry Centre of Excellence, Department of Chemistry
University of York
Heslington, YO10 5DD (UK)
E-mail: michael.north@york.ac.uk
A feature of catalysts 1 and 2 is the Al-O-Al unit, which has
been shown to play an important role in the catalysis at elevat-
ed temperatures and pressures by reacting with carbon diox-
ide to form a carbonate complex.[16] Separately, however, we
have reported polymetallic aluminium–scorpionate complexes,
Supporting Information for this article can be found under:
http://dx.doi.org/10.1002/cssc.201601131.
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such as 3, which are also highly active aluminium-based cata-
lysts for cyclic carbonate synthesis, but which do not always
possess an intramolecular Al-O-Al unit.[17] Therefore, it was of
interest to investigate bimetallic aluminium(salen)-type com-
plexes with a geometry that would prevent the formation of
an intramolecular Al-O-Al unit as catalysts for cyclic carbonate
synthesis.
Thomas[18] and Kleij,[12c,19] have previously reported metal
complexes of salphen ligand 4, which has a planar geometry,
thus preventing formation of an intramolecular bond between
two coordinated metal ions. Herein, therefore, we report on
the use of bimetallic aluminium(salphen) complex 5 for the
coupling of carbon dioxide and epoxides to form cyclic carbo-
nates.
Scheme 3. Synthesis of cyclic carbonates using catalyst 5.
Table 1. Optimisation of the synthesis of styrene carbonate 7a using
complex 5 and TBAB.[a]
Entry Complex 5 [mol%] TBAB [mol%] T [8C] P [bar] Conversion[b] [%]
1
2
3
4
5
2.5
0.1
0.25
0.25
0
5.0
0.2
0.5
0
25
50
50
50
50
1
10
10
10
10
96
56
90
0
Bimetallic aluminium(salphen) complex 5 was synthesised
from commercially available 1,2,4,5-benzenetetramine tetrahy-
drochloride and 3,5-di-tert-butylsalicylaldehyde to first provide
salphen ligand 4.[20] Upon treatment with diethylaluminium
chloride under refluxing conditions, aluminium(salphen) com-
plex 5 was obtained as a bright orange solid that was insolu-
ble in most organic solvents (Scheme 2).
0.5
20
[a] Reactions were carried out for 24 h. [b] Determined by 1H NMR spec-
troscopy.
tions (Table 1, entry 1), it was noted that complex 5 was not
fully soluble in the initial reaction mixture. Therefore, both the
temperature and pressure were increased to allow the loading
of both complex 5 and TBAB to be reduced. Hence, at 508C
and 10 bar carbon dioxide pressure, a range of complex 5 and
TBAB concentrations were investigated while keeping the 5/
TBAB molar ratio at 1:2. At a complex 5 loading of 0.1 mol%
and TBAB loading of 0.2 mol%, 56% conversion of styrene
oxide 6a into styrene carbonate 7a was observed (Table 1,
entry 2). When the concentrations of complex 5 and TBAB
were increased to 0.25 and 0.5 mol% respectively, the conver-
sion to styrene carbonate 6a increased to 90% (Table 1,
entry 3). Control experiments showed that neither complex 5
nor TBAB alone displayed significant catalytic activity in the ab-
sence of the other catalyst component under these reaction
conditions (Table 1, entries 4 and 5).
A series of terminal epoxides 6a–j was then studied as sub-
strates for the formation of the corresponding cyclic carbo-
nates 7a–j using bimetallic aluminium(salphen) complex 5 and
TBAB as the catalytic system (Figure 2). Interestingly, it was
found that this catalytic system was most active when alkyl (or
hydroxyalkyl) substituted terminal epoxides 6b–f were used as
substrates. In these cases, excellent yields of cyclic carbonates
7b–f were obtained using 0.1 mol% of complex 5 and
0.2 mol% of TBAB. In contrast, for substituents that contain ar-
omatic rings or halogens, a combination of 0.25 mol% of com-
plex 5 and 0.5 mol% of TBAB was required to achieve high
conversions. Nevertheless, the use of complex 5 in the pres-
ence of TBAB proved to be an efficient catalytic system for the
synthesis of cyclic carbonates from both functionalised and un-
functionalised terminal epoxides.
Scheme 2. Synthesis of bimetallic aluminium(salphen) complex 5.
Having prepared bimetallic aluminium(salphen) complex 5,
it was first tested for the conversion of styrene oxide 6a into
styrene carbonate 7a at 258C and 1 bar carbon dioxide pres-
sure under solvent-free condition for 24 h using 2.5 mol% of
catalyst 5 and 5 mol% of TBAB, as shown in Scheme 3. Al-
though a 96% conversion was achieved under these condi-
To further expand the substrate scope, a series of internal
epoxides were then examined. Internal epoxides have always
been considered as challenging substrates for cyclic carbo-
nates synthesis. However, a number of research groups have
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Scheme 4. Synthesis of cyclic carbonates 9a–g from internal epoxides 8a–g
and carbon dioxide. *) Reaction was carried out at 908C. **) Mixture of 90%
cis- and 10% trans-cyclic carbonate.
Having optimised the reaction conditions, a number of inter-
nal epoxides were subjected to the same conditions for the
synthesis of their corresponding cyclic carbonates (Scheme 4).
Pleasingly, the formation of cyclic carbonates 9b and 9c were
achieved with good yields. Surprisingly cyclohexene oxide 8d
was not a good substrate, giving only a 17% yield of cis-cyclo-
hexene carbonate 9d. No polycarbonate was detected in this
or any other reaction catalysed by complex 5. More volatile ep-
oxides also turned out to be challenging substrates. Hence,
both cis- and trans-2,3-butene oxide 8e,f and 1,1-dimethyl-
ethylene oxide 8g gave only low yields of their cyclic carbo-
nates 9e–g (30–36%). Notably, the reaction of cis-2,3-butene
oxide 8e was not completely stereoselective, giving a 90:10
mixture of cis- and trans-cyclic carbonates 9e,f, whilst reaction
of trans-2,3-butene oxide 8 f gave only trans-cyclic carbonate
9 f.
Figure 2. Synthesis of cyclic carbonates 7a–j from terminal epoxides 6a–j
and carbon dioxide.
developed effective catalytic systems in recent years.[5a,8d,9,13d]
In view of the known synthetic difficulties associated with
using internal epoxides, 0.5 mol% complex 5 and 1 mol% of
TBAB were first tested using (1S,2S)-phenylpropylene oxide 8a
as substrate and the reaction was carried out at 508C and
10 bar carbon dioxide pressure for 24 h. It was found that
under these reaction conditions, 56% conversion to the corre-
sponding cyclic carbonate 9a was observed (Table 2, entry 1).
Table 2. Optimisation of the synthesis of cyclic carbonate 9a using com-
plex 5 and TBAB.[a]
The poor solubility of complex 5 resulted in initially hetero-
geneous reaction mixtures, which prevented a kinetic study of
this catalyst system. However, mechanistic information was ob-
tained from the stereochemistry of the reactions. Thus, cyclo-
hexene carbonate 9d was obtained exclusively as the cis-
isomer, indicating that the reaction proceeds with overall re-
tention of epoxide stereochemistry. This was confirmed as also
applying to terminal epoxides by the use of trans-deuterated
epoxide 10,[17c] which was transformed exclusively into trans-
deuterated cyclic carbonate 11 with >99% conversion as
shown in Scheme 5.
Entry Catalyst 5
TBAB
[mol%]
Time
[h]
Conversion[b]
[%]
Yield[c]
[%]
[mol%]
1
2
3
0.5
1
1
1
2
2
24
24
48
56
70
77
n.d.
60
54
[a] Reactions were carried out at 508C and 10 bar carbon dioxide pres-
sure. [b] Determined by 1H NMR spectroscopy. [c] Yield of isolated prod-
uct after purification by column chromatography; n.d.=not determined.
To investigate whether the two aluminium centers in com-
plex 5 function separately or cooperatively, the effect of
changing the complex 5/TBAB ratio was investigated. If they
When the concentration of the catalyst and cocatalyst were in-
creased to 1 and 2 mol%, respectively, 70% conversion was
observed and product 9a was isolated in 60% yield (Table 2,
entry 2). When the reaction time was prolonged to 48 h, al-
though the conversion increased slightly, the isolated yield of
the cyclic carbonate was lower than that obtained from a reac-
tion carried out for 24 h (Table 2, entry 3). Therefore, there
were no advantages in prolonging the reaction time beyond
24 h.
Scheme 5. Synthesis of trans-deuterated cyclic carbonate 11.
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function separately, then two equivalents of TBAB per complex
5 will be required, whilst if they function cooperatively then
only one equivalent of TBAB per complex 5 will be needed. In
the event, using epoxide 6d at 508C and 10 bar carbon diox-
ide pressure for 24 hours, 94% conversion was obtained when
using 0.1 mol% of complex 5 and 0.2 mol% of TBAB whilst
85% conversion was obtained using 0.1 mol% of complex 5
and 0.1 mol% of TBAB. The small reduction in conversion on
halving the concentration of TBAB is not large enough to be
consistent with a mechanism in which the two aluminium cen-
ters act independently (a conversion of around 47% would
have been expected). However, the result is consistent with
Figure 4. Monometallic aluminium(salphen) complex 12.
cyclic carbonate 7d was observed. Even when the catalyst
loading was increased to 0.2 mol% of both complex 12 and
TBAB (to give the same mol% of aluminium as reactions using
0.1 mol% of bimetallic complex 5), the conversion only in-
creased to 70%. Thus, higher conversions (85–94%) were ob-
tained with bimetallic complex 5 than with the monometallic
analogue 5 (27–70%) under identical reaction conditions, sup-
porting the occurrence of intramolecular cooperative catalysis
with complex 5.
a mechanism analogous to that previously proposed for com-
[8b]
plex 1
in which one aluminium center activates the epoxide
whilst the other activates the carbon dioxide to allow intramo-
lecular carbonate formation as illustrated in Figure 3. The 9%
In summary, we have reported the synthesis of bimetallic
aluminium(salphen) complex 5 from commercially available
chemicals for the formation of cyclic carbonates. It was found
that the combination of aluminium(salphen) complex 5 and
TBAB was an effective catalytic system for a variety of sub-
strates. Under relatively mild reaction conditions, terminal ep-
oxides and carbon dioxide generated cyclic carbonates in 50–
94% yield, whereas more challenging internal epoxides afford-
ed the corresponding cyclic carbonates in 30–71% yield. Com-
plex 5 displays an unusual and unexpected substrate prefer-
ence, being more reactive with aliphatic epoxides than those
that contain an aromatic ring and more reactive with cyclopen-
tene oxide than the widely studied cyclohexene oxide. Mecha-
nistic studies are consistent with a cooperative mechanism in-
volving activation and preorganization of both substrates
during the catalytic cycle.
Figure 3. Proposed mechanism for cyclic carbonate synthesis catalysed by
complex 5.
Acknowledgements
reduction in conversion on reducing the TBAB concentration
could then be accounted for by halide exchange between the
chlorides of complex 5 and the TBAB, which will reduce the ef-
fective concentration of bromide available in solution to ring-
open the epoxide. The effect of this halide exchange will
become more pronounced as the concentration of TBAB is
lowered relative to the concentration of complex 5. Consistent
with the mechanism shown in Figure 3, tributylamine was de-
tected in the reaction mixture by GCMS when complex 5 was
used to catalyse the conversion of epoxide 6d into cyclic car-
bonate 7d. The mechanism shown in Figure 3 also accounts
for the observed retention of epoxide stereochemistry as it in-
volves two inversions at the less hindered end of the epoxi-
de.[8b]
We gratefully acknowledge financial support from the European
Union Seventh Framework Programme FP7-NMP-2012 under
grant agreement number 309497.
Keywords: aluminium · carbon dioxide · catalyst · cyclic
carbonate · epoxide
[1] a) Carbon Dioxide as Chemical Feedstock (Ed.: M. Aresta), Wiley-VCH,
Weinheim, 2010, pp. 1–375; b) New and Future Developments in Cataly-
sis, Activation of Carbon Dioxide (Ed.: S. L. Suib), Elsevier, Amsterdam,
2013; c) Carbon Dioxide Utilization: Closing the Carbon Cycle (Ed.: P. Styr-
ing), Elsevier, Amsterdam, 2014; d) A. Dibenedetto, A. Angelini, Advan-
ces in Inorganic Chemistry: CO2 Chemistry, Vol. 66 (Ed.: R. van Eldik, M.
Aresta), Elsevier, Cambridge, 2014, pp. 25–81.
To further study the cooperative nature of the catalysis,
known[21] monometallic aluminium(salphen) chloride 12
(Figure 4) was prepared and tested as a catalyst for the synthe-
sis of cyclic carbonate 7d at 508C and 10 bar carbon dioxide
pressure for 24 h. When 0.1 mol% each of 12 and TBAB were
used as the catalyst, just 27% conversion of epoxide 6d into
[2] a) M. Peters, B. Kçhler, W. Kuckshinrichs, W. Leitner, P. Markewitz, T. E.
Mꢁller, ChemSusChem 2011, 4, 1216–1240; b) M. Cokoja, C. Bruckmeier,
B. Rieger, W. A. Hermann, F. E. Kꢂhn, Angew. Chem. Int. Ed. 2011, 50,
8510–8537; Angew. Chem. 2011, 123, 8662–8690; c) M. Aresta, A. Dibe-
nedetto, A. Angelini, Chem. Rev. 2014, 114, 1709–1742; d) A. Dibenedet-
to, A. Angelini, P. Stufano, J. Chem. Technol. Biotechnol. 2014, 89, 334–
353.
&
ChemSusChem 2016, 9, 1 – 6
www.chemsuschem.org
4
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communications
[3] For recent reviews of polycarbonate synthesis see: a) S. Klaus, M. W. Le-
henmeier, C. E. Anderson, B. Rieger, Coord. Chem. Rev. 2011, 255, 1460–
1479; b) M. R. Kember, A. Buchard, C. K. Williams, Chem. Commun. 2011,
47, 141–163; c) X.-B. Lu, W.-M. Ren, G.-P. Wu, Acc. Chem. Res. 2012, 45,
1721–1735; d) D. J. Darensbourg, S. J. Wilson, Green Chem. 2012, 14,
2665–2671; e) N. Ikpo, J. C. Flogeras, F. M. Kerton, Dalton Trans. 2013,
42, 8998–9006; f) D. J. Darensbourg, A. D. Yeung, Polym. Chem. 2014, 5,
3949–3962; g) M. Taherimehr, P. P. Pescarmona, J. Appl. Polym. Sci.
2014, 131, 41141; h) Y. Qin, X. Sheng, S. Liu, G. Ren, X. Wang, F. J. Wang,
J. CO2 Util. 2015, 11, 3–9; i) S. Paul, Y. Zhu, C. Romain, R. Brooks, P. K.
Saini, C. K. Williams, Chem. Commun. 2015, 51, 6459–6479.
[4] For recent reviews covering cyclic and polycarbonate synthesis see:
a) R. Martꢃn, A. W. Kleij, ChemSusChem 2011, 4, 1259–1263; b) X.-B. Lu,
D. J. Darensbourg, Chem. Soc. Rev. 2012, 41, 1462–1484; c) W. N. R. W.
Isahak, Z. A. C. Ramli, M. W. M. Hisham, M. A. Yarmo, Renewable Sustain-
able Energy Rev. 2015, 47, 93–106.
[5] For recent reviews of cyclic carbonate synthesis see: a) C. Martꢃn, G.
Fiorani, A. W. Kleij, ACS Catal. 2015, 5, 1353–1370; b) A. C. Kathalikkattil,
R. Babu, J. Tharun, R. Roshan, D.-W. Park, Catal. Surv. Asia 2015, 19,
223–235; c) B. Yu, L.-N. He, ChemSusChem 2015, 8, 52–62; d) M.
Cokoja, M. E. Wilhelm, M. H. Anthofer, W. A. Herrmann, F. E. Kꢂhn, Chem-
SusChem 2015, 8, 2436–2454; e) B.-H. Xu, J.-Q. Wang, J. Sun, Y. Huang,
J.-P. Zhang, X.-P. Zhang, S.-J. Zhang, Green Chem. 2015, 17, 108–122;
f) V. D’Elia, J. D. A. Pelletier, J.-M. Basset, ChemCatChem 2015, 7, 1906–
1917.
[6] a) A.-A. G. Shaikh, S. Sivaram, Chem. Rev. 1996, 96, 951–976; b) K. Xu,
Chem. Rev. 2004, 104, 4303–4417; c) B. Schꢄffner, F. Schꢄffner, S. P. Ver-
evkin, A. Bçrner, Chem. Rev. 2010, 110, 4554–4581.
[7] a) N. Kielland, C. J. Whiteoak, A. W. Kleij, Adv. Synth. Catal. 2013, 355,
2115–2138; b) J. W. Comerford, I. D. V. Ingram, M. North, X. Wu, Green
Chem. 2015, 17, 1966–1987; c) G. Fiorani, W. Guo, A. W. Kleij, Green
Chem. 2015, 17, 1375–1389; d) H. Bꢂttner, J. Steinbauer, T. Werner,
ChemSusChem 2015, 8, 2655–2669.
[8] a) J. Melꢅndez, M. North, R. Pasquale, Eur. J. Inorg. Chem. 2007, 3323–
3326; b) M. North, R. Pasquale, Angew. Chem. Int. Ed. 2009, 48, 2946–
2948; Angew. Chem. 2009, 121, 2990–2992; c) J. A. Castro-Osma, M.
North, X. Wu, Chem. Eur. J. 2014, 20, 15005–15008; d) J. A. Castro-
Osma, M. North, X. Wu, Chem. Eur. J. 2016, 22, 2100–2107.
ni, C. J. Whiteoak, E. Martin, E. Escudero-Adꢆn, A. W. Kleij, Angew. Chem.
Int. Ed. 2014, 53, 10416–10419; Angew. Chem. 2014, 126, 10584–10587.
[10] a) T. Chang, L. Jin, H. Jing, ChemCatChem 2009, 1, 379–383; b) T. Roy,
R. I. Kureshy, N. H. Khan, S. H. R. Abdi, H. C. Bajaj, Catal. Sci. Technol.
2013, 3, 2661–2667.
[11] a) R. L. Paddock, S. T. Nguyen, J. Am. Chem. Soc. 2001, 123, 11498–
11499; b) X. Zhang, Y.-B. Jia, X.-B. Lu, B. Li, H. Wang, L.-C. Sun, Tetrahe-
dron Lett. 2008, 49, 6589–6592; c) J. A. Castro-Osma, K. J. Lamb, M.
North, ACS Catal. 2016, 6, 5012–5025.
[12] a) A. Decortes, M. M. Belmonte, J. Benet-Buchholz, A. W. Kleij, Chem.
Commun. 2010, 46, 4580–4582; b) A. Decortes, A. W. Kleij, ChemCatCh-
em 2011, 3, 831–834; c) D. Anselmo, G. Salassa, E. C. Escudero-Adꢆn, E.
Martin, A. W. Kleij, Dalton Trans. 2013, 42, 7962–7970.
[13] a) C. Whiteoak, E. Martin, M. M. Belmonte, J. Benet-Buchholz, A. W. Kleij,
Adv. Synth. Catal. 2012, 354, 469–476; b) C. J. Whiteoak, B. Gjoka, E.
Martin, M. M. Belmonte, E. C. Escudero-Adꢆn, C. Zonta, G. Licini, A. W.
Kleij, Inorg. Chem. 2012, 51, 10639–10649; c) M. Taherimehr, S. M. Al-
Amsyar, C. J. Whiteoak, A. W. Kleij, P. P. Pescarmona, Green Chem. 2013,
15, 3083–3090; d) C. J. Whiteoak, E. Martin, E. Escudero-Adꢆn, A. W.
Kleij, Adv. Synth. Catal. 2013, 355, 2233–2239.
[14] A. Tullo, Chem. Eng. News 2008, 86, 21.
[15] M. North, ARKIVOC 2012, 610–628.
[16] J. A. Castro-Osma, M. North, W. K. Offermans, W. Leitner, T. E. Mꢂller,
ChemSusChem 2016, 9, 791–794.
[17] a) J. A. Castro-Osma, A. Lara-Sꢆnchez, M. North, A. Otero, P. Villuendas,
Catal. Sci. Technol. 2012, 2, 1021–1026; b) J. A. Castro-Osma, C. Alonso-
Moreno, A. Lara-Sꢆnchez, J. Martꢃnez, M. North, A. Otero, Catal. Sci. Tech-
nol. 2014, 4, 1674–1684; c) J. Martꢃnez, J. A. Castro-Osma, A. Earlam, C.
Alonso-Moreno, A. Otero, A. Lara-Sanchez, M. North, A. Rodrꢃguez-Diꢅ-
guez, Chem. Eur. J. 2015, 21, 9850–9862.
[18] O. Rotthaus, O. Jarjayes, F. Thomas, C. Philouze, E. Saint-Aman, J. Pierre,
Dalton Trans. 2007, 889–895.
[19] G. Salassa, M. J. J. Coene, S. J. Wezenberg, B. L. M. Hendriksen, S. Speller,
J. A. A. W. Elemans, A. W. Kleij, J. Am. Chem. Soc. 2012, 134, 7186–7192.
[20] G. Magadur, J.-S. Lauret, G. Charron, F. Bouanis, E. Norman, V. Huc, C.-S.
Cojocaru, S. Gꢈmez-Coca, E. Ruiz, T. Mallah, J. Am. Chem. Soc. 2012, 134,
7896–7901.
[21] D. Rutherford, D. A. Atwood, Organometallics 1996, 15, 4417–4422.
[9] a) C. J. Whiteoak, N. Kielland, V. Laserna, E. C. Escudero-Adꢆn, E. Martin,
A. W. Kleij, J. Am. Chem. Soc. 2013, 135, 1228–1231; b) C. J. Whiteoak, N.
Kielland, V. Laserna, F. Castro-Gꢇmez, E. Martin, E. C. Escudero-Adꢆn, C.
Bo, A. W. Kleij, Chem. Eur. J. 2014, 20, 2264–2275; c) V. Laserna, G. Fiora-
Received: August 17, 2016
Published online on && &&, 0000
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X. Wu, M. North*
Co-op catalysis: In the presence of tet-
rabutylammonium bromide as a cocata-
lyst, a bimetallic aluminium(salphen)
complex catalyses the synthesis of cyclic
carbonates from both terminal and in-
ternal epoxides at 508C and 10 bar
carbon dioxide pressure. Mechanistic
studies using deuterated epoxides and
an analogous monometallic aluminium-
(salphen) chloride complex support
a mechanism for catalysis by the bimet-
allic complex, which involves intramo-
lecular cooperative catalysis between
the two aluminium centres.
&& – &&
A Bimetallic Aluminium(Salphen)
Complex for the Synthesis of Cyclic
Carbonates from Epoxides and Carbon
Dioxide
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