Aerobic oxidative carboxylation of olefins with metalloporphyrin catalysts

Article abstract of DOI:10.1039/b916042f

Dioxo(tetraphenylporphyrinato)ruthenium(vi) and quaternary onium salt were successfully developed as catalysts to initiate a three component reaction of olefin, O₂, and CO₂ at ambient temperature under low pressure. The reaction can be carried out under solvent-free or solvent conditions. Styrene carbonate was obtained in 76% yield with 100% selectivity using 4 mol% of catalyst under optimized conditions.

Full text of DOI:10.1039/b916042f

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COMMUNICATION
www.rsc.org/greenchem | Green Chemistry
Aerobic oxidative carboxylation of olefins with metalloporphyrin catalysts†
Dongsheng Bai and Huanwang Jing*
Received 5th August 2009, Accepted 19th October 2009
First published as an Advance Article on the web 27th October 2009
DOI: 10.1039/b916042f
Dioxo(tetraphenylporphyrinato)ruthenium(VI) and quater-
nary onium salt were successfully developed as catalysts to
but it also suffers from high pressure, high temperature and by-
25–30
products such as benzaldehyde and benzoic acid.
Li et al.
initiate a three component reaction of olefin, O
2
, and CO
2
developed a catalytic system of N-bromosuccinimide (NBS)
at ambient temperature under low pressure. The reaction
can be carried out under solvent-free or solvent conditions.
Styrene carbonate was obtained in 76% yield with 100%
selectivity using 4 mol% of catalyst under optimized condi-
tions.
together with 1,8-diazabicyclo[5.4.0]undecenc-7-ene (DBU) to
synthesize carbonate with aqueous H
high pressure and temperature.
2
2
O as an oxidant under
31
In the search for an alternative homogeneous catalyst for this
aerobic oxidative carboxylation approach and expanding our
own efforts toward the development of efficient catalysts for
3
The catalytic transformation of carbon dioxide into useful
organic compounds has attracted much attention during the
last two decades due to economic and environmental benefits
arising from the utilization of renewable sources and a growing
cycloaddition of CO
2
to epoxides, we initiated our investiga-
tions using metalloporphyrin catalysts following the principle
that ruthenium porphyrin catalysts can catalyze the epoxidation
32,33
of alkenes without reductive aldehyde additives.
demonstrate a convenient route to synthesize cyclic carbonates
by an aerobic oxidative carboxylation of olefins using O as
an oxidant and CO as a carboxylation reagent with 100%
Herein, we
1,2
concern about the greenhouse effect. The preparation of cyclic
carbonates (CC) via cycloaddition of CO with epoxides is one of
fixation in terms of their valuable
uses such as organic synthetic intermediates, monomers, aprotic
2
2
3–11
the methodologies for CO
2
2
selectivity and high yield under lower pressure at ambient
temperature.
12–20
polar solvents, pharmaceutical/fine chemical intermediates.
The direct oxidative carboxylation of olefins seems to be an ef-
ficient method for the synthesis of cyclic carbonates (Scheme 1).
Aresta et al. reported the one-pot synthesis of styrene carbonate
We have discovered that dioxo(tetraphenylporphyrinato)
ruthenium(VI) [Ru(TPP)(O) ](1)/quaternary onium salt can
2
effectively catalyze the aerobic oxidative carboxylation of olefins
at ambient temperature under 1.6 MPa pressure of oxygen and
carbon dioxide. Styrene reacts with 2 equivalents of TBAB in the
presence of 0.4 mol% of catalyst 1 to generate styrene carbonate
from styrene, CO
homogeneous rhodium complex catalysts
2
and molecular oxygen as an oxidant with
21,22
23
or metal oxide,
which, however, suffer from high pressure, low yields of the
desired carbonates and by-products such as benzaldehyde,
benzoic acid, acetophenone, phenylacetaldehyde and styrene
oxide. Srivastava et al. used titanosilicate catalysts for the direct
synthesis of cyclic carbonate from styrene in a single reactor;
◦
(SC) in 19.7% yield within 48 h at 30 C under solvent-free
conditions. It is noteworthy that this three component reaction
does not lead to any by-products. Moreover, with catalyst
loading as low as 0.1 mol%, NMR monitoring of the reaction
showed a slight conversion in the product after 48 h. These
results outshine the use of heterogeneous catalysts of metal
oxide or homogeneous rhodium complex catalysts which require
higher temperature and pressure.
initially they conducted the epoxidation of olefin with H
or tert-butyl hydroperoxide (TBHP) at 60 C and then added
2
O
2
◦
CO
2
and a co-catalyst with an organic base at a temperature
◦
of 120 C. The yield of carbonate was not high although the
reaction conditions were optimized. Arai et al. used TBHP
as an oxidant to synthesize carbonates from styrene and CO
24
The analysis and identification of products were performed
1
.
by GC-MS, H NMR, and IR etc. As shown in Table 1,
2
The yield of carbonate was higher than in the literature above,
these attractive reactions can be carried out under solvent-free
conditions or with solvent. The ruthenium catalyst 1 combined
with tetrabutylammonium bromide (TBAB) was found to be the
best catalyst for this three component reaction (Entries 1-10).
Any additives diminished the reaction rate (Entries 7, 8–10).
The cocatalyst of CrO
3
/CrCl induced many by-products of
3
benzaldehyde and benzoic acid (Entry 10). In dichloromethane,
the reaction was carried out very well to yield the desired SC in
about 76% yield with 100% selectivity (Entry 13) using 2 equiva-
lents of tetrabutylammonium iodide (TBAI) as cocatalyst. More
or less cocatalyst loading decelerated the reaction rate under
both solvent-free conditions and with solvent (Entries 1, 3 and
Scheme 1 The synthesis of carbonate from olefins.
State Key Laboratory of Applied Organic Chemistry, College of
Chemistry and Chemical Engineering, Lanzhou University, 730000,
Lanzhou, Gansu, China. E-mail: hwjing@lzu.edu.cn; Fax: (+) 86 931
8
†
91 2582; Tel: 18919992189
1
2-14). Surprisingly, this reaction can be achieved in air
Electronic supplementary information (ESI) available: Experimental
1
(Entry 20) and can also be accomplished in other solvents
such as ethanol (Entry 21) and THF (Entry 22). The common
details and spectra of IR, H NMR, GC-MS and GC trace. See DOI:
1
0.1039/b916042f
This journal is © The Royal Society of Chemistry 2010
Green Chem., 2010, 12, 39–41 | 39

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a
Table 1 Aerobic oxidative carboxylation of styrene
green reaction. The results are listed in Table 2 and reveal
that the cocatalyst of phenyltrimethylammonium tribromide
h
Entry
Co-catalyst
Styrene
Time/h
SC Yield (%)
(
PTAT) was more active than TBAI (Entry 2-5) for 1-hexene,
b
1-octene, cyclohexene, and cyclooctene etc. The best example
is that 1-octene can be transformed to cyclic carbonate in
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
1TBAB
2TBAB
3TBAB
2TBAF
2TBAC
2TBAI
2TBAB/imidazole
2TBAB/V
250
250
250
250
48
48
48
48
48
48
48
120
48
120
48
48
48
48
48
48
48
48
48
72
60
48
48
48
trace
19.7
<1
trace
2.2
1.5
trace
4.6
b
b
7
8.4% yield when the ratio of 1-octene to catalyst was 25
b
b
(Entry 3). Under these reaction conditions, some branched
carbonates of cyclohexene and bromination addition species of
other olefins were found as by-products. It is well known that the
cyclohexene is easily converted to polycarbonate in the presence
250
b
b
b
b
b
250
250
250
250
250
50
2 5
O
2 PTAT
<1
2
of catalyst. For example, the vibration of the carbonyl group of
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
2CrO
3
/CrCl
3
trace
23.9
9.8
76
7.1
79.3
14.7
8.3
17.5
50.5
7.5
89
14.5
3.6
-
1
2TBAI
1TBAI
2TBAI
3TBAI
2TBAI
2TBAF
2TBAC
2TBAB
2PTAT
2TBAI
2TBAI
2TBAI
2TBAI
polycarbonate formed from cyclohexene appeared at 1746 cm
25
25
25
10
25
25
25
25c
whereas the carbonyl group of cyclic carbonate appeared at
-1
1
793 cm . A little cyclooctene oxide was also detected by
GC-MS in the presence of PTAT as cocatalyst.
Hence it is evident that the cocatalyst plays an important role
in initiating the reaction. These findings impelled us to propose
a mechanism for this attractive green reaction (Scheme 2). The
formation of the target is rationalized by the transfer of an
oxygen atom from the catalyst to form the epoxide intermediate
which is attacked by active carbon dioxide. The intermediate
then undergoes intramolecular cyclization to yield the cyclic
carbonate and metalloporphyrin that reacts immediately with
oxygen and olefin to form a new intermediate. The new interme-
diate is attacked by active carbon dioxide to regenerate the oxo-
metalloporphyrin catalyst accompanied by another molecule of
target compound, which completes the catalytic cycle.
25
d
25e
25
f
25
25
g
m-CPBA/TBAI
40.7
a
Catalyst 1 37.5 mg (0.05 mmol), cocatalyst 1-3 equivalents of catalyst,
) 0.5 MPa, P(CO ) 1.1 MPa,
styrene 10-250 equivalents of catalyst, P(O
2
2
◦
b
c
d
e
CH
5
by H NMR
2
Cfl 5 ml, T 30 C. Neagt. P(air) 2.0 MPa. Ethanol 5 ml. THF
2
h
ml. Catalyst Fe(TPP)Cl. Catalyst Ru(Salen)(PPh
3
)
2
.
Determined
1
a
Table 2 Aerobic oxidative carboxylation of olefins
b
Entry
Olefin
Co-catalyst
Yield (%) of CC
1
2
3
4
5
3-Chloropropylene
1-Hexene
TBAI
PTAT
TBAI
PTAT
TBAI
PTAT
TBAI
PTAT
TBAI
PTAT
56.7
4.6
11.1c
28.6
<1 c
78.4
1-Octene
d
Cyclohexene
Cyclooctene
6.8
c,d
30.5
1.8
49.8
c,e
a
Catalyst 1 37.5 mg (0.05 mmol), cocatalyst 0.1 mmol, olefin 1.25 mmol
◦
(
25 equivalents). P(O
2
) 0.5 MPa, P(CO
2
) 1.1 MPa, CH
2
Cl
2
5 ml, T 30 C,
b
1
c
Scheme 2 Proposed mechanism of aerobic oxidative carboxylation of
olefins.
4
8 h. Determined by H NMR. Combined bromination by-products
d
indicated by GC-MS. Some branched carbonate by-product can be
e
found by IR. Some epoxide by-product can be found by GC-MS.
In summary, we have developed a one-pot, highly selec-
tive synthetic method for forming cyclic carbonate using
biomimetic catalyst of Fe(TPP)Cl can lead to styrene carbonate
formation in poor yield (3.6%) accompanied by benzoic acid
Ru(TPP)(O) as catalyst and quaternary onium salt as cocat-
2
(
55.3%) and benzaldehyde (37.5%) as major products because
alyst. The most important feature of this methodology can be
attributed to the use of 4 mol% of catalyst providing a high
yield of product. Thus, this simple methodology would be a
novel protocol to directly approach the cyclic carbonate from
various alkenes. To the best of our knowledge, this is the first
example of a homogenous protocol towards the formation of
styrene carbonate with 100% selectivity at ambient temperature
under low pressure reported in the literature. The investigation
of this reaction mechanism and optimization of catalyst systems
to enhance their catalytic efficiency are under way in our
laboratory.
of its good oxidative property and poor coupling property from
epoxide to cyclic carbonate (Entry 23). Meanwhile, the in situ
catalyst of Ru(Salen)(O) generated from Ru(Salen)(PPh
oxidation with m-CPBA can convert styrene to styrene car-
bonate in considerable yield (40.7%) with a little benzaldehyde
(
3
2
) by
2.3%) as a by-product (Entry 24).
The best catalysts were thus found to be 1/TBAB under
solvent-free conditions and 1/TBAI in dichloromethane for
styrene and 3-chloropropylene (Table 2, entry 1). To expand
the scope of the reaction, various olefins were used with this
4
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