CO2 as a chemical feedstock
School of ChemistryProfessor Michael North
Synthesis of heterocycles from epoxides
All are known reactions but often with harsh reaction conditions (e.g. 20 bar CO2 pressure and >100 oC for cyclic carbonate synthesis)
Could a bimetallic catalyst activate both substrates?Can we use only sustainable elements in the catalyst?
O
R
OO
O
R SO
S
R
and SS
S
RNR'O
O
R
R'N=C=O
CO2
CS2
Sustainable catalysis
Red/orange = rising threat from increased use; Red = serious threat in next 100 years;
Orange = limited availability;Many elements are endangered.
http://www.chemistryinnovation.co.uk/
A bimetallic aluminium(salen) catalyst
M. North et al., Eur. J. Inorg. Chem. 2007, 3323–3326; Chem. Eur. J. 2010, 16, 6828–6843; Patent WO/2008/132474.
N N
OH HO
tBu
tBu
tBu
tBu
Al / EtOH, I2 (cat) then H2O
(salen)Al O Al(salen)
1 bimetallic catalyst
Cyclic carbonate synthesis from terminal epoxides
R Yield R Yield R Yield
Ph 62% Me 77% CH2OCOMe 50%
PhCH2 44% H 76% CH2OCOPh 58%
Bu 87% CH2OH 36% CH2OPh 55%
C8H17 64% CH2Cl 60% CH2OtBu 50%
O
R
OO
O
R
CO2 (1 atmosphere) /
1 (2.5 mol%) / Bu4N+Br- (2.5 mol%)room temperature, 3h, no solvent
M. North et al., Eur. J. Inorg. Chem. 2007, 3323–3326; Chem. Eur. J. 2010, 16, 6828–6843.
Supported catalysts
tBu-catalystsupport = polystyrene (PS), n = 1all other supports, n = 3
N
N
O
O
tBu
tBu
Et2N
Al O
N
N
O
O
tBu
tBu
N(Bn)Et2
Al
N(Bn)Et2
Et2(Bn)N Br Br
Br Br
nsupport H-catalyst3
N
N
O
O
Et2N
Al O
N
N
O
O
N(Bn)Et
Al
N(Bn)Et2
Et2(Bn)N Br Br
Br Br
silica
Results with supported catalysts
Support YieldtBu-silica 69%tBu-MCM-41 (silica) 57%tBu-Solgel (silica) 52%tBu-Aluminium pillared clay 21%
M. North et al. Patent WO/2009/109765; Chem. Commun. 2009, 2577–2579; Dalton Trans. 2011, 40, 3885–3902
O
PhOO
O
Ph
Gas phase flow reactor
M. North, et al. Chem. Eur. J. 2009, 11454–11457; Dalton Trans. 2011, 40, 3885–3902
Column dimensions:3-15 cm x 1 cm.
Continuous flow results at 60 oC
Catalyst / support
Catalyst amount
mL / min evaporation rate EO
% CO2
consumedTOF (h-1)CO2 N2
tBu-silica 2.17 g 1.0 2.5 0.15 mL/h 97 2.6tBu-MCM41 1.57 g 1.1 2.5 0.15 mL/h 95 8.3tBu-solgel 1.94 g 1.0 2.5 0.15 mL/h 97 5.2tBu-PS 1.94 g 1.0 2.5 0.15 mL/h 63 2.6
H-silica 2.17 g 1.0 2.5 0.15 mL/h 98 1.1In each case, CO2 is 21% of the gases passing into the reactor. Ethylene oxide (EO) flow rate ca 1.2 mL / min. Column length 15 cm
M. North, et al. Chem. Eur. J. 2009, 11454–11457; Dalton Trans. 2011, 40, 3885–3902.
1 2 3 4 5 6 7 80
2
4
6
8
10
12
14
16
time (days)
%C
O2
ab
so
rbe
dContinuous flow results with
tBu-silica catalyst at 100 oC3cm reactor containing 0.65g catalyst.
Catalyst reactivatedwith BnBr
M. North, et al. Chem. Eur. J. 2009, 11454–11457; Dalton Trans. 2011, 40, 3885–3902
Doosan Power systems test facility
Flue gas compositionFlow rate 20 mL/min
Gas Coal
T 53 oC 52 oC
CO2 5% 15%
O2 9% 3%
SO2 26ppm 291ppm
CO 189ppm 40ppm
NOx 33ppm 443ppmM. North et al. Energy Environ. Sci., 2011, 4, 4163–4170.
Used El Cerrejon coal (typical hard coal): 74%C; 0.5%S; 1.5%N; 5%H; 7% H2O
0
0.4
0.8
1.2
0 3 6 9 12
TO
F (
h-1
)
Time (days)
control
combined 8 and 16 h coal
Real flue gas flow reactor results with ethylene oxide
M. North, et al. Energy Environ. Sci., 2011, 4, 4163–4170.
Catalyst reactivated
Synthesis of di- and trithiocarbonates
M. North, et al. Synlett 2010, 623–627; J. Org. Chem. 2010, 75, 6201–6207.
R1 R2 50 oC 90 oC
yield A:B yield A:B
CH3 H 97 89:11 94 5:95
CH2Me H 54 85:15 90 47:53
(CH2)3Me H 56 66:34 87 43:57
(CH2)5Me H 61 70:30 81 39:61
CH2Cl H 76 85:15 84 36:64
CH2OPh H 97 97:3 87 71:29
(CH2)4 35 58:42 76 19:81
Ph H 62 0:100 91 0:100
O
SO
S
SS
S
1 (5 mol%) / Bu4NBr (5 mol%)CS2 (1.8 equiv.) 50-90 oC
+
R1 R2 R1 R2
R1 R2
A B
Stereochemistry
• Internal epoxides are substrates.• Reaction involves inversion of epoxide stereochemistry.
OS
OS
CS2
CS2 (-COS)
S
SS
M. North, et al. J. Org. Chem. 2010, 75, 6201–6207.
Oxazolidinone synthesis1 Cocatalyst Conv. A:B
5 mol% - 86% 1.8:1
2.5 mol% - 63% 2:1
- Bu4NBr 37% 1:1.8
2.5 mol% Bu4NBr 18% 1:0
2.5 mol% Et3N 38% 1:8.5
2.5 mol% DMAP 24% 1:5
2.5 mol% Ph3PO 29% 3.1:1
2.5 mol% PyNO 64% 1:1.1
1 (2.5-5 mol%) / cocatalyst (2.5 mol%), 80 oC, 24 h
+ Ph-N=C=OO
Ph
OPhN
O
Ph
+ OPhN
O
PhA B
Best conditions eventually found to be 5 mol% 1 at 80 oC in toluene for 24 h with no cocatalyst. Gave 100% yield with A:B = 2.2:1
Other epoxides and isocyanates
ONPh
OO
1 (10 mol%),80 oC, toluene
63%
+
only cis-isomer formed
PhNCO
1, toluene, 80 oC, 24 h
+ Ar-N=C=OO
ROArN
O
R
+ OArN
O
RA B
7 epoxides7 isocyanates
31-100%
All except R= Ph and R = CH2OH give B as major product A:B = 1:5 to 0:1. R = CH2OH gives only A
Acknowledgements
Dr. Riccardo PasqualeDr. Jaisiel MelendezDr. Pedro VilluendasDr. Carl Young
Professor Bill CleggDr. Ross Harrington
EPSRC, TSB, SSEDoosanBabcockCarbonConnections Newcastle University