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