"Activating Carbon Monoxide and Carbon Dioxide with Organometallic Uranium Complexes- Closing

the Carbon Cycle"

Geoff Geoff ClokeCloke

CPD Conference June 22nd 2012

The Carbon Cycle

• ~80 % of current global energy supply depends on fossil fuels

• End product of combustion is CO2

• Oil reserves are finite- peak oil will occur

Create C-C bonds and/or C-H bonds from CO or CO2

“Uncertainty in petroleum cost and supply demands that alternative sources of primary organic materials be developed. Carbon monoxide as a component of synthesis gas (H2 + CO) from coal and biomass will have a leading role in meeting these needs. ..........develop strategies that use CO as a two-carbon or larger building block to construct the organic materials needed for fuels and chemical manufacturing.”

Wayland, Science, 2006

Sandwiches!

CrFe

Wilkinson FischerFerrocene Dibenzenechromium

U

StreitweiserUranocene

U

CH3

CH3 CH3

CH3CH3

SiiPr3

SiiPr3

Mixed Sandwich

Why Uranium ??

E / volts

UIV/III: E½ = -2.18 V

UIV

SiiPr3

SiiPr3

Cl UIII

SiiPr3

SiiPr3 + Cl-+ e-

- e-

What to do with all the depleted uranium??!

U235 0.7%U238 99.3%5,404,000 tonnes!

Uranium(III)- highly reducing

Cyclisation of Carbon Monoxide

O. T. Summerscales, F. G. N. Cloke, P. B. Hitchcock, J. C. Green, and N. Hazari, Science, 2006, 311, 829.

U

SiiPr3

SiiPr31 bar CO, Et2O

-80oC to RTTHF

The Oxocarbons (CO)n2-

The Next One in the Series- Squarate

O. T. Summerscales, F. G. N. Cloke, P. B. Hitchcock, J. C. Green, and N. Hazari, J.Am.Chem. Soc, 2006, 128, 9602.

U

CH3

CH3

CH3CH3

iPr3Si

iPr3Si

CO, toluene,

-30C

CH3 removed

Carbon Dioxide Activation

U

CH3

CH3

CH3CH3

iPr3Si

iPr3Si

1 bar CO2, -30C

toluene,

2CO2 + 2 e- CO32- + CO

from U

+

A.S.P. Frey, O.T. Summerscales, F.G.N. Cloke, M.P. Coles, P.B. Hitchcock, Chem.Commun., 2009

Carbon Dioxide Activation 2

Nikos Tsoureas, unpublished results 2012

CO2+CO

N2

Coupling of Nitric Oxide and Carbon Monoxide

U

SiiPr3

SiiPr3 CO +NO, toluene-80oC to 25oC

+CO

U

iPr3Si

iPr3SiN. . +

NO

CO + NO CO2 + N2Heterogeneous Pt, Rh Catalyst

600-700oC

catalyst surface

O N N O> 6000C

catalyst surface

O N N OCO

CO

>2000C<3000C

A.S.P.Frey, F.G.N.Cloke,M.P.Coles, P.B.Hitchcock,Chem. Eur. J., 2010, 16, 9305.

“Methanol Synthesis”

CO/H2 MeOH

U

SiiPr3

SiiPr3CO + xs H2

toluene, -80oC to 25oC

A.S. P. Frey, F. G. N. Cloke, M. P. Coles, L. Maron, and T. Davin, Angew. Chem. Int. Ed. 2011, 50, 6881

The Future…..

reductively (2e)activated/coupled

productUIVUIV2 UIII small molecule(s)

e.g. CO, H2, CO2, etc

reductively activated/coupled

product2 electrons

Chemically?Electrochemically- controlled potential electrolysis?