Chem 3000Chem 3000

February 26th, 2009

Literature Presentation

“Towards Uranium Catalysts”

Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C.

Uranium as a CatalystUranium as a Catalyst

• Exploit catalytic activity of uranium

• Bind uranium to a ligand framework

• Complex uranium to small inert molecules

Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C. Towards Uranium Catalysts. Nature 2008, 455, 341-349

ObjectivesObjectives

Previously Studied

• Hydrogenation of alkenes• Oligomerization• Dimerization• Hydrosilation• Hydroamination of terminal alkynes

New Goals

• Carbon-hydrogen bond activation• Dinitrogen binding and reduction• Carbon monoxide binding• Carbon dioxide reduction• Azide and amine activation• Reactions of unsaturated groups and polymerizations

Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C. Towards Uranium Catalysts. Nature 2008, 455, 341-349

Background - UraniumBackground - Uranium

•Is the heaviest naturally occurring element of the periodic table

Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C. Towards Uranium Catalysts. Nature 2008, 455, 341-349

• Provides a source of carbon-free energy (nuclear power)

• Used in nuclear warfare

Why Uranium?Why Uranium?

•f orbitals

m = +3, -3

m = +2, -2

m = +1, -1

http://www.uky.edu/~holler/html/chemistry.html

• Readily available

• Radioactivity

• Stable oxidation states

Haber – Bosch ProcessHaber – Bosch Process

Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C. Towards Uranium Catalysts. Nature 2008, 455, 341-349Cloke, F.G.N; Hitchcock, P.B. Reversible Binding of Dinitrogen by a Uranium (III) Pentalene Complex. J. Am. Chem. Soc. 2002, 124, 9352-9353Odom, A.L; Arnold, P.L; Cummins, C.C. Heterodinuclear Uranium/Molybdenum Dinitrogen Complexes. J. Am. Chem. Soc. 1998, 120, 5836-5837

N2(g) + 3H2(g) 2NH3 (aq) Haber, F. Ammonia. German Patent DE 229126 (1909)

Uranium and Dinitrogen Uranium and Dinitrogen Binding and ReductionBinding and Reduction

σ

σ*

π

π*

U N N UN

N

Bond Order = 3Bond Order = 2.5

RelevanceRelevance• Nitrogen and Uranium abundance

• Ammonia and fertilizers

Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C. Towards Uranium Catalysts. Nature 2008, 455, 341-349

• Novel chemistry

End-on Binding of End-on Binding of DinitrogenDinitrogen

Evans, W. J, Kozimor, S. A, Ziller, J.W. A monometallic f element complex of dinitrogen: (C5Me5)3U(ƞ1-N2). J. Am. Chem. Soc. 2003, 125, 14264 - 14265

Bond-Length (Å) (Before)

Bond-Length (Å) (Adduct)

N1 – N2 1.0975 1.120

U - N 2.492

U – Cp* 2.823 – 2.927

U – Cp* center

2.588

Results – End-on Results – End-on CoordinationCoordination

Evans, W. J, Kozimor, S. A, Ziller, J.W. A monometallic f element complex of dinitrogen: (C5Me5)3U(ƞ1-N2). J. Am. Chem. Soc. 2003, 125, 14264 - 14265

Complex IR Absorption (cm-1)

N2 (literature) 2331

N2 (experimental)

2207

N22- 1568

Synthesis of Ligand for Synthesis of Ligand for Binding and Reduction of NBinding and Reduction of N22

• Intermediate of UCp*I2 (not shown)

Cloke, F.G.N; Hitchcock, P.B. Reversible Binding of Dinitrogen by a Uranium (III) Pentalene Complex. J. Am. Chem. Soc. 2002, 124, 9352-9353

R = SiiPr3

Side-on Binding of Side-on Binding of DinitrogenDinitrogen

Cloke, F.G.N; Hitchcock, P.B. Reversible Binding of Dinitrogen by a Uranium (III) Pentalene Complex. J. Am. Chem. Soc. 2002, 124, 9352-9353

R = SiiPr3

Results – Side-on Results – Side-on CoordinationCoordination

Bond Length (Before) (Å)

Bond Length (Adduct) (Å)

N1 – N2 1.109 1.232

U - N 2.401 – 2.423

U – ring C

2.688 – 2.775

2.688 – 2.775

U2 – M2 2.486 2.524

U1 – M1 2.486 2.505Cloke, F.G.N; Hitchcock, P.B. Reversible Binding of Dinitrogen by a Uranium (III) Pentalene Complex. J. Am. Chem. Soc. 2002, 124, 9352-9353

• % Yield = 40%

ConclusionsConclusions

• End-on Vs. Side-on

• Activation and reduction

• Uranium and ligands

• Ammonia