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%