Chem 3000 February 26 th, 2009 Literature Presentation “Towards Uranium Catalysts” Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C.

Uranium 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,

Objectives 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,

Background - 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, Provides a source of carbon-free energy (nuclear power) Used in nuclear warfare

Why Uranium? f orbitals m = +3, -3 m = +2, -2 m = +1, -1 Readily available Radioactivity Stable oxidation states

Haber – Bosch Process Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C. Towards Uranium Catalysts. Nature 2008, 455, Cloke, F.G.N; Hitchcock, P.B. Reversible Binding of Dinitrogen by a Uranium (III) Pentalene Complex. J. Am. Chem. Soc. 2002, 124, Odom, A.L; Arnold, P.L; Cummins, C.C. Heterodinuclear Uranium/Molybdenum Dinitrogen Complexes. J. Am. Chem. Soc. 1998, 120, N 2(g) + 3H 2(g) 2NH 3 (aq) Haber, F. Ammonia. German Patent DE (1909)

Uranium and Dinitrogen Binding and Reduction σ σ*σ* π π*π* U N N U N N Bond Order = 3Bond Order = 2.5

Relevance Nitrogen and Uranium abundance Ammonia and fertilizers Fox, A.R; Bart, S.C; Meyer, K; Cummins, C.C. Towards Uranium Catalysts. Nature 2008, 455, Novel chemistry

End-on Binding of Dinitrogen Evans, W. J, Kozimor, S. A, Ziller, J.W. A monometallic f element complex of dinitrogen: (C 5 Me 5 ) 3 U( ƞ 1 -N 2 ). J. Am. Chem. Soc. 2003, 125,

Bond-Length (Å) (Before) Bond-Length (Å) (Adduct) N1 – N U - N2.492 U – Cp*2.823 – U – Cp* center Results – End-on Coordination Evans, W. J, Kozimor, S. A, Ziller, J.W. A monometallic f element complex of dinitrogen: (C 5 Me 5 ) 3 U( ƞ 1 -N 2 ). J. Am. Chem. Soc. 2003, 125, ComplexIR Absorption (cm -1 ) N 2 (literature)2331 N 2 (experimental)2207 N

Synthesis of Ligand for Binding and Reduction of N 2 Intermediate of UCp*I 2 (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, R = Si i Pr 3

Side-on Binding of Dinitrogen Cloke, F.G.N; Hitchcock, P.B. Reversible Binding of Dinitrogen by a Uranium (III) Pentalene Complex. J. Am. Chem. Soc. 2002, 124, R = Si i Pr 3

Results – Side-on Coordination Bond Length (Before) (Å) Bond Length (Adduct) (Å) N1 – N U - N2.401 – U – ring C – U2 – M U1 – M Cloke, F.G.N; Hitchcock, P.B. Reversible Binding of Dinitrogen by a Uranium (III) Pentalene Complex. J. Am. Chem. Soc. 2002, 124, % Yield = 40%

Conclusions End-on Vs. Side-on Activation and reduction Uranium and ligands Ammonia