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Nickel-N-Heterocyclic Carbenes: Synthesis and Reactivity with O2
Dr. Benjamin Dible
University of Rochester
|02/16/2009 - 3:00 pm - Chemical Sciences & Engineering Building, Room 101|
π-allylchloro(NHC)nickel(II) complexes were synthesized and their reactions with O2 were studied. Ligand steric effects were found to determine the difference between rapid oxidation of the allyl group to produce bis-μ-hydroxonickel complexes and no observable reaction. In the initially observed systems, the ability of the metal-NHC bond to rotate correlates with the ability of the complex to react with O2. In the limiting cases, conformationally-restricted complexes are stable to O2 and complexes with rapid Ni-NHC bond rotation react rapidly with O2. Complexes with intermediate conformational flexibility were found to exhibit lesser reactivity with O2. Based on the observed inertness of complexes with saddle-shaped ligands to O2, the adoption of a nonplanar geometry upon reaction with O2 is proposed to be required. The issue of conformational flexibility versus rigidity is expected to directly impact the catalytic behavior of metal-NHC complexes.