AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuA

Paper SS1-TuA6
The Ullmann Coupling Reaction: Atomic Scale Study of the Reactive Intermediates and Products of a Surface Catalyzed Reaction

Tuesday, November 16, 2004, 3:00 pm, Room 210B

Session: Hydrocarbon Reactions on Metal Surfaces
Presenter: S.U. Nanayakkara, The Pennsylvania State University
Authors: S.U. Nanayakkara, The Pennsylvania State University
E.C.H. Sykes, The Pennsylvania State University
L.C. Fernández-Torres, The Pennsylvania State University
P. Han, The Pennsylvania State University
P.S. Weiss, The Pennsylvania State University
Correspondent: Click to Email
We present an atomic-scale study of the Ullmann coupling reaction on Cu{111} using low temperature scanning tunneling microscopy and spectroscopy. We have studied the reactive intermediates and the products of the Ullmann coupling reaction between bromobenzene molecules, which form biphenyl at room temperature (293 K). Chemical identification of the surface-bound species has been achieved using their tunneling spectroscopic signatures. We demonstrate that bromobenzene molecules dissociatively chemisorb at 293 K and form phenyl intermediates, which travel distances of up to a few 1000 @Ao@ over Cu{111} terraces to bind preferentially at step edges. This preference is due to the anisotropic electron density distribution at the step edges. We identify the surface step edge as the active site of this reaction on Cu{111} for C-C bond formation. Once two phenyl intermediates combine to form biphenyl, these product molecules diffuse onto the terraces and arrange as clusters. Our interpretations of the preferred adsorption sites and the intermolecular interactions of adsorbates are explained in terms of the local electronic perturbations on the surface by surface steps and adsorbates.