J. M. Meyers, A. Gellman
Aug 20, 1995
Citations
1
Influential Citations
31
Citations
Journal
Surface Science
Abstract
Abstract By using selectively substituted iodobenzenes, we have been able to study the kinetics of the Ullmann phenyl coupling reaction on the Cu(111) surface. The substituted iodobenzenes used in these experiments were (iodobenzene (C6H5I), 3-iodotoluene (m-CH3C6H4I), 1-fluoro-2-iodobenzene (o-FC6H4I), 1-fluoro-3-iodobenzene (m-FC6H4I) and 1-fluoro-4-iodobenzene (p-FC6H4I)). Variable heating rate temperature programmed reaction (TPR) experiments were used to determine the energy barriers and preexponential factors in the rate constant for phenyl coupling. These studies have allowed us to probe the nature of charge separation in the transition state. Fluorination of iodobenzene in the meta or para position decreased the activation barrier, indicating that the transition state is electron rich with respect to the initial state. Reaction rate constants were calculated from the kinetic parameters and linear free energy relationships (LFER) or Hammett plots were constructed using tabulated values of the substituent constants. The reaction constant, ϱ, was determined to be 6.0 ± 3.3 from the Hammett plot. The sign of the reaction constant indicates the electron rich character of the transition state relative to the initial state.