Gas-phase reactions of copper atoms with alkynes: sequential ligand addition via steady-state kinetics
作者:M. A. Blitz、S. A. Mitchell、P. A. Hackett
DOI:10.1021/j100122a021
日期:1993.5
A time-resolved study of gas-phase reactions of copper atoms with methylacetylene (MA) and dimethylacetylene (DMA) has been undertaken, using Ar buffer ps at total pressures in the range 10-600 Torr. At 292 and 325 K, both reactions display kinetics consistent with formation of a 1:1 complex, which may either redissociate or add a second ligand to form a 1:2 complex. The copper atom decay kinetics followed single-exponential behavior, which indicates that the intermediate 1:1 complex was at steady-state. Perturbations to the kinetics were observed due to the presence of large mole fractions of reactant in the buffer gas. These include a novel ''chemical activation'' reaction channel, which occurs by successive collision of two ligand molecules with Cu, without intervening third-body stabilization of the 1:1 collision complex by inert buffer gas. Analysis of the data yielded rate parameters for both the first and second ligand addition reactions, from which binding energies of the 1:1 complexes were estimated: DELTAE0-degrees [Cu-MA] = 32 +/- 6 kJ mol-1; DELTAE0-degrees [Cu-DMA] = 36 +/- 6 kJ mol-1. RRKM unimolecular reaction theory calculations were performed to model the kinetics of the first ligand addition reactions and to provide estimates of lower limits for the binding energies of the 1:2 complexes. For both alkynes, the second ligands are bound significantly more strongly than the first.