State-Specific Reactions of Cu super(+)( super(1)S, super(3)D) with CH sub(3)X and CF sub(3)X (X = Cl, Br, I): Exploring the Influence of Dipole Orientation on Association and C-X Bond Activation

The reactions of gas-phase Cu super(+)( super(1)S) and Cu super(+)( super(3)D) with CF sub(3)X and CH sub(3)X (X = Cl, Br, and I) have been examined experimentally using the drift cell technique at 3.5 Torr in He at room temperature. State-specific product channels and overall bimolecular rate constants for depletion of the two Cu super(+) states were determined using electronic state chromatography. The results showed that Cu super(+)( super(1)S) participates exclusively in association with all of these neutrals, whereas, depending on the neutral, Cu super(+)( super(3)D) initiates up to three bimolecular processes, resulting in the formation of CuX super(+), CuC(H/F) sub(3) super(+), and C(H/F) sub(3)X super(+). Possible structures for the singlet association products were explored using density functional methods. These calculations indicated that Cu super(+) preferentially associates with the labile halogen (Cl, Br, I) with all neutrals except CF sub(3)Cl, for which a "backside" geometry occurs in which Cu super(+)( super(1)S) is weakly bound to the -CF sub(3) end of the molecule. All products observed on the triplet reaction surface can be understood in terms of either known or calculated thermochemical requirements. Product distributions and overall reaction efficiencies for C-X bond activation (X = Br, I) through Cu super(+)( super(3)D) suggest that the orientation of the neutral dipole has little or no effect in controlling access to specific product channels. Likewise, second-order rate constants for reactions with X = Br and I indicate efficient depletion of Cu super(+)( super(3)D) and do not exhibit the dramatic variations in reaction efficiency previously observed with CH sub(3)Cl and CF sub(3)Cl. These results suggest that C-X bond activation proceeds through a bond-insertion mechanism as opposed to direct abstraction.