Density Functional Theory Study of the Reaction Mechanism for Competitive Carbon—Hydrogen and Carbon—Halogen Bond Activations Catalyzed by Transition Metal Complexes

摘要

Carbon—hydrogen and carbon—halogen bond activations between halobenzenes and metal centers were studied by density functional theory with the nonempirical meta-GGA Tao—Perdew—Staroverov—Scuseria functional and an all-electron correlation-consistent polarized valence double-c basis set. Our calculations demonstrate that the hydrogen on the metal center and halogen in halobenzene could exchange directly through a kite-shaped transition state. Transition states with this structure were previously predicted to have high energy barriers (J. Am. Chem. Soc. 2005, 127, 279), and this prediction misled others in proposing a mechanism for their recent experimental study (J. Am. Chem. Soc. 2006, 128, 3303). Furthermore, other halo—carbon activation pathways were found in the detailed mechanism for the competitive reactions between cationic titanium hydride complex [Cp*(~tBu_3P=N)TiH]~+ and chlorobenzene under different pressure of H_2. These pathways include the ortho-C—H and Ti—H bond activations for the formation and release of H_2 and the indirect C—Cl bond activation via β-halogen elimination for the movement of the C_6H_4 ring and the formation of a C—N bond in the observed final product. A new stable isomer of the observed product with a similar total energy and an unexpected bridging between the Cp~* ring and the metal center by a phenyl ring is also predicted.