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

Abstract

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-ζ 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*(tBu3PN)TiH]+ and chlorobenzene under different pressure of H2. These pathways include the ortho-C−H and Ti−H bond activations for the formation and release of H2 and the indirect C−Cl bond activation via β-halogen elimination for the movement of the C6H4 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