Activation of CH4 and H2 molecules by cationic zirconium(IV) complexes:: a DFT study

Reactions of methane and hydrogen molecules with [(eta(5)-C5H5)(2)ZrCH3](+) (1) and [(eta(5)-C5H5)(2)ZrH](+) (2) cations were studied using nonempirical density functional theory (DFT). In all cases, the reactions begin with the formation of agostic complexes between the substrate molecules and I or 2. Transformation of these intermediates into transition states when moving along the reaction coordinate requires only slight changes in the geometry. The dihydrogen molecule reacts with 1 exothermically (-8.8 kcal mol(similar to 1)) and barrierlessly to form 2 and CH4. Exchange of sigma-bonded ligands in the 1--CH4 system proceeds through a symmetric transition state with an activation energy of 15.0 kcal mol(-1). According to calculations, organometallic Zr-IV complexes are promising for activation of C--H and H--H bonds under mild conditions.