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The mechanism of C-H bond activation of ethane was catalyzed by palladium halide cations (PdX+ (X = F, Cl, Br, H, and CH3)), which was investigated using density functional theory (DFT) at B3LYP level. The reaction mechanism was taken into account in triplet and singlet spin state potential energy surfaces. For PdF+, PdCl+, and PdBr+, the high spin states were the ground states, whereas the ground states were the low spin states in PdH+ and PdCH3+. The reaction of PdF+, PdCl+, and PdBr+ with ethane occurred via a typical "two-state reactivity" mechanism. In contrast, for PdH+ and PdCH3+, the overall reaction performed on the ground state PESs in a spin-conserving manner. The crossing points between two potential energy surfaces were observed and effectively decreased the activation barrier in PdX+/C2H6 (X = F, Cl, and Br). The minimum energy crossing points (MECP) were obtained used the algorithm in Harvey method. The natural valence electron configuration calculations were analyzed by natural bond orbital. The distribution and contribution of the front molecular orbital of the initial complexes could be further understand by the density of states. The feature of the bonding evolution in the main pathways was studied using topological analysis including localized orbital locator and atoms in molecules. [ABSTRACT FROM AUTHOR]

The dehydrogenation reaction mechanism of cyclohexane catalyzed by dimer transition metal cluster V2+ has been investigated at the B3LYP/6-31G (d, p) level of density functional theory. Density of states (DOS) graph is used to understand more deeply the roles of the front molecular orbital of the initial complexes. After the first molecular dehydrogenation, the reaction mainly consists of two competition mechanisms. First, the C-H bonds of cyclohexane can be effectively activated by the V2+ cation, yielding the same-face dehydrogenation products. Second, the C-C bonds are activated, forming the different-face dehydrogenation products. Our calculations indicate that the reaction takes place more easily along the low-spin potential energy surface on the same-face and is a low-barrier or even barrier-free transformation. Carbon-carbon single bonds are nonpolar and generally far less reactive. A comparison of the reaction mechanism of V2+ and congener Ti2+ with cyclohexane has been presented. The bond dissociation energies (BDEs) of V2+ are greater than that of Ti2+, leading to difficulties in forming sandwich complexes in the different-face dehydrogenation of cyclohexane, and the same-face dehydrogenation is an important reaction channel. [ABSTRACT FROM AUTHOR]