Theoretical investigation on cyclohexane dehydrogenation catalyzed by V2+ in gas-phase.

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]