Enhancement of the Catalytic Activities of Heteronuclear Bimetallic Cations for the C–H Bond Activation of Cyclohexane

Abstract

Heterometallic cations NiCu + and CoNi + can easily induce triple dehydrogenation of cyclohexane with high yield, and monometallic cations Ni + and Co + only give rise to double dehydrogenation with low yield. Reaction mechanisms of the six C−H bond activations for cyclohexane are systematically investigated by comparing the difference between bimetallic cations and monometallic ones. Fragment molecular orbital analysis clearly indicates that charge transfer (CT) occurs from the occupied interacting orbital of the metallic cation to the σ*-antibonding orbital of the first, third, and fifth activated C−H bonds in transition states. The synergistic effects of heteronuclear bimetallic cations result in the destabilization of the occupied interacting orbital in bimetallic cations, which raise the reactivity of bimetallic cations and enhance the CT between catalysts and substrates. Contrary to the absence of the third dehydrogenation product in the mononuclear metallic cation catalytic reaction, a significant amount of the third dehydrogenation product is observed in the presence of heteronuclear cations (NiCu + and CoNi + ). π back-bonding between Ni of heteronuclear metallic cations and the substrate cyclohexadiene plays an essential role in lowering the energies of transition states, which accelerate the third dehydrogenation. The reasons why heteronuclear bimetallic cations are more reactive than monometallic ones are discussed in detail.

Fully Exposed Metal Clusters: Fabrication and Application in Alkane Dehydrogenation

“…On Pt FECCs, the moderate interactions between Pt atoms and benzene product enabled fast product desorption and hindered the poisoning. Theoretically, Geng et al constructed heterometallic cations NiCu + and CoNi + on the basis of monometallic cations Ni + and Co + . Because of the stronger interaction between 3d orbitals of the metallic cation and σ*-antibonding orbital of the C–H bond, the C–H bond length of transition state on heterometallic cation was shorter than that on monometallic cation.…”

“…Theoretically, Geng et al constructed heterometallic cations NiCu + and CoNi + on the basis of monometallic cations Ni + and Co + . 215 Because of the stronger interaction between 3d orbitals of the metallic cation and σ*-antibonding orbital of the C−H bond, the C−H bond length of transition state on heterometallic cation was shorter than that on monometallic cation. On heterometallic cation, the stable transition state maintained a high activity for CDH.…”