Activation of Methane by Os⁺: Guided‐Ion‐Beam and Theoretical Studies

Abstract

Activation of methane by the third‐row transition‐metal cation Os+ is studied experimentally by examining the kinetic energy dependence of reactions of Os+ with CH4 and CD4 using guided‐ion‐beam tandem mass spectrometry. A flow tube ion source produces Os+ in its electronic ground state and primarily in the ground spin–orbit level. Dehydrogenation to form [Os,C,2 H]++H2 is exothermic, efficient, and the only process observed at low energies for reaction of Os+ with methane, whereas OsH+ dominates the product spectrum at higher energies. The kinetic energy dependences of the cross sections for several endothermic reactions are analyzed to give 0 K bond dissociation energies (in eV) of D0(Os+C)=6.20±0.21, D0(Os+CH)=6.77±0.15, and D0(Os+CH3)=3.00±0.17. Because it is formed exothermically, D0(Os+CH2) must be greater than 4.71 eV, and a speculative interpretation suggests the exothermicity exceeds 0.6 eV. Quantum chemical calculations at the B3LYP/def2‐TZVPP level show reasonable agreement with the experimental bond energies and with previous theoretical values available. Theory also provides the electronic structures of the product species as well as intermediates and transition states along the reactive potential energy surfaces. Notably, the structure of the dehydrogenation product is predicted to be HOsCH+, rather than OsCH2+, in contrast to previous work.

Activation of CH4 by Th+ as Studied by Guided Ion Beam Mass Spectrometry and Quantum Chemistry

“…22,23,25,27,28,30,53,69,70,86 In all cases, the difference is attributed to competition with the formation of the metal carbene because of a shared, common intermediate. Because reactions of M + with H 2 produce only one product, no competition exists that may delay the onset of reaction.…”

Selective Activation of the C−H Bond in Methane by Single Platinum Atomic Anions

“…Gas‐phase studies of methane activation by metal atoms and clusters have provided insight into methane functionalization at the molecular level . In the case of platinum the reactivities of its cationic, neutral, and anionic atoms and clusters with methane have been widely investigated .…”

Reactions of liquid and solid aluminum clusters with N2: The role of structure and phase in Al114+, Al115+, and Al117+

“…Dissociation of Al n N 2 + leads to the formation of secondary products and causes the cross sections for the Al n N 2 + product to roll over. [45][46][47][48][49][50] This rollover is not immediately apparent in the measured cross sections shown in Figure 1; however, it is much more important for smaller clusters. 29 We assume that the lowest energy dissociation pathway is loss of an aluminum atom from the Al n N 2 + product.…”