Kohn–Sham density-functional study of the formation of benzene from acetylene on iron clusters, Fe/Fen+ (n=1–4)

Abstract

This is part of a series dealing with the formation of benzene from acetylene on iron clusters, Fenq+ (n=1–4, q=0,1). In this paper, we show that the formation of benzene from acetylene on Fe and Fen+ (n=1–4) is favorable from a thermodynamic point of view. We explain the variation of the rate constants observed for the successive adsorption of acetylene molecules on an iron cation and the experimental observations about the cyclodimerization of acetylene molecules in Fe(C2H2)2+ by referring to the spin conservation principle. Our results indicate that the complexes resulting from the cyclodimerization of Fen(C2H2)2+/Fe(C2H2)2 and Fen(C2H2)3+/Fe(C2H2)3(n=1–4) contain an n-C4H4 ligand (formation of a metallacycle) rather than a cyclobutadiene molecule. However, it is possible to observe the formation of cyclobutadiene from Fe(C2H2)2+ and Fe2(C2H2)3+ only if spin–orbit coupling is significant. A post-self-consistent-field method that includes a multideterminantal treatment is needed to get a quantitative energetic description of the various steps of the reaction. Finally, we discuss various difficulties met in this study and possible ways to deal with them.

Impact of Metals on (Star)Dust Chemistry: A Laboratory Astrophysics Approach

“…Further chemistry will then proceed leading to the formation of larger aromatic compounds via C 2 H 2 and CH 3 (for the plasma) addition to the first aromatic ring. The role of metal ions and small clusters in the cyclization of unsaturated hydrocarbons has been previously demonstrated (Schnabel et al, 1991;Wesendrup and Schwarz, 1997;Chrétien and Salahub, 2003;Marks et al, 2019). We suggest here that Ag 2 would act as a catalyst for the formation of the first aromatic ring.…”

CH Activation by a Heavy Metal Cation: Production of H2 from the Reaction of Acetylene with C4H4-Os(+) in Gas phase

“…In this report we extend our theoretical investigations to osmium cation reactions with acetylene, which, compared to the modeling of Iron cation systems [16,17], seems to be largely neglected. We hope the structures and energetics we report here can guide the interpretation of the future experimental data on gas-phase systems and single-atom catalytic processes involving a single atom on a surface.…”

“…We hope the structures and energetics we report here can guide the interpretation of the future experimental data on gas-phase systems and single-atom catalytic processes involving a single atom on a surface. The Fe(+) structures we already reported [16] included some that were not studied previously [17]. These are the Fe analogies to 6, 7A and 7B, 8, 12, 13, S1 and S2.…”

“…Eta-2 coordination can connect adjacent C atoms (7A) or nonadjacent C atoms (7B). Species 11 may be what Chretien and Salahub [17] call Fe(c-C 4 H 4 )(C 2 H 2 ) cation; in that species Fe participates in a ferro-cyclopentyl ring and a three-membered ferro-cyclopropenyl ring, according to these authors. Structure 12 is called chair and structure 13 is called saddle for easy reference and visualization.…”

Cyclotrimerization of Acetylene on Clusters Con+/Fen+/Nin+(n = 1–16)

“…The size-dependent properties of transition metal clusters at the low size end, with high specific surface areas and low coordination surface active sites, are of significant relevance to heterogeneous catalysis. − Experiments in recent years with various metal clusters have pointed to a number of future potential developments in catalysis. − There are also extensive research interest in and efforts devoted to probing gas-phase reactivity of acetylene on metal clusters, − and supported metal clusters and nanocatalysts. − In particular, a few gas-phase naked metal clusters and supported metal clusters have been studied with respect to the possible catalysis of cyclotrimerization of acetylene. − Of special interest here is the evidence for low-pressure catalysis in the gas phase by a naked Fe 4 + cluster, which is interpreted as a route to the formation of benzene. , Also, cyclotrimerization of acetylene was observed on supported, size-selected Pd n clusters, , and a preliminary conclusion was reached that a single palladium atom was sufficient to catalyze the acetylene-to-benzene reaction . This pioneering study opened for subsequent efforts to seek metal ions as catalysts for the acetylene cyclotrimerization. − …”