Gas-Phase Ion−Molecule Reactions of Metal−Carbide Cations MC_n⁺ (M=Y and La; n=2, 4, and 6) with Benzene and Cyclohexane Investigated by FTICR Mass Spectrometry and DFT Calculations

Abstract

Yttrium- and lanthanum-carbide cluster cations YC(n)(+) and LaC(n)(+) (n = 2, 4, and 6) are generated by laser ablation of carbonaceous material containing Y(2)O(3) or La(2)O(3). YC(2)(+), YC(4)(+), LaC(2)(+), LaC(4)(+), and LaC(6)(+) are selected to undergo gas-phase ion-molecule reactions with benzene and cyclohexane. The FTICR mass spectrometry study shows that the reactions of YC(2)(+) and LaC(2)(+) with benzene produce three main series of cluster ions. They are in the form of M(C(6)H(4))(C(6)H(6))(n)(+), M(C(8)H(4))(C(6)H(6))(n)(+), and M(C(8)H(6))(C(6)H(6))(m)(+) (M = Y and La; n = 0-3; m = 0-2). For YC(4)(+), LaC(4)(+), and LaC(6)(+), benzene addition products in the form of MC(n)(C(6)H(6))(m)(+) (M = Y and La; n = 4, 6; m = 1, 2) are observed. In the reaction with cyclohexane, all the metal-carbide cluster ions are observed to form metal-benzene complexes M(C(6)H(6))(n)(+) (M = Y and La; n= 1-3). Collision-induced-dissociation experiments were performed on the major reaction product ions, and the different levels of energy required for the fragmentation suggest that both covalent bonding and weak electrostatic interaction exist in these organometallic complexes. Several major product ions were calculated using DFT theory, and their ground-state geometries and energies were obtained.

Molecular structure and thermodynamic properties of the gaseous ThC2 and ThC4 species

“…However, recent quantum chemical calculations for the lanthanum carbides by Roszak and Balasubramanian [9] indicated that LaC 2 has a cyclic (or 'fan') structure. Similar results have been reported for the LaC þ 2 ion [10]. This raises the question whether the gaseous actinide carbide species also have cyclic structures.…”

Theoretical Study of the Structure and Bonding in ThC2 and UC2

“…In our CASPT2 calculations, the electronic ground states of ThC 2 and UC 2 adopted the symmetric triangular molecular structure I (similar to those found for rare earth dicarbides, − while the asymmetric triangular structures II lie very close in energy. The bent and the two linear molecular arrangements are considerably (generally by a few hundreds of kJ/mol) higher in energy.…”

Cracking and Dehydrogenation of Cyclohexane by [(phen)M(X)]+ (M = Ni, Pd, Pt; X = H, CH3) in the Gas Phase

“…Similar interactions were found in the gas phase in Pd and Ni complexes with alkyl chains with two carbons or longer, 9,10 as well as in solution and in the solid phase for Ni, Pd, and Pt complexes. 19,20 It is worth noting that the energy of both axial and equatorial versions of TS4-5Pd lies below the energy of the separated reactants (selected as zero in Figure 1), consistent with the fact that the ion−molecule reactions (IMRs) are observed to occur under the near-thermal conditions of the ion trap mass spectrometer. 29,30 Scheme 2 illustrates the nomenclature for structures 1−9 and is designed to assist with the identification of structures throughout the manuscript.…”

“…Gas-phase experimental studies in combination with density functional theory (DFT) calculations offer a unique way of dissecting complex catalytic processes into individual elementary steps . Mass spectrometric experiments with bare metal cations M + have revealed dehydrogenation of cyclohexane to benzene, while Fe + , Co + , and Ni + produce small amounts of ethylene and propylene upon the collisional activation of M + /cyclohexane complexes. − Nickel­(II) cationic species CpNi + (where Cp = cyclopentadienyl) react with cyclohexane by eliminating one, two, or three hydrogen molecules . More recently, Gronert and co-workers published an elegant example of a Ni(0)/fluorenyl anionic complex dehydrogenating cyclohexane in a similar fashion …”