Gas-Phase Coordination of Mg⁺, (c-C₅H₅)Mg⁺, and (c-C₅H₅)₂Mg⁺ with Saturated Hydrocarbons

Abstract

The coordination of the electronic ground states of Mg+, (c-C5H5)Mg+, and (c-C5H5)2Mg+ with the straight-chain saturated hydrocarbons methane, ethane, n-propane, n-butane, n-pentane, n-hexane, and n-heptane has been investigated in the gas phase in helium at room temperature and moderate pressures. Reaction rate coefficients and product distributions were measured with the selected-ion flow tube (SIFT) technique operating at 294 ± 3 K and a helium buffer-gas pressure of 0.35 ± 0.01 Torr. Rate coefficients were measured for all observed ligation steps (or upper limits in the case of nonreactions), and bond connectivities in the coordinated ions were probed with multicollision-induced dissociation. Only single ligation was observed. The rate of ligation was found to depend on the size of the saturated hydrocarbon, increasing with increasing size until the collision rate is reached, and on the degree of ligation with c-C5H5. Mg+ was found to be unreactive with methane and ethane, k < 10-13 cm3 molecule-1 s-1, but ligation was observed with the other hydrocarbons, k ≥ 7 × 10-12 cm3 molecule-1 s-1. Single ligation of Mg+ with c-C5H5 substantially enhances the efficiency of subsequent ligation: the ligation is rapid, k ≥ 1.4 × 10-10 cm3 molecule-1 s-1, with all the saturated hydrocarbons investigated. Double ligation with c-C5H5 completely shuts down the efficiency of ligation: no reaction was observed between the saturated hydrocarbons and the full-sandwich magnesocene cation, k < 10-13 cm3 molecule-1 s-1. A linear correlation is reported between the measured thresholds for multicollision-induced dissociation and the polarizability of the hydrocarbon ligand. With a view to published calculations by Bauschlicher et al. for Mg+−CH4 and Mg+−C2H4, this correlation is consistent with end-on structures for the Mg+−L and (c-C5H5)Mg+−L species observed in this study. A detailed study using density functional theory for the interaction of Mg+ with three rotamers of n-pentane indicates that interconversion of different isomers of Mg+−n-C5H12 should be easy, even at room temperature and that the ligated species Mg+−n-C5H12 is “dynamic” rather than “static”. Stronger bonding (by a factor of about two) is indicated for (c-C5H5)Mg+−L by the multicollision CID experiments, and this is consistent with a formal description of (c-C5H5)Mg+ as (c-C5H5)-Mg2+.

Reductions of Oxygen, Carbon Dioxide, and Acetonitrile by the Magnesium(II)/Magnesium(I) Couple in Aqueous Media: Theoretical Insights from a Nano-Sized Water Droplet

“…The actual roles of Mg(I) in chemical reactions are largely unexplored probably because detail experimental investigation of its chemical properties is challenging because of its metastable characters in condensed phases. Isolation of ions in the gas phase inside a mass spectrometer provides a great opportunity to examine the reactivity of transient intermediates on the molecular level. − Although the subvalent Mg •+ is unstable in the condensed phases, gas-phase [Mg(H 2 O) n ] •+ clusters are isolable and exhibit rich redox chemistry that has attracted much experimental − and theoretical − interests in the past two decades. The solvation structure of [Mg(H 2 O) n ] •+ has been well-characterized; each cluster consists of a Mg 2+ and a hydrated electron solvated out from the 3 s orbital of the original Mg •+ center (reaction ). ,− The solvated electron can reduce a water molecule to liberate a hydrogen atom, leaving the hydroxide ion solvated in the cluster (reaction ).…”

pH‐Triggered Dethreading–Rethreading and Switching of Cucurbit[6]uril on Bistable [3]Pseudorotaxanes and [3]Rotaxanes

“…Although a similar situation has been found for bare Mg +. ,39 for almost all transition‐metal cations, olefins are much more strongly bound than the corresponding alkanes,40 for which Dewar, Chatt, and Dunkinson provided a seminal rationale 41. Interestingly, the only examples in which exchanges of olefin ligands by alkanes so far have been observed for transition‐metal ions are the dications Y 2+ and La 2+ 42.…”

Alkaline Earth Organometallics

“…[242][243][244] Relative binding energies and standard enthalpies of formation have been estimated with DFT calculations, and single-point energy calculations have been completed with large basis sets at both the DFT and MP4 levels of theory. [242][243][244] Relative binding energies and standard enthalpies of formation have been estimated with DFT calculations, and single-point energy calculations have been completed with large basis sets at both the DFT and MP4 levels of theory.…”