Abstract
Structural characterization of gas-phase [M,C,2H]+ (M = Ta, Ir, Pt), formed by reacting laser ablation formed M+ with ethylene oxide (c-C2H4O) or methane under multiple collision conditions, is achieved using infrared multiple-photon dissociation (IR-MPD) spectroscopy with the intracavity free-electron laser FELICE. After product formation, part of the product distribution is complexed with Ar, allowing for simultaneous recording of IR-MPD spectra of both bare [M,C,2H]+, which dissociates via dehydrogenation, and [M,C,2H]+∙Ar, which loses Ar. Comparison of the spectra with density functional theory (DFT) calculations allows for an internally consistent assignment of the spectra to the Ta+CH2 (3A′′) distorted carbene, Pt+CH2 (2A1) carbene, and to the HIr+CH (1A′) carbyne-hydride. Evidence for a symmetric Ta+CH2∙Ar (3B2) complex is also obtained. For Pt and Ir, these structures match those found in previous work when these species were formed by reaction of M+ with methane, CH4 and CD4. Under the current conditions, no clear signs of the previously observed Ir+CH2 (3A2) carbene product were found, consistent with its higher energy, especially after Ar complexation. Potential energy surfaces for the reactions of Pt+ and Ir+ with c-C2H4O are also computed.
Highlights
Interactions between methane and transition metal cations have attracted wide interest because they can provide insight for the rational design of future methane activation catalysts [1,2]
Cations of five of the 3rd row transition metal elements (Ta, W, Os, Ir, and Pt) have been shown to dehydrogenate methane to form [M,C,2H]+ ions at room temperature [3,4,5,6,7,8,9,10,11,12]. [M,C,2H]+ can be formed for additional metal cations at room temperature when they are reacted with either cyclopropane, c-C3H6, or ethylene oxide, c-C2H4O [13,14,15,16]
We structurally characterized the products formed by reacting Pt+ and Ir+ ions with ethylene oxide (c-C2H4O) and Ta+ with methane under multiple collision conditions using IR spectroscopy
Summary
Interactions between methane and transition metal cations have attracted wide interest because they can provide insight for the rational design of future methane activation catalysts [1,2]. IR-MPD spectroscopy of these stable and small (four atom) cations has not been easy: irradiation of [M,C,2H]+ (M = Ta, Ir, and Pt) using the light produced by the infrared free-electron laser FELIX did not result in observed fragmentation [25,26,27] It took the pulse energies of the intracavity free-electron laser FELICE to succeed in resonant fragmentation [16,18,19,20], but the intensities required to overcome the fragmentation energy led to broadening effects, prohibiting the observation of individual ro-vibrational transitions.
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