Abstract
The products of methane dehydrogenation by gas‐phase Ta4 + clusters are structurally characterized using infrared multiple photon dissociation (IRMPD) spectroscopy in conjunction with quantum chemical calculations. The obtained spectra of [4Ta,C,2H]+ reveal a dominance of vibrational bands of a H2Ta4C+ carbide dihydride structure over those indicative for a HTa4CH+ carbyne hydride one, as is unambiguously verified by studies employing various methane isotopologues. Because methane dehydrogenation by metal cations M+ typically leads to the formation of either MCH2 + carbene or HMCH+ carbyne hydride structures, the observation of a H2MC+ carbide dihydride structure implies that it is imperative to consider this often‐neglected class of carbonaceous intermediates in the reaction of metals with hydrocarbons.
Highlights
Activation of the CÀH bond in small hydrocarbons, like methane, attracts currently considerable research efforts because of its potential utilization in industrial processes employed for the production of liquid fuels and other valuable chemical commodities, such as methanol and higher hydrocarbons
Activation of the CÀH bond in methane at mild conditions has been found to be feasible in reactions with thirdrow transition metal cations in a variety of environments,[2] in line with further studies performed in flow tubes[3] and using guided-ion-beam techniques.[1f]. Among these metals, tantalum has been identified as a favorable element with the prospect of serving as a successful catalyst, in light of the experimental observation of the catalytic non-oxidative coupling of methane facilitated by silica-supported tantalum hydrides under realistic conditions.[4]
Among the pertinent results from recent investigations on this topic (i.e.Ta4+),[8] we note: (i) The reaction of Ta4+ with methane starts with the formation of [4Ta,C,2H]+, followed by a facile second dehydrogenation reaction. (ii) First-principles density functional theory (DFT) calculations predicted that in the first step of the reaction, a H2Ta4C+ carbide dihydride structure is energetically favored over carbene (Ta4CH2+).[8]
Summary
Activation of the CÀH bond in small hydrocarbons, like methane, attracts currently considerable research efforts because of its potential utilization in industrial processes employed for the production of liquid fuels and other valuable chemical commodities, such as methanol and higher hydrocarbons. Comparing this spectrum to the calculated spectra of different structural isomers of [4Ta,C,2H]+, we observe first the lack of any significant IR activity for the Ta4CH2+ carbene structure (Figure 1 A-III) near the prominent peak at 1400 cmÀ1.
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