Activation of methane by Ru+: Experimental and theoretical studies of the thermochemistry and mechanism
Graphical abstract
Introduction
Considerable research has been done to study the reactions of first-row [1], [2], [3], [4], [5], [6], second-row [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], and third-row [6], [7], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35] transition-metal cations (M+) with small hydrocarbons. Such studies provide insight into the electronic requirements for the M+ activation of CH and CC bonds [36], [37], [38], [39], [40], [41], [42], periodic trends in the reactivity [1], [2], [6], and metal-hydrogen and metal-carbon bond dissociation energies (BDEs) [43], [44], [45], [46]. The thermochemistry obtained from these studies is of obvious fundamental interest and also has implications in understanding a variety of catalytic reactions involving transition-metal systems [47]. For the second-row transition metal cations, guided ion beam mass spectrometry (GIBMS) was previously used to study the activation of methane by Y+ [7], Zr+ [19], Nb+ [21], Mo+ [23], Rh+ [48], [49], and Pd+ [50]. This method allows the energetics of the reactions to be determined and mechanisms to be probed. Although others have examined the reaction of methane with Ru+ at room temperature (finding no reactivity and only adduct formation at elevated pressures) [6], [14], [15], the activation of methane by Ru+ has not previously been examined at elevated energies. The present study of the reaction of Ru+ with methane is partially motivated by our recent analogous work on its third-row congener, Os+, reacting with methane [30]. Comparison of these studies along with that of the first-row congener, Fe+ [51], [52], should allow elucidation of the periodic trends in the reactivity of the group 8 transition metal cations.
Although results for the reaction of Ru+ with methane at elevated energies have not previously been reported, we have previously reported such a study of Ru+ reacting with dihydrogen, ethane, propane, isobutane, and cyclopropane [53], [54], primarily to determine appropriate thermochemistry for RuH, RuCH3, RuH+, and RuCHx+ species. Information relevant to the present system is collected in Table 1, and supplants previous studies that reported BDEs for RuH+, RuH, and RuCH3+ [14], [17]. In addition, theoretical calculations have been performed for the BDEs of cationic and neutral ruthenium‐hydrides [55], [56], [57], [58], ruthenium‐methyls [59], [60], and ruthenium‐methylenes [58], [61], [62]. Most relevant to the present work is the density functional theoretical (DFT) study of the activation of methane by Ru+ [63], although several aspects of this work are extended theoretically in the present study at an advanced level of theory, B3LYP/def2-TZVPPD along with CCSD(T) calculations of the reactants and products. Furthermore, the comparison of the experimental results and the theory permits a rather complete elucidation of the reaction mechanism.
Section snippets
General procedures
These experiments were performed using a guided ion beam tandem mass spectrometer described in detail elsewhere [64], [65]. Ions were created in a direct current discharge flow tube source described below, extracted from the source, then accelerated and focused into a magnetic sector momentum analyzer for mass analysis. Ru+ ions containing the 102Ru isotope (31.55% natural abundance) were selected, decelerated to a desired kinetic energy, and focused into an octopole ion guide that traps the
Experimental cross sections for the reaction of Ru+ with methane
Reaction of Ru+ with CH4 yields the product ions shown in Reactions (2)–(6)Ru+ + CH4 → RuH+ + CH3 2.86 ± 0.05 eV→RuCH3+ + H 2.82 ± 0.06 eV→RuCH2+ + H2 1.14 ± 0.05 eV→RuCH+ + H2 + H 3.87 ± 0.12 eV→RuC+ + 2H2 3.36 ± 0.11 eV
Endothermicities for each process are shown on the basis of the experimental data in Table 1 (and the literature value for RuC+). Results for CH4 and CD4 are analogous although the larger mass separation between product ions in the CD4 system allows a lower mass resolution to resolve them. In turn, this permits
Mechanism for dehydrogenation of methane by Ru+
On the quartet surface, the energy of 4TS2/4 is the rate limiting step for dehydrogenation. This TS lies at 1.03 eV above ground state reactants, 0.09 eV above ground state products, RuCH2+ (4B2) + H2, at the B3LYP/def2 level. This TS, along with 4TS2/3, 4TS3/4, and the dihydride HRuHCH2+, 43, lie at high energies because the quartet high spin does not allow formation of the four covalent bonds needed to stabilize these species. Therefore, this is unlikely to be the path observed experimentally
Conclusion
Ground-state Ru+ ions are found to react with methane at hyperthermal energies to dehydrogenate and form RuCH2+ + H2. At higher collision energies, this product undergoes further dehydrogenation to form RuC+ and also competes with pathways yielding RuH+ + CH3 (the dominant product channel above 3 eV) and RuCH3+ + H. The latter product rapidly dehydrogenates to form RuCH+. At still higher energies, the RuCH3+ product undergoes loss of a H atom to form RuCH2+.
Analyses of the kinetic energy dependences
Acknowledgement
PBA thanks Prof. Kirk A. Peterson for help with the aug-cc-pwcVTZ-(PP,DK) calculations. This work is supported by the National Science Foundation, Grant No. CHE-1359769. A grant of computer time from the Center for High Performance Computing in University of Utah is gratefully acknowledged.
References (103)
- et al.
Activation of CH4, C2H6, and C3H8 by gas-phase Nb+ and the thermochemistry of Nb-ligand complexes
Int. J. Mass Spectrom.
(2000) - et al.
Why is hafnium so unreactive? Experimental and theoretical studies of the reaction of Hf + with methane
Int. J. Mass Spectrom.
(2006) - et al.
The most reactive third-row transition metal: guided ion beam and theoretical studies of the activation of methane by Ir+
Int. J. Mass Spectrom.
(2006) - et al.
Pt+-Mediated activation of methane: theory and experiment
Chem. Phys. Lett.
(1995) - et al.
Activation of CH4, C2H6, C3H8, and c-C3H6 by gas-phase Pd+ and the thermochemistry of Pd-ligand complexes
Int. J. Mass Spectrom. Ion Process.
(1997) - et al.
Activation of C2H6, C3H8, HC(CH3)3, and c-C3H6 by gas-phase Ru+ and the thermochemistry of Ru-ligand complexes
J. Am. Soc. Mass Spectrom.
(1999) - et al.
PCI-X, a parametrized correlation method containing a single adjustable parameter X
Chem. Phys. Lett.
(1994) - et al.
DFT studies for dehydrogenation of methane by gas-phase Ru+
Comp. Theor. Chem.
(2011) - et al.
Reactions of N4+ with rare gases from thermal to 10 eV c.m.: Collision-induced dissociation, charge transfer, and ligand exchange
Int. J. Mass Spectrom. Ion Process.
(1991) - et al.
Integral cross sections for ion-molecule reactions. 1. The guided beam technique
Chem. Phys.
(1974)
Augmented Gaussian basis sets for the elements K, Sc-Kr, Rb, and Y-Xe: Application in HF, MP2, and DFT calculations of molecular electric properties
Comput. Theor. Chem.
The performance of density functional/Hartree-Fock hybrid methods: The bonding in cationic first-row transition metal methylene complexes
Chem. Phys. Lett.
The gas-phase chemistry of transition-metal ions with organic molecules
Prog. Inorg. Chem.
Gas-phase transition-metal negative ion chemistry
Chem. Rev.
Organometallic chemistry in the gas phase
Chem. Rev.
Gas Phase Inorganic Chemistry
Selective activation of alkanes by gas-phase metal ions
Chem. Rev.
Reactions of atomic cations with methane: Gas phase room-temperature kinetics and periodicities in reactivity
J. Phys. Chem. A
Periodic trends in chemical reactivity: reactions of Sc+, Y+, La+, and Lu+ with methane and ethane
J. Am. Chem. Soc.
Thermochemistry of C H and C C bond activation: translational energy dependence of reactions of Sc+ with propane and 2-butenes
Organometallics
Gas-phase reactions of rhodium(+) ion with alkanes
J. Am. Chem. Soc.
Gas-phase reactions of yttrium and lanthanum ions with alkanes by Fourier transform mass spectrometry
Organometallics
Gas-phase reactions of niobium(1+) and tantalum(1+) with alkanes and alkenes. Carbonhydrogen bond activation and ligand-coupling mechanisms
Inorg. Chem.
Formation of thermodynamically stable dications in the gas phase by thermal ion-molecule reactions: tantalum(2+) and zirconium(2+) with small alkanes
J. Phys. Chem.
Formation of thermodynamically stable dications in the gas phase by thermal ion–molecule reactions: Nb2+ with small alkanes
J. Chem. Phys.
Determination of the metal-hydrogen and metal-methyl bond dissociation energies of the second row group 8 transition metal cations
J. Am. Chem. Soc.
Activation of alkanes by ruthenium, rhodium, and palladium ions in the gas phase: Striking differences in reactivity of first- and second-row metal ions
J. Am. Chem. Soc.
What is wrong with gas-phase chromium? A comparison of the unreactive chromium(1+) cation with the alkane-activating molybdenum cation
Organometallics
Homolytic and heterolytic bond dissociation energies of the second row group 8, 9 and 10 diatomic transition-Metal hydrides: correlation with electronic structure
J. Phys. Chem.
Reaction of second-row transition-metal cations with methane
J. Phys. Chem.
Activation of CH4 by gas-phase Zr+ and the thermochemistry of Zr ligand complexes
J. Phys. Chem. A
Activation of C2H6, C3H8, and c-C3H6 by gas-phase Zr+ and the thermochemistry of Zr-ligand complexes
Organometallics
Guided ion beam studies of the reactions of Ag+ with C2H6, C3H8, HC(CH3)3 and c-C3H6
J. Phys. Chem.
Activation of CH4 by gas-phase Mo+ and the thermochemistry of Mo-ligand complexes
J. Phys. Chem. A
Activation of C2H6 and C3H8 by gas-phase Mo+: Thermochemistry of Mo-ligand complexes
Organometallics
Activation of hydrocarbons by W+ in the gas phase
Organometallics
Experimental and theoretical studies of the activation of methane by Ta+
J. Phys. Chem. C
Guided-ion beam and theoretical study of the potential energy surface for activation of methane by W+
J. Phys. Chem. A
Is spin conserved in heavy metal systems? Experimental and theoretical studies of the reaction of Re+ with methane
J. Phys. Chem. A
Activation of methane by Os+: Guided ion beam and theoretical studies
ChemPlusChem
Pt+-catalyzed oxidation of methane: theory and experiment
J. Phys. Chem. A
The potential energy surface for activation of methane by Pt+: a detailed guided-Ion beam study
J. Am. Chem. Soc.
Activation of methane by gold cations: Guided ion beam and theoretical studies
J. Chem. Phys.
The chemistry of atomic transition metal ions: insight into fundamental aspects of organometallic chemistry
Accts. Chem. Res.
Electronic state-specific transition metal ion chemistry
Annu. Rev. Phys. Chem.
Chemistry of excited electronic states
Science
Control of transition-metal cation reactivity by electronic state selection
Bare transition metal atoms in the gas phase: Reactions of M, M+ and M2+ with hydrocarbons
Acc. Chem. Res.
Electronic state-selected reactivity of transition metal ions: Co+ and Fe+ with propane
J. Am. Chem. Soc.
Reactions of ground-State Ti+ and V+ with propane: Factors that govern C–H and C–C bond cleavage product branching ratios
J. Am. Chem. Soc.
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