title: Thermal activation of methane and ethene by bare MO·+ (M=Ge, Sn, and Pb): a combined theoretical/experimental study.
abstract: The thermal ion/molecule reactions (IMRs) of the Group 14 metal oxide radical cations MO(·+) (M=Ge, Sn, Pb) with methane and ethene were investigated. For the MO(·+)/CH(4) couples abstraction of a hydrogen atom to form MOH(+) and a methyl radical constitutes the sole channel. The nearly barrier-free process, combined with a large exothermicity as revealed by density functional theory (DFT) calculations, suggests a fast and efficient reaction in agreement with the experiment. For the IMR of MO(·+) with ethene, two competitive channels exist: hydrogen-atom abstraction (HAA) from and oxygen-atom transfer (OAT) to the organic substrate. The HAA channel, yielding C(2)H(3·) and MOH(+) predominates for the GeO(·+)/ethene system, while for SnO(·+) and PbO(·+) the major reaction observed corresponds to the OAT producing M(+) and C(2)H(4)O. The DFT-derived potential-energy surfaces are consistent with the experimental findings. The behavior of the metal oxide cations towards ethene can be explained in terms of the bond dissociation energies (BDEs) of MO(+)-H and M(+)-O, which define the hydrogen-atom affinity of MO(+) and the oxophilicity of M(+), respectively. Since the differences among the BDEs(MO(+)-H) are rather small and the hydrogen-atom affinities of the three radical cations MO(·+) exceed the BDE(CH(3)H) and BDE(C(2)H(3)-H), hydrogen-atom abstraction is possible thermochemically. In contrast, the BDEs(M(+)-O) vary quite substantially; consequently, the OAT channel becomes energetically less favorable for GeO(·+) which exhibits the highest oxophilicity among these three group 14 metal ions.
authors.affiliation: Laboratory of Chemical Genomics, Shenzhen Graduate School of Peking University, Shenzhen, P R China.
authors.forename: Kai
authors.initials: K
authors.lastname: Chen
authors.forename: Zhe-Chen
authors.initials: ZC
authors.lastname: Wang
authors.forename: Maria
authors.initials: M
authors.lastname: Schlangen
authors.forename: Yun-Dong
authors.initials: YD
authors.lastname: Wu
authors.forename: Xinhao
authors.initials: X
authors.lastname: Zhang
authors.forename: Helmut
authors.initials: H
authors.lastname: Schwarz
mesh_terms: D005030:Ethylenes / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry*; D005857:Germanium / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D008697:Methane / Q000737:chemistry*; D008962:Models, Theoretical; D015394:Molecular Structure; D009942:Organometallic Compounds; D010087:Oxides / Q000737:chemistry*; D013816:Thermodynamics; D014001:Tin / Q000737:chemistry*
chemical_list: D005030:Ethylenes; D005609:Free Radicals; D008670:Metals; D009942:Organometallic Compounds; D010087:Oxides; D005857:Germanium; D007854:Lead; D014001:Tin; C036216:ethylene; D008697:Methane