Lanthanum-mediated C-H bond activation of propyne and identification of La(C3H2) isomers

Dilrukshi Hewage, Mourad Roudjane, W. Ruchira Silva, Sudesh Kumari, Dong Sheng Yang

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n2-Propadienylidenelanthanum [La(n2-CCCH2)] and deprotiolanthanacyclobutadiene [La(HCCCH)] of La(C3H2) are identified from the reaction mixture of neutral La atom activation of propyne in the gas phase. The two isomers are characterized with mass-analyzed threshold ionization spectroscopy combined with electronic structure calculations and spectral simulations. La(n2-CCCH2) and La(HCCCH) are formed by concerted 1,3- and 3,3-dehydrogenation, respectively. Both isomers prefer a doublet ground state with a La 6s-based unpaired electron, and La(n2-CCCH2) is slightly more stable than La(HCCCH). Ionization of the neutral doublet state of either isomer produces a singlet ion state by removing the La-based electron. The geometry change upon ionization results in the excitation of a symmetric metal-hydrocarbon stretching mode in the ionic state, whereas thermal excitation leads to the observation of the same stretching mode in the neutral state. Although the La atom is in a formal oxidation state of +2, the ionization energies of these metal-hydrocarbon radicals are lower than that of the neutral La atom. Deuteration has a very small effect on the ionization energies of the two isomers and the metal-hydrocarbon stretching mode of La(n2-CCCH2), but it reduces considerably the metal-ligand stretching frequencies of La(HCCCH).

Original languageEnglish
Pages (from-to)2857-2862
Number of pages6
JournalJournal of Physical Chemistry A
Issue number12
StatePublished - Mar 26 2015

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© 2015 American Chemical Society.

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry


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