La(C3H4) and La(C3H6) are observed from the reaction of laser-vaporized La atoms with propene by photoionization time-of-flight mass spectrometry and characterized by mass-analyzed threshold ionization spectroscopy. Two isomers of La(C3H4) are identified as methyl-lanthanacyclopropene [La(CHCCH3)] (Cs) and lanthanacyclobutene [La(CHCHCH2)] (C1); La(C3H6) is determined to be H—La(η3-allyl) (Cs), a C—H bond inserted species. All three metal-hydrocarbon radicals prefer a doublet ground state with a La 6s-based electron configuration. Ionization of the neutral doublet state of each of these radicals produces a singlet ion state by removing the La-based 6s electron. The threshold ionization allows accurate measurements of the adiabatic ionization energy of the neutral doublet state and metal-ligand and ligand-based vibrational frequencies of the neutral and ionic states. The formation of the three radicals is investigated by density functional theory computations. The inserted species is formed by La inserting into an allylic C—H bond and lanthanacyclopropene by concerted vinylic H2 elimination, whereas lanthanacyclobutene involves both allylic and vinylic dehydrogenations. The inserted species is identified as an intermediate for the formation of lanthanacyclobutene.
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We are grateful for the financial support from the National Science Foundation Division of Chemistry (Chemical Structure, Dynamics, and Mechanisms, Grant No. CHE-1362102).
See supplementary material for the geometries of La(CHCCH3), La(CHCHCH2), and H—La(η" role="presentation">η3-C3H5) and their ion states; electronic states and energies of the three isomers of La(C3H6), energies of the stationary points along the reaction coordinates for the formation of three La-hydrocarbon radicals, and MATI spectra of La(C3H6) and simulations of its various isomers.
Kumari, Sudesh; Cao, Wenjin; Hewage, Dilrukshi C.; Silva, Ruchira; and Yang, Dong-Sheng, "Mass-Analyzed Threshold Ionization Spectroscopy of Lanthanum-Hydrocarbon Radicals Formed by C—H Bond Activation of Propene" (2017). Chemistry Faculty Publications. 111.