Lanthanum-mediated C-H bond activation of propyne and identification of La(C₃H₂) isomers.
η(2)-Propadienylidenelanthanum [La(η(2)-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(η(2)-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(η(2)-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(η(2)-CCCH2), but it reduces considerably the metal-ligand stretching frequencies of La(HCCCH).
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, United States.
Dilrukshi
D
Hewage
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, United States.
Mourad
M
Roudjane
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, United States.
W Ruchira
WR
Silva
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, United States.
Sudesh
S
Kumari
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, United States.
Dong-Sheng
DS
Yang