La atom reaction with isoprene is carried out in a laser-vaporization molecular beam source. The reaction yields an adduct as the major product and C—C cleaved and dehydrogenated species as the minor ones. La(C5H8), La(C2H2), and La(C3H4) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of all three species exhibit a strong origin band and several weak vibronic bands corresponding to La-ligand stretch and ligand-based bend excitations. La(C5H8) is a five-membered metallacycle, whereas La(C2H2) and La(C3H4) are three-membered rings. All three metallacycles prefer a doublet ground state with a La 6s1-based valence electron configuration and a singlet ion. The five-membered metallacycle is formed through La addition and isoprene isomerization, whereas the two three-membered rings are produced by La addition and insertion, hydrogen migration, and carbon-carbon bond cleavage.
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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). We also acknowledge additional support from the Kentucky Science and Engineering Foundation.
See supplementary material for the geometries of La(C5H8) and its singly charged positive ion and the energies of the stationary points along the reaction coordinates for the formation of La(C5H8) (Iso A), La(C2H2), and La(C3H4) from the La atom reaction with isoprene.
Cao, Wenjin; Hewage, Dilkrushi; and Yang, Dong-Sheng, "Spectroscopy and Formation of Lanthanum-Hydrocarbon Radicals Formed by Association and Carbon-Carbon Bond Cleavage of Isoprene" (2018). Chemistry Faculty Publications. 119.