Ce-promoted bond activation of propene probed by mass-analyzed threshold ionization spectroscopy

Abstract

The reaction of Ce + propene (CH$_{2}$=CH-CH$_{3}$) was carried out in a laser-ablation supersonic molecular beam source. \chem{CeC_2H_2}, \chem{CeC_3H_4}, \chem{CeC_3H_6}, \chem{CeC_4H_6}, \chem{CeC_6H}$_{10}$, and \chem{CeC_6H}$_{12}$ were identified by photoionization time-of-flight mass spectrometric measurements, and their structures and electronic states were investigated with mass-analyzed threshold ionization (MATI) spectroscopy and theoretical calculations. The metal complexes containing two or three carbon atoms were formed by the C-C bond breakage (\chem{CeC_2H_2}), dehydrogenation (\chem{CeC_3H_4}), or metal insertion into a C-H bond (\chem{CeC_3H_6}) of a propene molecule. The larger complexes with four to six carbons are formed through secondary reactions involving C-C bond coupling and dehydrogenation. The ground electronic states of the neutral \chem{CeC_2H_2}, \chem{CeC_3H_4}, \chem{CeC_3H_6}, and \chem{CeC_4H_6} complexes are triplets with a 4f$^{1}$6s$^{1}$ electron configuration on the Ce center, and those of the corresponding ions are doublet with a 4f$^{1}$ configuration. Their MATI spectra are much more complex than those of the corresponding La species formed in the La + propene reaction previously observed by our group. The spectral complexity arises from possibly multiple electronic transitions due to the existence of a 4f electron of the Ce atom which could be located in any one of the seven f-atomic orbitals or involved in considerable spin-orbit interactions.