Photofragmentation Pathways for Gas-Phase Lanthanide Tris(isopropylcyclopentadienyl) Complexes

Photofragmentation mechanisms of gas-phase lanthanide tris(isopropylcyclopentadienyl) complexes, Ln(iCp)3, were studied through experimental photoionization time-of-flight mass spectrometry (PI-TOF-MS). A DFT-based time-dependent excited-state molecular dynamics (TDESMD) algorithm, under standard approximations, was used to simulate the photofragmentation process. Two competing reaction pathways, intact ligand stripping and ligand cracking within the metal-ligand complex, were hypothesized based on experimental data. It was evident that intramolecular hydrogen, methyl, and isopropyl abstraction play an important role in the ligand-cracking reaction pathway, leading to metal carbide and metal hydrocarbide products. The TDESMD simulations also produced branching reaction pathways for ligand ejection and ligand cracking and further suggested that both pathways are initiated by ligand-to-metal charge transfer. Although the simulations reproduced several of the proposed reactions and several of the products of cracking observed in the PI-TOF mass spectra, differences between the simulation and experimental results suggest specific directions for improvement in the computational model.