Unimolecular
gas-phase laser-photodissociation reaction mechanisms of open-shell
lanthanide cyclopentadienyl complexes, Ln(Cp)3 and Ln(TMCp)3, are analyzed from experimental and computational perspectives.
The most probable pathways for the photoreactions are inferred from
photoionization time-of-flight mass spectrometry (PI-TOF-MS), which
provides the sequence of reaction intermediates and the distribution
of final products. Time-dependent excited-state molecular dynamics
(TDESMD) calculations provide insight into the electronic mechanisms
for the individual steps of the laser-driven photoreactions for Ln(Cp)3. Computational analysis correctly predicts several key reaction
products as well as the observed branching between two reaction pathways:
(1) ligand ejection and (2) ligand cracking. Simulations support our
previous assertion that both reaction pathways are initiated via a
ligand-to-metal charge-transfer (LMCT) process. For the more complex
chemistry of the tetramethylcyclopentadienyl complexes Ln(TMCp)3, TMESMD is less tractable, but computational geometry optimization
reveals the structures of intermediates deduced from PI-TOF-MS, including
several classic “tuck-in” structures and products of
Cp ring expansion. The results have important implications for metal–organic
catalysis and laser-assisted metal–organic chemical vapor deposition
(LCVD) of insulators with high dielectric constants.
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