Half-Sandwich Cerium and Lanthanum Dialkyl Complexes: Synthesis, Structure, and Reactivity Studies

Abstract

Cerium and lanthanum dialkyl complexes [η⁵-1,2,4-(Me₃C)₃C₅H₂]Ln(CH₂C₆H₄-o-NMe₂)₂ (Ln = Ce 1 and La 2), supported by a tri-tert-butylcyclopentadienyl ligand, have been successfully synthesized. Studies demonstrate that these complexes possess diverse reactivity toward various small molecules. For example, the reaction of complexes 1 and 2 with diphenyl dichalcogenides PhEEPh (E = S, Se) results in the formation of lanthanide thiolates [(η⁵-1,2,4-(Me₃C)₃C₅H₂)Ln(SPh)(μ-SPh)]₂ (Ln = Ce 3 and La 4) and selenolates [(η⁵-1,2,4-(Me₃C)₃C₅H₂)Ln(SePh)(μ-SePh)]₂ (Ln = Ce 5 and La 6), concomitantly releasing PhE(CH₂C₆H₄-o-NMe₂). Furthermore, complexes 1 and 2, upon reaction with dibenzyl disulfide, yield tetranuclear rare-earth metallomacrocyclic compounds {[(η⁵-1,2,4-(Me₃C)₃C₅H₂)Ln(μ-SCH₂C₆H₅)]₂(μ–η³:η³-SCHC₆H₅)}₂ (Ln = Ce 7 and La 8). This reaction may involve a process of σ-bond metathesis and C–H activation. While the reaction of 1 and 2 with dibenzyl diselenide in the presence of LiCH₂C₆H₄-o-NMe₂ leads to the formation of lanthanide-lithium selenido clusters [(η⁵-1,2,4-(Me₃C)₃C₅H₂)La(μ-SeCH₂C₆H₅)]₃(μ₃-Se)[μ₃-SeLi(THF)₃] (Ln = Ce 9 and La 10). Meanwhile, lanthanide selenido clusters [(η⁵-1,2,4-(Me₃C)₃C₅H₂)La(μ-SeCH₂C₆H₄-o-NMe₂)]₄(μ₃-Se)₂ (Ln = Ce 11 and La 12) can be obtained by treating 1 and 2 with elemental selenium in a 1:2 molar ratio. Additionally, the treatment of 1 and 2 with benzoxazole generates ring-opening/C–C coupling/C–N coupling products {(η⁵-1,2,4-(Me₃C)₃C₅H₂)La[μ-OC₆H₄-o-N═CHN(CH(CH₂C₆H₄-o-NMe₂)₂C₆H₄-o-O]}₂ (Ln = Ce 13 and La 14). All new compounds were characterized by various spectroscopic methods, and their solid-state structures were confirmed by single-crystal X-ray diffraction analyses.