Rare-Earth Metallacycloheptatrienes: Synthesis, Structure, and Reactivity

Abstract

As the key intermediates in metal-catalyzed [2 + 2 + 2] cycloaddition reactions of three alkynes, main-group and transitionmetal metallacycloheptatrienes have been studied for decades, but rareearth analogues have remained illusive. Herein, we report the welldefined rare-earth metallacycloheptatrienes 2-Sc and 2-Lu obtained in high yields via the reaction of Cp*Li (Cp* = pentamethylcyclopentadienyl) and RECl 3 (RE = Sc, Lu) with TMEDA-coordinated 2,2′dilithio-Z-stilbene 1. The single-crystal structure of 2-Sc (RE = Sc) reveals it to be a separate ion pair, and the scandacycloheptatriene ring adopts a nonplanar boat-like conformation. The reactivity of compounds 2-Sc and 2-Lu has been investigated. When 2-Sc was treated with 2,6-dimethylphenyl isocyanide, compound 3 was obtained via the successive 1,1-insertion and 1,2-insertion of the isocyanide. The structure of 3 was also fully characterized.

Nonplanar Aromaticity of Dinuclear Rare-Earth Metallacycles

“…The bonding analyses revealed the nature of the nonplanar aromaticity and the existence of rare σ-type orbital overlap. Very recently, we synthesized the first rare-earth metallacycloheptatrienes with six π-electrons . The compounds which adopt a nearly planar geometry (Figure a) do not exhibit any aromatic characters.…”

sp2–sp cross-carbanion coupling at a rare-earth center leading to the formation of carbon–carbon double bonds

“…We have always been interested in the synthesis and reactivity of rare-earth metallacycles, 34–48 and have recently reported the reactivity of rare-earth azametallacyclopentadienes toward nitriles. 49,50 Herein, we report experimental and computational studies on the reaction chemistry of rare-earth azametallacyclopentadienes toward terminal alkynes (Scheme 1b).…”