Synthesis, structure, and bonding of spiro rare-earth metallacyclopent-3-enes via the reduction of metallacyclopentadienes

Synthesis and characterization of metallacycles is an important research issue because they have acted as important building blocks and key intermediates in synthetic and catalytic chemistry. However, spiro rare-earth metallacyclopent-3-enes and metallacyclopentadienes are two kinds of untouched species. Herein, we report the construction of the spiro rare-earth metallacyclopent-3-enes 2 by ligand-based 4e- reduction of spiro rare-earth metallacyclopentadienes 3 with excess lithium. Complexes 3 represent a class of spiro rare-earth metallacyclopentadienes and could be easily synthesized from the reaction of 1,4-dilithio-1,3-butadiene 1 with 0.5 equiv of ScCl3. X-ray characterization and theoretical analyses (molecular orbitals [Mos], nucleus-independent chemical shift [NICS], anisotropy of induced current density [AICD], isochemical shielding surface [ICSS], and isomerization stabilization energy [ISE]) are performed to visualize the structure and bond characteristics of 2. Density functional theory (DFT) calculations reveal that the Li cations play a vital role in stabilizing its geometric and electronic structures. Therefore, this work promotes the cooperative development of rare-earth organometallic chemistry and coordination chemistry.