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2‑Butene Tetraanion Bridged Dinuclear Samarium(III) Complexes via Sm(II)-Mediated Reduction of Electron-Rich Olefins

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journal contribution
posted on 29.05.2020, 19:05 by Yu Zheng, Chang-Su Cao, Wangyang Ma, Tianyang Chen, Botao Wu, Chao Yu, Zhe Huang, Jianhao Yin, Han-Shi Hu, Jun Li, Wen-Xiong Zhang, Zhenfeng Xi
While reduction reactions are ubiquitous in chemistry, it is very challenging to further reduce electron-rich compounds, especially the anionic ones. In this work, the reduction of 1,3-butadienyl dianion, the anionic conjugated olefin, has been realized by divalent rare-earth metal compounds (SmI2), resulting in the formation of novel 2-butene tetraanion bridged disamarium­(III) complexes. Density functional theory (DFT) analyses reveal two features: (i) the single electron transfer (SET) from 4f atomic orbitals (AOs) of each Sm center to the antibonding π*-orbitals of 1,3-butadienyl dianion is feasible and the new HOMO formed by the bonding interaction between Sm 5d orbitals (AOs) and the π*-orbitals of 1,3-butadienyl dianion can accept favorably 2e from 4f AOs of Sm­(II); (ii) the 2-butene tetraanionic ligand serves as a unique 10e donating system, in which 4e act as two σ-donation bonding interactions while the rest 6e as three π-donation bonding interactions. The disamarium­(III) complexes represent a unique class of the bridged bis-alkylidene rare-earth organometallic complexes. The ligand-based reductive reactivity of 2-butene tetraanion bridged disamarium­(III) complexes demonstrates that 2-butene tetraanionic ligand serves as a 3e reductant toward cyclooctatetraene (COT) to provide doubly COT-supported disamarabutadiene complexes. The reaction of the disamarium­(III) complexes with Cp*Li produces the doubly Cp*-coordinated Sm­(III) complexes via salt metathesis. In addition, the reaction with Mo­(CO)6 affords the oxycyclopentadienyl dinuclear complex via CO insertion.