title: Isolation and Characterization, Including by X-ray Crystallography, of Contact and Solvent-Separated Ion Pairs of Silenyl Lithium Species.
abstract: Reaction of bromoacylsilane 1 (pink solution) with tBu2 MeSiLi (3.5 equiv) in a 4:1 hexane:THF solvent mixture at -78 °C to room temperature yields the solvent separated ion pair (SSIP) of silenyl lithium E-[(tBuMe2 Si)(tBu2 MeSi)C=Si(SiMetBu2 )](-) [Li⋅4THF](+) 2 a (green-blue solution). Removal of the solvent and addition of benzene converts 2 a into the corresponding contact ion pair (CIP) 2 b (violet-red solution) with two THF molecules bonded to the lithium atom. The 2 a⇌2 b interconversion is reversible upon THF⇌ benzene solvent change. Both 2 a and 2 b were characterized by X-ray crystallography, NMR and UV/Vis spectroscopy, and theoretical calculations. The degree of dissociation of the Si-Li bond has a large effect on the visible spectrum (and thus color) and on the silenylic (29) Si NMR chemical shift, but a small effect on the molecular structure. This is the first report of the X-ray molecular structure of both the SSIP and the CIP of any R2 E=E'RM species (E=C, Si; E'=C, Si; M=metal).
authors.affiliation: Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa, 32000, Israel.
authors.forename: Daniel
authors.initials: D
authors.lastname: Pinchuk
authors.affiliation: Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa, 32000, Israel.
authors.forename: Jomon
authors.initials: J
authors.lastname: Mathew
authors.affiliation: Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa, 32000, Israel.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kaushansky
authors.affiliation: Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa, 32000, Israel. chrbrzh@tx.technion.ac.il.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Bravo-Zhivotovskii
authors.affiliation: Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa, 32000, Israel. apeloig@technion.ac.il.
authors.forename: Yitzhak
authors.identifier: 0000-0002-1923-9236
authors.initials: Y
authors.lastname: Apeloig
keywords: bis(silyl)ketone; ion pairs; lithium; low-valent compounds; silicon