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Isolation and Characterization, Including by X‐ray Crystallography, of Contact and Solvent‐Separated Ion Pairs of Silenyl Lithium Species
Author(s) -
Pinchuk Daniel,
Mathew Jomon,
Kaushansky Alexander,
BravoZhivotovskii Dmitry,
Apeloig Yitzhak
Publication year - 2016
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201603640
Subject(s) - chemistry , solvent , lithium (medication) , molecule , crystallography , nuclear magnetic resonance spectroscopy , dissociation (chemistry) , lithium atom , benzene , ion , metal , nmr spectra database , hexane , inorganic chemistry , stereochemistry , spectral line , organic chemistry , ionization , medicine , physics , astronomy , endocrinology
Reaction of bromoacylsilane 1 (pink solution) with t Bu 2 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 ‐[( t BuMe 2 Si)( t Bu 2 MeSi)C=Si(SiMe t Bu 2 )] − [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 R 2 E=E′RM species (E=C, Si; E′=C, Si; M=metal).