[{(tBu₂Me)₂Si}₃Li₄]²⁻: An Aggregated Dianion of a 1,1‐Dilithiosilane with a Unique Structural Motif

Abstract

An anionic dilithium compound: The dianion [(R2Si)3Li4]2− (R=tBu2MeSi) as salt 2 was synthesized as the first of its kind by dissolving 1 in THF. The structure of 2 was solved by X‐ray crystallography and studied by solid‐state and solution NMR spectroscopy. Compound 2 reacts as a dilithiosilane.

Lithiated 1,3-Disilabicyclo[1.1.0]butanes Synthesized via Selective Cleavage of Exocyclic Si–Si Bonds on Bridgehead Silicon Atoms

“…Each bridgehead anionic silicon atom in 2 coordinates to the terminal and central lithium atoms to form the Si 4 Li 3 framework. Similar flat hexagonal aggregates comprised of silicon and lithium atoms have been found in some dilithium silandiide derivatives such as A – C (Chart ), ,, but aggregates with three lithium atoms arranged linearly remain quite rare . The Si1–Li2* [2.784(5) Å] and Si2–Li2 [2.775(5) Å] distances are longer than the Si1–Li1 [2.6068(8) Å] and Si2–Li1 [2.6146(10) Å] distances, but these distances fall in the typical range of the Si–Li distance in the dimers of lithium silanides [2.59–2.78 Å]. − The Li1···Li2 distance is [2.666(5) Å].…”

“…The low-field-shifted 7 Li signal at 8.84 ppm can be tentatively due to the central unsolvated 7 Li nuclei in the aggregated silyl anion moiety, while the other signals (0.23, 1.17, and 2.15 ppm) can be due to more-solvated 7 Li nuclei such as terminal Li(dme) in the aggregate and lithium cations solvated in DME and/or THF-d 8 , as the solvated 7 Li nuclei usually resonate in a higher-field region. 70,71 Similar lowfield-shifted 7 Li resonances were observed for dilithium silandiides with unsolvated lithium atom A [ 7 Li MAS: 7 (br) and 0.1 ppm; 7 Li NMR (THF) 6.3 (br, low-intensity), 4.5 to −0.5 (br)] 61 and C [ 7 Li CP/MAS NMR: 5.80, 2.28, and − 0.57 (1:2:1)]. 44 Although the details of the structure of 2 in solution remain unclear at this time, more than one process such as the facile exchange of 7 Li nuclei and the dissociation equilibrium between the dimeric form and a monomeric form on the NMR time scale should be responsible for the observed temperature dependence of 29 Si and 7 Li NMR spectra.…”

Structural Characterization and Dynamic Solution Behavior of the Disodio and Lithio−Sodio Geminal Organodimetallics [{{Ph2P(Me3Si)N}2CNa2}2] and [{{Ph2P(Me3Si)N}2CLiNa}2]

“…A handful of mixed-anion complexes containing both a dilithio geminal dianion and either a monometalated ligand fragment or an Li 2 O unit are also known . The characterization of heavier alkali-metal derivatives remains even more inadequate, with their existence generally only inferred by indirect quenching studies or through the use of theoretical calculations. − Nevertheless, the generation of such complexes is useful to access dianions of weakly acidic substrates…”