page_title: Organolithium reagent
section_title: Solid state structure
hierarchical_section_title: Organolithium reagent / Structure / Solid state structure
caption_attribution_description: English: Tetrahedron and octahedron metal cores formed by aggregation of the Li3 triangle - carbanion coordinate complex
context_page_description: Organolithium reagents are organometallic compounds that contain carbon – lithium bonds. They are important reagents in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C-Li bond is highly ionic. Owing to the polar nature of the C-Li bond, organolithium reagents are good nucleophiles and strong bases. For laboratory organic synthesis, many organolithium reagents are commercially available in solution form. These reagents are highly reactive, and are sometimes pyrophoric.
context_section_description: Like other species consisting of polar subunits, organolithium species aggregate.
  Formation of aggregates is influenced by electrostatic interactions, the coordination between lithium and surrounding solvent molecules or polar additives, and steric effects.
  A basic building block toward constructing more complex structures is a carbanionic center interacting with a Li₃ triangle in an η- ₃ fashion.
  In simple alkyllithium reagents, these triangles aggregate to form tetrahedron or octahedron structures. For example, methyllithium, ethyllithium and tert-butyllithium all exist in the tetramer [RLi]₄. Methyllithium exists as tetramers in a cubane-type cluster in the solid state, with four lithium centers forming a tetrahedron. Each methanide in the tetramer in methyllithium can have agostic interaction with lithium cations in adjacent tetramers.
  Ethyllithium and tert-butyllithium, on the other hand, do not exhibit this interaction, and are thus soluble in non-polar hydrocarbon solvents. Another class of alkyllithium adopts hexameric structures, such as n-butyllithium, isopropyllithium, and cyclohexanyllithium.
  Common lithium amides, e.g. lithium bis(trimethylsilyl)amide and lithium diisopropylamide, are also subject to aggregation. Lithium amides adopt polymeric-ladder type structures in non-coordinating solvent in the solid state, and they generally exist as dimers in ethereal solvents. In the presence of strongly donating ligands, tri- or tetrameric lithium centers are formed. 
  
  For example, LDA exists primarily as dimers in THF. The structures of common lithium amides, such as lithium diisopropylamide (LDA) and lithium hexamethyldisilazide (LiHMDS) have been extensively studied by Collum and coworkers using NMR spectroscopy.
  Another important class of reagents is silyllithiums, extensively used in the synthesis of organometallic complexes and polysilane dendrimers.
  In the solid state, in contrast with alkyllithium reagents, most silyllithiums tend to form monomeric structures coordinated with solvent molecules such as THF, and only a few silyllithiums have been characterized as higher aggregates.
  This difference can arise from the method of preparation of silyllithiums, the steric hindrance caused by the bulky alkyl substituents on silicon, and the less polarized nature of Si-Li bonds. The addition of strongly donating ligands, such as TMEDA and (-)-sparteine, can displace coordinating solvent molecules in silyllithiums.
caption: Tetrahedron and octahedron metal cores formed by aggregation of the Li3 triangle - carbanion coordinate complex[5]
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