Editing Organolithium reagent (section)

===Solid state structure===
[[File:Building block of alkyllithium aggregates.png|thumb|270px|left|Tetrahedron and octahedron metal cores formed by aggregation of the Li3 triangle - carbanion coordinate complex<ref name=leadstructure />]]

Like other species consisting of polar subunits, organolithium species aggregate.<ref name=Strohmann>{{cite journal|last=Strohmann|first=C|title=Structure Formation Principles and Reactivity of Organolithium Compounds.|journal= Chem. Eur. J.|year=2009|volume=15|issue=14|pages=3320–3334|url=http://onlinelibrary.wiley.com/store/10.1002/chem.200900041/asset/3320_ftp.pdf?v=1&t=hnc3zl4k&s=90cd763c5affe82ca5d8208a75ea074deede3187|doi=10.1002/chem.200900041|pmid=19260001|display-authors=etal}}</ref><ref name=Power>{{cite journal|last=Power|first=P.P|author2=Hope H.|title=Isolation and crystal structures of the halide-free and halide-rich phenyllithium etherate complexes [(PhLi.Et2O)4] and [(PhLi.Et2O)3.LiBr].|journal=Journal of the American Chemical Society|year=1983|volume=105|issue=16|pages=5320–5324|doi=10.1021/ja00354a022}}</ref>
Formation of aggregates is influenced by [[electrostatic]] interactions, the coordination between lithium and surrounding solvent molecules or polar additives, and steric effects.<ref name=Strohmann />

A basic building block toward constructing more complex structures is a carbanionic center interacting with a Li<sub>3</sub> triangle in an η<sup>3</sup>- fashion.<ref name=leadstructure />
In simple alkyllithium reagents, these triangles aggregate to form tetrahedron or octahedron structures. For example, [[methyllithium]], [[ethyllithium]] and [[tert-Butyllithium|''tert''-butyllithium]] all exist in the tetramer [RLi]<sub>4</sub>. 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.<ref name=leadstructure /><ref name=Strohmann />
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|''n''-butyllithium]], isopropyllithium, and cyclohexanyllithium.<ref name=leadstructure />

[[File:dimerliamide.jpg|thumb|250px|left|LDA dimer with THF coordinated to Li cations]]

Common lithium amides, e.g. [[lithium bis(trimethylsilyl)amide]] and [[lithium diisopropylamide]], are also subject to aggregation.<ref name="Williard, P. G.; Salvino, J. M. 1993 1–3">{{cite journal|author1=Williard, P. G. |author2=Salvino, J. M. |journal=[[Journal of Organic Chemistry]]|year=1993| volume=58|issue=1|pages=1–3|title=Synthesis, isolation, and structure of an LDA-THF complex |doi=10.1021/jo00053a001}}</ref> 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. 
<ref name=Liamides>{{cite book| last1 = Hilmersson | first1 = Goran| last2 = Granander | first2 = Johan | chapter = Structure and dynamics of chiral lithium amides| title = PATAI'S Chemistry of Functional Groups.| publisher = John Wiley & Sons, Ltd | year = 2009| isbn = 9780470682531 | doi = 10.1002/9780470682531.pat0342}}</ref>
For example, LDA exists primarily as dimers in THF.<ref name="Williard, P. G.; Salvino, J. M. 1993 1–3"/> 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]].<ref name=Collumamides>{{cite journal| title = Lithium Diisopropylamide: Solution Kinetics and Implications for Organic Synthesis| author = Collum, D.B.| journal = Angew. Chem. Int. Ed. | year = 2007| volume = 49| issue = 17| pages = 3002–3017| doi = 10.1002/anie.200603038 | pmid = 17387670|display-authors=etal}}</ref>
Another important class of reagents is silyllithiums, extensively used in the synthesis of organometallic complexes and polysilane [[dendrimers]].<ref name=Strohmann /><ref name=lithiosilanes>{{cite journal|title=Lithiosilanes and their application to the synthesis of polysilane dendrimers |author=Sekiguchi, Akira.|journal=Coord. Chem. Rev.|year=2000 |volume=210 |pages=11–45 |doi=10.1016/S0010-8545(00)00315-5 |display-authors=etal}}</ref>
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.<ref name=Strohmann />
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.<ref name=Strohmann />