Editing Alkali metal (section)

=== Organometallic ===

==== Organolithium ====
{{Main|Organolithium reagent}}
[[File:Butyllithium-hexamer-from-xtal-3D-balls-A.png|thumb|upright=1.15|Structure of the octahedral [[n-butyllithium|''n''-butyllithium]] hexamer, (C<sub>4</sub>H<sub>9</sub>Li)<sub>6</sub>.<ref>{{cite journal
|title= Structures of Classical Reagents in Chemical Synthesis: (nBuLi)<sub>6</sub>, (tBuLi)<sub>4</sub>, and the Metastable (tBuLi · Et<sub>2</sub>O)<sub>2</sub>
|last=T. Kottke|first=D. Stalke
|journal= Angew. Chem. Int. Ed. Engl.
|date= September 1993
|volume= 32
|issue= 4
|pages= 580–582
|doi= 10.1002/anie.199305801
|url=http://resolver.sub.uni-goettingen.de/purl?goescholar/3373}}</ref> The aggregates are held together by delocalised covalent bonds between lithium and the terminal carbon of the butyl chain.<ref>Elschenbroich, C. "Organometallics" (2006) Wiley-VCH: Weinheim. {{ISBN|3-527-29390-6}}.</ref> There is no direct lithium–lithium bonding in any organolithium compound.<ref name=King />{{rp|264}}]]
[[File:Phenyllithium-chain-from-xtal-Mercury-3D-balls.png|thumb|upright=1.15|Solid [[phenyllithium]] forms monoclinic crystals that can be described as consisting of dimeric Li<sub>2</sub>([[phenyl group|C<sub>6</sub>H<sub>5</sub>]])<sub>2</sub> subunits. The lithium atoms and the ''[[arene substitution pattern|ipso]]'' carbons of the phenyl rings form a planar four-membered ring. The plane of the phenyl groups is perpendicular to the plane of this Li<sub>2</sub>C<sub>2</sub> ring. Additional strong intermolecular bonding occurs between these phenyllithium dimers and the π electrons of the phenyl groups in the adjacent dimers, resulting in an infinite polymeric ladder structure.<ref>{{Cite journal |last1= Dinnebier |first1= R. E. |last2= Behrens |first2= U. |last3= Olbrich |first3= F. |title= Lewis Base-Free Phenyllithium: Determination of the Solid-State Structure by Synchrotron Powder Diffraction |journal= [[Journal of the American Chemical Society]] |year= 1998 |volume= 120 |issue= 7 |pages= 1430–1433 |doi= 10.1021/ja972816e|bibcode= 1998JAChS.120.1430D }}</ref>]]

Being the smallest alkali metal, lithium forms the widest variety of and most stable [[organometallic compound]]s, which are bonded covalently. [[Organolithium]] compounds are electrically non-conducting volatile solids or liquids that melt at low temperatures, and tend to form [[oligomer]]s with the structure (RLi)<sub>''x''</sub> where R is the organic group. As the electropositive nature of lithium puts most of the [[charge density]] of the bond on the carbon atom, effectively creating a [[carbanion]], organolithium compounds are extremely powerful [[base (chemistry)|bases]] and [[carbon nucleophile|nucleophiles]]. For use as bases, [[butyllithium]]s are often used and are commercially available. An example of an organolithium compound is [[methyllithium]] ((CH<sub>3</sub>Li)<sub>''x''</sub>), which exists in tetrameric (''x'' = 4, tetrahedral) and hexameric (''x'' = 6, octahedral) forms.<ref name=generalchemistry /><ref name=Brown1957>{{cite journal |last1=Brown|first1=T. L. |last2=Rogers|first2=M. T. |title= The Preparation and Properties of Crystalline Lithium Alkyls |journal= Journal of the American Chemical Society |year= 1957 |volume= 79 |issue= 8 |pages= 1859–1861 |doi= 10.1021/ja01565a024|bibcode=1957JAChS..79.1859B }}</ref> Organolithium compounds, especially ''n''-butyllithium, are useful reagents in organic synthesis, as might be expected given lithium's diagonal relationship with magnesium, which plays an important role in the [[Grignard reaction]].<ref name="Greenwood&Earnshaw" />{{rp|102}} For example, alkyllithiums and aryllithiums may be used to synthesise [[aldehyde]]s and [[ketone]]s by reaction with metal [[carbonyl]]s. The reaction with [[nickel tetracarbonyl]], for example, proceeds through an unstable acyl nickel carbonyl complex which then undergoes [[electrophilic substitution]] to give the desired aldehyde (using H<sup>+</sup> as the electrophile) or ketone (using an alkyl halide) product.<ref name="Greenwood&Earnshaw" />{{rp|105}}

:<chem>LiR \ + \ Ni(CO)4 \ \longrightarrow Li^{+}[RCONi(CO)3]^{-}</chem>
:<chem>Li^{+}[RCONi(CO)3]^{-}->[\ce{H^{+}}][\ce{solvent}] \ Li^{+} \ + \ RCHO \ + \ [(solvent)Ni(CO)3]</chem>
:<chem>Li^{+}[RCONi(CO)3]^{-}->[\ce{R^{'}Br}][\ce{solvent}] \ Li^{+} \ + \ RR^{'}CO \ + \ [(solvent)Ni(CO)3]</chem>

Alkyllithiums and aryllithiums may also react with ''N'',''N''-disubstituted [[amide]]s to give aldehydes and ketones, and symmetrical ketones by reacting with [[carbon monoxide]]. They thermally decompose to eliminate a β-hydrogen, producing [[alkene]]s and [[lithium hydride]]: another route is the reaction of [[ether]]s with alkyl- and aryllithiums that act as strong bases.<ref name="Greenwood&Earnshaw" />{{rp|105}} In non-polar solvents, aryllithiums react as the carbanions they effectively are, turning carbon dioxide to aromatic [[carboxylic acid]]s (ArCO<sub>2</sub>H) and aryl ketones to tertiary carbinols (Ar'<sub>2</sub>C(Ar)OH). Finally, they may be used to synthesise other organometallic compounds through metal-halogen exchange.<ref name="Greenwood&Earnshaw" />{{rp|106}}

==== Heavier alkali metals ====
Unlike the organolithium compounds, the organometallic compounds of the heavier alkali metals are predominantly ionic. The application of [[organosodium]] compounds in chemistry is limited in part due to competition from [[organolithium compound]]s, which are commercially available and exhibit more convenient reactivity. The principal organosodium compound of commercial importance is [[sodium cyclopentadienide]]. [[Sodium tetraphenylborate]] can also be classified as an organosodium compound since in the solid state sodium is bound to the aryl groups. Organometallic compounds of the higher alkali metals are even more reactive than organosodium compounds and of limited utility. A notable reagent is [[Schlosser's base]], a mixture of [[n-Butyllithium|''n''-butyllithium]] and [[potassium tert-butoxide|potassium ''tert''-butoxide]]. This reagent reacts with [[propene]] to form the compound [[allylpotassium]] (KCH<sub>2</sub>CHCH<sub>2</sub>). [[cis-2-butene|''cis''-2-Butene]] and [[trans-2-butene|''trans''-2-butene]] equilibrate when in contact with alkali metals. Whereas [[isomerisation]] is fast with lithium and sodium, it is slow with the heavier alkali metals. The heavier alkali metals also favour the [[steric hindrance|sterically]] congested conformation.<ref>{{cite journal |title= Superbases for organic synthesis |last=Schlosser|first=Manfred|journal= Pure Appl. Chem. |volume= 60 |issue= 11 |pages= 1627–1634 |year= 1988 |doi= 10.1351/pac198860111627|s2cid=39746336|url= http://old.iupac.org/publications/pac/1988/pdf/6011x1627.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://old.iupac.org/publications/pac/1988/pdf/6011x1627.pdf |archive-date=2022-10-09 |url-status=live}}</ref> Several crystal structures of organopotassium compounds have been reported, establishing that they, like the sodium compounds, are polymeric.<ref name=Klett>{{cite journal|doi=10.1002/ejic.201000983|title=Synthesis and Structures of \(Trimethylsilyl)methyl]sodium and -potassium with Bi- and Tridentate N-Donor Ligands|year=2011|last1=Clegg|first1=William|last2=Conway|first2=Ben|last3=Kennedy|first3=Alan R.|last4=Klett|first4=Jan|last5=Mulvey|first5=Robert E.|last6=Russo|first6=Luca|journal=European Journal of Inorganic Chemistry|volume=2011|issue=5|pages=721–726|url=https://www.researchgate.net/publication/210286264|doi-access=|archive-date=1 August 2020|access-date=16 November 2016|archive-url=https://web.archive.org/web/20200801104355/https://www.researchgate.net/publication/210286264_Synthesis_and_Structures_of_Trimethylsilylmethylsodium_and_-potassium_with_Bi-_and_Tridentate_N-Donor_Ligands|url-status=live}}</ref> Organosodium, organopotassium, organorubidium and organocaesium compounds are all mostly ionic and are insoluble (or nearly so) in nonpolar solvents.<ref name=generalchemistry />

Alkyl and aryl derivatives of sodium and potassium tend to react with air. They cause the cleavage of [[ether]]s, generating alkoxides. Unlike alkyllithium compounds, alkylsodiums and alkylpotassiums cannot be made by reacting the metals with alkyl halides because [[Wurtz coupling]] occurs:<ref name=King />{{rp|265}}
:RM + R'X → R–R' + MX

As such, they have to be made by reacting [[organomercury compound|alkylmercury]] compounds with sodium or potassium metal in inert hydrocarbon solvents. While methylsodium forms tetramers like methyllithium, methylpotassium is more ionic and has the [[nickel arsenide]] structure with discrete methyl anions and potassium cations.<ref name=King />{{rp|265}}

The alkali metals and their hydrides react with acidic hydrocarbons, for example [[cyclopentadiene]]s and terminal alkynes, to give salts. Liquid ammonia, ether, or hydrocarbon solvents are used, the most common of which being [[tetrahydrofuran]]. The most important of these compounds is [[sodium cyclopentadienide]], NaC<sub>5</sub>H<sub>5</sub>, an important precursor to many transition metal cyclopentadienyl derivatives.<ref name=King />{{rp|265}} Similarly, the alkali metals react with [[cyclooctatetraene]] in tetrahydrofuran to give alkali metal [[cyclooctatetraenide]]s; for example, [[dipotassium cyclooctatetraenide]] (K<sub>2</sub>C<sub>8</sub>H<sub>8</sub>) is an important precursor to many metal cyclooctatetraenyl derivatives, such as [[uranocene]].<ref name=King />{{rp|266}} The large and very weakly polarising alkali metal cations can stabilise large, aromatic, polarisable radical anions, such as the dark-green [[sodium naphthalenide]], Na<sup>+</sup>[C<sub>10</sub>H<sub>8</sub>•]<sup>−</sup>, a strong reducing agent.<ref name=King />{{rp|266}}