Editing Gilman reagent

{{Short description|Class of chemical compounds}}
[[Image:gilman reagent2.gif|thumb|right|General structure of a Gilman reagent]]

A '''Gilman reagent''' is a [[organocopper compound|diorganocopper]] compound with the formula Li[CuR<sub>2</sub>], where R is an [[alkyl]] or [[aryl]]. They are colorless solids.{{Citation needed|date=January 2024}}

==Use in organic chemistry==
[[File:Cuprate_conjugate_addition_with_lewis_acid.png|none|thumb|305x305px|A conjugated 1,4 addition using a Gilman reagent with an arbitrary R group]]

These reagents are useful because, unlike related [[Grignard reagent]]s and [[organolithium reagent]]s, they react with [[Organic halide|organic]] [[halide]]s to replace the [[halides|halide]] group with an R group (the [[Corey–House synthesis|Corey–House reaction]]).  Such displacement reactions allow for the synthesis of complex products from simple building blocks.<ref>{{cite journal | title = Organocopper(I) Compounds and Organocuprates in Synthesis| journal = Synthesis  | author = J. F. Normant| pages = 63–80| doi = 10.1055/s-1972-21833| volume = 1972 | issue = 2| year = 1972}}</ref><ref name=":4">{{Cite journal |last=Woodward |first=Simon |date=2000-01-01 |title=Decoding the 'black box' reactivity that is organocuprate conjugate addition chemistry |url=https://pubs.rsc.org/en/content/articlelanding/2000/cs/b002690p |journal=Chemical Society Reviews |language=en |volume=29 |issue=6 |pages=393–401 |doi=10.1039/B002690P |issn=1460-4744|url-access=subscription }}</ref> [[Lewis acids and bases|Lewis acids]] can be used to modify the reagent.<ref name=":4" /> 


{{Image frame|content=<math chem>
[\ce{R}{-}{\color{Blue}\ce{Cu}}\ce{-R}]^-\ce{Li+}\ 
\xrightarrow{\color{Red}\ce{R'-X}}\ 
\overbrace{\left[\ce R{-}\overset{{\displaystyle \color{Red} \ce R'} \atop |}\underset{| \atop {\displaystyle \color{Red} \ce X}}{\color{Blue}\ce{Cu}}\ce{-R} \right]^-\ce{Li+}}^\text{planar intermediate} 
\ce{-> R}{-}{\color{Blue}\ce{Cu}} + \ce{R}{-}{\color{Red}\ce{R'}} + \ce{Li}{-}{\color{Red}\ce{X}}
</math>|align=center|width=540|caption=Generalized [[chemical reaction]] showing '''Gilman’s reagent''' reacting with [[organic halide]] to form products and showing Cu(III) [[reaction intermediate]]}}

== History ==
These reagents were discovered by [[Henry Gilman]] and coworkers.<ref>{{cite journal | title = The Preparation of Methylcopper and some Observations on the Decomposition of Organocopper Compounds| author = [[Henry Gilman]], Reuben G. Jones, and L. A. Woods| pages = 1630–1634| journal = [[Journal of Organic Chemistry]]| doi = 10.1021/jo50012a009| volume = 17| issue = 12| year = 1952}}</ref> '''Lithium dimethylcopper''' (CH<sub>3</sub>)<sub>2</sub>CuLi can be prepared by adding [[copper(I) iodide]] to [[methyllithium]] in [[tetrahydrofuran]] at −78&nbsp;°C. In the reaction depicted below,<ref>''Modern Organocopper Chemistry, '' N. Krause Ed. Wiley-VCH, 2002.</ref> the Gilman reagent is a methylating reagent reacting with an [[alkyne]] in a [[conjugate addition]], and the [[ester]] group forms a cyclic [[Alpha-beta Unsaturated carbonyl compounds|enone]].

[[Image:Gilman reaction example.png|center|400px|Scheme 1. Example Gilman reagent reaction]]

:[[File:Gilman vs Grignard.jpg|frameless|310x310px]]

==Structure==
Lithium dimethylcuprate exists as a [[Dimer (chemistry)|dimer]] in [[diethyl ether]] forming an 8-membered ring. Similarly, lithium diphenylcuprate crystallizes as a dimeric etherate, {{chem2|[{Li(OEt2)}(CuPh2)]2}}.<ref>{{cite journal | journal = [[Angewandte Chemie|Angew. Chem. Int. Ed.]] | volume = 29 | issue = 3 | pages = 300–302 | year = 1990 |author1=N. P. Lorenzen |author2=E. Weiss | doi = 10.1002/anie.199003001 | title = Synthesis and Structure of a Dimeric Lithium Diphenylcuprate:[{Li(OEt)<sub>2</sub>}(CuPh<sub>2</sub>)]<sub>2</sub>}}</ref>

<div class="center">[[File:Lithium-diphenylcuprate-dietherate-dimer-from-xtal-3D-sticks-C.png|200px|Lithium diphenylcuprate etherate dimer from crystal structure - 3D stick model]] [[File:Lithium-diphenylcuprate-etherate-dimer-from-xtal-2D-skeletal.png|180px|Skeletal formula of lithium diphenylcuprate etherate dimer]]</div>

If the Li<sup>+</sup> ions is complexed with the [[crown ether]] [[12-crown-4]], the resulting diorganylcuprate anions adopt a linear [[coordination geometry]] at copper.<ref>{{ cite journal | journal = [[Journal of the American Chemical Society]] | title = Isolation and x-ray crystal structures of the mononuclear cuprates [CuMe<sub>2</sub>]<sup>−</sup>, [CuPh<sub>2</sub>]<sup>−</sup>, and [Cu(Br)CH(SiMe<sub>3</sub>)<sub>2</sub>]<sup>−</sup> |author1=H. Hope |author2=M. M. Olmstead |author3=P. P. Power |author4=J. Sandell |author5=X. Xu | year = 1985 | volume = 107 | issue = 14 | pages = 4337–4338 | doi = 10.1021/ja00300a047| bibcode = 1985JAChS.107.4337H }}</ref>

<div class="center">[[File:Dimethylcuprate-anion-from-xtal-3D-balls.png|100px|Dimethylcuprate anion from crystal structure]] [[File:Diphenylcuprate-anion-from-xtal-3D-balls.png|220px|Diphenylcuprate anion from crystal structure]]</div>

For the 'higher order cyanocuprate' Li<sub>2</sub>CuCN(CH<sub>3</sub>)<sub>2</sub>, Lipshutz and coworkers have claimed that the cyanide ligand is coordinated to Li and π-bound to Cu.<ref>{{cite journal|author=Bruce H. Lipshutz; Brian James|title=New 1H and 13C NMR Spectral Data on "Higher Order" Cyanocuprates. If the Cyano Ligand Is Not On Copper, Then Where Is It?|journal=J. Org. Chem.|year=1994|volume=59 |issue=25 |pages=7585–7587|doi=10.1021/jo00104a009}}</ref>  However, the existence of 'mixed higher order organocuprates' has been disputed by Bertz and coworkers, who rejoined that the cyano ligand is actually bound solely to the lithium atom, and that such a structure could still explain the enhanced reactivity of cuprate prepared from CuCN.<ref>{{Cite journal |last=Bertz |first=Steven H. |last2=Miao |first2=Guobin |last3=Eriksson |first3=Magnus |date=1996-01-01 |title=It's on lithium! an answer to the recent communication which asked the question: ‘if the cyano ligand is not on copper, then where is it?’ |url=https://pubs.rsc.org/en/content/articlelanding/1996/cc/cc9960000815 |journal=Chemical Communications |language=en |issue=7 |pages=815–816 |doi=10.1039/CC9960000815 |issn=1364-548X|url-access=subscription }}</ref><ref>{{Cite web |last=Bertz |first=Steven H. |date=2002-05-01 |title=New copper chemistry. 17. Higher-order cyanocuprates: are they real? |url=https://pubs.acs.org/doi/pdf/10.1021/ja00166a046 |access-date=2025-04-18 |website=ACS Publications |language=EN |doi=10.1021/ja00166a046}}</ref> To date, no crystallographic evidence for the existence of 'mixed higher order cuprates' ([R<sub>2</sub>CuX]<sup>2–</sup>, X ≠ R) has been obtained.  On the other hand, a homoleptic higher order cuprate in the form of a [Ph<sub>3</sub>Cu]<sup>2–</sup> moiety has been observed in Li<sub>3</sub>Cu<sub>2</sub>Ph<sub>5</sub>(SMe<sub>2</sub>)<sub>4</sub>, prepared by Olmstead and Power.<ref>{{Cite journal |last=Olmstead |first=Marilyn M. |last2=Power |first2=Philip P. |date=1989-05-01 |title=Structural characterization of a higher order cuprate: x-ray crystal structure of [Li3Cu2Ph5(SMe2)4] |url=https://pubs.acs.org/doi/10.1021/ja00193a075 |journal=Journal of the American Chemical Society |volume=111 |issue=11 |pages=4135–4136 |doi=10.1021/ja00193a075 |issn=0002-7863|url-access=subscription }}</ref>

==Mixed cuprates==
More useful generally than the Gilman reagents are the so-called mixed cuprates with the formula [RCuX]<sup>−</sup> and [R<sub>2</sub>CuX]<sup>2−</sup> (see above for the controversy over existence of the latter).  Such compounds are often prepared by the addition of the organolithium reagent to copper(I) halides and cyanide. These mixed cuprates are more stable and more readily purified.<ref name=eEROS>Steven H. Bertz, Edward H. Fairchild, Karl Dieter, "Copper(I) Cyanide" in Encyclopedia of Reagents for Organic Synthesis 2005, John Wiley & Sons. {{doi|10.1002/047084289X.rc224.pub2}}</ref> One problem addressed by mixed cuprates is the economical use of the alkyl group. Thus, in some applications, the mixed cuprate with the formula {{chem|Li|2|[Cu(2-thienyl)(CN)R]}} is prepared by combining thienyllithium and cuprous cyanide followed by the organic group to be transferred. In this higher order mixed cuprate, both the cyanide and thienyl groups do not transfer, only the R group does.<ref>[[Bruce H. Lipshutz]], Robert Moretti, Robert Crow "Mixed Higher-order Cyanocuprate-induced Epoxide Openings: 1-Benzyloxy-4-penten-2-ol" Org. Synth. 1990, volume 69, pp. 80. {{doi|10.15227/orgsyn.069.0080}}</ref>

==See also==
* [[Cuprate (chemistry)]]

==References==
{{reflist}}

{{organometallics}}
{{Lithium compounds}}

[[Category:Organolithium compounds]]
[[Category:Organocopper compounds]]
[[Category:Reagents for organic chemistry]]