View source for Samarium(II) iodide

{{chembox
| Watchedfields = changed
| verifiedrevid = 464386740
| ImageFile = EuI2.png
| ImageSize = 
| ImageCaption = 
| ImageName = Ball-and-stick model of a samarium(II) iodide-THF complex
| IUPACName = samarium(II) iodide
| OtherNames = samarium diiodide
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 125002
| PubChem = 141689
| InChI = 1/2HI.Sm/h2*1H;/q;;+2/p-2
| InChIKey = UAWABSHMGXMCRK-NUQVWONBAD
| SMILES = I[Sm]I
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/2HI.Sm/h2*1H;/q;;+2/p-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = UAWABSHMGXMCRK-UHFFFAOYSA-L
| CASNo = 32248-43-4
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = L15T8U41LC
 }}
|Section2={{Chembox Properties
| Formula = SmI<sub>2</sub>
| MolarMass = 404.16 g/mol
| Appearance = green solid
| Density =
| Solubility =
| MeltingPtC = 520
| BoilingPt =
 }}
|Section4={{Chembox Thermochemistry
| DeltaHf =
| Entropy =
 }}
|Section7={{Chembox Hazards
| ExternalSDS = 
| HPhrases = 
| PPhrases = 
| GHS_ref  = 
| NFPA-H = 
| NFPA-F = 
| NFPA-R = 
| NFPA-S = 
| FlashPt = Non-flammable
  }}
|Section8={{Chembox Related
| OtherAnions = [[Samarium(II) chloride]]<br />[[Samarium(II) bromide]]
| OtherCations = [[Samarium(III) iodide]]<br />[[Europium(II) iodide]]
  }}
}}
[[File:Иодид самария.jpg|alt=Samarium(II) iodide in an ampule|thumb|Samarium(II) iodide]]
'''Samarium(II) iodide''' is an [[inorganic compound]] with the formula SmI<sub>2</sub>.  When employed as a solution for [[organic synthesis]], it is known as '''[[Henri B. Kagan|Kagan]]'s reagent'''.  SmI<sub>2</sub> is a green solid and forms a dark blue solution in [[Tetrahydrofuran|THF]].<ref>{{Cite web | url=https://www.sigmaaldrich.com/GB/en/sds/aldrich/347116?userType=anonymous | title=SAFETY DATA SHEET - Samarium(II) iodide solution | website=www.sigmaaldrich.com}}</ref>  It is a strong one-electron [[reducing agent]] that is used in [[organic synthesis]].

==Structure==
In solid samarium(II) iodide, the metal centers are seven-coordinate with a face-capped [[Octahedral molecular geometry|octahedral geometry]].<ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref>
[[Image:Diiodopenta(THF)samarium(II)-3D-balls.png|thumb|220px|left|Structure of the samarium(II) iodide-[[tetrahydrofuran]] complex]] 
In its [[ether complex|ether adducts]], samarium remains heptacoordinate with five ether and two terminal iodide ligands.<ref>{{cite journal |author1=William J. Evans |author2=Tammy S. Gummersheimer |author3=Joseph W. Ziller  |name-list-style=amp | year = 1995 | title = Coordination Chemistry of Samarium Diiodide with Ethers Including the Crystal Structure of Tetrahydrofuran-Solvated Samarium Diiodide, SmI<sub>2</sub>(THF)<sub>5</sub> | journal = [[J. Am. Chem. Soc.]] | volume = 117 | issue = 35 | pages = 8999–9002 | doi = 10.1021/ja00140a016|bibcode=1995JAChS.117.8999E }}</ref>

==Preparation==
Samarium iodide is easily prepared in nearly quantitative yields from samarium metal and either [[diiodomethane]] or [[1,2-Diiodoethane|1,2-diiodoethane]].<ref>{{cite journal | author = P. Girard, J. L. Namy and H. B. Kagan | title = Divalent Lanthanide Derivatives in Organic Synthesis. 1. Mild Preparation of SmI<sub>2</sub> and YbI<sub>2</sub> and Their Use as Reducing or Coupling Agents | year = 1980 | journal = [[J. Am. Chem. Soc.]] | volume = 102 | issue = 8 | pages = 2693–2698 | doi = 10.1021/ja00528a029}}</ref> When prepared in this way, its solutions is most often used without purification of the inorganic reagent.
{{NumBlk|:|<math chem>\begin{array}{cl}{}\\
\ce{{Sm} + ICH2I ->[\ce{THF}] SmI2} + 0.5\ce{H2C=CH2} \\
\ce{{Sm} + I(CH2)2I ->[\ce{THF}] {SmI2} + H2C=CH2} \\
{}\end{array}</math>|}}

Solid, solvent-free SmI<sub>2</sub> forms by high temperature [[chemical decomposition|decomposition]] of [[samarium(III) iodide]] (SmI<sub>3</sub>).<ref name="SM_1930">G. Jantsch, N. Skalla: "Zur Kenntnis der Halogenide der seltenen Erden. IV. – Über Samarium(II)jodid und den thermischen Abbau des Samarium(III)jodids", ''[[Zeitschrift für Allgemeine und Anorganische Chemie]]'', '''1930''', ''193'', 391–405; {{doi|10.1002/zaac.19301930132}}.</ref><ref>G. Jantsch: "Thermischer Abbau von seltenen Erd(III)halogeniden", ''[[Die Naturwissenschaften]]'', '''1930''', ''18&nbsp;(7)'', 155–155; {{doi|10.1007/BF01501667}}.</ref><ref name="GMELIN">''[[Gmelins Handbuch der anorganischen Chemie]]'', System Nr. 39, Band C 6, p. 192–194.</ref>

== Reactions ==
Samarium(II) iodide is a powerful [[reducing agent]] – for example it rapidly reduces [[water]] to [[hydrogen]].<ref name = "Greenwood"/> It is available commercially as a dark blue 0.1 [[Concentration|M]] solution in THF.  Although used typically in superstoichiometric amounts, catalytic applications have been described.<ref>{{cite journal |doi=10.1038/s41929-018-0219-x|title=SmI2-catalysed cyclization cascades by radical relay|year=2019|last1=Huang|first1=Huan-Ming|last2=McDouall|first2=Joseph J. W.|last3=Procter|first3=David J.|journal=Nature Catalysis|volume=2|issue=3|pages=211–218|s2cid=104423773|url=https://www.research.manchester.ac.uk/portal/en/publications/smi2catalyzed-cyclization-cascades-by-radical-relay(d64241b6-d89c-4ee2-b1a1-0eec1827ac0a).html}}</ref>

===Organic chemistry===
{{Main|Reductions with samarium(II) iodide}}
Samarium(II) iodide is a reagent for [[carbon-carbon bond]] formation, for example in a [[Barbier reaction]] (similar to the [[Grignard reaction]]) between a [[ketone]] and an alkyl iodide to form a [[tertiary alcohol]]:<ref>{{cite journal | journal = [[Synlett]] | year = 1996 | pages = 633–634 |author1=Machrouhi, Fouzia |author2=Hamann, Béatrice |author3=Namy, Jean-Louis |author4=Kagan, Henri B. | title = Improved Reactivity of Diiodosamarium by Catalysis with Transition Metal Salts | doi = 10.1055/s-1996-5547 | volume = 1996 | issue = 7| s2cid = 196761752 }}</ref>

:R<sup>1</sup>I + R<sup>2</sup>COR<sup>3</sup> → R<sup>1</sup>R<sup>2</sup>C(OH)R<sup>3</sup>

[[Image:Samariumiodide.jpg|thumb|left|Barbier reaction using SmI<sub>2</sub>]]
Typical reaction conditions use SmI<sub>2</sub> in THF in the presence of catalytic NiI<sub>2</sub>.

[[Ester]]s react similarly (adding two R groups), but [[aldehyde]]s give by-products. The reaction is convenient in that it is often very rapid (5 minutes or less in the cold). Although samarium(II) iodide is considered a powerful single-electron reducing agent, it does display remarkable [[chemoselectivity]] among functional groups. For example, [[sulfone]]s and [[sulfoxide]]s can be reduced to the corresponding [[sulfide]] in the presence of a variety of [[carbonyl]]-containing functionalities (such as [[ester]]s, [[ketone]]s, [[amide]]s, [[aldehyde]]s, etc.). This is presumably due to the considerably slower reaction with [[carbonyl]]s as compared to [[sulfone]]s and [[sulfoxide]]s. Furthermore, hydrodehalogenation of halogenated [[hydrocarbons]] to the corresponding [[hydrocarbon]] compound can be achieved using samarium(II) iodide. Also, it can be monitored by the color change that occurs as the dark blue color of SmI<sub>2</sub> in THF discharges to a light yellow once the reaction has occurred. The picture shows the dark colour disappearing immediately upon contact with the [[Barbier reaction]] mixture.

Work-up is with dilute [[hydrochloric acid]], and the samarium is removed as aqueous Sm<sup>3+</sup>.

Carbonyl compounds can also be coupled with simple alkenes to form five, six or eight membered rings.<ref>{{cite journal |author1=Molander, G. A. |author2=McKiie, J. A. | journal = [[Journal of Organic Chemistry|J. Org. Chem.]] | year = 1992 | volume = 57 | pages = 3132–3139 | doi = 10.1021/jo00037a033 | title = Samarium(II) iodide-induced reductive cyclization of unactivated olefinic ketones. Sequential radical cyclization/intermolecular nucleophilic addition and substitution reactions | issue = 11}}</ref>

[[Tosyl]] groups can be removed from ''N''-tosylamides almost instantaneously, using SmI<sub>2</sub> in conjunction with distilled water and an amine base. The reaction is even effective for deprotection of  sensitive substrates such as [[aziridines]]:<ref name="Ankner2009">{{cite journal|last=Ankner|first=Tobias|author2=Göran Hilmersson |year=2009|title=Instantaneous Deprotection of Tosylamides and Esters with SmI2/Amine/Water|journal=Organic Letters|publisher=American Chemical Society|volume=11|pages=503–506|doi=10.1021/ol802243d|pmid=19123840|issue=3}}</ref>

:[[File:SmI2detosylation.png|thumb|left|600px|Removal of a tosyl group from an ''N''-tosylamide using SmI<sub>2</sub>]] {{clear left}}

In the [[Markó-Lam deoxygenation]], an alcohol could be almost instantaneously deoxygenated by reducing their toluate ester in presence of SmI<sub>2</sub>.
:[[File:General_MarkoLam_reaction.svg|thumb|left|600px| Markó-Lam deoxygenation using SmI<sub>2</sub>]] {{clear left}}

SmI<sub>2</sub> can also be used in the [[transannulation]] of [[Bicyclic molecule|bicyclic molecules]]. An example is the SmI<sub>2</sub> induced [[ketone]] - [[alkene]] [[cyclization]] of 5-methylenecyclooctanone which proceeds through a [[ketyl]] intermediate:
:[[File:KetoneOlefinCyclization.png|380x380px|Ketone olefin cyclization]]
:

The applications of SmI<sub>2</sub> have been reviewed.<ref>{{cite journal | journal = [[J. Chem. Soc., Perkin Trans. 1]] | year = 2001 | pages = 2727–2751 | title =Recent developments in lanthanide mediated organic synthesis | author = Patrick G. Steel | doi = 10.1039/a908189e | issue = 21}}</ref><ref>{{cite journal |author1=Molander, G. A. |author2=Harris, C. R. | journal = [[Chem. Rev.]] | year = 1996 | volume = 96 | pages = 307–338 | doi = 10.1021/cr950019y | title = Sequencing Reactions with Samarium(II) Iodide | pmid=11848755 | issue = 1}}</ref><ref>{{cite journal |author1=K. C. Nicolaou |author2=Shelby P. Ellery |author3=Jason S. Chen | journal = [[Angew. Chem. Int. Ed.]] | year = 2009 | volume = 48 | issue = 39 |pages = 7140–7165 | doi = 10.1002/anie.200902151 | title = Samarium Diiodide Mediated Reactions in Total Synthesis | pmid = 19714695 | pmc = 2771673}}</ref> The book ''Organic Synthesis Using Samarium Diiodide'', published in 2009, gives a detailed overview of reactions mediated by SmI<sub>2</sub>.<ref>{{cite book |last1=Procter |first1=David J. |last2=Flowers,II |first2=Robert A. |last3=Skydstrup |first3=Troels |year=2009 |title=Organic Synthesis Using Samarium Diiodide |publisher=Royal Society of Chemistry |isbn= 978-1-84755-110-8 }}</ref>

== References ==
{{reflist}}

{{Samarium compounds}}
{{Iodides}}
{{Lanthanide halides}}

[[Category:Iodides]]
[[Category:Samarium(II) compounds]]
[[Category:Lanthanide halides]]
[[Category:One-electron reducing agents]]
[[Category:Reagents for organic chemistry]]