 | |
| Names | |
|---|---|
| IUPAC name samarium(II) iodide | |
| Other names samarium diiodide | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
|
| UNII | |
| |
| |
| Properties | |
| SmI2 | |
| Molar mass | 404.16 g/mol |
| Appearance | green solid |
| Melting point | 520 °C (968 °F; 793 K) |
| Hazards | |
| Flash point | Non-flammable |
| Related compounds | |
Otheranions | Samarium(II) chloride Samarium(II) bromide |
Othercations | Samarium(III) iodide Europium(II) iodide |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Samarium(II) iodide is aninorganic compound with the formula SmI2. When employed as a solution fororganic synthesis, it is known asKagan's reagent, named afterHenri B. Kagan. SmI2 is a green solid and forms a dark blue solution inTHF.[1] It is a strong one-electronreducing agent that is used inorganic synthesis.
In solid samarium(II) iodide, the metal centers are seven-coordinate with a face-cappedoctahedral geometry.[2]
samarium(II)-3D-balls.png)
In itsether adducts, samarium remains heptacoordinate with five ether and two terminal iodide ligands.[3]
Samarium iodide is easily prepared in nearly quantitative yields from samarium metal usingdiiodomethane,1,2-diiodoethane, or moleculariodine, typically usingTHF as solvent.[4] The resulting solutions are most often used directly, without isolation of the inorganic reagent itself.
Solid, solvent-free SmI2 forms by high temperaturedecomposition ofsamarium(III) iodide (SmI3).[5][6][7]
Samarium(II) iodide is a powerfulreducing agent – for example it rapidly reduceswater tohydrogen.[2] It is available commercially as a dark blue 0.1M solution in THF. Although used typically in superstoichiometric amounts, catalytic applications have been described.[8]
Samarium(II) iodide is a reagent forcarbon-carbon bond formation, for example in aBarbier reaction (similar to theGrignard reaction) between aketone and an alkyl iodide to form atertiary alcohol:[9]
Typical reaction conditions use SmI2 in THF in the presence of catalytic NiI2.
Esters react similarly (adding two R groups), butaldehydes 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 remarkablechemoselectivity among functional groups. For example,sulfones andsulfoxides can be reduced to the correspondingsulfide in the presence of a variety ofcarbonyl-containing functionalities (such asesters,ketones,amides,aldehydes, etc.). This is presumably due to the considerably slower reaction withcarbonyls as compared tosulfones andsulfoxides. Furthermore, hydrodehalogenation of halogenatedhydrocarbons to the correspondinghydrocarbon 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 SmI2 in THF discharges to a light yellow once the reaction has occurred. The picture shows the dark colour disappearing immediately upon contact with theBarbier reaction mixture.
Work-up is with dilutehydrochloric acid, and the samarium is removed as aqueous Sm3+.
Carbonyl compounds can also be coupled with simple alkenes to form five, six or eight membered rings.[10]
Tosyl groups can be removed fromN-tosylamides almost instantaneously, using SmI2 in conjunction with distilled water and an amine base. The reaction is even effective for deprotection of sensitive substrates such asaziridines:[11]
In theMarkó-Lam deoxygenation, an alcohol could be almost instantaneously deoxygenated by reducing their toluate ester in presence of SmI2.
SmI2 can also be used in thetransannulation ofbicyclic molecules. An example is the SmI2 inducedketone -alkenecyclization of 5-methylenecyclooctanone which proceeds through aketyl intermediate:
The applications of SmI2 have been reviewed.[12][13][14] The bookOrganic Synthesis Using Samarium Diiodide, published in 2009, gives a detailed overview of reactions mediated by SmI2.[15]
