Expedient Method for Samarium(II) Iodide Preparation Utilizing a Flow Approach

Abstract

A facile method of SmI₂ preparation is presented which utilizes a continuous-flow system. The notoriously cumbersome handling and storage of the reagent can thus be avoided as appropriate amounts of SmI₂ can be conveniently prepared when needed. The method is illustrated and the reagent quality demonstrated by a series of typical SmI₂-induced transformations.

Key words

flow - samarium - samarium(II) iodide - reduction - reductive coupling

• References and Notes

• 1 Namy J.-L, Girard P, Kagan HB. New J. Chem. 1977; 1: 5
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• 3a Kagan HB. Tetrahedron 2003; 59: 10351
• 3b Procter DJ, Flowers RA, Skrydstrup T. Organic Synthesis Using Samarium Diiodide. A Practical Guide . RSC Publishing; Cambridge: 2010. ISBN: 978-1-84755-110-8
• 4 Girard P, Namy JL, Kagan HB. J. Am. Chem. Soc. 1980; 102: 2693
• 5 Typically, the reagent is prepared using the Schlenk technique, and its quality varies depending on whether remaining Sm metal is present in the resulting solution or not. The reaction time in batch setting is much longer. See: Szostak M, Spain M, Procter DJ. J. Org. Chem. 2012; 77: 3049 ; and references cited therein
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• 7 Concellón JM, Rodríguez-Solla H, Bardales E, Huerta M. Eur. J. Org. Chem. 2003; 1775
• 8 After the reaction is successfully concluded and the substrate is consumed the SmI₂ addition (and preparation) can be discontinued. New reaction can commence without any further initiation procedure by starting the pumping process again [(CH₂)₂I₂ or iodine solution]. The same cartridge can be used in the multiple experiments until almost all the Sm metal is depleted.
• 9 For screening of the resulting reagent quality we developed the titration method which reliably provides the active SmI₂ molar concentration (see the experimental section).
• 10 This may be true up to 0.13 M solution (solubility of SmI₂ in THF); see ref. 5.