Sodium naphthalenide solution (NaC10H8)

Reducing Agents
1

The following procedure was used to generate a 0.44M sodium naphthalenide solution in THF: In the glovebox, a 50mL round-bottom flask with a glass-coated stir-bar was charged with sodium metal (0.243g, 10.6mmol) and naphthalene (1.128g, 8.80mmol), followed by anhydrous tetrahydrofuran (20mL). The dark green mixture was then stirred at room temperature overnight and subsequently used in subsequent reactions.

Notes

  • The sodium naphthalenide solution is allowed to react overnight to ensure complete dissolution of one equivalent of sodium, which is difficult to gauge by eye due to the intense color of the solution. Use within five days.
  • Sodium naphthalenide is a stronger reducing agent than potassium graphite.
  • Other alkali metal (i.e. lithium, potassium, even rubidium) naphthalenides can also be generated using the same procedure.
  • Other solvents have been used instead of THF, namely diglyme, dimethoxyethane, dioxane, 2-MeTHF.[1] Diethyl ether is not polar enough for reaction to take place.[2]
  • The reducing power of the reagent can be modulated by using different arenes instead of naphthalene (i.e. more reducing power with di-tert-butylbiphenyl, less reducing power with anthracene) as shown by Reisman et al. See supporting information of reference [3].
  • Although alkali metal naphthalenides are typically prepared in solution and used in situ, a few publications have reported isolable species for stoichiometric use. These have been stabilized by trapping the cation (Li, Na, or K) in a crown ether,[4] or by crystallization of the THF solvate via precipitation from a THF/diethyl ether mixture.[5]

[1] Atherton, N. M.; Weissman, S. I. Association Between Sodium and Naphthalenide Ions. J. Am. Chem. Soc. 1961, 83, 1330-1334.
[2] Azuma, T.; Yanagida, S.; Sakurai, H.; Sasa, S.; Yoshino, K. A Facile Preparation of Aromatic Anion Radicals by Ultrasound Irradiation. Synth.
Commun. 1982, 12, 137-140.
[3] Han, A.; Tao, Y.; Reisman, S. E. A 16-step synthesis of the isoryanodane diterpene (+)-perseanol. Nature 2019, 573, 563-567.
[4] Castillo, M.; Metta-Magaña, A. J.; Fortier, S. Isolation of gravimetrically quantifiable alkali metal arenides using 18-crown-6. New J. Chem. 2016, 40, 1923-1926.
[5] Scott, T. A.; Ooro, B. A.; Collins, D. J.; Shatruk, M.; Yakovenko, A.; Dunbar, K. R.; Zhou, H.-C. After 118 years, the isolation of two common radical anion reductants as simple, stable solids. Chem. Commun. 2009, 65-67.