Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres?

Organic & Biomolecular Chemistry Pub Date: 2011-04-06 DOI: 10.1039/C0OB00999G

Abstract

In this paper, we report a novel synthesis of anhydrous 1-hydroxy-2,2,6,6-tetramethyl-piperidine (TEMPO-H). An X-ray crystal structure and full characterization of the compound are included. Compared to hydrated TEMPO-H, its anhydrous form exhibits improved stability and a differing chemical reactivity. The reactions of anhydrous TEMPO-H with a variety of low-valent carbon centres are described. For example, anhydrous TEMPO-H was reacted with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), an unsaturated NHC. Crystals of [CHNC6H2(CH3)3]2C?HO(NC5H6(CH3)4), IMes?TEMPO-H, were isolated and a crystal structure determined. The experimental structure is compared to the results of theoretical calculations on the hydrogen-bonded dimer. Anhydrous TEMPO-H was also reacted with the saturated NHC, 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr), giving the product [CH2Ni-Pr2C6H3]2CH?O(NC5H6(CH3)4). In contrast, the reaction of hydrated TEMPO-H with 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene gave small amounts of the hydrolysis product, N-(2,6-diisopropylphenyl)-N-[2-(2,6-diisopropylphenylamino)ethyl]formamide. Finally, anhydrous TEMPO-H was reacted with (triphenylphosphoranylidene)ketene to generate Ph3PC(H)C([double bond, length as m-dash]O)O(NC5H6(CH3)4). A full characterization of the product, including an X-ray crystal structure, is described.

Graphical abstract: Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres
Recommended Literature