Solvated Alkali and Calcium 2,2,6,6‐Tetramethylpiperidides: Synthesis and Reactivity

Alkali 2,2,6,6‐tetramethylpiperidides (TMP) are quintessential bases in organic chemistry. The syntheses and characterization of solvated lithium, potassium, and calcium tetramethylpiperidides are reported herein. The molecular solid‐state structures of the homometallic salts [(TMP)Li(thp)] 2 , [(TMP)Li(pmdta)], [(μ‐TMP)K(pmdta)] 2 , [(TMP) 2 Ca(thp) 2 ], and [(TMP) 2 Ca(thf) 2 ] are described (pmdta = N , N , N ′, N ″, N ″‐pentamethyldiethylenetriamine; thp = tetrahydropyran). In addition, the structure of the heterobimetallic [K{pmdta}{μ 3 ‐NMe 2 }{μ 2 ‐TMP}Li] 2 , a compound obtained upon decomposition of pmdta in the presence of (TMP)Li and t BuOK in petroleum ether, is also presented. These six complexes complement the body of s ‐block metal tetramethylpiperidides that have been structurally authenticated, with, in particular, the addition of two new calcium–TMP complexes. To probe their reactivity, these bases have been used to mediate the deprotometallation of 1,3‐dimethoxybenzene in thf, followed by quenching with iodine. While the calcium complexes show little efficacy, good to high yields are achieved with the different [(TMP)M] n (M = Li, K, Na) and (TMP)Li· t BuOK alkali bases. The influence of temperature in this reaction is demonstrated, allowing for a better understanding of the overall behavior of the metal bases.