Synthesis and crystal structure of trimeric sodium 2,2,6,6-tetramethylpiperidide (NaTMP)

The title compound has been synthesised in powder form by two distinct methods: namely by sodiation of the parent amine 2,2,6,6-tetramethylpiperidine with n-butylsodium in a hydrocarbon solvent or by transmetallation from lithium 2,2,6,6-tetramethylpiperidide through the action of sodium t-butoxide in hexane solution. An alternative crystalline specimen suitable for X-ray crystallographic study was grown from a solution which additionally contained n,s-dibutylmagnesium. This study reveals a trimeric molecule of C-3h symmetry, its salient feature being a strictly planar (NaN)(3) ring. The sterically encumbered amide anions are separated by large N-Na-N bond angles of 143.76(6)degrees, the bonding in which is slightly asymmetrical (Na-N bond lengths: 2.307(2) and 2.362(2) Angstrom). Discussion focuses on the contrast between the tetrameric ring arrangement of the lithium congener, which was reported several years ago. (C) 1999 Elsevier Science S.A. All rights reserved.