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Molecular Structures of THF‐Solvated Alkali‐Metal 2,2,6,6‐Tetramethylpiperidides Finally Revealed: X‐ray Crystallographic, DFT, and NMR (including DOSY) Spectroscopic Studies
Author(s) -
Armstrong David R.,
GarcíaÁlvarez Pablo,
Kennedy Alan R.,
Mulvey Robert E.,
Robertson Stuart D.
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201100523
Subject(s) - chemistry , alkali metal , dimer , lithium amide , amide , crystallography , lithium (medication) , oligomer , monomer , nuclear magnetic resonance spectroscopy , ring (chemistry) , molecule , metal , nmr spectra database , inorganic chemistry , stereochemistry , polymer chemistry , polymer , spectral line , organic chemistry , medicine , enantioselective synthesis , endocrinology , catalysis , physics , astronomy
The often studied THF solvates of the utility alkali‐metal amides lithium and sodium 2,2,6,6‐tetramethylpiperidide are shown to exist in the solid state as asymmetric cyclic dimers containing a central M 2 N 2 ring and one molecule of donor per metal to give a distorted trigonal planar metal coordination. DFT studies support these structures and confirm the asymmetry in the ring. In C 6 D 12 solution, the lithium amide displays a concentration‐dependent equilibrium between a solvated and unsolvated species which have been shown by diffusion‐ordered NMR spectroscopy (DOSY) to be a dimer and larger oligomer, respectively. A third species, a solvated monomer, is also present in very low concentration, as proven by spiking the NMR sample with THF. In contrast, the sodium amide displays a far simpler C 6 D 12 solution chemistry, consistent with the solid‐state dimeric arrangement but with labile THF ligands.