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Correlation between the 6 Li, 15 N Coupling Constant and the Coordination Number at Lithium
Author(s) -
Granander Johan,
Sott Richard,
Hilmersson Göran
Publication year - 2006
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.200501371
Subject(s) - chemistry , lithium (medication) , lithium amide , tetrahydrofuran , ether , thioether , amide , chelation , crystallography , medicinal chemistry , diethyl ether , inorganic chemistry , stereochemistry , organic chemistry , medicine , endocrinology , solvent , enantioselective synthesis , catalysis
Abstract The 6 Li, 15 N coupling constants of lithium amide dimers and their mixed complexes with n ‐butyllithium, formed from five different chiral amines derived from ( S )‐[ 15 N]phenylalanine, were determined in diethyl ether (Et 2 O), tetrahydrofuran (THF) and toluene. Results of NMR spectroscopy studies of these complexes show a clear difference in 6 Li, 15 N coupling constants between di‐, tri‐ and tetracoordinated lithium atoms. The lithium amide dimers with a chelating ether group exhibit 6 Li, 15 N coupling constants of ∼3.8 and ∼5.5 Hz for the tetracoordinated and tricoordinated lithium atoms, respectively. The lithium amide dimers with a chelating thioether group show distinctly larger 6 Li, 15 N coupling constants of ∼4.4 Hz for the tetracoordinated lithium atoms, and the tricoordinated lithium atoms have smaller 6 Li, 15 N coupling constants, ∼4.9 Hz, than their ether analogues. In diethyl ether and tetrahydrofuran, mixed dimeric complexes between the lithium amides and n ‐butyllithium are formed. The tetracoordinated lithium atoms of these complexes have 6 Li, 15 N coupling constants of ∼4.0 Hz, and the 6 Li, 15 N coupling constants of the tricoordinated lithium atoms differ somewhat, depending on whether the chelating group is an ether or a thioether; ∼5.1 and ∼4.6 Hz, respectively. In toluene, mixed trimeric complexes are formed from two lithium amide moieties and one n ‐butyllithium. In these trimers, two lithium atoms are tricoordinated with 6 Li, 15 N coupling constants of ∼4.6 Hz and one lithium is dicoordinated with 6 Li, 15 N coupling constants of ∼6.5 Hz.