Premium
Mixed Dimer and Mixed Trimer Complexes of n BuLi and a Chiral Lithium Amide
Author(s) -
Hilmersson Göran,
Malmros Birgitta
Publication year - 2001
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 - 10.1002/1521-3765(20010119)7:2<337::aid-chem337>3.0.co;2-i
Subject(s) - chemistry , trimer , dimer , isotopes of lithium , lithium amide , lithium (medication) , isopropyl , nuclear magnetic resonance spectroscopy , ether , crystallography , amide , stereochemistry , medicinal chemistry , ion , ion exchange , organic chemistry , medicine , endocrinology , enantioselective synthesis , catalysis
Multinuclear and multidimensional NMR spectroscopy have shown that lithium ( S ) ‐N ‐isopropyl‐ O ‐methyl‐valinol ( 1 ‐[ 6 Li]) exists in a mixed 2:1 complex with n Bu[ 6 Li], ( 1 ‐[ 6 Li]) 2 / n Bu[ 6 Li], in non‐coordinating solvents such as hexane or toluene. A 6 Li, 1 H‐HOESY NMR spectrum indicates that the complex is a cyclic trimer with a large distance between the di‐coordinated lithium and the carbanion of n Bu[ 6 Li]. Such arrangements are present in the solid state as previously reported by Williard and Sun. The exchange of lithium atoms within the trimer is slow at −33 °C. The exchange barrier (Δ G ≠ ) was determined to be 14.7 kcal mol −1 from quantitative 6 Li, 6 Li‐EXSY spectra. Addition of diethyl ether results in the formation of mixed dimers of ( 1 ‐[ 6 Li])/ n Bu[ 6 Li], tetramers of n Bu[ 6 Li], and homodimers ( 1 ‐[ 6 Li]) 2 . The apparent equilibrium constant of the mixed dimer was determined from the 6 Li NMR integrals as K =7.