Sodium dialkyl-amidozincates: Alkyl or amido bases? An experimental and theoretical case study

P.C. Andrikopoulos, D.R. Armstrong, H.R.L. Barley, W. Clegg, S.H. Dale, E. Hevia, G.W. Honeyman, A.R. Kennedy, R.E. Mulvey

Research output: Contribution to journalArticle

103 Citations (Scopus)

Abstract

Alkali metal zincate reagents are attracting considerable attention at present in respect to their often special reactivity/selectivity in hydrogen-metal and halogen-metal interconversion reactions. Heteroleptic diorgano-amidozincates, typified by lithium di-tert-butyltetramethylpiperidinozincate, have proved to be especially useful reagents in such applications. In this paper the related sodium TMP-zincate, prepared as its TMEDA (N,N,N',N'-tetramethylethylenediamine) adduct, [TMEDA·Na(-tBu)(-TMP)Zn(tBu)], 1, is introduced. This new zincate was synthesized from a 1:1:1 mixture of tBu2Zn, NaTMP, and TMEDA in hexane solution, as a colorless crystalline solid in an isolated yield of 58%. It has been characterized in solution by 1H and 13C NMR spectroscopic studies. An X-ray crystallographic study reveals that 1 adopts a five-membered (NaNZnCC) ring system featuring a TMP bridge and an unusual, asymmetrical tBu bridge involving a Na···Me agostic contact. Probing the basicity of 1, reaction with benzene affords the new hetero(tri)leptic zincate [TMEDA·Na(-Ph)(-TMP)Zn(tBu)], 2, which has also been crystallographically characterized. Thus, in this hydrogen-metal exchange reaction 1 functions as an alkyl base, with the elimination of butane, as opposed to an amido base. Also reported are DFT calculations using B3LYP functionals and the 6-311G** basis set on model zincate systems, which intimate that the preference of 1 for tBu ligand transfer over TMP ligand transfer in the reaction toward benzene is due to favorable thermodynamic factors.
Original languageEnglish
Pages (from-to)6184-6185
Number of pages1
JournalJournal of the American Chemical Society
Volume127
Issue number17
DOIs
Publication statusPublished - 4 May 2005

Keywords

  • macrocyclic amide
  • inverse crowns
  • ate complexes
  • chemistry
  • selectivity
  • magnesium

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