TY - JOUR
T1 - Sodium dialkyl-amidozincates: Alkyl or amido bases? An experimental and theoretical case study
AU - Andrikopoulos, P.C.
AU - Armstrong, D.R.
AU - Barley, H.R.L.
AU - Clegg, W.
AU - Dale, S.H.
AU - Hevia, E.
AU - Honeyman, G.W.
AU - Kennedy, A.R.
AU - Mulvey, R.E.
PY - 2005/5/4
Y1 - 2005/5/4
N2 - 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.
AB - 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.
KW - macrocyclic amide
KW - inverse crowns
KW - ate complexes
KW - chemistry
KW - selectivity
KW - magnesium
UR - http://pubs.acs.org/journal/jacsat
U2 - 10.1021/ja050860l
DO - 10.1021/ja050860l
M3 - Article
SN - 0002-7863
VL - 127
SP - 6184
EP - 6185
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 17
ER -