Closer insight into the reactivity of TMP-dialkyl zincates in directed ortho-zincation of anisole: experimental evidence of amido basicity and structural elucidation of key reaction intermediates

W. Clegg, B. Conway, E. Hevia, M.D. McCall, L. Russo, R.E. Mulvey

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Abstract

The new dialkyl(aryl) lithium zincates [(THF)2Li(C6H4−OMe)MeZnMe] (4), [(TMEDA)Li(C6H4−OMe)MeZnMe] (6), [(THF)3Li(C6H4−OMe)tBuZntBu] (7), and [(PMDETA)Li(C6H4−OMe)tBuZntBu] (8) have been prepared by co-complexation reactions of lithiated anisole with the relevant dialkylzinc compound and the relevant Lewis base. These new heterobimetallic compounds have been characterized in solution using 1H, 13C{H}, and 7Li NMR spectroscopy, and the molecular structures of 6 and 8 have been elucidated by X-ray crystallography. In 6 the distinct metals are connected through the anisole ligand which binds in an ambidentate fashion (through carbon−zinc and oxygen−lithium contacts) and also through one of the methyl groups, to close a [LiOCCZnC] six-membered ring; whereas 8 displays an open structure where anisole connects the two metals (in the same mode as in 6) but with the tert-butyl groups exclusively bonded terminally to zinc. Reactivity studies of zincates 4 and 7 with the amine TMP(H) supply experimental evidence that these heterobimetallic compounds are intermediates in the two-step deprotonation reaction of anisole by TMP−dialkyl zincates and show the relevance of the alkyl groups in the efficiency of TMP−dialkyl zincate bases. In addition, important solvent effects have also been evaluated. When hexane is added to THF solutions of compounds 4 or 7, the homoleptic tetraorganozincate [(THF)2Li2Zn(C6H4−OMe)4] (5) is obtained as the result of a disproportionation process. This lithium-rich zincate has also been spectroscopically and crystallographically characterized.
LanguageEnglish
Pages2375-2384
Number of pages10
JournalJournal of the American Chemical Society
Volume131
Issue number6
DOIs
Publication statusPublished - 26 Jan 2009

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Thymidine Monophosphate
Reaction intermediates
Alkalinity
Lithium
Zinc
Deprotonation
Metals
X ray crystallography
Lewis Bases
Hexane
Complexation
Molecular structure
Nuclear magnetic resonance spectroscopy
Amines
X Ray Crystallography
Hexanes
Molecular Structure
Display devices
Ligands
Carbon

Keywords

  • spectroscopy
  • crystallography
  • solvent effects
  • mollecular structures

Cite this

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title = "Closer insight into the reactivity of TMP-dialkyl zincates in directed ortho-zincation of anisole: experimental evidence of amido basicity and structural elucidation of key reaction intermediates",
abstract = "The new dialkyl(aryl) lithium zincates [(THF)2Li(C6H4−OMe)MeZnMe] (4), [(TMEDA)Li(C6H4−OMe)MeZnMe] (6), [(THF)3Li(C6H4−OMe)tBuZntBu] (7), and [(PMDETA)Li(C6H4−OMe)tBuZntBu] (8) have been prepared by co-complexation reactions of lithiated anisole with the relevant dialkylzinc compound and the relevant Lewis base. These new heterobimetallic compounds have been characterized in solution using 1H, 13C{H}, and 7Li NMR spectroscopy, and the molecular structures of 6 and 8 have been elucidated by X-ray crystallography. In 6 the distinct metals are connected through the anisole ligand which binds in an ambidentate fashion (through carbon−zinc and oxygen−lithium contacts) and also through one of the methyl groups, to close a [LiOCCZnC] six-membered ring; whereas 8 displays an open structure where anisole connects the two metals (in the same mode as in 6) but with the tert-butyl groups exclusively bonded terminally to zinc. Reactivity studies of zincates 4 and 7 with the amine TMP(H) supply experimental evidence that these heterobimetallic compounds are intermediates in the two-step deprotonation reaction of anisole by TMP−dialkyl zincates and show the relevance of the alkyl groups in the efficiency of TMP−dialkyl zincate bases. In addition, important solvent effects have also been evaluated. When hexane is added to THF solutions of compounds 4 or 7, the homoleptic tetraorganozincate [(THF)2Li2Zn(C6H4−OMe)4] (5) is obtained as the result of a disproportionation process. This lithium-rich zincate has also been spectroscopically and crystallographically characterized.",
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author = "W. Clegg and B. Conway and E. Hevia and M.D. McCall and L. Russo and R.E. Mulvey",
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T1 - Closer insight into the reactivity of TMP-dialkyl zincates in directed ortho-zincation of anisole

T2 - Journal of the American Chemical Society

AU - Clegg, W.

AU - Conway, B.

AU - Hevia, E.

AU - McCall, M.D.

AU - Russo, L.

AU - Mulvey, R.E.

PY - 2009/1/26

Y1 - 2009/1/26

N2 - The new dialkyl(aryl) lithium zincates [(THF)2Li(C6H4−OMe)MeZnMe] (4), [(TMEDA)Li(C6H4−OMe)MeZnMe] (6), [(THF)3Li(C6H4−OMe)tBuZntBu] (7), and [(PMDETA)Li(C6H4−OMe)tBuZntBu] (8) have been prepared by co-complexation reactions of lithiated anisole with the relevant dialkylzinc compound and the relevant Lewis base. These new heterobimetallic compounds have been characterized in solution using 1H, 13C{H}, and 7Li NMR spectroscopy, and the molecular structures of 6 and 8 have been elucidated by X-ray crystallography. In 6 the distinct metals are connected through the anisole ligand which binds in an ambidentate fashion (through carbon−zinc and oxygen−lithium contacts) and also through one of the methyl groups, to close a [LiOCCZnC] six-membered ring; whereas 8 displays an open structure where anisole connects the two metals (in the same mode as in 6) but with the tert-butyl groups exclusively bonded terminally to zinc. Reactivity studies of zincates 4 and 7 with the amine TMP(H) supply experimental evidence that these heterobimetallic compounds are intermediates in the two-step deprotonation reaction of anisole by TMP−dialkyl zincates and show the relevance of the alkyl groups in the efficiency of TMP−dialkyl zincate bases. In addition, important solvent effects have also been evaluated. When hexane is added to THF solutions of compounds 4 or 7, the homoleptic tetraorganozincate [(THF)2Li2Zn(C6H4−OMe)4] (5) is obtained as the result of a disproportionation process. This lithium-rich zincate has also been spectroscopically and crystallographically characterized.

AB - The new dialkyl(aryl) lithium zincates [(THF)2Li(C6H4−OMe)MeZnMe] (4), [(TMEDA)Li(C6H4−OMe)MeZnMe] (6), [(THF)3Li(C6H4−OMe)tBuZntBu] (7), and [(PMDETA)Li(C6H4−OMe)tBuZntBu] (8) have been prepared by co-complexation reactions of lithiated anisole with the relevant dialkylzinc compound and the relevant Lewis base. These new heterobimetallic compounds have been characterized in solution using 1H, 13C{H}, and 7Li NMR spectroscopy, and the molecular structures of 6 and 8 have been elucidated by X-ray crystallography. In 6 the distinct metals are connected through the anisole ligand which binds in an ambidentate fashion (through carbon−zinc and oxygen−lithium contacts) and also through one of the methyl groups, to close a [LiOCCZnC] six-membered ring; whereas 8 displays an open structure where anisole connects the two metals (in the same mode as in 6) but with the tert-butyl groups exclusively bonded terminally to zinc. Reactivity studies of zincates 4 and 7 with the amine TMP(H) supply experimental evidence that these heterobimetallic compounds are intermediates in the two-step deprotonation reaction of anisole by TMP−dialkyl zincates and show the relevance of the alkyl groups in the efficiency of TMP−dialkyl zincate bases. In addition, important solvent effects have also been evaluated. When hexane is added to THF solutions of compounds 4 or 7, the homoleptic tetraorganozincate [(THF)2Li2Zn(C6H4−OMe)4] (5) is obtained as the result of a disproportionation process. This lithium-rich zincate has also been spectroscopically and crystallographically characterized.

KW - spectroscopy

KW - crystallography

KW - solvent effects

KW - mollecular structures

U2 - 10.1021/ja8087168

DO - 10.1021/ja8087168

M3 - Article

VL - 131

SP - 2375

EP - 2384

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 6

ER -