Contrasting reactivity of mono- versus Bis-2,2,6,6-tetramethylpiperidide lithium aluminates towards polydentate lewis bases: co-complexation versus deprotonation

R. Campbell, E. Crosbie, A.R. Kennedy, R.E. Mulvey, R.A. Naismith, Stuart Robertson

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Abstract

Two closely related lithium alkylaluminium amides LiAl(TMP)2iBu2 and LiAl(TMP)iBu3 (TMP: 2,2,6,6-tetramethylpiperidide) have been compared in their reactivity towards six polydentate Lewis bases containing either N or O donor atoms or a mixed N,O donor set. Seven of the twelve potential organometallic products of these reactions, which were carried out in hexane solution, have been crystallographically characterised. Three of these structures, [Li(-Me2NCH2CHCH2CH2CHO)(-TMP)Al(iBu)2], [Li(-Me2NCH2CH2OCH2)(-TMP)Al(iBu)2], and [Li(-Me2NCH2CH2OCHCH2NMe2)(-TMP)Al(iBu)2] reveal that the bis-amide LiAl(TMP)2iBu2 deprotonates (aluminates) the multifunctional Lewis base selectively at the carbon atom adjacent to oxygen with the anion generated captured by the residue of the base. In contrast, the mono-amide LiAl(TMP)iBu3 in general fails to deprotonate the Lewis bases but instead forms co-complexes with them as evidenced by the molecular structures of [Me2NCH2CHCH2CH2CH2O·Li(-iBu)(-TMP)Al(iBu)2], [Me2NCH2CH2OMe·Li(- iBu)(-TMP)Al(iBu)2], and [MeOCH2CH2OMe·Li(-iBu)(-TMP)Al(iBu)2]. Providing an exception to this pattern, the mono-amide reagent deprotonates chiral R,R,-N,N,N′,N′-tetramethylcyclohexanediamine to afford [Li(-CH2NMeC6H10NMe2)2Al(iBu)2], the final complex to be crystallographically characterised. All new products have been spectroscopically characterised through 1H, 7 Li, and 13C NMR studies. Reaction mixtures have also been quenched with D2O and analysed by 2D NMR spectroscopy to ascertain the full metallation versus co-complexation picture taking place in solution.
LanguageEnglish
Pages1189-1201
Number of pages13
JournalAustralian Journal of Chemistry
Volume66
Issue number10
DOIs
Publication statusPublished - 3 Jul 2013

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Lewis Bases
Thymidine Monophosphate
Deprotonation
Complexation
Amides
lithium 2,2,6,6-tetramethylpiperidide
Atoms
Hexanes
Organometallics
Lithium
Molecular structure
Nuclear magnetic resonance spectroscopy
Anions

Keywords

  • amides
  • molecular structures
  • lithium alkylaluminium

Cite this

@article{166dcdebec3949a9a1f8157a7c4ab048,
title = "Contrasting reactivity of mono- versus Bis-2,2,6,6-tetramethylpiperidide lithium aluminates towards polydentate lewis bases: co-complexation versus deprotonation",
abstract = "Two closely related lithium alkylaluminium amides LiAl(TMP)2iBu2 and LiAl(TMP)iBu3 (TMP: 2,2,6,6-tetramethylpiperidide) have been compared in their reactivity towards six polydentate Lewis bases containing either N or O donor atoms or a mixed N,O donor set. Seven of the twelve potential organometallic products of these reactions, which were carried out in hexane solution, have been crystallographically characterised. Three of these structures, [Li(-Me2NCH2CHCH2CH2CHO)(-TMP)Al(iBu)2], [Li(-Me2NCH2CH2OCH2)(-TMP)Al(iBu)2], and [Li(-Me2NCH2CH2OCHCH2NMe2)(-TMP)Al(iBu)2] reveal that the bis-amide LiAl(TMP)2iBu2 deprotonates (aluminates) the multifunctional Lewis base selectively at the carbon atom adjacent to oxygen with the anion generated captured by the residue of the base. In contrast, the mono-amide LiAl(TMP)iBu3 in general fails to deprotonate the Lewis bases but instead forms co-complexes with them as evidenced by the molecular structures of [Me2NCH2CHCH2CH2CH2O·Li(-iBu)(-TMP)Al(iBu)2], [Me2NCH2CH2OMe·Li(- iBu)(-TMP)Al(iBu)2], and [MeOCH2CH2OMe·Li(-iBu)(-TMP)Al(iBu)2]. Providing an exception to this pattern, the mono-amide reagent deprotonates chiral R,R,-N,N,N′,N′-tetramethylcyclohexanediamine to afford [Li(-CH2NMeC6H10NMe2)2Al(iBu)2], the final complex to be crystallographically characterised. All new products have been spectroscopically characterised through 1H, 7 Li, and 13C NMR studies. Reaction mixtures have also been quenched with D2O and analysed by 2D NMR spectroscopy to ascertain the full metallation versus co-complexation picture taking place in solution.",
keywords = "amides, molecular structures, lithium alkylaluminium",
author = "R. Campbell and E. Crosbie and A.R. Kennedy and R.E. Mulvey and R.A. Naismith and Stuart Robertson",
year = "2013",
month = "7",
day = "3",
doi = "10.1071/CH13157",
language = "English",
volume = "66",
pages = "1189--1201",
journal = "Australian Journal of Chemistry",
issn = "0004-9425",
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TY - JOUR

T1 - Contrasting reactivity of mono- versus Bis-2,2,6,6-tetramethylpiperidide lithium aluminates towards polydentate lewis bases

T2 - Australian Journal of Chemistry

AU - Campbell, R.

AU - Crosbie, E.

AU - Kennedy, A.R.

AU - Mulvey, R.E.

AU - Naismith, R.A.

AU - Robertson, Stuart

PY - 2013/7/3

Y1 - 2013/7/3

N2 - Two closely related lithium alkylaluminium amides LiAl(TMP)2iBu2 and LiAl(TMP)iBu3 (TMP: 2,2,6,6-tetramethylpiperidide) have been compared in their reactivity towards six polydentate Lewis bases containing either N or O donor atoms or a mixed N,O donor set. Seven of the twelve potential organometallic products of these reactions, which were carried out in hexane solution, have been crystallographically characterised. Three of these structures, [Li(-Me2NCH2CHCH2CH2CHO)(-TMP)Al(iBu)2], [Li(-Me2NCH2CH2OCH2)(-TMP)Al(iBu)2], and [Li(-Me2NCH2CH2OCHCH2NMe2)(-TMP)Al(iBu)2] reveal that the bis-amide LiAl(TMP)2iBu2 deprotonates (aluminates) the multifunctional Lewis base selectively at the carbon atom adjacent to oxygen with the anion generated captured by the residue of the base. In contrast, the mono-amide LiAl(TMP)iBu3 in general fails to deprotonate the Lewis bases but instead forms co-complexes with them as evidenced by the molecular structures of [Me2NCH2CHCH2CH2CH2O·Li(-iBu)(-TMP)Al(iBu)2], [Me2NCH2CH2OMe·Li(- iBu)(-TMP)Al(iBu)2], and [MeOCH2CH2OMe·Li(-iBu)(-TMP)Al(iBu)2]. Providing an exception to this pattern, the mono-amide reagent deprotonates chiral R,R,-N,N,N′,N′-tetramethylcyclohexanediamine to afford [Li(-CH2NMeC6H10NMe2)2Al(iBu)2], the final complex to be crystallographically characterised. All new products have been spectroscopically characterised through 1H, 7 Li, and 13C NMR studies. Reaction mixtures have also been quenched with D2O and analysed by 2D NMR spectroscopy to ascertain the full metallation versus co-complexation picture taking place in solution.

AB - Two closely related lithium alkylaluminium amides LiAl(TMP)2iBu2 and LiAl(TMP)iBu3 (TMP: 2,2,6,6-tetramethylpiperidide) have been compared in their reactivity towards six polydentate Lewis bases containing either N or O donor atoms or a mixed N,O donor set. Seven of the twelve potential organometallic products of these reactions, which were carried out in hexane solution, have been crystallographically characterised. Three of these structures, [Li(-Me2NCH2CHCH2CH2CHO)(-TMP)Al(iBu)2], [Li(-Me2NCH2CH2OCH2)(-TMP)Al(iBu)2], and [Li(-Me2NCH2CH2OCHCH2NMe2)(-TMP)Al(iBu)2] reveal that the bis-amide LiAl(TMP)2iBu2 deprotonates (aluminates) the multifunctional Lewis base selectively at the carbon atom adjacent to oxygen with the anion generated captured by the residue of the base. In contrast, the mono-amide LiAl(TMP)iBu3 in general fails to deprotonate the Lewis bases but instead forms co-complexes with them as evidenced by the molecular structures of [Me2NCH2CHCH2CH2CH2O·Li(-iBu)(-TMP)Al(iBu)2], [Me2NCH2CH2OMe·Li(- iBu)(-TMP)Al(iBu)2], and [MeOCH2CH2OMe·Li(-iBu)(-TMP)Al(iBu)2]. Providing an exception to this pattern, the mono-amide reagent deprotonates chiral R,R,-N,N,N′,N′-tetramethylcyclohexanediamine to afford [Li(-CH2NMeC6H10NMe2)2Al(iBu)2], the final complex to be crystallographically characterised. All new products have been spectroscopically characterised through 1H, 7 Li, and 13C NMR studies. Reaction mixtures have also been quenched with D2O and analysed by 2D NMR spectroscopy to ascertain the full metallation versus co-complexation picture taking place in solution.

KW - amides

KW - molecular structures

KW - lithium alkylaluminium

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U2 - 10.1071/CH13157

DO - 10.1071/CH13157

M3 - Article

VL - 66

SP - 1189

EP - 1201

JO - Australian Journal of Chemistry

JF - Australian Journal of Chemistry

SN - 0004-9425

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