Probing the metallating ability of a polybasic sodium alkylmagnesiate supported by a bulky bis(amido) ligand: deprotomagnesiation reactions of nitrogen-based aromatic substrates

D.R. Armstrong, W. Clegg, Alberto Hernan-Gomez, A.R. Kennedy, Z. Livingstone, S.D. Robertson, L. Russo, E. Hevia

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Exploring the reactivity of sodium butylmagnesiate reagent [{Na(THF) }{(PhSi(NAr*))Mg(Bu)(THF)} ] (1) supported by the bulky chelating silyl(bisamido) ligand {PhSi(NAr*)} (Ar* = 2,6-iPr-CH) towards N-methylbenzimidazole (bIm), pyrrole and 2,6-diisopropylaniline (NHAr*) , this study provides new insights into the ability of this bimetallic base to facilitate direct Mg-H exchange reactions as well as to exhibit polybasicity. Thus 1 effectively promotes the deprotomagnesiation of bIm under mild reaction conditions to give the α-metallated intermediate [{Na(THF)}{(PhSi(NAr*) )Mg(bIm*)}] (2) (bIm * = 2-N-methylbenzimidazolyl). Analysis of crystallographic and NMR data of 2 combined with DFT calculations show that the metallated C in the bIm* ligands possesses a significant carbenic character. Contrasting with previous studies of benzothiazole (btz), 1 does not react with an excess of bIm even under forcing refluxing conditions. Contrastingly, the amination reactions of equimolar amounts of 1 with pyrrole and 2,6-diisopropylaniline allowed the isolation of [{(Ph Si(NAr*)(NHAr*))Mg(NCH) (THF)Na(THF)}] (3) and [{Na(THF)} {(PhSi(NAr*)(NHAr*))Mg(NHAr*) (THF)}] (4) respectively as crystalline solids. Highlighting the ability of 1 to act as a polybasic reagent, 3 and 4 are formed as the result of the deprotonation of two molecules of the relevant amine via its butyl group and one amido arm of the silyl(bisamido) ligand. Similarly, the reactions of 1 with 3 molar equivalents of the relevant amine yielded homoleptic tris(amido) compounds [(THF)NaMg(NCH) ] (5) and [{Na(THF)}{Mg(NHAr*) }] (7), with the concomitant formation of bis(amine) PhSi(NHAr), as a result of the complete amination of 1 using its three basic sites. The structures in the solid state of 3 and 4 were elucidated by X-ray crystallography. Despite their similar constitution, these heteroleptic tris(amido)magnesiates adopt contrasting structures, with the former displaying a contacted ion-pair structure, where Na and Mg are connected by two bridging pyrrolyl anions, whereas the latter gives rise to a solvent-separated ion pair motif. To the best of our knowledge 3 represents the first crystallographically characterized magnesium compound containing an anionic non-substituted form of pyrrole. Noticeably, Mg interacts exclusively with the N atoms of the pyrrolyl ligands, forming strong σ-bonds, whereas Na prefers to engage with the π-systems of both NC-rings.
LanguageEnglish
Pages4361-4369
Number of pages9
JournalDalton Transactions
Volume43
Issue number11
Early online date25 Oct 2013
DOIs
Publication statusPublished - 21 Mar 2014

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Pyrroles
Nitrogen
Sodium
Ligands
Amines
Amination
Substrates
Magnesium Compounds
Ions
Deprotonation
X ray crystallography
Chelation
Discrete Fourier transforms
Anions
Nuclear magnetic resonance
Crystalline materials
Atoms
Molecules

Keywords

  • aromatic substrates
  • sodium butylmagnesiate reagent
  • Mg–H exchange reactions

Cite this

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abstract = "Exploring the reactivity of sodium butylmagnesiate reagent [{Na(THF) }{(PhSi(NAr*))Mg(Bu)(THF)} ] (1) supported by the bulky chelating silyl(bisamido) ligand {PhSi(NAr*)} (Ar* = 2,6-iPr-CH) towards N-methylbenzimidazole (bIm), pyrrole and 2,6-diisopropylaniline (NHAr*) , this study provides new insights into the ability of this bimetallic base to facilitate direct Mg-H exchange reactions as well as to exhibit polybasicity. Thus 1 effectively promotes the deprotomagnesiation of bIm under mild reaction conditions to give the α-metallated intermediate [{Na(THF)}{(PhSi(NAr*) )Mg(bIm*)}] (2) (bIm * = 2-N-methylbenzimidazolyl). Analysis of crystallographic and NMR data of 2 combined with DFT calculations show that the metallated C in the bIm* ligands possesses a significant carbenic character. Contrasting with previous studies of benzothiazole (btz), 1 does not react with an excess of bIm even under forcing refluxing conditions. Contrastingly, the amination reactions of equimolar amounts of 1 with pyrrole and 2,6-diisopropylaniline allowed the isolation of [{(Ph Si(NAr*)(NHAr*))Mg(NCH) (THF)Na(THF)}] (3) and [{Na(THF)} {(PhSi(NAr*)(NHAr*))Mg(NHAr*) (THF)}] (4) respectively as crystalline solids. Highlighting the ability of 1 to act as a polybasic reagent, 3 and 4 are formed as the result of the deprotonation of two molecules of the relevant amine via its butyl group and one amido arm of the silyl(bisamido) ligand. Similarly, the reactions of 1 with 3 molar equivalents of the relevant amine yielded homoleptic tris(amido) compounds [(THF)NaMg(NCH) ] (5) and [{Na(THF)}{Mg(NHAr*) }] (7), with the concomitant formation of bis(amine) PhSi(NHAr), as a result of the complete amination of 1 using its three basic sites. The structures in the solid state of 3 and 4 were elucidated by X-ray crystallography. Despite their similar constitution, these heteroleptic tris(amido)magnesiates adopt contrasting structures, with the former displaying a contacted ion-pair structure, where Na and Mg are connected by two bridging pyrrolyl anions, whereas the latter gives rise to a solvent-separated ion pair motif. To the best of our knowledge 3 represents the first crystallographically characterized magnesium compound containing an anionic non-substituted form of pyrrole. Noticeably, Mg interacts exclusively with the N atoms of the pyrrolyl ligands, forming strong σ-bonds, whereas Na prefers to engage with the π-systems of both NC-rings.",
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Probing the metallating ability of a polybasic sodium alkylmagnesiate supported by a bulky bis(amido) ligand : deprotomagnesiation reactions of nitrogen-based aromatic substrates. / Armstrong, D.R.; Clegg, W.; Hernan-Gomez, Alberto; Kennedy, A.R.; Livingstone, Z.; Robertson, S.D.; Russo, L.; Hevia, E.

In: Dalton Transactions, Vol. 43, No. 11, 21.03.2014, p. 4361-4369.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Probing the metallating ability of a polybasic sodium alkylmagnesiate supported by a bulky bis(amido) ligand

T2 - Dalton Transactions

AU - Armstrong, D.R.

AU - Clegg, W.

AU - Hernan-Gomez, Alberto

AU - Kennedy, A.R.

AU - Livingstone, Z.

AU - Robertson, S.D.

AU - Russo, L.

AU - Hevia, E.

PY - 2014/3/21

Y1 - 2014/3/21

N2 - Exploring the reactivity of sodium butylmagnesiate reagent [{Na(THF) }{(PhSi(NAr*))Mg(Bu)(THF)} ] (1) supported by the bulky chelating silyl(bisamido) ligand {PhSi(NAr*)} (Ar* = 2,6-iPr-CH) towards N-methylbenzimidazole (bIm), pyrrole and 2,6-diisopropylaniline (NHAr*) , this study provides new insights into the ability of this bimetallic base to facilitate direct Mg-H exchange reactions as well as to exhibit polybasicity. Thus 1 effectively promotes the deprotomagnesiation of bIm under mild reaction conditions to give the α-metallated intermediate [{Na(THF)}{(PhSi(NAr*) )Mg(bIm*)}] (2) (bIm * = 2-N-methylbenzimidazolyl). Analysis of crystallographic and NMR data of 2 combined with DFT calculations show that the metallated C in the bIm* ligands possesses a significant carbenic character. Contrasting with previous studies of benzothiazole (btz), 1 does not react with an excess of bIm even under forcing refluxing conditions. Contrastingly, the amination reactions of equimolar amounts of 1 with pyrrole and 2,6-diisopropylaniline allowed the isolation of [{(Ph Si(NAr*)(NHAr*))Mg(NCH) (THF)Na(THF)}] (3) and [{Na(THF)} {(PhSi(NAr*)(NHAr*))Mg(NHAr*) (THF)}] (4) respectively as crystalline solids. Highlighting the ability of 1 to act as a polybasic reagent, 3 and 4 are formed as the result of the deprotonation of two molecules of the relevant amine via its butyl group and one amido arm of the silyl(bisamido) ligand. Similarly, the reactions of 1 with 3 molar equivalents of the relevant amine yielded homoleptic tris(amido) compounds [(THF)NaMg(NCH) ] (5) and [{Na(THF)}{Mg(NHAr*) }] (7), with the concomitant formation of bis(amine) PhSi(NHAr), as a result of the complete amination of 1 using its three basic sites. The structures in the solid state of 3 and 4 were elucidated by X-ray crystallography. Despite their similar constitution, these heteroleptic tris(amido)magnesiates adopt contrasting structures, with the former displaying a contacted ion-pair structure, where Na and Mg are connected by two bridging pyrrolyl anions, whereas the latter gives rise to a solvent-separated ion pair motif. To the best of our knowledge 3 represents the first crystallographically characterized magnesium compound containing an anionic non-substituted form of pyrrole. Noticeably, Mg interacts exclusively with the N atoms of the pyrrolyl ligands, forming strong σ-bonds, whereas Na prefers to engage with the π-systems of both NC-rings.

AB - Exploring the reactivity of sodium butylmagnesiate reagent [{Na(THF) }{(PhSi(NAr*))Mg(Bu)(THF)} ] (1) supported by the bulky chelating silyl(bisamido) ligand {PhSi(NAr*)} (Ar* = 2,6-iPr-CH) towards N-methylbenzimidazole (bIm), pyrrole and 2,6-diisopropylaniline (NHAr*) , this study provides new insights into the ability of this bimetallic base to facilitate direct Mg-H exchange reactions as well as to exhibit polybasicity. Thus 1 effectively promotes the deprotomagnesiation of bIm under mild reaction conditions to give the α-metallated intermediate [{Na(THF)}{(PhSi(NAr*) )Mg(bIm*)}] (2) (bIm * = 2-N-methylbenzimidazolyl). Analysis of crystallographic and NMR data of 2 combined with DFT calculations show that the metallated C in the bIm* ligands possesses a significant carbenic character. Contrasting with previous studies of benzothiazole (btz), 1 does not react with an excess of bIm even under forcing refluxing conditions. Contrastingly, the amination reactions of equimolar amounts of 1 with pyrrole and 2,6-diisopropylaniline allowed the isolation of [{(Ph Si(NAr*)(NHAr*))Mg(NCH) (THF)Na(THF)}] (3) and [{Na(THF)} {(PhSi(NAr*)(NHAr*))Mg(NHAr*) (THF)}] (4) respectively as crystalline solids. Highlighting the ability of 1 to act as a polybasic reagent, 3 and 4 are formed as the result of the deprotonation of two molecules of the relevant amine via its butyl group and one amido arm of the silyl(bisamido) ligand. Similarly, the reactions of 1 with 3 molar equivalents of the relevant amine yielded homoleptic tris(amido) compounds [(THF)NaMg(NCH) ] (5) and [{Na(THF)}{Mg(NHAr*) }] (7), with the concomitant formation of bis(amine) PhSi(NHAr), as a result of the complete amination of 1 using its three basic sites. The structures in the solid state of 3 and 4 were elucidated by X-ray crystallography. Despite their similar constitution, these heteroleptic tris(amido)magnesiates adopt contrasting structures, with the former displaying a contacted ion-pair structure, where Na and Mg are connected by two bridging pyrrolyl anions, whereas the latter gives rise to a solvent-separated ion pair motif. To the best of our knowledge 3 represents the first crystallographically characterized magnesium compound containing an anionic non-substituted form of pyrrole. Noticeably, Mg interacts exclusively with the N atoms of the pyrrolyl ligands, forming strong σ-bonds, whereas Na prefers to engage with the π-systems of both NC-rings.

KW - aromatic substrates

KW - sodium butylmagnesiate reagent

KW - Mg–H exchange reactions

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DO - 10.1039/c3dt52639a

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