Neutral zinc, lower-order zincate and higher-order zincate derivatives of pyrrole: synthesis and structural characterisation of zinc complexes with one, two, three or four pyrrolyl ligands

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Abstract

Towards a systematic development of the zinc chemistry of the important five-membered nitrogen heterocycle pyrrole, this work reports the synthesis and characterisation of five crystalline zinc-pyrrolyl complexes. Pyrrolyl in this context means where conversion of the N-H bond to an N-zinc bond has occurred. Two neutral complexes, [(BuZn)-Bu-t(NC4H4)(TMEDA)center dot HNC4H4] 1 and [Zn(NC4H4)(2)(TMEDA)] 2, containing one and two pyrrolyl ligands, respectively, were synthesised by reacting di-t-butylzinc with different amounts of pyrrole in the presence of TMEDA (TMEDA is N,N,N',N'-tetramethylethylenediamine). X-ray crystallographic studies established that both adopt mononuclear structures with the salient feature of the former the presence of an additional parent protonated pyrrole molecule which engages its anionic counterpart in N-H center dot center dot center dot pi C-C interactions. Employing a similar synthetic approach but adding n-butylsodium to the reaction mixture in attempts to form ate derivatives delivered three distinct sodium zincate (anionic zinc) compounds in [{(THF)(2)center dot NaZn(THF)(NC4H4)(3)}(infinity)] 3, [{(TMEDA)center dot Na}(2)Zn(NC4H4)(4)] 4, and [{(PMDETA)center dot Na}(2)Zn(NC4H4)(4)] 5 (PMDETA is N, N, N', N '', N ''-pentamethyldiethylenetriamine). From their crystal structures, the 1 : 1, Na: Zn complex 3 can be classified as a lower-order zincate having three pyrrolyl ligands bound to zinc in a polymeric chain arrangement, while the 2 : 1, Na:Zn complexes 4 and 5 are molecular higher-order zincates having Zn centres fully saturated by four pyrrolyl ligands. Discussion of the structures of 1-5 focuses on the interplay of sigma-bonding and pi-bonding between the pyrrolyl ligands and the metal centres. Revealingly, the zinc-free sodiopyrrole complex [{(PMDETA)center dot Na(NC4H4)}(2)] 6, made and characterised for comparison, shows that on its own sodium prefers the former type of bonding, but is forced to switch to the latter type when combined with the stronger Lewis acid zinc in the zincate compositions. Complexes 1-6 have also been characterised in solution by NMR spectroscopy.

LanguageEnglish
Pages11945-11954
Number of pages10
JournalDalton Transactions
Volume40
Issue number44
DOIs
Publication statusPublished - 2011

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Pyrroles
Zinc
Ligands
Derivatives
Zinc Compounds
Sodium
Lewis Acids
Nuclear magnetic resonance spectroscopy
Nitrogen
Crystal structure
Metals
Switches
phenyllithium
Crystalline materials
X rays
Molecules
Chemical analysis

Keywords

  • directed ortho metalation
  • mixed lithium-zinc
  • x-ray
  • deprotonative metalation
  • mediated zincation
  • crystal structures
  • functionalized aromatics
  • nmr-spectroscopy
  • tmp-zincate
  • sodium

Cite this

@article{9d56b348f3d940b0b12a6fa660e291a3,
title = "Neutral zinc, lower-order zincate and higher-order zincate derivatives of pyrrole: synthesis and structural characterisation of zinc complexes with one, two, three or four pyrrolyl ligands",
abstract = "Towards a systematic development of the zinc chemistry of the important five-membered nitrogen heterocycle pyrrole, this work reports the synthesis and characterisation of five crystalline zinc-pyrrolyl complexes. Pyrrolyl in this context means where conversion of the N-H bond to an N-zinc bond has occurred. Two neutral complexes, [(BuZn)-Bu-t(NC4H4)(TMEDA)center dot HNC4H4] 1 and [Zn(NC4H4)(2)(TMEDA)] 2, containing one and two pyrrolyl ligands, respectively, were synthesised by reacting di-t-butylzinc with different amounts of pyrrole in the presence of TMEDA (TMEDA is N,N,N',N'-tetramethylethylenediamine). X-ray crystallographic studies established that both adopt mononuclear structures with the salient feature of the former the presence of an additional parent protonated pyrrole molecule which engages its anionic counterpart in N-H center dot center dot center dot pi C-C interactions. Employing a similar synthetic approach but adding n-butylsodium to the reaction mixture in attempts to form ate derivatives delivered three distinct sodium zincate (anionic zinc) compounds in [{(THF)(2)center dot NaZn(THF)(NC4H4)(3)}(infinity)] 3, [{(TMEDA)center dot Na}(2)Zn(NC4H4)(4)] 4, and [{(PMDETA)center dot Na}(2)Zn(NC4H4)(4)] 5 (PMDETA is N, N, N', N '', N ''-pentamethyldiethylenetriamine). From their crystal structures, the 1 : 1, Na: Zn complex 3 can be classified as a lower-order zincate having three pyrrolyl ligands bound to zinc in a polymeric chain arrangement, while the 2 : 1, Na:Zn complexes 4 and 5 are molecular higher-order zincates having Zn centres fully saturated by four pyrrolyl ligands. Discussion of the structures of 1-5 focuses on the interplay of sigma-bonding and pi-bonding between the pyrrolyl ligands and the metal centres. Revealingly, the zinc-free sodiopyrrole complex [{(PMDETA)center dot Na(NC4H4)}(2)] 6, made and characterised for comparison, shows that on its own sodium prefers the former type of bonding, but is forced to switch to the latter type when combined with the stronger Lewis acid zinc in the zincate compositions. Complexes 1-6 have also been characterised in solution by NMR spectroscopy.",
keywords = "directed ortho metalation, mixed lithium-zinc, x-ray, deprotonative metalation, mediated zincation, crystal structures, functionalized aromatics, nmr-spectroscopy, tmp-zincate, sodium",
author = "Garden, {Jennifer A.} and Alan Kennedy and Robert Mulvey and Stuart Robertson",
year = "2011",
doi = "10.1039/c1dt11430a",
language = "English",
volume = "40",
pages = "11945--11954",
journal = "Dalton Transactions",
issn = "1477-9226",
number = "44",

}

TY - JOUR

T1 - Neutral zinc, lower-order zincate and higher-order zincate derivatives of pyrrole: synthesis and structural characterisation of zinc complexes with one, two, three or four pyrrolyl ligands

AU - Garden, Jennifer A.

AU - Kennedy, Alan

AU - Mulvey, Robert

AU - Robertson, Stuart

PY - 2011

Y1 - 2011

N2 - Towards a systematic development of the zinc chemistry of the important five-membered nitrogen heterocycle pyrrole, this work reports the synthesis and characterisation of five crystalline zinc-pyrrolyl complexes. Pyrrolyl in this context means where conversion of the N-H bond to an N-zinc bond has occurred. Two neutral complexes, [(BuZn)-Bu-t(NC4H4)(TMEDA)center dot HNC4H4] 1 and [Zn(NC4H4)(2)(TMEDA)] 2, containing one and two pyrrolyl ligands, respectively, were synthesised by reacting di-t-butylzinc with different amounts of pyrrole in the presence of TMEDA (TMEDA is N,N,N',N'-tetramethylethylenediamine). X-ray crystallographic studies established that both adopt mononuclear structures with the salient feature of the former the presence of an additional parent protonated pyrrole molecule which engages its anionic counterpart in N-H center dot center dot center dot pi C-C interactions. Employing a similar synthetic approach but adding n-butylsodium to the reaction mixture in attempts to form ate derivatives delivered three distinct sodium zincate (anionic zinc) compounds in [{(THF)(2)center dot NaZn(THF)(NC4H4)(3)}(infinity)] 3, [{(TMEDA)center dot Na}(2)Zn(NC4H4)(4)] 4, and [{(PMDETA)center dot Na}(2)Zn(NC4H4)(4)] 5 (PMDETA is N, N, N', N '', N ''-pentamethyldiethylenetriamine). From their crystal structures, the 1 : 1, Na: Zn complex 3 can be classified as a lower-order zincate having three pyrrolyl ligands bound to zinc in a polymeric chain arrangement, while the 2 : 1, Na:Zn complexes 4 and 5 are molecular higher-order zincates having Zn centres fully saturated by four pyrrolyl ligands. Discussion of the structures of 1-5 focuses on the interplay of sigma-bonding and pi-bonding between the pyrrolyl ligands and the metal centres. Revealingly, the zinc-free sodiopyrrole complex [{(PMDETA)center dot Na(NC4H4)}(2)] 6, made and characterised for comparison, shows that on its own sodium prefers the former type of bonding, but is forced to switch to the latter type when combined with the stronger Lewis acid zinc in the zincate compositions. Complexes 1-6 have also been characterised in solution by NMR spectroscopy.

AB - Towards a systematic development of the zinc chemistry of the important five-membered nitrogen heterocycle pyrrole, this work reports the synthesis and characterisation of five crystalline zinc-pyrrolyl complexes. Pyrrolyl in this context means where conversion of the N-H bond to an N-zinc bond has occurred. Two neutral complexes, [(BuZn)-Bu-t(NC4H4)(TMEDA)center dot HNC4H4] 1 and [Zn(NC4H4)(2)(TMEDA)] 2, containing one and two pyrrolyl ligands, respectively, were synthesised by reacting di-t-butylzinc with different amounts of pyrrole in the presence of TMEDA (TMEDA is N,N,N',N'-tetramethylethylenediamine). X-ray crystallographic studies established that both adopt mononuclear structures with the salient feature of the former the presence of an additional parent protonated pyrrole molecule which engages its anionic counterpart in N-H center dot center dot center dot pi C-C interactions. Employing a similar synthetic approach but adding n-butylsodium to the reaction mixture in attempts to form ate derivatives delivered three distinct sodium zincate (anionic zinc) compounds in [{(THF)(2)center dot NaZn(THF)(NC4H4)(3)}(infinity)] 3, [{(TMEDA)center dot Na}(2)Zn(NC4H4)(4)] 4, and [{(PMDETA)center dot Na}(2)Zn(NC4H4)(4)] 5 (PMDETA is N, N, N', N '', N ''-pentamethyldiethylenetriamine). From their crystal structures, the 1 : 1, Na: Zn complex 3 can be classified as a lower-order zincate having three pyrrolyl ligands bound to zinc in a polymeric chain arrangement, while the 2 : 1, Na:Zn complexes 4 and 5 are molecular higher-order zincates having Zn centres fully saturated by four pyrrolyl ligands. Discussion of the structures of 1-5 focuses on the interplay of sigma-bonding and pi-bonding between the pyrrolyl ligands and the metal centres. Revealingly, the zinc-free sodiopyrrole complex [{(PMDETA)center dot Na(NC4H4)}(2)] 6, made and characterised for comparison, shows that on its own sodium prefers the former type of bonding, but is forced to switch to the latter type when combined with the stronger Lewis acid zinc in the zincate compositions. Complexes 1-6 have also been characterised in solution by NMR spectroscopy.

KW - directed ortho metalation

KW - mixed lithium-zinc

KW - x-ray

KW - deprotonative metalation

KW - mediated zincation

KW - crystal structures

KW - functionalized aromatics

KW - nmr-spectroscopy

KW - tmp-zincate

KW - sodium

UR - http://www.scopus.com/inward/record.url?scp=80755175193&partnerID=8YFLogxK

U2 - 10.1039/c1dt11430a

DO - 10.1039/c1dt11430a

M3 - Article

VL - 40

SP - 11945

EP - 11954

JO - Dalton Transactions

T2 - Dalton Transactions

JF - Dalton Transactions

SN - 1477-9226

IS - 44

ER -