Structural chemistry of monodentate donor-solvated mixed lithium-magnesium secondary amide complexes

G.C. Forbes, A.R. Kennedy, R.E. Mulvey, P.J.A. Rodger, R.B. Rowlings

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

The monodentate donor-solvated intermetallic lithium-magnesium amide complexes [Mg(HMDS)(3)Li . (THF)] 1 [HMDS=N(SiMe3)(2)], [Mg(HMDS)(3)Li . (Pyr)] 2 and [Mg{N(Cy)(2)}(3)Li . (THF)] 3 [N(Cy)(2)=dicyclohexylamide] have been prepared and characterised by NMR spectroscopy and X-ray crystallography. Synthesis was achieved by the reaction of equimolar amounts of n-BuLi and n,sec-Bu2Mg with three equivalents of the appropriate amine in hexane/donor solution. The molecular structures of 1, 2 and 3 are essentially isostructural containing a central, planar LiNMgN four-membered ring: two amide units bridge to the metal centres whilst the third binds exclusively to magnesium in the terminal position to complete a three-coordinate distorted trigonal planar geometry. The lithium achieves a similar geometry with solvation from a single monodentate donor molecule. Three co-crystalline by-products were also isolated from solution and are included for completeness: [Mg(HMDS)(2)(Bu)Li . Pyr] 4, [(LiHMDS . Pyr)(2)] 5 and [Mg(HMDS)(2). (Pyr)(2)] 6. Complex 4 exhibits a similar structure to 1, 2 and 3 with an alkyl group (consisting of disordered n- and sec-butyl groups) replacing the terminal amido functionality. Complex 4 is produced by a similar method to 2 via incomplete amination in the presence of two equivalents of hexamethyldisilazane (HMDS(H)). In contrast, 5 and 6 are simple homometallic amides formed when an excess of pyridine is introduced into the reaction system. To conclude the study a series of reactions were undertaken in which the stoichiometry of both amine and donor was altered systematically. The results from this study imply that intermetallic aggregation is hindered by the presence of excess donor solvent.
LanguageEnglish
Pages1477-1484
Number of pages7
JournalJournal of the Chemical Society, Dalton Transactions
Volume2001
Issue number9
DOIs
Publication statusPublished - 2001

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Lithium
Amides
Magnesium
Intermetallics
Amines
Amination
Geometry
X ray crystallography
Solvation
Hexanes
Stoichiometry
Molecular structure
Nuclear magnetic resonance spectroscopy
Byproducts
Agglomeration
Metals
Crystalline materials
Molecules

Keywords

  • crown ether complexes
  • crystal structures
  • macrocyclic amide
  • metal amides
  • hexamathyldislazide
  • benzonitrile
  • reactivity
  • prydine

Cite this

@article{3f616059d96342f9b99998aadb0cddd4,
title = "Structural chemistry of monodentate donor-solvated mixed lithium-magnesium secondary amide complexes",
abstract = "The monodentate donor-solvated intermetallic lithium-magnesium amide complexes [Mg(HMDS)(3)Li . (THF)] 1 [HMDS=N(SiMe3)(2)], [Mg(HMDS)(3)Li . (Pyr)] 2 and [Mg{N(Cy)(2)}(3)Li . (THF)] 3 [N(Cy)(2)=dicyclohexylamide] have been prepared and characterised by NMR spectroscopy and X-ray crystallography. Synthesis was achieved by the reaction of equimolar amounts of n-BuLi and n,sec-Bu2Mg with three equivalents of the appropriate amine in hexane/donor solution. The molecular structures of 1, 2 and 3 are essentially isostructural containing a central, planar LiNMgN four-membered ring: two amide units bridge to the metal centres whilst the third binds exclusively to magnesium in the terminal position to complete a three-coordinate distorted trigonal planar geometry. The lithium achieves a similar geometry with solvation from a single monodentate donor molecule. Three co-crystalline by-products were also isolated from solution and are included for completeness: [Mg(HMDS)(2)(Bu)Li . Pyr] 4, [(LiHMDS . Pyr)(2)] 5 and [Mg(HMDS)(2). (Pyr)(2)] 6. Complex 4 exhibits a similar structure to 1, 2 and 3 with an alkyl group (consisting of disordered n- and sec-butyl groups) replacing the terminal amido functionality. Complex 4 is produced by a similar method to 2 via incomplete amination in the presence of two equivalents of hexamethyldisilazane (HMDS(H)). In contrast, 5 and 6 are simple homometallic amides formed when an excess of pyridine is introduced into the reaction system. To conclude the study a series of reactions were undertaken in which the stoichiometry of both amine and donor was altered systematically. The results from this study imply that intermetallic aggregation is hindered by the presence of excess donor solvent.",
keywords = "crown ether complexes, crystal structures, macrocyclic amide, metal amides, hexamathyldislazide, benzonitrile, reactivity, prydine",
author = "G.C. Forbes and A.R. Kennedy and R.E. Mulvey and P.J.A. Rodger and R.B. Rowlings",
year = "2001",
doi = "10.1039/b100052g",
language = "English",
volume = "2001",
pages = "1477--1484",
journal = "Journal of the Chemical Society, Dalton Transactions",
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Structural chemistry of monodentate donor-solvated mixed lithium-magnesium secondary amide complexes. / Forbes, G.C.; Kennedy, A.R.; Mulvey, R.E.; Rodger, P.J.A.; Rowlings, R.B.

In: Journal of the Chemical Society, Dalton Transactions, Vol. 2001, No. 9, 2001, p. 1477-1484.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Structural chemistry of monodentate donor-solvated mixed lithium-magnesium secondary amide complexes

AU - Forbes, G.C.

AU - Kennedy, A.R.

AU - Mulvey, R.E.

AU - Rodger, P.J.A.

AU - Rowlings, R.B.

PY - 2001

Y1 - 2001

N2 - The monodentate donor-solvated intermetallic lithium-magnesium amide complexes [Mg(HMDS)(3)Li . (THF)] 1 [HMDS=N(SiMe3)(2)], [Mg(HMDS)(3)Li . (Pyr)] 2 and [Mg{N(Cy)(2)}(3)Li . (THF)] 3 [N(Cy)(2)=dicyclohexylamide] have been prepared and characterised by NMR spectroscopy and X-ray crystallography. Synthesis was achieved by the reaction of equimolar amounts of n-BuLi and n,sec-Bu2Mg with three equivalents of the appropriate amine in hexane/donor solution. The molecular structures of 1, 2 and 3 are essentially isostructural containing a central, planar LiNMgN four-membered ring: two amide units bridge to the metal centres whilst the third binds exclusively to magnesium in the terminal position to complete a three-coordinate distorted trigonal planar geometry. The lithium achieves a similar geometry with solvation from a single monodentate donor molecule. Three co-crystalline by-products were also isolated from solution and are included for completeness: [Mg(HMDS)(2)(Bu)Li . Pyr] 4, [(LiHMDS . Pyr)(2)] 5 and [Mg(HMDS)(2). (Pyr)(2)] 6. Complex 4 exhibits a similar structure to 1, 2 and 3 with an alkyl group (consisting of disordered n- and sec-butyl groups) replacing the terminal amido functionality. Complex 4 is produced by a similar method to 2 via incomplete amination in the presence of two equivalents of hexamethyldisilazane (HMDS(H)). In contrast, 5 and 6 are simple homometallic amides formed when an excess of pyridine is introduced into the reaction system. To conclude the study a series of reactions were undertaken in which the stoichiometry of both amine and donor was altered systematically. The results from this study imply that intermetallic aggregation is hindered by the presence of excess donor solvent.

AB - The monodentate donor-solvated intermetallic lithium-magnesium amide complexes [Mg(HMDS)(3)Li . (THF)] 1 [HMDS=N(SiMe3)(2)], [Mg(HMDS)(3)Li . (Pyr)] 2 and [Mg{N(Cy)(2)}(3)Li . (THF)] 3 [N(Cy)(2)=dicyclohexylamide] have been prepared and characterised by NMR spectroscopy and X-ray crystallography. Synthesis was achieved by the reaction of equimolar amounts of n-BuLi and n,sec-Bu2Mg with three equivalents of the appropriate amine in hexane/donor solution. The molecular structures of 1, 2 and 3 are essentially isostructural containing a central, planar LiNMgN four-membered ring: two amide units bridge to the metal centres whilst the third binds exclusively to magnesium in the terminal position to complete a three-coordinate distorted trigonal planar geometry. The lithium achieves a similar geometry with solvation from a single monodentate donor molecule. Three co-crystalline by-products were also isolated from solution and are included for completeness: [Mg(HMDS)(2)(Bu)Li . Pyr] 4, [(LiHMDS . Pyr)(2)] 5 and [Mg(HMDS)(2). (Pyr)(2)] 6. Complex 4 exhibits a similar structure to 1, 2 and 3 with an alkyl group (consisting of disordered n- and sec-butyl groups) replacing the terminal amido functionality. Complex 4 is produced by a similar method to 2 via incomplete amination in the presence of two equivalents of hexamethyldisilazane (HMDS(H)). In contrast, 5 and 6 are simple homometallic amides formed when an excess of pyridine is introduced into the reaction system. To conclude the study a series of reactions were undertaken in which the stoichiometry of both amine and donor was altered systematically. The results from this study imply that intermetallic aggregation is hindered by the presence of excess donor solvent.

KW - crown ether complexes

KW - crystal structures

KW - macrocyclic amide

KW - metal amides

KW - hexamathyldislazide

KW - benzonitrile

KW - reactivity

KW - prydine

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DO - 10.1039/b100052g

M3 - Article

VL - 2001

SP - 1477

EP - 1484

JO - Journal of the Chemical Society, Dalton Transactions

T2 - Journal of the Chemical Society, Dalton Transactions

JF - Journal of the Chemical Society, Dalton Transactions

SN - 0300-9246

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