Structural Studies of the Chiral Lithium Amides [{PhC(H)Me}2NLi] and [PhCH2{PhC(H)Me}NLi.THF Derived from a-Methybenzylamine

D.R. Armstrong, K.W. Henderson, A.R. Kennedy, W.J. Kerr, F.S. Mair, J.H. Moir, P.H. Moran, R. Snaith

Research output: Contribution to journalArticle

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Abstract

Reaction of (R,R)- or (S,S)-bis(1-phenylethyl)amine with nBuLi in hexane solution gave the chiral amide [{PhC(H)Me}2NLi] 1. Complex 1 crystallises with approximate D3 symmetry as a ring trimer (13) from hexane solution, as determined by X-ray crystallography. In direct contrast to the crystal structure of the related compound dibenzylamidolithium, [{(PhCH2)2NLi}3], no significant agostic Li· · ·C(H) contacts are present in 13. Solution 1H and 7Li NMR spectra of 1 in d8-toluene show the presence of two distinct aggregated species which have been assigned as a trimer and a monomer. The complex [PhCH2{PhC(H)Me}NLi·THF] 2·THF, was prepared by reaction of nBuLi with (R)-N-benzyl--methylbenzylamine in a hexane-THF solution and has been determined by X-ray crystallography to adopt a dimeric structure (22·2THF) in the solid state with C1 symmetry. As in 13, no short Li· · ·C(H) contacts are present in 22·2THF. The lack of Li· · ·C(H) interactions in both 13 and 22·2THF suggests that the rotameric conformations adopted for the benzyl groups in the complexes are governed mainly by steric effects. Using ab initio molecular orbital calculations (HF/6-31G*), the minimum energy structure for unsolvated monomeric 11 was determined to be a C2 symmetric molecule, I, where the faces of both phenyl groups are directed towards the metal, maximising the Li-aromatic interactions. The related C2 symmetric molecule with both methyl groups directed towards the metal is 8.68 kcal mol-1 less stable than I. Therefore, in the absence of aggregation and external solvation, significant stabilisation is achieved through Li· · ·C(H) benzyl interactions. The energy barrier to rotation for one benzyl sidearm for geometry I is 4.76 kcal mol-1, representing a significant lifetime for this conformer.
LanguageEnglish
Pages4063-4068
Number of pages5
JournalJournal of the Chemical Society, Dalton Transactions
Volume1999
Issue number22
DOIs
Publication statusPublished - Oct 1999

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Lithium
Amides
Hexanes
X ray crystallography
Metals
Orbital calculations
Molecules
Energy barriers
Solvation
Toluene
Molecular orbitals
Contacts (fluid mechanics)
Amines
Conformations
Agglomeration
Stabilization
Monomers
Crystal structure
Nuclear magnetic resonance
Geometry

Keywords

  • hexane
  • chiral amide
  • crystal structure
  • dibenzylamidolithium

Cite this

Armstrong, D.R. ; Henderson, K.W. ; Kennedy, A.R. ; Kerr, W.J. ; Mair, F.S. ; Moir, J.H. ; Moran, P.H. ; Snaith, R. / Structural Studies of the Chiral Lithium Amides [{PhC(H)Me}2NLi] and [PhCH2{PhC(H)Me}NLi.THF Derived from a-Methybenzylamine. In: Journal of the Chemical Society, Dalton Transactions. 1999 ; Vol. 1999, No. 22. pp. 4063-4068.
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title = "Structural Studies of the Chiral Lithium Amides [{PhC(H)Me}2NLi] and [PhCH2{PhC(H)Me}NLi.THF Derived from a-Methybenzylamine",
abstract = "Reaction of (R,R)- or (S,S)-bis(1-phenylethyl)amine with nBuLi in hexane solution gave the chiral amide [{PhC(H)Me}2NLi] 1. Complex 1 crystallises with approximate D3 symmetry as a ring trimer (13) from hexane solution, as determined by X-ray crystallography. In direct contrast to the crystal structure of the related compound dibenzylamidolithium, [{(PhCH2)2NLi}3], no significant agostic Li· · ·C(H) contacts are present in 13. Solution 1H and 7Li NMR spectra of 1 in d8-toluene show the presence of two distinct aggregated species which have been assigned as a trimer and a monomer. The complex [PhCH2{PhC(H)Me}NLi·THF] 2·THF, was prepared by reaction of nBuLi with (R)-N-benzyl--methylbenzylamine in a hexane-THF solution and has been determined by X-ray crystallography to adopt a dimeric structure (22·2THF) in the solid state with C1 symmetry. As in 13, no short Li· · ·C(H) contacts are present in 22·2THF. The lack of Li· · ·C(H) interactions in both 13 and 22·2THF suggests that the rotameric conformations adopted for the benzyl groups in the complexes are governed mainly by steric effects. Using ab initio molecular orbital calculations (HF/6-31G*), the minimum energy structure for unsolvated monomeric 11 was determined to be a C2 symmetric molecule, I, where the faces of both phenyl groups are directed towards the metal, maximising the Li-aromatic interactions. The related C2 symmetric molecule with both methyl groups directed towards the metal is 8.68 kcal mol-1 less stable than I. Therefore, in the absence of aggregation and external solvation, significant stabilisation is achieved through Li· · ·C(H) benzyl interactions. The energy barrier to rotation for one benzyl sidearm for geometry I is 4.76 kcal mol-1, representing a significant lifetime for this conformer.",
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Structural Studies of the Chiral Lithium Amides [{PhC(H)Me}2NLi] and [PhCH2{PhC(H)Me}NLi.THF Derived from a-Methybenzylamine. / Armstrong, D.R.; Henderson, K.W.; Kennedy, A.R.; Kerr, W.J.; Mair, F.S.; Moir, J.H.; Moran, P.H.; Snaith, R.

In: Journal of the Chemical Society, Dalton Transactions, Vol. 1999, No. 22, 10.1999, p. 4063-4068.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Structural Studies of the Chiral Lithium Amides [{PhC(H)Me}2NLi] and [PhCH2{PhC(H)Me}NLi.THF Derived from a-Methybenzylamine

AU - Armstrong, D.R.

AU - Henderson, K.W.

AU - Kennedy, A.R.

AU - Kerr, W.J.

AU - Mair, F.S.

AU - Moir, J.H.

AU - Moran, P.H.

AU - Snaith, R.

PY - 1999/10

Y1 - 1999/10

N2 - Reaction of (R,R)- or (S,S)-bis(1-phenylethyl)amine with nBuLi in hexane solution gave the chiral amide [{PhC(H)Me}2NLi] 1. Complex 1 crystallises with approximate D3 symmetry as a ring trimer (13) from hexane solution, as determined by X-ray crystallography. In direct contrast to the crystal structure of the related compound dibenzylamidolithium, [{(PhCH2)2NLi}3], no significant agostic Li· · ·C(H) contacts are present in 13. Solution 1H and 7Li NMR spectra of 1 in d8-toluene show the presence of two distinct aggregated species which have been assigned as a trimer and a monomer. The complex [PhCH2{PhC(H)Me}NLi·THF] 2·THF, was prepared by reaction of nBuLi with (R)-N-benzyl--methylbenzylamine in a hexane-THF solution and has been determined by X-ray crystallography to adopt a dimeric structure (22·2THF) in the solid state with C1 symmetry. As in 13, no short Li· · ·C(H) contacts are present in 22·2THF. The lack of Li· · ·C(H) interactions in both 13 and 22·2THF suggests that the rotameric conformations adopted for the benzyl groups in the complexes are governed mainly by steric effects. Using ab initio molecular orbital calculations (HF/6-31G*), the minimum energy structure for unsolvated monomeric 11 was determined to be a C2 symmetric molecule, I, where the faces of both phenyl groups are directed towards the metal, maximising the Li-aromatic interactions. The related C2 symmetric molecule with both methyl groups directed towards the metal is 8.68 kcal mol-1 less stable than I. Therefore, in the absence of aggregation and external solvation, significant stabilisation is achieved through Li· · ·C(H) benzyl interactions. The energy barrier to rotation for one benzyl sidearm for geometry I is 4.76 kcal mol-1, representing a significant lifetime for this conformer.

AB - Reaction of (R,R)- or (S,S)-bis(1-phenylethyl)amine with nBuLi in hexane solution gave the chiral amide [{PhC(H)Me}2NLi] 1. Complex 1 crystallises with approximate D3 symmetry as a ring trimer (13) from hexane solution, as determined by X-ray crystallography. In direct contrast to the crystal structure of the related compound dibenzylamidolithium, [{(PhCH2)2NLi}3], no significant agostic Li· · ·C(H) contacts are present in 13. Solution 1H and 7Li NMR spectra of 1 in d8-toluene show the presence of two distinct aggregated species which have been assigned as a trimer and a monomer. The complex [PhCH2{PhC(H)Me}NLi·THF] 2·THF, was prepared by reaction of nBuLi with (R)-N-benzyl--methylbenzylamine in a hexane-THF solution and has been determined by X-ray crystallography to adopt a dimeric structure (22·2THF) in the solid state with C1 symmetry. As in 13, no short Li· · ·C(H) contacts are present in 22·2THF. The lack of Li· · ·C(H) interactions in both 13 and 22·2THF suggests that the rotameric conformations adopted for the benzyl groups in the complexes are governed mainly by steric effects. Using ab initio molecular orbital calculations (HF/6-31G*), the minimum energy structure for unsolvated monomeric 11 was determined to be a C2 symmetric molecule, I, where the faces of both phenyl groups are directed towards the metal, maximising the Li-aromatic interactions. The related C2 symmetric molecule with both methyl groups directed towards the metal is 8.68 kcal mol-1 less stable than I. Therefore, in the absence of aggregation and external solvation, significant stabilisation is achieved through Li· · ·C(H) benzyl interactions. The energy barrier to rotation for one benzyl sidearm for geometry I is 4.76 kcal mol-1, representing a significant lifetime for this conformer.

KW - hexane

KW - chiral amide

KW - crystal structure

KW - dibenzylamidolithium

UR - http://dx.doi.org/10.1039/a904725e

U2 - 10.1039/a904725e

DO - 10.1039/a904725e

M3 - Article

VL - 1999

SP - 4063

EP - 4068

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

IS - 22

ER -