Structure and reactivity of lithium diphenylamide.  Role of aggregates, mixed aggregates, monomers, and free ions on the rates and selectivities of N-alkylation and E2 elimination

DePue, Jeffrey S.; Collum, David B.

doi:10.1021/ja00224a042

Cited by 83 publications

(51 citation statements)

References 4 publications

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“…The linear and slightly inverse THF concentration dependence observed for k sulf is consistent with secondary shell (medium) effects accompanying the increasing THF concentration 6b,12 Figures 10. and 11 illustrate the dependence of k alk and k sulf on the Et 2 NLi concentration (0.03–0.40 M) in 6.0 M THF.…”

Section: Resultssupporting

confidence: 62%

“…Plots of k obsd versus THF concentration (Figure 6) and k obsd versus Et 2 NLi concentration (Figure 7) furnish orders of 2.0 ± 0.1 and 0.54 ± 0.03, respectively. Replacing toluene cosolvent with 2,2,4,4-tetramethyltetrahydrofuran revealed no measurable cosolvent dependence, arguing against long-range medium effects as the source of second-order THF dependence 6b,12…”

Section: Resultsmentioning

confidence: 95%

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Reaction of Lithium Diethylamide with an Alkyl Bromide and Alkyl Benzenesulfonate: Origins of Alkylation, Elimination, and Sulfonation

2010

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A combination of NMR, kinetic, and computational methods are used to examine reactions of lithium diethylamide in tetrahydrofuran (THF) with n-dodecyl bromide and n-octyl benzenesulfonate. The alkyl bromide undergoes competitive S N 2 substitution and E2 elimination in proportions independent of all concentrations except for a minor medium effect. Rate studies show that both reactions occur via trisolvated-monomer-based transition structures. The alkyl benzenesulfonate undergoes competitive S N 2 substitution (minor) and N-sulfonation (major) with N-sulfonation promoted at low THF concentrations. The S N 2 substitution is shown to proceed via a disolvated monomer suggested computationally to involve a cyclic transition structure. The dominant N-sulfonation follows a disolvated-dimer-based transition structure suggested computationally to be a bicyclo[3.1.1] form. The differing THF and lithium diethylamide orders for the two reactions explain the observed concentration-dependent chemoselectivities.

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Section: Resultssupporting

confidence: 62%

Section: Resultsmentioning

confidence: 95%

Reaction of Lithium Diethylamide with an Alkyl Bromide and Alkyl Benzenesulfonate: Origins of Alkylation, Elimination, and Sulfonation

2010

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“…The solution structure of LiNPh 2 in thf (in the presence/absence of LiBr) has been comprehensively studied by Collum. [32,33] In the solid state, the majority of the complexes reported to date, take the form of solventseparated alkali metal ate species, whereby the second metal is a transition metal, [34][35][36][37][38] lanthanide, [39][40][41][42][43][44][45] actinide, [46] or a group 13 element. [47,48] Contacted ate complexes are also prevalent, predominantly with the heavier alkali metals (sodium and potassium) due to their need for further stabilisation by metal-arene π-interactions.…”

Section: Introductionmentioning

confidence: 99%

Structural Elucidation of tmeda‐Solvated Alkali Metal Diphenylamide Complexes

et al. 2009

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Lithium, sodium and potassium salts of diphenylamine have been prepared by using a deprotonative route and characterised in both, solid state (by X‐ray crystallography) and solution (by NMR spectroscopic studies). In each case the metal atom's coordination sphere is completed by coordination to the synthetically important co‐ligand N,N,N′,N′‐tetramethylethylenediamine (tmeda). Complexes 1 and 2 [{(tmeda)M(NPh2)}2] (M = Li for 1, Na for 2) can be prepared by treating 1 mol.‐equiv. of the parent amine with an equimolar quantity of nBuM and tmeda in hexane solution. In the solid state, 1 and 2 are essentially isostructural, being dimeric with a four‐atom M–N–M–N framework. The coordination sphere of each M atom is completed by a bidentate tmeda molecule. Complex 3 [{(tmeda)3/2K(NPh2)}2] has been prepared in a similar way to 1 and 2 except that benzylpotassium has been utilised as the metallating agent. In addition, 4 mol‐equiv. of tmeda is required to fully solubilise the heavy alkali metal amide mixture. In the solid state, 3 exists as a polymeric array of dinuclear K–N–K–N rings. Akin to 1 and 2, the K atom is coordinated to a bidentate tmeda molecule; however, each K atom is also bound to another tmeda molecule that acts as a monodentate bridge, thus producing the coordination polymer. Crystalline 1 and 2 are soluble in C6D6; hence, NMR spectroscopic studies could be performed. These show that the solid‐state structure appears to stay intact in arene solution. On the other hand, 3 is not soluble in C6D6; so solution studies have been performed in [D8]thf. These studies reveal that 3 readily looses tmeda during in‐vacuo isolation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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“…We observed a seventh -order dependence for Ph 2 NLi alkylations in 1988 consistent with a decasolvated cation, + Li(THF) 10 . 32 In that instance, we invoked secondary-shell effects stemming from the requisite ionization of a solvent-separated ion pair. Conductivity studies show that full ionization of the LiClO 4 separated ion pair is significantly endothermic, 40 presumably requiring considerable secondary-shell solvation (eq 13).…”

Section: Discussionmentioning

confidence: 99%

Lithium Hexamethyldisilazide-Mediated Enolization of Acylated Oxazolidinones: Solvent, Cosolvent, and Isotope Effects on Competing Monomer- and Dimer-Based Pathways

2017

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Lithium hexamethyldisilazide (LiHMDS)-mediated enolization of (+)-4-benzyl-3-propionyl-2-oxazolidinone in THF–hydrocarbon mixtures shows unusual sensitivity to the choice of hydrocarbon cosolvent (hexane versus toluene) and to isotopic labeling. Four mechanisms corresponding to monosolvated monomers, trisolvated dimers, octasolvated monomers, and octasolvated dimers were identified. Even under conditions in which the LiHMDS monomer was the dominant observable form, dimer-based metalation was significant. The mechanism-dependent isotope and cosolvent effects are discussed in the context of ground state stabilization and transition-state tunneling.

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Structure and reactivity of lithium diphenylamide. Role of aggregates, mixed aggregates, monomers, and free ions on the rates and selectivities of N-alkylation and E2 elimination

Cited by 83 publications

References 4 publications

Reaction of Lithium Diethylamide with an Alkyl Bromide and Alkyl Benzenesulfonate: Origins of Alkylation, Elimination, and Sulfonation

Reaction of Lithium Diethylamide with an Alkyl Bromide and Alkyl Benzenesulfonate: Origins of Alkylation, Elimination, and Sulfonation

Structural Elucidation of tmeda‐Solvated Alkali Metal Diphenylamide Complexes

Lithium Hexamethyldisilazide-Mediated Enolization of Acylated Oxazolidinones: Solvent, Cosolvent, and Isotope Effects on Competing Monomer- and Dimer-Based Pathways

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