A nuclear magnetic resonance spectroscopic technique for the characterization of lithium ion pair structures in THF and THF/HMPA solution

Reich, Hans J.; Borst, Joseph P.; Dykstra, Robert R.; Green, Patrick D.

doi:10.1021/ja00072a028

Cited by 128 publications

(71 citation statements)

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“…Previous studies showed LiCl to be dimeric in THF solution 26,27. Mixtures of LDA with very low LiCl concentrations used in the rate studies described below (≤2 mol % LiCl) afford a LiCl-concentration-independent 1:8 mixture of 6 and 7 to the exclusion of free LiCl 27,28…”

Section: Resultsmentioning

confidence: 94%

1,4-Addition of Lithium Diisopropylamide to Unsaturated Esters: Role of Rate-Limiting Deaggregation, Autocatalysis, Lithium Chloride Catalysis, and Other Mixed Aggregation Effects

Hoepker

Gupta

et al. 2010

J. Am. Chem. Soc.

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Lithium diisopropylamide (LDA) in tetrahydrofuran at −78 °C undergoes 1,4-addition to an unsaturated ester via a rate-limiting deaggregation of LDA dimer followed by a post-rate-limiting reaction with the substrate. Muted autocatalysis is traced to a lithium enolate-mediated deaggregation of the LDA dimer and the intervention of LDA-lithium enolate mixed aggregates displaying higher reactivities than LDA. Striking accelerations are elicited by <1.0 mol % LiCl. Rate and mechanistic studies reveal that the uncatalyzed and catalyzed pathways funnel through a common monosolvated-monomer-based intermediate. Four distinct classes of mixed aggregation effects are discussed.

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Section: Resultsmentioning

confidence: 94%

1,4-Addition of Lithium Diisopropylamide to Unsaturated Esters: Role of Rate-Limiting Deaggregation, Autocatalysis, Lithium Chloride Catalysis, and Other Mixed Aggregation Effects

Hoepker

Gupta

et al. 2010

J. Am. Chem. Soc.

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“…Downloaded by [Northeastern University] at 03:47 08 January 2015 It is worth to mention that no P,Li coupling was observed in the 31 P NMR spectra of the studied complexes 1 and 2. The quartet line patterns reported by Reich et al 18 …”

Section: P Nmr Spectramentioning

confidence: 83%

Evidences for Chelating Complexes of Lithium with Phenylphosphinic and Phenylphosphonic Acids: A Spectroscopic and DFT Study

Sunjuk

El‐Eswed

Dawoud

et al. 2014

Phosphorus, Sulfur, and Silicon and the Related Elements

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Lithium complexes were prepared with phenylphosphinic and phenylphosphonic acids. The complexes were studied in the solid state using Fourier transform infrared spectroscopy spectroscopy and in solution (methanol) using 1 H, 13 C, and 31 P Nuclear magnetic resonance spectroscopy (NMR) spectroscopy; the most preferred structures of the complexes were determined by density functional theory (DFT) computational method. Although methanol has a strong solvation effect on lithium ions and ligands, which causes dissociation of the complexes, significant changes of the NMR spectra of the complexes (relative to those of the free ligands) were observed. The new spectroscopic results indicate the presence of the phenylphosphinic acid tautomer (I: C 6 H 5 PH( O)OH) rather than that of phenyl-phosphorous acid (II: C 6 H 5 P(OH) 2 ) in deuterated methanol showing PH/PD exchange. On the other hand, tautomer I predominates in the complex with lithium without showing PH/PD exchange. The DFT PREPARATION OF LITHIUM COMPLEXES WITH PHENYLPHOSPHINIC 559calculations predict that tautomer I is the preferred structure in the case of free ligand and lithium complex. The absence of a PH/PD exchange in the complex is due to the formation of a chelating complex, rather than of a simple salt between lithium ion and the two oxygen atoms of I, which prevent tautomerization of I into II. DFT calculations support the formation of lithium chelating complexes. The lithium ion was found to affect the spectroscopic properties of phenylphosphinic acid more dramatically than those of phenylphosphonic acid.

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“…The discovery of a 2 J coupling between the phosphorus atom of hexamethylphosphoric triamide (HMPTA) and coordinated 7 Li 109,110 has been used in an interesting NMR technique for the characterization of lithium ion pair structures. 68 …”

Section: Homonuclear Couplingmentioning

confidence: 99%

Lithium NMR

G��nther

2007

Encyclopedia of Magnetic Resonance

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A nuclear magnetic resonance spectroscopic technique for the characterization of lithium ion pair structures in THF and THF/HMPA solution

Cited by 128 publications

References 0 publications

1,4-Addition of Lithium Diisopropylamide to Unsaturated Esters: Role of Rate-Limiting Deaggregation, Autocatalysis, Lithium Chloride Catalysis, and Other Mixed Aggregation Effects

1,4-Addition of Lithium Diisopropylamide to Unsaturated Esters: Role of Rate-Limiting Deaggregation, Autocatalysis, Lithium Chloride Catalysis, and Other Mixed Aggregation Effects

Evidences for Chelating Complexes of Lithium with Phenylphosphinic and Phenylphosphonic Acids: A Spectroscopic and DFT Study

Lithium NMR

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