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Various NMR techniques were used to study a chiral lithium amide and n-BuLi in tol-[d.sub.8] solution system. The results provide insight into the critical role of Li-amide/n-BuLi complex in the asymmetric addition of n-BuLi to aldehydes.

We report the direct measurement of ligand-binding constants of organolithium complexes using a ¹H NMR/diffusion-ordered NMR spectroscopy (DOSY) titration technique. Lithium hexamethyldisilazide complexes with ethereal and ester donor ligands (THF, diethyl ether, MTBE, THP, tert-butyl acetate) are characterized using ¹H NMR and X-ray crystallography. Their aggregation and solvation states are confirmed using diffusion coefficient-formula weight correlation analysis, and the ¹H NMR/DOSY titration technique is applied to obtain their binding constants. Our work suggests that steric hindrance of ethereal ligands plays an important role in the aggregation, solvation, and reactivity of these complexes. It is noteworthy that diffusion methodology is utilized to obtain binding constants. [ABSTRACT FROM AUTHOR]

We report on the generation of a perfluoroalkyl Grignard reagent (FRMgX) by exchange reaction between a perfluoroalkyl iodide (FR-I) and a Grignard reagent (RMgX). 19F NMR was applied to monitor the generation of n-C3F7MgCl. Additional NMR techniques, including 19F COSY, NOESY, and pulsed gradient spin-echo (PGSE) diffusion NMR, were invoked to assign peaks observed in 19F spectrum. Schlenk equilibrium was observed and was significantly influenced by solvent, diethyl ether, or THF. [ABSTRACT FROM AUTHOR]

We report extension of the D-FW analysis using referenced ²H DOSY. This technique was developed in response to limitations due to peak overlay in ¹H DOSY spectra. We find a corresponding linear relationship (R² > 0.99) between log D and log FW as the basis of the D-FW analysis. The solution-state structure of THF solvated lithium diisopropyl amide (LDA) in hydrocarbon solvent was chosen to demonstrate the reliability of the methodology. We observe an equilibrium between monosolvated and disolvated dimeric LDA complexes at room temperature. Additionally we demonstrate the application of the ²H D-FW analysis using a compound with an exchangeable proton that is readily labeled with ²H. Hence, the ²H DOSY D-FW analysis is shown to provide results consistent with the ¹H DOSY method, thereby greatly extending the applicability of the D-FW analysis. [ABSTRACT FROM AUTHOR]

We report the development of isotopic-labeled 13C diffusion-ordered NMR spectroscopy (DOSY) NMR with diffusion coefficient-formula weight (D-FW) analysis and its application in characterizing the aggregation state of methyllithium aggregates and complexes with several widely used diamines. Commercially available 13c-labeled benzene and several easily synthesized 13C-labeled compounds using 13C-labeled iodomethane as the isotopic source are developed as internal references for diflusion-formula weight analysis (D-FW). The technique greatly expands die applicability of DOSY D-FW analysis to a much wider variety of compounds because of isotopic labeling. These results reveal that methyllithium exists as a tetrasolvated tetramer in diethyl ether and exclusively as bis-solvated dirners with chelating diamines [ABSTRACT FROM AUTHOR]

The solid state structure of lithiated (S)-N¹,N¹-bis(2-methoxyethyl)-N²,3-dimethylbutane-1,2-diamine, which is a chiral amide base synthesized from (S)-valine was determined by single-crystal X-ray diffraction. The complex in solution state is also characterized by a variety of NMR experiments including diffusion-ordered NMR spectroscopy (DOSY) with diffusion coefficient-formula weight correlation analyses and other one- and two-dimensional NMR techniques by dissolving the crystal in toluene-d8. The crystallography and NMR results suggest that the chiral amide is dimeric in both solid and solution states. [ABSTRACT FROM AUTHOR]

We report the direct measurement of ligand-binding constants of organolithium complexes using a 1 H NMR/diffusion-ordered NMR spectroscopy (DOSY) titration technique. Lithium hexamethyldisilazide complexes with ethereal and ester donor ligands (THF, diethyl ether, MTBE, THP, tert-butyl acetate) are characterized using 1 H NMR and X-ray crystallography. Their aggregation and solvation states are confirmed using diffusion coefficient-formula weight correlation analysis, and the 1 H NMR/DOSY titration technique is applied to obtain their binding constants. Our work suggests that steric hindrance of ethereal ligands plays an important role in the aggregation, solvation, and reactivity of these complexes. It is noteworthy that diffusion methodology is utilized to obtain binding constants.

We report on the generation of a perfluoroalkyl Grignard reagent ((F)RMgX) by exchange reaction between a perfluoroalkyl iodide ((F)R-I) and a Grignard reagent (RMgX). (19)F NMR was applied to monitor the generation of n-C3F7MgCl. Additional NMR techniques, including (19)F COSY, NOESY, and pulsed gradient spin-echo (PGSE) diffusion NMR, were invoked to assign peaks observed in (19)F spectrum. Schlenk equilibrium was observed and was significantly influenced by solvent, diethyl ether, or THF.

We report extension of the D-FW analysis using referenced (2)H DOSY. This technique was developed in response to limitations due to peak overlay in (1)H DOSY spectra. We find a corresponding linear relationship (R(2) > 0.99) between log D and log FW as the basis of the D-FW analysis. The solution-state structure of THF solvated lithium diisopropyl amide (LDA) in hydrocarbon solvent was chosen to demonstrate the reliability of the methodology. We observe an equilibrium between monosolvated and disolvated dimeric LDA complexes at room temperature. Additionally we demonstrate the application of the (2)H D-FW analysis using a compound with an exchangeable proton that is readily labeled with (2)H. Hence, the (2)H DOSY D-FW analysis is shown to provide results consistent with the (1)H DOSY method, thereby greatly extending the applicability of the D-FW analysis.

We report the development of isotopic-labeled (13)C diffusion-ordered NMR spectroscopy (DOSY) NMR with diffusion coefficient-formula weight (D-FW) analysis and its application in characterizing the aggregation state of methyllithium aggregates and complexes with several widely used diamines. Commercially available (13)C-labeled benzene and several easily synthesized (13)C-labeled compounds using (13)C-labeled iodomethane as the isotopic source are developed as internal references for diffusion-formula weight analysis (D-FW). The technique greatly expands the applicability of DOSY D-FW analysis to a much wider variety of compounds because of isotopic labeling. These results reveal that methyllithium exists as a tetrasolvated tetramer in diethyl ether and exclusively as bis-solvated dimers with chelating diamines.

The solid state structure of lithiated (S)-N(1),N(1)-bis(2-methoxyethyl)-N(2),3-dimethylbutane-1,2-diamine, which is a chiral amide base synthesized from (S)-valine was determined by single-crystal X-ray diffraction. The complex in solution state is also characterized by a variety of NMR experiments including diffusion-ordered NMR spectroscopy (DOSY) with diffusion coefficient-formula weight correlation analyses and other one- and two-dimensional NMR techniques by dissolving the crystal in toluene-d8. The crystallography and NMR results suggest that the chiral amide is dimeric in both solid and solution states.

A system consisting of a chiral lithium amide and n-BuLi in tol-d(8) solution was investigated with (1)H and (13)C INEPT DOSY, (6)Li and (15)N NMR, and other 2D NMR techniques. A mixed 2:1 trimeric complex was identified as the major species as the stoichiometry approached 1.5 equiv of n-BuLi to 1 equiv of amine compound. (1)H and (13)C INEPT DOSY spectra confirmed this lithium aggregate in the solution. The formula weight of the aggregate, correlated with diffusion coefficients of internal references, indicated the aggregation number of this complex. Plots of log D(rel) vs log FW are linear (r > 0.9900). (6)Li and (15)N NMR titration experiments also corroborated these results. These NMR experiments indicate that this mixed aggregate is the species that is responsible for asymmetric addition of n-BuLi to aldehydes.