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- W1976996141 abstract "The kinetics of 7Li exchange between LiR and LiAlR4, where R = CH3, C2H5 and CH2Si(CH3)3, have been observed in diethyl ether solutions. In agreement with earlier conclusions, the exchange is found to be rate-determined by dissociation of alkyllithium tetramer, with rate constant k1. Line shape analysis of the NMR spectra over a wide range of temperature yields an Arrhenius activation energy of 12.4 ± 1.5 kcal/mole (99% confidence level) and pre-exponential term of 1.43 x 1013 sect-1 for R = CH3; 11.3 ± 1.7 kcal/mole and 2.12 x 1012 sec−1 for R = C2H5. For R = Me3SiCH2, 7Li exchange is rapid on the NMR time scale (i.e., k1>∼103 sec−1) at −90°C. It thus appears that dissociation of the alkyllithium tetramer is promoted by increased electron release and/or increased steric requirement of the alkyl group. Alkyl group exchange is slow at room temperature in mixtures of Me3SiCH2LiLiAl(CH2SiMe3)4 and Me3SiCH2LiLiCr(CH2SiMe3)4. 7Li exchange is rapid at −95°C in mixtures of Me3SiCH2Li and Me3SiCH2Cu at various ratios. In the 1H spectrum distinct resonances corresponding to a 11 Li/Cu species and Me3SiCH2Li are seen for Li/Cu ratios > 1, at −50°C and below. The NMR results show that the only significant mixed species in the solutions is the 11, probably a dimeric species (Me3siCH2)4Li2Cu2." @default.
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- W1976996141 title "1H and 7Li NMR observations of exchange processes in alkyllithium-ate complexes" @default.
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- W1976996141 doi "https://doi.org/10.1016/s0022-328x(00)86464-5" @default.
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