CeCl3/n-BuLi: Unraveling Imamoto's Organocerium Reagent

CeCl3(thf) reacts at low temperatures with MeLi, t-BuLi, and n-BuLi to isolable organocerium complexes. Solvent-dependent extensive n-BuLi dissociation is revealed by Li-7 NMR spectroscopy, suggesting Ce(n-Bu)(3)(thf)(x) or solvent-separated ion pairs like [Li(thf)(4)][Ce(n-Bu)(4)(thf)(y)] as as the dominant species of the Imamoto reagent. The stability of complexes Li(3)Ln(n-Bu)(6)(thf)(4) increases markedly with decreasing Ln(III) size. Closer inspection of the solution behavior of crystalline Li3Lu(n-Bu)(6)(thf)(4) and mixtures of LuCl3(thf)(2)/n-BuLi in THF indicates occurring n-BuLi dissociation only at molar ratios of <1:3. n-BuLi-depleted complex LiLu(n-Bu)(3)Cl(tmeda)(2) was obtained by treatment of Li2Lu(n-Bu)(5)(tmeda)(2) with ClSiMe3, at the expense of LiCl incorporation. Imamoto's ketone/tertiary alcohol transformation was examined with 1,3-diphenylpropan-2-one, affording 99 % of alcohol.

Automated summary

CeCl3(thf) reacts with MeLi, t-BuLi, and n-BuLi to form isolable organocerium complexes; Li-7 NMR spectroscopy reveals solvent-dependent n-BuLi dissociation behavior; the stability of complexes is significantly influenced by the size of Ln(III) ion.