Structures of lithium N-monosubstituted anilides: trisolvated monomer to tetrasolvated dimer.

Crystal structure determination of lithiated N-methylaniline with a variety of ligands, including tetrahydrofuran, methyltetrahydrofuran, trans-2,5-dimethyltetrahydrofuran, dimethoxyethane, tetrahydropyran and N,N-diethylpropionamide, reveals a common Li–N–Li–N four-membered-ring dimeric structure motif. A progression of solvation from tetrasolvated dimer (PhNMeLi·S2)2 through trisolvated dimer to disolvated dimer (PhNMeLi·S)2 was observed by increasing the steric hindrance of the ligand. Solid-state structures of several other lithium N-alkylanilides solvated by tetrahydrofuan are also reported. When the methyl group of N-methylaniline is replaced by an isopropyl or a phenyl group, trisolvated monomers are formed instead of dimers. Interestingly, the solid-state structure of lithiated N-isobutylaniline in tetrahydrofuran is a trisolvated dimer while that of lithium N-neopentylanilide is a disolvated dimer.