Structure and properties of lithium n-butyl amidinates

Lithium n-butyl amidinates (formally lithium salts of N',N-disubstituted amidoimides of pentanoic acid) with various substituents were prepared and characterized in solution by ¹H, ⁷Li, ¹³C and ¹⁵N NMR spectra parameters in C₆D₆, THF-d₈ and Et₂O-d₁₀. The characteristic spectral parameters were compared with parent carbodiimides and amidines prepared by hydrolysis, where large solvent effects were described. Five of studied compounds were studied by X-ray diffraction techniques in the solid state. Lithium n-butyl amidinates containing less bulky substituents like isopropyl or cyclohexyl crystallize with Et₂O or THF as centrosymmetric dimers with mutually parallel amidinate moieties. The lithium N,N'-bis2,6-di(propan-2-yl)phenyl]n-butylamidinate crystallizes from Et₂O solution as an asymmetric dimer. The first unit is composed by one ligand coordinated to one of lithium atoms. The lithium atom is also coordinated by one of the nitrogen atoms of the second ligand. The second nitrogen atom of the same ligand is coordinated to the second lithium atom which is also connected to the Et₂O molecule and the aromatic ring of the ligand in a η³-fashion. The same compound crystallizes from the THF solution as a monomeric bis-tetrahydrofuranate.