Monomeric and Dimeric Amidinate Complexes of Magnesium

Treatment of anhydrous magnesium bromide with 2 equiv of (1,3-di-tert-butylacetamidinato)lithium, (1,3-di-tert-butylbenzamidinato)lithium, (1,3-diisopropylacetamidinato)lithium, or (1-tert-butyl-3-ethylacetamidinato)lithium (prepared in situ from the corresponding carbodiimide and alkyllithium) in diethyl ether at ambient
temperature afforded bis(N,N‘-di-tert-butylacetamidinato)magnesium (81%), bis(N,N‘-di-tert-butylbenzamidinato)magnesium (82%), bis[bis(N,N‘-diisopropylacetamidinato)magnesium] (70%), or bis[bis(1-tert-butyl-3-ethylacetamidinato)magnesium] (93%), respectively, as colorless crystalline solids. These complexes were characterized
by spectral and analytical data and by single-crystal X-ray crystallography for bis(N,N‘-di-tert-butylbenzamidinato)magnesium, bis[bis(N,N‘-diisopropylacetamidinato)magnesium], and bis[bis(1-tert-butyl-3-ethylacetamidinato)magnesium]. In the solid-state structure, bis[bis(1-tert-butyl-3-ethylacetamidinato)magnesium] was found to contain
μ,η2:η1-amidinato ligands. Bis[bis(N,N‘-diisopropylacetamidinato)magnesium] exists in a monomer−dimer
equilibrium in toluene-d8 between −20 and +60 °C. A van't Hoff analysis of this equilibrium afforded ΔH° =
−14.7 ± 0.2 kcal/mol, ΔS° = −44.9 ± 0.2 cal/(mol·K), and ΔG°(298 K) = −1.32 ± 0.2 kcal/mol. The potential
application of the new compounds in the chemical vapor deposition of magnesium-doped group 13 compound
semiconductor films is discussed.