N,N,N′,N′-Tetramethylethylendiamine adducts of amido calcium bases – Synthesis of monomeric [(tmeda)Ca{N(SiMe3)2}2], [(tmeda)Ca{NiPr2}2], and dimeric Hauser base-type [(tmeda)Ca(tmp)(μ-I)]2 (tmp = 2,2,6,6-tetramethylpiperidide)

The metathetical reaction of calcium diiodide with KNR2 in the presence of N,N,N′,N′-tetramethylethylendiamine yields the corresponding amido calcium bases [(tmeda)Ca(tmp)2] (1), [(tmeda)Ca{N(SiMe3)2}2] (3), and [(tmeda)Ca(NiPr2)2] (4) regardless of the stoichiometric ratio of the starting compounds. All compounds are highly air and moisture sensitive. Only in the case of NR2 being a tmp group very few crystals of the Hauser base-type dimeric derivative [(tmeda)Ca(tmp)(μ-I)]2 (2) with bridging iodide ions can be isolated. In all these calcium complexes the amides are bound terminally and contain planarily coordinated nitrogen atoms. The calcium complex [(tmeda)Ca(NiPr2)2] (4) is much more reactive than the lighter magnesium congener and therefore, it has to be stored below 0 °C in order to avoid decomposition reactions.