Solution Interaction of Potassium and Calcium Bis(trimethylsilyl)amides; Preparation of Ca[N(SiMe3)2]2 from Dibenzylcalcium

Ca[N(SiMe3)(2)](2) (1) is isolated in nearly quantitative yield from the room temperature reaction of Ca(CH2Ph)(2)(THF) and HN(SiMe3)(2) in toluene. A commonly used preparation of 1 involving the reaction of potassium bis(trimethylsilyl)amide, K[N(SiMe3)(2)] (2), with CaI2 can produce material that contains substantial amounts of potassium, probably in the form of a calciate such as K[Ca{N(SiMe3)(2)}(3)]. The favorable formation of K[Ca{N(SiMe3)(2)}(3)] from 1 and 2 was confirmed with density functional theory calculations. Deliberate doping of solutions of 1 with 2 initially causes only an upfield shift in the single H-1 NMR resonance observed for 1; not until K/Ca ratios exceed 1:1 is the presence of the added potassium obvious by the appearance of an additional peak in the spectrum.