SYNTHESIS AND SPECTROSCOPIC PROPERTIES OF BIS(TRIMETHYLSILYL)AMIDES OF THE ALKALINE-EARTH METALS MAGNESIUM, CALCIUM, STRONTIUM, AND BARIUM

Alkaline-earth-metal bis[bis(trimethylsilyl)amides] of magnesium, calcium, strontium, and barium have been isolated in high yield from bis[bis(trimethylsilyl)amido]tin(II) by utilizing the transmetalation reaction in common organic solvents. When this reaction is performed in 1,2-dimethoxyethane, an ether adduct with two DME molecules is formed for each metal. The alkaline-earth-metal diamides without complexating reagents appear to be dimeric in benzene and toluene. Only the magnesium bis[bis(trimethylsilyl)amide] shows a temperature-dependent equilibrium with a high percentage of monomeric units at high temperatures. In the gaseous phase, this compound as well as the calcium derivative appears to be monomeric; the strontium and the barium amides show fragmentation patterns in the mass spectrum for dimeric species. The dimeric appearance of the ether-free amides is confirmed by the C-13{H-1} NMR and Si-29{H-1} NMR measurements, where two signals can be observed for two chemically different trimethylsilyl groups, as well as by the IR spectra and the cryoscopically (in benzene) determined molecular weights.