SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF ALKALINE-EARTH METAL BIS[BIS(TRIMETHYLSILYL)PHOSPHANIDE] - MOLECULAR-STRUCTURE OF CA[P(SIME(3))(2)](2)CENTER-DOT-2TMTA AND BA[PA(SIME(3))(2)](2)CENTER-DOT-4THF

The metallation of bis(trimethylsilyl)phosphine by alkaline earth metal bis[bis(trimethylsilyl)amides] or magnesium dibutanide yields the corresponding alkaline earth metal bis[bis(trimethylsilyl)phosphides]. With increasing size of the alkaline earth metal atom, an increasing low field shift of the P-31(H-1) NMR resonance and an increasing value of the (1)J(P-31-Si-29) coupling constant is observable. Calcium-bis[bis(trimethylsilyl)phosphide].2TMTA.THF crystallizes in the monoclinic space group C2/c with a = 1442.4(5), b = 3547.8(5), c = 2136.1(5) pm, beta = 108.97(1)degrees and Z = 4. The phosphorus atom is planar because of the steric demand of the three-dentate 1,3,5-trimethyl-1,3,5-triazinane ligands. The P-Si distances have rather short values of 219 pm, whereas the Ca-P bond lengths of 299 pm exclude the possibility of backbonding from the phosphorus atom to the metal center. In barium-bis[bis(trimethylsilyl)phosphide].4THF, which crystallizes from THF in the monoclinic space group Cc (a = 2905.9(11), b = 966.3(3), c = 1950.8(6) pm, beta = 127.90(2)degrees and Z = 4), the phosphorus atoms display a pyramidal coordination with angle sums of 345 degrees. The different Ba-P-Si bond angles of about 104 degrees and 137 degrees in the trans-configurated molecule are remarkable.