STRUCTURES OF STRONTIUM BIS[BIS(TRIMETYLSILYL)PHOSPHANIDES] AS FUNCTION OF THF CONCENTRATION

The reaction of strontium bis[bis(trimethylsilyl)amide] with bis(trimethylsilyl) phosphine yields strontium bis[bis(trimethylsilyl)phosphide]. If this reaction is performed in THF, the compound [(Me3Si)2P]2Sr . 4.5THF 1 can be isolated, which crystallizes from this solvent in the orthorhombic space group Pca2(1) (a = 1959.6(5) pm, b = 1294.9(5) pm, c = 1880.0(4) pm; Z = 4). The planar phosphide substituents are in trans-positions, and the normals of the Si2P-planes are nearly perpendicular to one another. Heating of compound 1 in vacuum or metalation of bis(trimethylsilyl)phosphine in toluene with subsequent addition of a few drops of THF yields {Sr2[P(SiMe3)2]4 . 3THF} . toluene 2 with three bridging and one terminal phosphide ligand. This compound 2 crystallizes in the orthorhombic space group P2(1)2(1)2(1) (a = 1257.8(3) pm, b = 2212.5(4) pm, c = 2458.0(5) pm; Z = 4). In toluene solution at + 60-degrees-C only the bicyclic complex 2 can be observed, whereas at - 60-degrees-C the mononuclear complex 1 is the dominating species.