Tris(tert-butyl)phosphine selenide, the missing link in tris(tert-butyl)-phosphine chalcogenide structures tBu(3)P=X (X = O, S, Se, Te)

In tris(tert-butyl)phosphine selenide, C12H27PSe, all the methyl ligands ar e disordered over two sites in the ratio 70/30. The molecule displays cryst allographic C-3 symmetry. The bond angles at the P atom are distorted tetra hedral [CD P-C 110.02 (5)degrees and Se=P-C 108.91 (5)degrees]. The P-C and P=Se bond lengths are 1.908 (1) and 2.1326 (6) Angstrom, respectively. A c omparison of the structural data of the complete series of tris(tert-butyl) phosphine chalcogenides ((Bu3PO)-Bu-t, (Bu3PS)-Bu-t, (Bu3PSe)-Bu-t and (Bu3 PTe)-Bu-t) with the corresponding data of other phosphine chalcogenides sub stituted by smaller organic groups shows the great influence of the bulky t ert-butyl ligands.