Preparation and NMR studies of tetraalkoxyselenuranes and tetraalkoxytelluranes

Article abstract of DOI:10.1021/ja00399a034

A series of tetraalkoxyselenuranes has been prepared. Methanol yielded 5, ethanol, 6, 2-propanol, 7, neopentyl alcohol, 8, trifluoroethanol, 9, ethylene glycol, 1, pinacol, 3, and neopentyl glycol, 4. These molecules varied greatly in their thermal stability. Compounds 5 and 6 could be detected by ⁷⁷Se NMR but they could not be isolated. Compounds 7 and 8 are somewhat more stable and can be isolated as crystalline solids. The remaining selenuranes are reasonably thermally stable. Variable-temperature NMR experiments show that these substances undergo both intermolecular and intramolecular ligand reorganization. The intermolecular process can often be slowed by addition of an acid scavenger, and the intramolecular ligand reorganization process can often be inhibited at low temperatures. Both NMR and X-ray studies show that these molecules adopt structures which are trigonal bipyramidal or very nearly so. Treatment of 9 with trifluoroethoxide ion yielded the pentacoordinated ate complex. A series of tetraalkoxytelluranes has also been prepared. Ethylene glycol yielded 19, pinacol, 20, neopentyl glycol, 21, methanol, 22, ethanol, 23, 2-propanol, 24, neopentyl alcohol, 25, trifluoroethanol, 26, and hexafluoro-2-propanol, 27, which was isolated as a 1:1 complex with tetrahydrofuran. Variable-temperature NMR studies on these substances, except for 19 and 21 which are too insoluble, show that they undergo ligand reorganization. In the case of 20 both NMR and X-ray studies show it has a distorted trigonal-bipyramidal structure. It was not possible to slow the reorganization of the ligands of the remaining telluranes sufficiently to determine their favored structure.