Oxidation of 1,3,2-diselenaphospholanes with an annelated dicarba-closo-dodecaborane(12) unit by addition of sulfur and selenium. Molecular structure of a novel 1,2,4,5-tetraselena-3-phospha heterocycle

1,3,2-Diselenaphospholanes with an annelated dicarba-closo-dodecaborane(12) unit are slowly oxidized, except of the phosphorus halides, by addition of sulfur without side reaction. The analogous reaction with selenium, also slow, is accompanied either by uncontrolled decomposition or by insertion of selenium into P–Se bonds to give novel seven-membered rings containing two μ-Se2 units. All products are characterized by multinuclear magnetic resonance methods (1H, 11B, 13C, 31P, 77Se NMR spectroscopy), supported by calculations on the B3LYP/6-311+G(d,p) level of theory, and the molecular structure of one example of a 1,2,4,5-tetraselena-3-phospha heterocycle was determined by X-ray crystallography.