Exploiting the Ring Strain of Diphosphetanes: A Synthetic and Computational Approach towards 1,2,5-Selenadiphospholanes.

A carboranyl-based meso-1,2,5-selenadiphospholane diselenide was synthesised starting from a strained carborane-substituted 1,2-diphosphetane and subsequently reduced to an unprecedented carboranyl-based meso-1,2,5-selenadiphospholane. The electronic structure and the bonding situation for both compounds were investigated by density functional theory (DFT), Natural Bond Orbital (NBO) analyses, Fractional Occupation Density (FOD) analysis, Complete Active Space Self Consistent Field (CASSCF) calculations and time-dependent DFT (TDDFT) calculations. Ring-opening reactions of meso-1,2,5-selenadiphospholane with nucleophiles and electrophiles are reported together with calculated reaction mechanisms (DFT level). Isolated compounds were characterised by NMR and IR spectroscopy, high-resolution mass spectrometry, elemental analysis and single-crystal X-ray diffraction.