Electronic Effects and Ring Strain Influences on the Electron Uptake by Selenium-Containing Bonds

摘要

The gas-phase electron attachment of thiaselena and diselena derivatives is investigated on model organic systems by ab initio calculations (level of theory MP2/DZP). Electronic contributions favor the one-electron addition on seleniumcontaining compounds, with adiabatic electron affinities of 0.03, 0.24, and 0.43 eV, respectively, for dimethyldisulfide, dimethylselenenylsulfide, and dimethyldiselenide. This ensures the possibility of an excess electron binding on OSeOSO and OSeOSeO linkages. The so-formed radical anionic intermediates present a three-electrons two-centers 2cO3e bond, whose nature is confirmed by Mulliken spin densities and NBO analysis. They are stable towards dissociation, with a low barrier evaluated between about 25–60 kJ/mol. Cyclization strongly enhances dichalcogen propensity to fix an excess electron. Adiabatic electron affinities of a series of 1,2-thiaselena-cycloalkanes and 1,2-diselena-cycloalkanes are positive and range from 0.24 to 1.30 eV. This can be traced back to the release of ring strain energy upon one-electron addition: this geometrical effect is nevertheless less marked than for disulfide analogs.