Phosphorus-Stabilized Geminal Dianions

After a presentation of the structures of the known dilithiomethane derivatives, full details on the synthesis and crystal structures of a bis(thiophosphinoyl)-stabilized geminal dianion (2) as well as the first synthesis of an analogous bis(phosphonate) derivative (6) are exposed. Two X-ray crystal structures were obtained for 2. They both exhibit a dimeric arrangement with different solvation states. Variable-temperature NMR experiments (31P and 7Li) show that in solution either several species (in a 1:1 equilibrium) or a single species (one aggregate with different Li/P environments) forms. DFT calculations have been performed on these dianions, and a precise electronic structure is presented on the basis of NBO analysis. The nucleophilic reactivity of these dianions toward CS2 readily provides new 1,1-ethylenedithiolate type compounds (7 and 8).