Reversible Stereoisomerization Of 1,3-Diphosphetane Frameworks Revealed By A Single-Electron Redox Approach

The discovery of pyramidal inversion has continued to impact modern organic and organometallic chemistry. Sequential alkylation reactions of an N-heterocyclic carbene (NHC) ligated dicarbondiphosphide 1 with RI (R = Me, Et, or iBu) and ZnMe2 give rise to the highly stereoselective synthesis of cis-1,3-diphosphetanes 3. cis-3 is conformationally favorable at room temperature, whereas inversion to trans-3 is observed at 110 degrees C. One-electron oxidation of cis-3 with Fc(+)(BArF) (Fc = [Fe(C5H5)(2)]; BArF = [B(3,5-(CF3)(2)C6H3)(4))](-)) leads to the stereoselective formation of trans-1,3-diphosphetane radical cation salts 3(center dot+)(BArF), which can be reversibly transformed to cis-3 upon one-electron reduction. Salts 3(center dot+)(BArF) represent the first examples of 1,3-diphosphetane radical cations. These results provide a potential application of planar four-membered heterocycle-based building blocks for electrically fueled molecular switches.