Ancillary Tethering Influences σ3-P vs σ5-P Speciation and Enables Intermolecular S–H Oxidative Addition to Nontrigonal Phosphorus Compounds

The design and synthesis of a nontrigonal phosphorus(III) triamide ( 2 ) bearing a peripheral ethylene bridge is described. By comparison to a compound lacking the ethylene bridge ( 1, (P{N[ o -NMe-C 6 H 4 ] 2 })), 2 is shown to exclusively form σ 5 -P oxidative addition products upon E–H addition (E = OR, SR) in preference to a σ 3 -P adduct from cooperative addition across one P–N bond. The resulting pentacoordinate phosphoranes have been characterized by multinuclear NMR spectroscopy and X-ray crystallography. DFT calculations on relative energies of σ 3 -P and σ 5 -P species indicate that the ethylene linker in 2 energetically destabilizes the σ 3 -P tautomer of the phosphorane product ( 2 ·[H][E]) by constraining rotation along the C–N bond, favoring formation of σ 5 -P phosphoranes by ring–chain tautomerism.