Reversible Intermolecular E–H Oxidative Addition to a Geometrically Deformed and Structurally Dynamic Phosphorous Triamide

The synthesis and reactivity of geometrically constrained tricoordinate phosphorus (σ³-P) compounds supported by tridentate triamide chelates (N­[o-NR-C₆H₄]₂^3–; R = Me or ⁱPr) are reported. Studies indicate that 2 (P­{N­[o-NMe-C₆H₄]₂}) adopts a C_s-symmetric structure in the solid state. Variable-temperature NMR studies demonstrate a low-energy inversion at phosphorus in solution (ΔG^⧧_exptl²⁹⁸ = 10.7(5) kcal/mol), for which DFT calculations implicate an edge-inversion mechanism via a metastable C₂-symmetric intermediate. In terms of reactivity, compound 2 exhibits poor nucleophilicity, but undergoes oxidative addition at ambient temperature of diverse O–H- and N–H-containing compounds (including alcohols, phenols, carboxylic acids, amines, and anilines). The resulting pentacoordinate adducts 2·[H]­[OR] and 2·[H]­[NHR] are characterized by multinuclear NMR spectroscopy and X-ray crystallography, and their structures (which span the pseudorotation coordinate between trigonal bipyramidal and square planar) are evaluated in terms of negative hyperconjugation. At elevated temperatures, the oxidative addition is shown to be reversible for volatile alcohols and amines.