Synthesis and Reactivity of Triphosphaallyl Cation Stabilized by N-Heterocyclic Carbenes.

Reduction of the triphosphaallyl species 6[GaCl] with Ga[GaCl] affords the imidazoliumyl-substituted (L) bicyclo[2.1.1]-triphosphane 10[GaCl], featuring an unprecedented GaCl-bridged P scaffold. Reactions of 10[GaCl] with nucleophiles (Cl or NHC) result in rare, selective P-C bond cleavages, affording GaCl-substituted triphosphiranes (LPGaCl, y =  5, 6) via an intramolecular ring closure mechanism. Protonation of 6[GaCl] gives rise to a similar ring closure, but without P-C bond cleavage, to afford the LPH salt 8[OTfGaCl]. Additionally, the palladium complex 26[GaCl], formed through the reaction of 10[GaCl] with [Pd(PPh)], presents a novel bicyclic PPd moiety (LPPd(PPh)[GaCl]). Comprehensive DFT calculations have been conducted to elucidate the bonding situation in 26[GaCl], uncovering significant metal-to-ligand π-back-donation and a distinctive 3-center-4-electron hyperbonding phenomenon in the P₃Pd framework. These findings offer valuable insights into chemistry of cyclic polyphosphorus compounds and, in particular, the reactivity, structural flexibility, and the coordination properties of cationic triphosphorus species.