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

Reduction of the triphosphaallyl species 6[GaCl4] with GaI[Ga2Cl7] affords the imidazoliumyl-substituted (L) bicyclo[2.1.1]-triphosphane 10[Ga2Cl7], featuring an unprecedented Ga2Cl5-bridged P3 scaffold. Reactions of 10[Ga2Cl7] with nucleophiles (Cl- or NHC) result in rare, selective P-C bond cleavages, affording Ga2Cly-substituted triphosphiranes (LP3Ga2Cly, y =  5, 6) via an intramolecular ring closure mechanism. Protonation of 6[GaCl4] gives rise to a similar ring closure, but without P-C bond cleavage, to afford the L2P3H+ salt 8[OTfGaCl3]2. Additionally, the palladium complex 26[GaCl4], formed through the reaction of 10[Ga2Cl7] with [Pd(PPh3)4], presents a novel bicyclic P3Pd moiety (LP3Pd(PPh3)2[GaCl4]). Comprehensive DFT calculations have been conducted to elucidate the bonding situation in 26[GaCl4], 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.