On the Reaction of Pacman-Phosphanes with Lewis Acids

The reactions of Pacman phosphanes (1a) with Lewis acids such as R₃B (R = C₆H₅, C₆F₅) and GaCl₃ were investigated. While equilibria between mono- and di-adducts were found in the reaction with BPh₃, B(C₆F₅)₃ preferentially formed the di-adduct (1a·2B(C₆F₅)₃), which could be isolated and fully characterized. density functional theory (DFT) calculations showed that the N-bonded adducts are thermodynamically more stable than the P-bonded adducts. In contrast to the reaction of the Pacman phosphane with boranes, GaCl₃ reacted with 1a to give an unusual [Pacman-GaCl₂]⁺[GaCl₄]^- salt, featuring a nearly planar GaN₂C₂ heterocycle as part of the Pacman macrocycle. In addition, the coordination geometry on one P atom changes from triple to an unusual quadruple coordination, although it is still a formal P atom in the + III oxidation state, as shown by quantum chemical calculations.