Gas-phase Lewis acidity of perfluoroaryl derivatives of group 13 elements

The gas-phase Lewis acidity of group 13 element aryl and perfluorinated aryl derivatives E(C6H5)(3), E(C6H4F)(3), and E(C5F5)(3) (E = B, Al, Ga) toward different donor molecules (NH3, H2O, PH3, H-, CH3-, F-) has been theoretically studied at the RI-BP86/def2-TZVPP level of theory. The following order of the acceptor ability has been established: E(C6H5)(3) approximate to E(C6H4F)(3) < E(C6F5)(3) approximate to ECl3. The acceptor strengths of E(C6H5)(3) and E(C6H4F)(3) are comparable to each other but much weaker compared to E(C6F5)(3), which has a similar acceptor strength to those of the corresponding trihalides ECl3. The acceptor ability of ER3 decreases in the order Al > Ga > B. In the gas phase, Al(C6F5)(3) is found to be a stronger Lewis acid than B(C6F5)(3) toward all electron donors but H-. In contrast to AlCl3, which forms stable dimers, Al(C6F3)(3) is monomeric and therefore has a much higher Lewis acid reactivity. The reactivity of perfluorinated derivatives E(C5F5)(3) (E = B, Al, Ga) toward ammonolysis and hydrolysis processes and L2ZrMe2 (L = Cl, Cp, Cp*) as cocatalysts in olefin polymerization is also discussed.