Dihydrogen Activation by B(p-C₆F₄H)₃ and Phosphines

The Grignard reagent (p-C6F4H)MgCl was used to prepare (Et2O)B(p-C6F4H)3 (2) and the free borane B(p-C6F4H)3 (1). On the basis of Lewis acidity tests, the borane 1 exhibits ca. 95% of the acidity of B(C6F5)3. 1 forms classical adducts with ethers and phosphines of the general formula (L)B(p-C6F4H)3 (L = Et2O (2), THF (3), Me3P (4), Et3P (5), i-Pr2(H)P (6), Ph3P (7), (3,5-Me2C6H3)3P (8), t-Bu2(H)P (9), and Cy3P (10)). Compounds 9 and 10 react with 4 atm of H2 to give the salts [t-Bu2PH2][HB(p-C6F4H)3] (11) and [Cy3PH][HB(p-C6F4H)3] (12). The sterically demanding phosphines R3P (R = t-Bu, i-Pr, 2,4,6-Me3C6H2, and 2-MeC6H4), R2R′P (R,R′ = t-Bu, i-Pr and t-Bu, Cy), and (Ph2CH)R2P (R = t-Bu (22), i-Pr (23), Cy (24), and C5H9 (25)) show no evidence of adduct formation with 1, but react with H2 to give the corresponding salts [R3PH][HB(p-C6F4H)3] (13−16), [R2R′PH][HB(p-C6F4H)3] (17−20), and [(Ph2CH)R2PH][HB(p-C6F4H)3] (26−29), respectively. The [t-Bu2PH2]+ species 11 is stable only under an H2 overpressure, whil...