Heterolytic Cleavage of Dihydrogen by Frustrated Lewis Pairs Derived from α-(Dimesitylphosphino)ferrocenes and B(C6F5)3

Treatment of the alpha-dimethylamino[3]ferrocenophane system 3 with methyl iodide followed by dimesitylphosphine (Mes(2)PH) gave the alpha-(dimesitylphosphino)[3]ferrocenophane 5. This forms a frustrated Lewis pair [5/8] with B(C6F5)(3) (8) that rapidly reacts with dihydrogen under ambient conditions to probably give the phosphonium cation/hydrido borate anion salt [5-H+/H-8(-)]. This, however, is unstable under the applied reaction conditions with regard to replacement of the newly formed phosphonium leaving Group at the ferrocenophane alpha-position for hydride from the [HB(C6F5)(3)(-)] counteranion to eventually yield the unfunctionalized [3]ferrocenophane product (10) and Mes(2)PH center dot B(C6F5)(3) (11)-both characterized by independent syntheses. Analogously, Ugi's amine (6) was converted to (1-(dimesitylphosphino)ethyl)ferrocene (7). The frustrated pair [7/8] consumes dihydrogen under similar conditions to yield the reduction products ethylferrocene (14) and Mes(2)PH center dot B(C6F5)(3) (11).