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

Treatment of the α-dimethylamino[3]ferrocenophane system 3 with methyl iodide followed by dimesitylphosphine (Mes2PH) gave the α-(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 α-position for hydride from the [HB(C6F5)3−] counteranion to eventually yield the unfunctionalized [3]ferrocenophane product (10) and Mes2PH·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 Mes2PH·B(C6F5)3 (11).