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 (Mes 2 PH) gave the α-(dimesitylphosphino)[3]ferrocenophane 5 . This forms a frustrated Lewis pair [ 5/8 ] with B(C 6 F 5 ) 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(C 6 F 5 ) 3 − ] counteranion to eventually yield the unfunctionalized [3]ferrocenophane product ( 10 ) and Mes 2 PH·B(C 6 F 5 ) 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·B(C 6 F 5 ) 3 ( 11 ).