关键词: 受限路易斯酸碱对, 芳香胺盐酸盐, 三(五氟苯基)硼, 硅烷, 氢胺化/还原反应

Although in recent years the frustrated Lewis pairs (FLPs) reactivity towards small molecule activation has been widely concerned, the reports on the FLPs derived from aromatic amines are few. This paper describes a new method of an one-pot hydroamination/reduction reaction of terminal alkynes with aromatic amines catalyzed by the B(C₆F₅)₃/aromatic ammonium chloride systems with a hydridosilane as a source of the hydride. We consider that the active intermediate[Ar₂NH₂]⁺[H-B(C₆F₅)₃]^- which formed by the aromatic ammonium chloride/B(C₆F₅)₃ reaction with silanes plays a very important role on the formation and reduction of the mediate product imines. The hydroamination reaction is firstly induced by the trace amount amines produced by the dissociation of the borohydride aromatic amine salt, which then reacts with the alkynes and forms the imines. Then the borohydride intermediate[Ar₂NH₂]⁺[H-B(C₆F₅)₃]^- reduces the imines to amines. It has been proved that the borohydride intermediate[Ar₂NH₂]⁺[H-B(C₆F₅)₃]^- could successfully reduce the corresponding imines to amines in an in-situ reaction condition. However it has been found that the usually most active mono-substituted hydridosilane, such as PhSiH₃ shows the poorest reactivity in this case. And the less active trisubstituted silanes such as Et₃SiH or Ph₃SiH exhibit the highest reactivity. To explain this abnormal phenomenon the different reaction speeds of the cascade hydroamination/reduction reaction and the dissociation of the borohydride aromatic amine salt should be concerned. Since the dissociation of[Ar₂NH₂]⁺[H-B(C₆F₅)₃]^- to H₂ is comparably quicker than the hydroamination reaction. By reacting with the less active trisubstituted silanes could not only slow down the formation and dissociation of[Ar₂NH₂]⁺[H-B(C₆F₅)₃]^-, but could also let the hydroamination and reduction steps proceeded completely. Moreover by slowly adding the diluted hydrosilanes to the reaction systems could also improve the reaction. The reaction yield is affected by the substituent on the terminal alkynes, too. The alkynes with the electron withdrawn group show comparably higher reactivity than with the electron donating ones.

Key words: frustrated Lewis pairs, aromatic ammonium chloride, B(C₆F₅)₃, silanes, hydroamination/reduction reaction