Mechanism Investigations of the Endo Cycloisomerization of Alkynols through Isolation and Characterization of Ruthenium Complexes from the Reactions of Alkynes with a Ruthenium Complex

In our efforts to probe the reaction mechanism of the endo cycloisomerization of alkynols catalyzed by the complex [Ru(N3P)(OAc)](BPh4) (1; NP3 = N,N-bis[(pyridin-2-yl)methyl][2-(diphenylphosphino)phenyl]methanamine), the reactions of 1 with alkynes were investigated. Several complexes related to intermediates in the catalytic reactions were isolated and characterized. In the presence of DIPEA (N,N-diisopropylethanamine), complex 1 reacted with 3-butyn-1-ol to afford the Ru−oxocyclocarbene complex {Ru(N3P)[C(CH2)3O](OAc)}(BPh4) (4). Under anhydrous conditions, the reaction of complex 1 with tert-butylacetylene afforded [Ru(N3P)(η3-tBuCCCCHBut)](BPh4) (8). In the presence of water, the reaction of complex 1 with tert-butylacetylene afforded [Ru(N3P)(CO)(η1-CH2But)](BPh4) (13). All the reactions are likely to proceed through ruthenium vinylidene intermediates. These results support that ruthenium vinylidene complexes are involved as the key intermediates in the cycloisomerization of alkynols catalyzed by complex 1.

为探究配合物[Ru(N3P)(OAc)](BPh4)（编号1；NP3=N,N-双[(吡啶-2-基)甲基][2-(二苯基膦基)苯基]甲胺）催化炔醇的内环异构化反应机理，本研究考察了该配合物与炔烃的反应。研究团队分离并表征了数种与该催化反应中间体相关的配合物。在DIPEA (N,N-diisopropylethanamine) 存在时，配合物1与3-丁炔-1-醇反应，生成钌-氧代环卡宾配合物{Ru(N3P)[=C(CH2)3O](OAc)}(BPh4)（编号4）。在无水条件下，配合物1与叔丁基乙炔反应，得到[Ru(N3P)(η³-tBuC≡C-CH=CHBut)](BPh4)（编号8）。在水存在时，配合物1与叔丁基乙炔反应，生成[Ru(N3P)(CO)(η¹-CH2But)](BPh4)（编号13）。上述所有反应均可能通过钌亚乙烯基中间体进行。本研究结果证实，钌亚乙烯基配合物作为关键中间体参与了配合物1催化的炔醇内环异构化反应。