化学
烯烃
钌
催化作用
异构化
炔烃
组合化学
选择性
硫醇
光化学
有机化学
作者
Jie Luo,Yaoyu Liang,Michael Montag,Yael Diskin‐Posner,Liat Avram,David Milstein
摘要
Catalytic semihydrogenation of internal alkynes using H2 is an attractive atom-economical route to various alkenes, and its stereocontrol has received widespread attention, both in homogeneous and heterogeneous catalyses. Herein, a novel strategy is introduced, whereby a poisoning catalytic thiol is employed as a reversible inhibitor of a ruthenium catalyst, resulting in a controllable H2-based semihydrogenation of internal alkynes. Both (E)- and (Z)-alkenes were obtained efficiently and highly selectively, under very mild conditions, using a single homogeneous acridine-based ruthenium pincer catalyst. Mechanistic studies indicate that the (Z)-alkene is the reaction intermediate leading to the (E)-alkene and that the addition of a catalytic amount of bidentate thiol impedes the Z/E isomerization step by forming stable ruthenium thiol(ate) complexes, while still allowing the main hydrogenation reaction to proceed. Thus, the absence or presence of catalytic thiol controls the stereoselectivity of this alkyne semihydrogenation, affording either the (E)-isomer as the final product or halting the reaction at the (Z)-intermediate. The developed system, which is also applied to the controllable isomerization of a terminal alkene, demonstrates how metal catalysis with switchable selectivity can be achieved by reversible inhibition of the catalyst with a simple auxiliary additive.
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