Switchable Ni-catalyzed bis-thiolation of acetylene with aryl disulfides as an access to functionalized alkenes and 1,3-dienes

Add time:08/21/2019    Source:sciencedirect.com

The article provides the first example of metal-catalyzed aryl disulfide addition to unsubstituted acetylene. The use of inexpensive Ni(acac)2 precatalyst with phosphine ligands results in competitive formation of (Z)-1,2-bis(arylthio)ethenes and (Z,Z)-1,4-bis(arylthio)buta-1,3-dienes. The process with the PPhCy2 as a ligand results in selective formation of diene molecular skeletons. Replacement of PPhCy2 with the PPh3 switches the reaction toward formation of alkenes. The use of substituted phenyl disulfides does not affect the selectivity and allows obtaining alkenes or dienes in good to high yields. Mechanistic investigations reveal major differences on the catalyst activation stage depending on the nature of phosphine ligand. Key novel point is to carry out video-monitoring of catalyst evolution with electron microscopy, which revealed the dynamic nature of the catalytic system and showed that the ligand played a prominent role in formation of the catalytically active phase. For PPh3, the development of catalytically active species proceeds through nickel thiolate [Ni(SAr)2]n formation, which renders the system heterogeneous. In contrast to PPh3, the PPhCy2 ligand promotes direct activation of the catalyst in its molecular form without disturbing the homogeneous state of the system.

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