Nature of the Copper-Oxide-Mediated C–S Cross-Coupling Reaction: Leaching of Catalytically Active Species from the Metal Oxide Surface

Abstract

Copper-oxide-catalyzed cross-coupling reaction is a well-known strategy in heterogeneous catalysis. A large number of applications have been developed, and catalytic cycles have been proposed based on the involvement of the copper oxide surface. In the present work, we have demonstrated that copper­(I) and copper­(II) oxides served as precursors in the coupling reaction between thiols and aryl halides, while catalytically active species were formed upon unusual leaching from the oxide surface. A powerful cryo-SEM technique has been utilized to characterize the solution-state catalytic system by electron microscopy. A series of different experimental methods were used to reveal the key role of copper thiolate intermediates in the studied catalytic reaction. The present study shows an example of leaching from a metal oxide surface, where the leaching process involved the formation of a metal thiolate and the release of water. A new synthetic approach was developed, and many functionalized sulfides were synthesized with yields of up to 96%, using the copper thiolate catalyst. The study suggests that metal oxides may not act as an innocent material under reaction conditions; rather, they may represent a source of reactive species for solution-state homogeneous catalysis.

Cobalt‐Catalyzed C−H Thiolation through Dehydrogenative Cross‐Coupling

“…Also,t he original sulfur source influences the reaction outcome (Table 1). [20] Our results are indicative of similar species as intermediates for the transmetalation of thiolates to cobalt. Thet hiolation also proceeds readily with CuSPh, providing 75 %y ield of 3a with, and 27 %w ithout Cu(OAc) 2 .T he nature of the ultimate thiol source in the reaction was probed by areactivity analysis of these sulfur compounds.After only 15 min, the reaction is almost complete with both PhSH and CuSPh, yet only traces of 3a are present with (PhS) 2 .Clearly, more time is required for the formation of an active thiolating agent from the disulfide.F or additional insight on the interchange of the sulfur species in the reaction, we performed ap retreatment test, adding the indole substrate only after stirring the rest of the reaction mixture at 60 8 8Cf or 30 min.…”

“…Evidently,P hSH is transformed into an active thiolating agent much faster than the disulfide.P hSCu is converted into al ess reactive species under the reaction conditions,likely to the disulfide.Anionic Cu I complexes like [Cu(SPh) 2 ] À have been suggested as the active species in copper-catalyzed CÀScross-coupling. [20] Our results are indicative of similar species as intermediates for the transmetalation of thiolates to cobalt.…”

Cobaltkatalysierte C‐H‐Thiolierung durch dehydrierende Kreuzkupplung

“…Unter den Reaktionsbedingungen wird PhSCu in eine weniger reaktive Spezies umgewandelt, vermutlich in das Disulfid. Anionische Cu I ‐Komplexe wie [Cu(SPh) 2 ] − wurden als aktive Spezies in kupferkatalysierten C‐S‐Kreuzkupplungen vorgeschlagen . Unsere Resultate lassen auf ähnliche Intermediate bei der Transmetallierung von Thiolaten auf Cobalt schließen.…”

Effect of Post‐Treatment on Structure and Catalytic Activity of CuCo‐based Materials for Glycerol Oxidation

“…where Pd dissolution and re‐deposition on carbon nanotubes was reported . Indeed, it is reported in the literature that CuO species used for direct C−H arylation and C−S cross‐coupling reactions undergo leaching and catalytically active species are formed in the solution. Hence, a cocktail‐type system with different metal species can be present in solution, which we cannot exclude for our system .…”