Iridium(I) complex of chelating pyridine-2-thiolate ligand: Synthesis, reactivity, and application to the catalytic E-selective terminal alkyne dimerization via C–H activation

A novel iridium(I) complex bearing a chelate-coordinated pyridine-2-thiolate ligand [Ir(η2-SNC5H4)(PPh3)2] (2) was prepared by the reaction of iridium ethylene complex [IrCl(C2H4)(PPh3)2] (1) with lithium salt of pyridine-2-thiol (Li[SNC5H4]). On the treatment of iridium(I) complex 2 with chloroform, iridium(III) dichloro-complex [IrCl2(η2-SNC5H4)(PPh3)2] (3) was formed. Reactions of complex 2 with methyldiphenylsilane, acetic acid, and p-tolylacetylene afforded iridium(III) hydride complexes [IrH(SiMePh2)(η2-SNC5H4)(PPh3)2] (4), [IrH(O2CCH3)(η2-SNC5H4)(PPh3)2] (5), and [IrH(Ctriple bond; length of mdashC(p-tolyl))(η2-SNC5H4)(PPh3)2] (6), respectively. Complex 2 catalyzed dimerization of terminal alkynes leading to enynes (7) with high E-selectivity via C–H bond activation.