Lanthanide- and Actinide-Mediated Terminal Alkyne Hydrothiolation for the Catalytic Synthesis of Markovnikov Vinyl Sulfides

Abstract

The Markovnikov-selective lanthanide- and actinide-mediated, intermolecular hydrothiolation of terminal alkynes by aliphatic, benzylic and aromatic thiols using Cp*2LnCH(TMS)2 (Cp* = C5Me5; Ln = La, Sm, Lu), Ln[N(TMS)2]3 (Ln = La, Nd, Y), Cp*2An(CH2TMS)2, and Me2SiCp′′2An(CH2R)2 (Cp′′ = C5Me4; An = Th, R = TMS; An = U, R = Ph) as precatalysts is studied in detail. These transformations are shown to be Markovnikov-selective, with selectivities as high as >99%. Kinetic investigations of the Cp*2SmCH(TMS)2-mediated reaction between 1-pentanethiol and 1-hexyne are found to be first-order in catalyst concentration, first-order in alkyne concentration, and zero-order in thiol concentration. Deuterium labeling of the alkyne −C≡C−H position reveals kH/kD = 1.40(0.1) and 1.35(0.1) for the organo-Sm- and organo-Th-catalyzed processes, respectively, along with evidence of thiol-mediated protonolytic detachment of the vinylic hydrothiolation product from the Sm center. Mechanistic findings indicate turnover-limiting ...