Lanthanide- and Actinide-Mediated Terminal Alkyne Hydrothiolation for the Catalytic Synthesis of Markovnikov Vinyl Sulfides
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- 作者：Charles J. Weiss ; Stephen D. Wobser ; Tobin J. Marks
- 刊名：Organometallics
- 出版年：2010
- 出版时间：December 13, 2010
- 年：2010
- 卷：29
- 期：23
- 页码：6308-6320
- 全文大小：1159K
- 年卷期：v.29,no.23(December 13, 2010)
- ISSN：1520-6041
文摘
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 alkyne insertion into the Sm−SR bond, followed by very rapid, thiol-induced M−C protonolysis to yield Markovnikov vinyl sulfides and regenerate the corresponding M−SR species. Comparisons of different substrates and metal complexes in catalyzing hydrothiolation reveal a strong dependence of hydrothiolation activity on the steric encumbrance in the insertive transition state. Observed deuterium exchange between alkyne −C≡C−H and thiol RS−H in the presence of Cp*2SmCH(TMS)2 and Me2SiCp′′2Th(CH2TMS)2 argues for a metal−alkynyl metal−thiolate equilibrium, favoring the M−SR species under hydrothiolation conditions. A mixture of free radical-derived anti-Markovnikov vinyl sulfides is occasionally observed and can be suppressed by γ-terpinene radical inhibitor addition. Previously reported metal thiolate complex aggregation to form insoluble species is observed and can be delayed kinetically by Cp-based ligation.