Lanthanide- and actinide-mediated terminal alkyne hydrothiolation for the catalytic synthesis of markovnikov vinyl sulfides

Charles J. Weiss, Stephen D. Wobser, Tobin J Marks

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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* = C 5Me5; 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 Me 2SiCp″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.

Original languageEnglish
Pages (from-to)6308-6320
Number of pages13
JournalOrganometallics
Volume29
Issue number23
DOIs
Publication statusPublished - Dec 13 2010

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Actinoid Series Elements
Lanthanoid Series Elements
Alkynes
Sulfides
alkynes
Sulfhydryl Compounds
thiols
sulfides
synthesis
Deuterium
metals
deuterium
Metals
Coordination Complexes
Metal complexes
detachment
free radicals
inhibitors
Labeling
marking

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Lanthanide- and actinide-mediated terminal alkyne hydrothiolation for the catalytic synthesis of markovnikov vinyl sulfides. / Weiss, Charles J.; Wobser, Stephen D.; Marks, Tobin J.

In: Organometallics, Vol. 29, No. 23, 13.12.2010, p. 6308-6320.

Research output: Contribution to journalArticle

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