TY - JOUR
T1 - Lanthanide- and actinide-mediated terminal alkyne hydrothiolation for the catalytic synthesis of markovnikov vinyl sulfides
AU - Weiss, Charles J.
AU - Wobser, Stephen D.
AU - Marks, Tobin Jay
PY - 2010/12/13
Y1 - 2010/12/13
N2 - 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.
AB - 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.
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U2 - 10.1021/om100697h
DO - 10.1021/om100697h
M3 - Article
AN - SCOPUS:78649849420
SN - 0276-7333
VL - 29
SP - 6308
EP - 6320
JO - Organometallics
JF - Organometallics
IS - 23
ER -