Carbostannolysis mediated by bis(pentamethylcyclopentadienyl)lanthanide catalysts. Utility in accessing organotin synthons

Stephen D. Wobser, Casey J. Stephenson, Massimiliano Delferro, Tobin J Marks

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Facile carbon-tin bond activation in the reaction of 2-(trimethylstannyl) pyridine (1) with the organolanthanide complexes Cp*2LaCH(TMS) 2 (2a) and [Cp*2LaH]2 (2b) yields Cp*2La(2-pyridyl) (3), as well as Me3SnCH(TMS) 2 and Me3SnH, respectively. At room temperature, ethylene then undergoes insertion into the resulting La-C(pyridyl) bond followed by carbostannolysis to catalytically generate 2-(2-(Me3Sn)ethyl)pyridine (4) or, with extended reaction times, 6-ethyl-2-(2-(trimethylstannyl)ethyl) pyridine (5). In contrast to 1, 6-methyl-2-(trimethylstannyl)pyridine (6) is unreactive, likely reflecting steric constraints. With terminal alkynes, this catalytic heterocycle-SnMe3 activation/carbostannylation process affords tin-functionalized conjugated enynes. Thus, at 60 C 2b catalyzes the conversion 1 + 1-hexyne to yield (E)-2-butyl-1-(Me3Sn)-oct-1-en-3-yne in a 60:1 ratio E:Z isomer ratio. This reaction is available to α-monosubstituted and α-disubstituted terminal alkynes, while α-trisubstituted alkynes are too hindered for reaction. The catalytic cycle is proposed to proceed via a spectroscopically detectable Me 3Sn-alkynyl intermediate which undergoes insertion into a Cp*2La-alkynyl bond to produce the conjugated alkynyl product, which is subsequently protonolyzed from the Cp*2La center by a new terminal alkyne substrate molecule. NMR spectroscopic and kinetic data support the proposed pathway and indicate turnover-limiting alkyne insertion.

Original languageEnglish
Pages (from-to)1317-1327
Number of pages11
JournalOrganometallics
Volume32
Issue number5
DOIs
Publication statusPublished - Mar 11 2013

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Lanthanoid Series Elements
Alkynes
alkynes
pyridines
catalysts
Catalysts
insertion
Tin
tin
Chemical activation
activation
reaction time
Isomers
ethylene
Carbon
isomers
Nuclear magnetic resonance
nuclear magnetic resonance
cycles
Molecules

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Carbostannolysis mediated by bis(pentamethylcyclopentadienyl)lanthanide catalysts. Utility in accessing organotin synthons. / Wobser, Stephen D.; Stephenson, Casey J.; Delferro, Massimiliano; Marks, Tobin J.

In: Organometallics, Vol. 32, No. 5, 11.03.2013, p. 1317-1327.

Research output: Contribution to journalArticle

Wobser, Stephen D. ; Stephenson, Casey J. ; Delferro, Massimiliano ; Marks, Tobin J. / Carbostannolysis mediated by bis(pentamethylcyclopentadienyl)lanthanide catalysts. Utility in accessing organotin synthons. In: Organometallics. 2013 ; Vol. 32, No. 5. pp. 1317-1327.
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abstract = "Facile carbon-tin bond activation in the reaction of 2-(trimethylstannyl) pyridine (1) with the organolanthanide complexes Cp*2LaCH(TMS) 2 (2a) and [Cp*2LaH]2 (2b) yields Cp*2La(2-pyridyl) (3), as well as Me3SnCH(TMS) 2 and Me3SnH, respectively. At room temperature, ethylene then undergoes insertion into the resulting La-C(pyridyl) bond followed by carbostannolysis to catalytically generate 2-(2-(Me3Sn)ethyl)pyridine (4) or, with extended reaction times, 6-ethyl-2-(2-(trimethylstannyl)ethyl) pyridine (5). In contrast to 1, 6-methyl-2-(trimethylstannyl)pyridine (6) is unreactive, likely reflecting steric constraints. With terminal alkynes, this catalytic heterocycle-SnMe3 activation/carbostannylation process affords tin-functionalized conjugated enynes. Thus, at 60 C 2b catalyzes the conversion 1 + 1-hexyne to yield (E)-2-butyl-1-(Me3Sn)-oct-1-en-3-yne in a 60:1 ratio E:Z isomer ratio. This reaction is available to α-monosubstituted and α-disubstituted terminal alkynes, while α-trisubstituted alkynes are too hindered for reaction. The catalytic cycle is proposed to proceed via a spectroscopically detectable Me 3Sn-alkynyl intermediate which undergoes insertion into a Cp*2La-alkynyl bond to produce the conjugated alkynyl product, which is subsequently protonolyzed from the Cp*2La center by a new terminal alkyne substrate molecule. NMR spectroscopic and kinetic data support the proposed pathway and indicate turnover-limiting alkyne insertion.",
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AB - Facile carbon-tin bond activation in the reaction of 2-(trimethylstannyl) pyridine (1) with the organolanthanide complexes Cp*2LaCH(TMS) 2 (2a) and [Cp*2LaH]2 (2b) yields Cp*2La(2-pyridyl) (3), as well as Me3SnCH(TMS) 2 and Me3SnH, respectively. At room temperature, ethylene then undergoes insertion into the resulting La-C(pyridyl) bond followed by carbostannolysis to catalytically generate 2-(2-(Me3Sn)ethyl)pyridine (4) or, with extended reaction times, 6-ethyl-2-(2-(trimethylstannyl)ethyl) pyridine (5). In contrast to 1, 6-methyl-2-(trimethylstannyl)pyridine (6) is unreactive, likely reflecting steric constraints. With terminal alkynes, this catalytic heterocycle-SnMe3 activation/carbostannylation process affords tin-functionalized conjugated enynes. Thus, at 60 C 2b catalyzes the conversion 1 + 1-hexyne to yield (E)-2-butyl-1-(Me3Sn)-oct-1-en-3-yne in a 60:1 ratio E:Z isomer ratio. This reaction is available to α-monosubstituted and α-disubstituted terminal alkynes, while α-trisubstituted alkynes are too hindered for reaction. The catalytic cycle is proposed to proceed via a spectroscopically detectable Me 3Sn-alkynyl intermediate which undergoes insertion into a Cp*2La-alkynyl bond to produce the conjugated alkynyl product, which is subsequently protonolyzed from the Cp*2La center by a new terminal alkyne substrate molecule. NMR spectroscopic and kinetic data support the proposed pathway and indicate turnover-limiting alkyne insertion.

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