La[N(SiMe3)2]3-Catalyzed Ester Reductions with Pinacolborane: Scope and Mechanism of Ester Cleavage

Christopher J. Barger, Alessandro Motta, Victoria L. Weidner, Tracy L. Lohr, Tobin J. Marks

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Tris[N,N-bis(trimethylsilyl)amido]lanthanum (LaNTMS) is an efficient, highly active, and selective homogeneous catalyst for ester reduction with pinacolborane (HBpin). Alkyl and aryl esters are cleaved to the corresponding alkoxy- and aryloxy-boronic esters which can then be straightforwardly hydrolyzed to alcohols. Ester reduction is achieved with 1 mol % catalyst loading at 25-60 °C, and most substrates are quantitatively reduced in 1 h. Nitro, halide, and amino functional groups are well tolerated, and ester reduction is completely chemoselective over potentially competing intra- or intermolecular alkene or alkyne hydroboration. Kinetic studies, isotopic labeling, and density functional theory calculations with energetic span analysis argue that ester reduction proceeds through a rate-determining hydride-transfer step that is ligand-centered (hydride is transferred directly from bound HBpin to bound ester) and not through a metal hydride-based intermediate that is often observed in organolanthanide catalysis. The active catalyst is proposed to be a La-hemiacetal, [(Me3Si)2N]2La-OCHR(OR)[HBpin], generated in situ from LaNTMS via hydroboronolysis of a single La-N(SiMe3)2 bond. These results add to the growing compendium of selective oxygenate transformations that LaNTMS is competent to catalyze, further underscoring the value and versatility of homoleptic lanthanide complexes in homogeneous catalytic organic synthesis.

Original languageEnglish
Pages (from-to)9015-9024
Number of pages10
JournalACS Catalysis
Volume9
Issue number10
DOIs
Publication statusPublished - Oct 4 2019

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Esters
Hydrides
Catalysts
Lanthanum
Lanthanoid Series Elements
Alkynes
Alkenes
4,4,5,5-tetramethyl(1,3,2)dioxaborolane
Rare earth elements
Labeling
Functional groups
Catalysis
Olefins
Density functional theory
Alcohols
Metals
Ligands
Kinetics
Substrates

Keywords

  • C-O bond cleavage
  • ester reduction
  • homogeneous catalysis
  • hydroboration
  • lanthanides

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

Cite this

La[N(SiMe3)2]3-Catalyzed Ester Reductions with Pinacolborane : Scope and Mechanism of Ester Cleavage. / Barger, Christopher J.; Motta, Alessandro; Weidner, Victoria L.; Lohr, Tracy L.; Marks, Tobin J.

In: ACS Catalysis, Vol. 9, No. 10, 04.10.2019, p. 9015-9024.

Research output: Contribution to journalArticle

Barger, Christopher J. ; Motta, Alessandro ; Weidner, Victoria L. ; Lohr, Tracy L. ; Marks, Tobin J. / La[N(SiMe3)2]3-Catalyzed Ester Reductions with Pinacolborane : Scope and Mechanism of Ester Cleavage. In: ACS Catalysis. 2019 ; Vol. 9, No. 10. pp. 9015-9024.
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