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 language | English |
|---|---|
| Pages (from-to) | 9015-9024 |
| Number of pages | 10 |
| Journal | ACS Catalysis |
| Volume | 9 |
| Issue number | 10 |
| DOIs | |
| Publication status | Published - Oct 4 2019 |
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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 journal › Article
}
TY - JOUR
T1 - La[N(SiMe3)2]3-Catalyzed Ester Reductions with Pinacolborane
T2 - Scope and Mechanism of Ester Cleavage
AU - Barger, Christopher J.
AU - Motta, Alessandro
AU - Weidner, Victoria L.
AU - Lohr, Tracy L.
AU - Marks, Tobin J.
PY - 2019/10/4
Y1 - 2019/10/4
N2 - 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.
AB - 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.
KW - C-O bond cleavage
KW - ester reduction
KW - homogeneous catalysis
KW - hydroboration
KW - lanthanides
UR - http://www.scopus.com/inward/record.url?scp=85072714217&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85072714217&partnerID=8YFLogxK
U2 - 10.1021/acscatal.9b02605
DO - 10.1021/acscatal.9b02605
M3 - Article
AN - SCOPUS:85072714217
VL - 9
SP - 9015
EP - 9024
JO - ACS Catalysis
JF - ACS Catalysis
SN - 2155-5435
IS - 10
ER -