Discovery of base metal-catalyzed methods for the preparation of chiral intermediates
has garnered great attention. Recently, through a systematic study of activators and
ligands, we have discovered Co(I)-catalyzed enantioselective heterodimerization of
linear 1,3-dienes with ethylene and acrylates. In these studies, cationic cobalt(I) has
been invoked as an active catalyst to carry out the transformation. However, the
synthesis and isolation of such active Co(I)-complexes which could give insight into of
reaction’s mechanism, remains challenging. Herein, we disclosed a reliable procedure
for the synthesis and isolation of Co(I)-complexes and characterized them by UV-Vis
spectroscopy and X-ray crystallography. The bis-phosphine ligated Co(I) complexes in
presence of activators, performed the regio- and enantioselective hydroboration of 2-
substituted 1,3-diene with pinacolborane (HBPin) to obtain homoallylic boronates
(enantiomeric excess, ee >90%). In the absence of activators, these complexes do not
catalyze the reaction suggesting the key role of cationic Co(I)-species in the catalytic
cycle. Currently, these Co(I) complexes are being further utilized in the hydroacylation
of 1,3-dienes with simple aliphatic aldehyde to produce enantiopure ketones. The
comprehensive protocols for the synthesis of Co(I) complexes and its application in
hydrovinylation, heterodimerization with acrylates, hydroboration, and hydroacylation of
1,3-dienes will be discussed.
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Mechanistic study of homoleptic trisamidolanthanide-catalyzed aldehyde and ketone hydroboration. Chemically non-innocent ligand participation
Carbonyl bond hydroboration is a valuable synthetic route to functionalized alcohols but relies on sometimes unselective and sluggish reagents. While rapid and selective aldehyde and ketone hydroboration mediated by trisamidolanthanide catalysts is known, the origin of the selectivity is not well-understood and is the subject of this contribution. Here the aldehyde and ketone HBpin hydroboration reaction mechanisms catalyzed by La[N(SiMe 3 ) 2 ] 3 are investigated both experimentally and theoretically. The results support initial carbonyl oxygen coordination to the acidic La center, followed by intramolecular ligand-assisted hydroboration of the carbonyl moiety by bound HBpin. Interestingly, ketone hydroboration has a higher energetic barrier than that of aldehydes due to the increased steric encumbrance and decreased electrophilicity. Utilizing NMR spectroscopy and X-ray diffraction, a bidentate acylamino lanthanide complex associated with the aldehyde hydroboration is isolated and characterized, consistent with the relative reaction rates. Furthermore, an aminomonoboronate–lanthanide complex produced when the La catalyst is exposed to excess HBpin is isolated and characterized by X-ray diffraction, illuminating unusual aminomonoboronate coordination. These results shed new light on the origin of the catalytic activity patterns, reveal a unique ligand-assisted hydroboration pathway, and uncover previously unknown catalyst deactivation pathways.
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- Award ID(s):
- 1856619
- PAR ID:
- 10447878
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 14
- Issue:
- 12
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 3247 to 3256
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2SC06442A
