Newly designed and prepared vanadium complexes bearing anionic pyrrole-based PNP-type pincer and aryloxy ligands were found to work as effective catalysts for the direct conversion of molecular dinitrogen into ammonia and hydrazine under mild reaction conditions. This is the first successful example of vanadium-catalyzed dinitrogen reduction under mild reaction conditions.
Iron-dinitrogen complexes bearing methyl- and phenyl-substituted pyrrole-based anionic PNP-type pincer ligands are prepared and characterized by X-ray analysis. The former complex is found to work as a more effective catalyst than that bearing a non-substituted PNP-type pincer ligand toward the transformation of nitrogen gas into ammonia and hydrazine under mild reaction conditions.
Dinitrogen-bridged dititanium and dizirconium complexes bearing anionic pyrrole-based PNP-type pincer ligands are prepared and characterized by X-ray analysis. Their catalytic activity is investigated toward reduction of nitrogen gas into ammonia and hydrazine under mild reaction conditions.
We
report herein cobalt-catalyzed enantioselective and chemodivergent
reactions between a cyclopropanol and an oxabicyclic alkene via a
cobalt homoenolate, which afford either an alkylative ring-opening
product or a hydroalkylation product, with the counterion of the cobalt
catalyst being a major chemoselectivity-controlling factor. A catalyst
generated from cobalt(II) chloride and a chiral diphosphine promotes
alkylative ring opening to afford 1,2-dihydronaphthalen-1-ol derivatives
in good yields with high enantioselectivity. By contrast, a catalyst
generated from cobalt(II) acetate and the same diphosphine ligand,
with the assistance of methanol, selectively affords hydroalkylation
products with retention of the bicyclic structure at a comparable
level of enantioselectivity.
We report herein an enantioselective conjugate addition reaction of a zinc homoenolate, catalytically generated via ring opening of a cyclopropanol, to an α,β-unsaturated ketone. The reaction is promoted by a zinc aminoalkoxide catalyst generated from Et2Zn and a chiral β-amino alcohol to afford 1,6-diketones, which undergo, upon heating, intramolecular aldol condensation to furnish highly substituted cyclopentene derivatives with good to high enantioselectivities. The reaction has proved applicable to various 1-substituted cyclopropanols as well as chalcones and related enones. The chiral amino alcohol has proved to enable ligand-accelerated catalysis of the homoenolate generation and its conjugate addition. Positive nonlinear effects and lower reactivity of a racemic catalyst have been observed, which can be attributed to a stable and inactive heterochiral zinc aminoalkoxide dimer. File list (2) download file view on ChemRxiv SI_ZnHomoenolate_YS.pdf (16.62 MiB) download file view on ChemRxiv ZnHomoenolate_YS.pdf (1.01 MiB)
We
report herein a nickel-catalyzed ring-opening allylation of
cyclopropanols with allylic carbonates that occurs under mild and
neutral conditions. The reaction displays linear selectivity for both
linear and branched acyclic allylic carbonates and is also applicable
to cyclic allylic carbonates, affording a variety of δ,ε-unsaturated
ketones in moderate to good yields. Mechanistic experiments are in
accord with a catalytic cycle involving decarboxylative oxidative
addition of allylic carbonate to Ni(0), alkoxide exchange with cyclopropanol,
cyclopropoxide-to-homoenolate conversion on Ni(II), and C–C
reductive elimination.
Direct
and diastereoselective synthesis of vicinal anti-sec,tert-diols has been achieved
by zinc-mediated α-hydroxyallylation of aldehydes with cyclopropanols.
The reaction features the action of the zinc-enolized homoenolate
as a γ-oxyallyl nucleophile toward the carbonyl electrophile.
The diastereoselectivity of the present reaction is ascribed to the
strong preference for a chelated (Z)-configuration
of the enolized homoenolate as well as the bicyclic chairlike transition
state it forms with the aldehyde, where the aldehyde substituent prefers
to occupy the pseudoaxial position.
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