Catalytic Enantioselective α-Alkylation of Amides by Unactivated Alkyl Electrophiles.

Carbonyl groups that bear an α stereocenter are commonly found in bioactive compounds, and intense effort has therefore been dedicated to the pursuit of stereoselective methods for constructing this motif. While the chiral auxiliary-enabled coupling of enolates with alkyl electrophiles represented groundbreaking progress in addressing this challenge, the next advance in the evolution of this enolate-alkylation approach would be to use a chiral catalyst to control stereochemistry. Herein we describe the achievement of this objective, demonstrating that a nickel catalyst can accomplish enantioselective intermolecular alkylations of racemic Reformatsky reagents with unactivated electrophiles; the resulting α-alkylated carbonyl compounds can be converted in one additional step into a diverse array of ubiquitous families of chiral molecules.

Photo-Initiated Cobalt-Catalyzed Radical Olefin Hydrogenation.

Outer-sphere radical hydrogenation of olefins proceeds via stepwise hydrogen atom transfer (HAT) from transition metal hydride species to the substrate. Typical catalysts exhibit M-H bonds that are either too weak to efficiently activate H or too strong to reduce unactivated olefins. This contribution evaluates an alternative approach, that starts from a square-planar cobalt(II) hydride complex.

The elusive abnormal CO insertion enabled by metal-ligand cooperative photochemical selectivity inversion.

Direct hydrogenation of CO to CO, the reverse water-gas shift reaction, is an attractive route to CO utilization. However, the use of molecular catalysts is impeded by the general reactivity of metal hydrides with CO. Insertion into M-H bonds results in formates (MO(O)CH), whereas the abnormal insertion to the hydroxycarbonyl isomer (MC(O)OH), which is the key intermediate for CO-selective catalysis, has never been directly observed.

Chemical Non-Innocence of an Aliphatic PNP Pincer Ligand.

The synthesis of the divinylamido PNP nickel(II) complex [NiBr{N(CHCHPtBu ) }] is reported. This compound exhibits reversible, ligand-centered oxidation and protonation reactions. The resulting pincer chemical non-innocence can be utilized for benzylic C-H hydrogen atom abstraction.