Formate-Mediated Reductive Cross-Coupling of Vinyl Halides and Aryl Iodides: -Substitution via Palladium(I) Catalysis.

Formate-mediated reductive cross-couplings of vinyl halides with aryl iodides via palladium(I) catalysis occur with highly uncommon -substitution. The active dianionic palladium(I) catalyst, [PdI][NBu], is generated from Pd(OAc), BuNI, and formate. Oxidative addition of aryl iodide followed by dissociation of the dimer provides the monomeric anionic T-shaped arylpalladium(II) species, [Pd(Ar)(I)(NBu)], which, upon vinyl halide carbopalladation, forms products of -substitution by way of palladium(IV) carbenes, as corroborated by deuterium-labeling experiments.

Leveraging the Stereochemical Complexity of Octahedral Diastereomeric-at-Metal Catalysts to Unlock Regio-, Diastereo-, and Enantioselectivity in Alcohol-Mediated C-C Couplings via Hydrogen Transfer.

Experimental and computational studies illuminating the factors that guide metal-centered stereogenicity and, therefrom, selectivity in transfer hydrogenative carbonyl additions of alcohol proelectrophiles catalyzed by chiral-at-metal-and-ligand octahedral d metal ions, iridium(III) and ruthenium(II), are described. To augment or invert regio-, diastereo-, and enantioselectivity, predominantly one from among as many as 15 diastereomeric-at-metal complexes is required. For iridium(III) catalysts, cyclometalation assists in defining the metal stereocenter, and for ruthenium(II) catalysts, iodide counterions play a key role.

Palladium(I)-Iodide-Catalyzed Deoxygenative Heck Reaction of Vinyl Triflates: A Formate-Mediated Cross-Electrophile Reductive Coupling with -Substitution.

The first deoxygenative Heck reactions are described, as illustrated by formate-mediated -substitutions of vinyl triflates with aryl iodides. The collective data corroborate a mechanism in which Pd(OAc) and BuNI form the dianionic iodide-bridged dimer [PdI][NBu], which, under reducing conditions, serves as a precursor to the palladium(I) complex [PdI][NBu]. Dinculear oxidative addition of aryl iodide forms [PdI(Ar)][NBu], which dissociates to the monometallic complex [PdI(Ar)][NBu].

Chiral-at-Ruthenium-SEGPHOS Catalysts Display Diastereomer-Dependent Regioselectivity: Enantioselective Isoprene-Mediated Carbonyl -Prenylation via Halide Counterion Effects.

The first correlation between metal-centered stereogenicity and regioselectivity in a catalytic process is described. Alternate -diastereomeric chiral-at-ruthenium complexes of the type RuX(CO)[η-prenyl][()-SEGPHOS] form in a halide-dependent manner and display divergent regioselectivity in catalytic C-C couplings of isoprene to alcohol proelectrophiles via hydrogen autotransfer. Whereas the chloride-bound ruthenium-SEGPHOS complex prefers a -relationship between the halide and carbonyl ligands and delivers products of carbonyl -prenylation, the iodide-bound ruthenium-SEGPHOS complex prefers a -relationship between the halide and carbonyl ligands and delivers products of carbonyl -prenylation.

Ruthenium-Catalyzed C-C Coupling of Terminal Alkynes with Primary Alcohols or Aldehydes: α,β-Acetylenic Ketones (Ynones) via Oxidative Alkynylation.

The first metal-catalyzed oxidative alkynylations of primary alcohols or aldehydes to form α,β-acetylenic ketones (ynones) are described. Deuterium labelling studies corroborate a novel reaction mechanism in which alkyne hydroruthenation forms a transient vinylruthenium complex that deprotonates the terminal alkyne to form the active alkynylruthenium nucleophile.

Historical perspective on ruthenium-catalyzed hydrogen transfer and survey of enantioselective hydrogen auto-transfer processes for the conversion of lower alcohols to higher alcohols.

Ruthenium-catalyzed hydrogen auto-transfer reactions for the direct enantioselective conversion of lower alcohols to higher alcohols are surveyed. These processes enable completely atom-efficient carbonyl addition from alcohol proelectrophiles in the absence of premetalated reagents or metallic reductants. Applications in target-oriented synthesis are highlighted, and a brief historical perspective on ruthenium-catalyzed hydrogen transfer processes is given.

Stereo- and Site-Selective Conversion of Primary Alcohols to Allylic Alcohols via Ruthenium-Catalyzed Hydrogen Auto-Transfer Mediated by 2-Butyne.

The first enantioselective ruthenium-catalyzed carbonyl vinylations via hydrogen autotransfer are described. Using a ruthenium-JOSIPHOS catalyst, primary alcohols - and 2-butyne are converted to chiral allylic alcohols - with excellent levels of absolute stereocontrol. Notably, 1°,2°-1,3-diols participate in site-selective C-C coupling, enabling asymmetric carbonyl vinylation beyond premetalated reagents, exogenous reductants, or hydroxyl protecting groups.

Understanding Halide Counterion Effects in Enantioselective Ruthenium-Catalyzed Carbonyl (α-Aryl)allylation: Alkynes as Latent Allenes and Trifluoroethanol-Enhanced Turnover in The Conversion of Ethanol to Higher Alcohols via Hydrogen Auto-transfer.

Crystallographic characterization of RuX(CO)(η-CH)(JOSIPHOS), where X = Cl, Br, or I, reveals a halide-dependent diastereomeric preference that defines metal-centered stereogenicity and, therefrom, the enantioselectivity of C-C coupling in ruthenium-catalyzed -diastereo- and enantioselective C-C couplings of primary alcohols with 1-aryl-1-propynes to form products of carbonyl -(α-aryl)allylation. Computational studies reveal that a non-classical hydrogen bond between iodide and the aldehyde formyl CH bond stabilizes the favored transition state for carbonyl addition. An improved catalytic system enabling previously unattainable transformations was developed that employs an iodide-containing precatalyst, RuI(CO)(η-CH), in combination with trifluoroethanol, as illustrated by the first enantioselective ruthenium-catalyzed C-C couplings of ethanol to form higher alcohols.

Tunneling by 16 Carbons: Planar Bond Shifting in [16]Annulene.

Midsized annulenes are known to undergo rapid π-bond shifting. Given that heavy-atom tunneling plays a role in planar bond shifting of cyclobutadiene, we computationally explored the contribution of heavy-atom tunneling to planar π-bond shifting in the major (CTCTCTCT, 5a) and minor (CTCTTCTT, 6a) known isomers of [16]annulene. UM06-2X/cc-pVDZ calculations yield bond-shifting barriers of ca.