Kinetically-Controlled Ni-Catalyzed Direct Carboxylation of Unactivated Secondary Alkyl Bromides without Chain Walking.

Herein, we report the direct carboxylation of unactivated secondary alkyl bromides enabled by the merger of photoredox and nickel catalysis, a previously inaccessible endeavor in the carboxylation arena. Site-selectivity is dictated by a kinetically controlled insertion of CO at the initial C(sp)-Br site by the rapid formation of Ni(I)-alkyl species, thus avoiding undesired β-hydride elimination and chain-walking processes. Preliminary mechanistic experiments reveal the subtleties of stereoelectronic effects for guiding the reactivity and site-selectivity.

Comproportionation and disproportionation in nickel and copper complexes.

Disproportionation and comproportionation reactions have become increasingly important electron transfer events in organometallic chemistry and catalysis. The renewed interest in these reactions is in part attributed to the improved understanding of first-row metals and their ability to occupy odd and even oxidation states. Disproportionation and comproportionation reactions enable metal complexes to shuttle between various oxidation states, a matter of utmost relevance for controlling the speciation and catalytic turnover.

Low Pressure Carbonylation of Benzyl Carbonates and Carbamates for Applications in C Isotope Labeling and Catalytic CO Reduction.

Herein, we report a methodology to access isotopically labeled esters and amides from carbonates and carbamates employing an oxygen deletion strategy. This methodology utilizes a decarboxylative carbonylation approach for isotope labeling with near stoichiometric, ex situ generated C, or C carbon monoxide. This reaction is characterized by its broad scope, functional group tolerance, and high yields, which is showcased with the synthesis of structurally complex molecules.

Rapid Access to Carbon-Isotope-Labeled Alkyl and Aryl Carboxylates Applying Palladacarboxylates.

Herein, we report a strategy for the formation of isotopically labeled carboxylic esters from boronic esters/acids using a readily accessible palladium carboxylate complex as an organometallic source of isotopically labeled functional groups. The reaction allows access to either unlabeled or full C- or C-isotopically labeled carboxylic esters, and the method is characterized by its operational simplicity, mild conditions, and general substrate scope. Our protocol is further extended to a carbon isotope replacement strategy, involving an initial decarbonylative borylation procedure.

Elucidating electron-transfer events in polypyridine nickel complexes for reductive coupling reactions.

Polypyridine-ligated nickel complexes are widely used as privileged catalysts in a variety of cross-coupling reactions. The rapid adoption of these complexes is tentatively attributed to their ability to shuttle between different oxidation states and engage in electron-transfer reactions. However, these reactions are poorly understood in mechanistic terms.

Remote Hydroamination of Disubstituted Alkenes by a Combination of Isomerization and Regioselective N-H Addition.

Remote hydrofunctionalizations of alkenes incorporate functional groups distal to existing carbon-carbon double bonds. While remote carbonylations are well-known, remote hydrofunctionalizations are most common for addition of relatively nonpolar B-H, Si-H, and C-H bonds with alkenes. We report a system for the remote hydroamination of disubstituted alkenes to functionalize an alkyl chain selectively at the subterminal, unactivated, methylene position.

Trifluoromethylation of Carbonyl and Unactivated Olefin Derivatives by C(sp )-C Bond Cleavage.

Herein, we report a Cu-mediated trifluoromethylation of carbonyl-type compounds and unactivated olefins enabled by visible-light irradiation via σ C(sp )-C bond-functionalization. The reaction is distinguished by its modularity, mild conditions and wide scope-even in the context of late-stage functionalization-thus offering a complementary approach en route to valuable C(sp )-CF architectures from easily accessible precursors.

Nickel-Catalyzed Site-Selective Intermolecular C(sp )-H Amidation.

A nickel-catalyzed site-selective intermolecular amidation of saturated C(sp )-H bonds is reported. This mild protocol exhibits a predictable reactivity pattern to incorporate amide functions at C(sp )-H sites adjacent to nitrogen and oxygen atoms in either cyclic or acyclic frameworks, thus offering a complementary reactivity profile to existing oxidative-type processes or metal-catalyzed C(sp )-N bond-forming reactions operating via two-electron manifolds.

Reductive Elimination from Sterically Encumbered Ni-Polypyridine Complexes.

Herein we disclose the synthesis of sterically encumbered dialkylnickel(II) complexes bearing 2,9-dimethyl-1,10-phenanthroline ligands. A comparison with their unsubstituted analogues by both X-ray crystallography and theoretical calculations revealed significant distortions in their molecular structures. Eyring plots along with stoichiometric and photoexcitation studies revealed that sterically encumbered dialkylnickel(II) complexes enable facile C( )-C( ) reductive elimination, thus offering an improved understanding of Ni catalysis.

Room-Temperature-Stable Magnesium Electride via Ni(II) Reduction.

Herein, we report the synthesis of highly reduced bipyridyl magnesium complexes and the first example of a stable organic magnesium electride supported by quantum mechanical computations and X-ray diffraction. These complexes serve as unconventional homogeneous reductants due to their high solubility, modular redox potentials, and formation of insoluble, non-coordinating byproducts. The applicability of these reductants is showcased by accessing low-valent (bipy)Ni(0) species that are challenging to access otherwise.

Catalytic Hydrodifluoroalkylation of Unactivated Olefins.

Herein, we report a modular catalytic technique that streamlines the preparation of -difluoroalkanes from unactivated precursors. The method is characterized by its simplicity, generality, and site selectivity, including the functionalization of advanced intermediates and olefin feedstocks. Our approach is enabled by a cooperative interplay of halogen- and hydrogen-atom transfer, thus offering a new entry point to difluorinated alkyl bioisosteres of interest in drug discovery.

Mechanistic Investigation of the Iron-Catalyzed Azidation of Alkyl C()-H Bonds with Zhdankin's λ-Azidoiodane.

An in-depth study of the mechanism of the azidation of C()-H bonds with Zhdankin's λ-azidoiodane reagent catalyzed by iron(II)(pybox) complexes is reported. Previously, it was shown that tertiary and benzylic C()-H bonds of a range of complex molecules underwent highly site-selective azidation by reaction with a λ-azidoiodane reagent and an iron(II)(pybox) catalyst under mild conditions. However, the mechanism of this reaction was unclear.

Site-Selective Defluorinative sp C-H Alkylation of Secondary Amides.

A site-selective defluorinative sp C-H alkylation of secondary amides that rapidly and reliably incorporates -difluoroalkene motifs into previously unfunctionalized sp sites is disclosed. This protocol is distinguished by its mild conditions, wide scope, and exquisite site-selectivity, thus unlocking a new platform to introduce carbonyl isosteres at saturated hydrocarbon sites.

Ni-Catalyzed Carboxylation of Aziridines en Route to β-Amino Acids.

A Ni-catalyzed reductive carboxylation of substituted aziridines with CO at atmospheric pressure is disclosed. The protocol is characterized by its mild conditions, experimental ease, and exquisite chemo- and regioselectivity pattern, thus unlocking a new catalytic blueprint to access β-amino acids, important building blocks with considerable potential as peptidomimetics.

sp Bis-Organometallic Reagents via Catalytic 1,1-Difunctionalization of Unactivated Olefins.

A catalytic 1,1-difunctionalization of unactivated olefins en route to sp bis-organometallic B,B(Si)-reagents is described. The protocol is characterized by exceptional reaction rates, mild conditions, wide scope, and exquisite selectivity pattern, constituting a new platform to access sp bis-organometallics.

Dual Catalytic Strategy for Forging spsp and spsp Architectures via βScission of Aliphatic Alcohol Derivatives.

A dual platform for forging spsp and spsp carbon bonds via catalytic β-scission of aliphatic alcohol derivatives with both aryl and alkyl halides is disclosed. This protocol is distinguished by its wide substrate scope and broad applicability, even in the context of late-stage functionalization.

Bimolecular Coupling as a Vector for Decomposition of Fast-Initiating Olefin Metathesis Catalysts.

The correlation between rapid initiation and rapid decomposition in olefin metathesis is probed for a series of fast-initiating, phosphine-free Ru catalysts: the Hoveyda catalyst HII, RuCl(L)(═CHCH- o-O Pr); the Grela catalyst nG (a derivative of HII with a nitro group para to O Pr); the Piers catalyst PII, [RuCl(L)(═CHPCy)]OTf; the third-generation Grubbs catalyst GIII, RuCl(L)(py)(═CHPh); and dianiline catalyst DA, RuCl(L)( o-dianiline)(═CHPh), in all of which L = HIMes = N,N'-bis(mesityl)imidazolin-2-ylidene. Prior studies of ethylene metathesis have established that various Ru metathesis catalysts can decompose by β-elimination of propene from the metallacyclobutane intermediate RuCl(HIMes)(κ-CH), Ru-2. The present work demonstrates that in metathesis of terminal olefins, β-elimination yields only ca.