Homogeneous Organic Reductant Based on 4,4'-Bu-2,2'-Bipyridine for Cross-Electrophile Coupling.

The synthesis of a new homogeneous reductant based on 4,4'-Bu-2,2'-bipyridine, Bu-OED, is reported. Bu-OED was prepared on a multigram scale in two steps from inexpensive and commercially available starting materials, with no chromatography required for purification. Bu-OED has a reduction potential of -1.

Effect of 6,6'-Substituents on Bipyridine-Ligated Ni Catalysts for Cross-Electrophile Coupling.

A family of 4,4'-Bu-2,2'-bipyridine (bpy) ligands with substituents in either the 6-position, 4,4'-Bu-6-Me-bpy (bpy), or 6 and 6'-positions, 4,4'-Bu-6,6'-R-bpy (bpy; R = Me, Pr, Bu, Ph, or Mes), was synthesized. These ligands were used to prepare Ni complexes in the 0, I, and II oxidation states. We observed that the substituents in the 6 and 6'-positions of the bpy ligand impact the properties of the Ni complexes.

Homogeneous Organic Electron Donors in Nickel-Catalyzed Reductive Transformations.

Many contemporary organic transformations, such as Ni-catalyzed cross-electrophile coupling (XEC), require a reductant. Typically, heterogeneous reductants, such as Zn or Mn, are used as the electron source in these reactions. Although heterogeneous reductants are highly practical for preparative-scale batch reactions, they can lead to complications in performing reactions on process scale and are not easily compatible with modern applications, such as flow chemistry.

Pd Reaction Intermediates in Suzuki-Miyaura Cross-Coupling Characterized by Mass Spectrometry.

Palladium-catalyzed Suzuki-Miyaura (SM) coupling is widely utilized in the construction of carbon-carbon bonds. In this study, nanoelectrospray ionization mass spectrometry (nanoESI-MS) is applied to simultaneously monitor precatalysts, catalytic intermediates, reagents, and products of the SM cross-coupling reaction of 3-Br-5-Ph-pyridine and phenylboronic acid. A set of Pd cluster ions related to the monoligated Pd (0) active catalyst is detected, and its deconvoluted isotopic distribution reveals contributions from two neutral molecules.

Tunable and Practical Homogeneous Organic Reductants for Cross-Electrophile Coupling.

The syntheses of four new tunable homogeneous organic reductants based on a tetraaminoethylene scaffold are reported. The new reductants have enhanced air stability compared to current homogeneous reductants for metal-mediated reductive transformations, such as cross-electrophile coupling (XEC), and are solids at room temperature. In particular, the weakest reductant is indefinitely stable in air and has a reduction potential of -0.

A Widely Applicable Dual Catalytic System for Cross-Electrophile Coupling Enabled by Mechanistic Studies.

A dual catalytic system for cross-electrophile coupling reactions between aryl halides and alkyl halides that features a Ni catalyst, a Co cocatalyst, and a mild homogeneous reductant is described. Mechanistic studies indicate that the Ni catalyst activates the aryl halide, while the Co cocatalyst activates the alkyl halide. This allows the system to be rationally optimized for a variety of substrate classes by simply modifying the loadings of the Ni and Co catalysts based on the reaction product profile.

Pharmaceutical diversification via palladium oxidative addition complexes.

Palladium-catalyzed cross-coupling reactions have transformed the exploration of chemical space in the search for materials, medicines, chemical probes, and other functional molecules. However, cross-coupling of densely functionalized substrates remains a major challenge. We devised an alternative approach using stoichiometric quantities of palladium oxidative addition complexes (OACs) derived from drugs or drug-like aryl halides as substrates.

Mechanism of Copper-Catalyzed Hydroalkylation of Alkynes: An Unexpected Role of Dinuclear Copper Complexes.

This article describes a mechanistic study of copper-catalyzed hydroalkylation of terminal alkynes. Relying on the established chemistry of N-heterocyclic carbene copper hydride (NHCCuH) complexes, we previously proposed that the hydroalkylation reaction proceeds by hydrocupration of an alkyne by NHCCuH followed by alkylation of the resulting alkenylcopper intermediate by an alkyl triflate. NHCCuH is regenerated from NHCCuOTf through substitution with CsF followed by transmetalation with silane.

Copper-catalyzed hydroalkylation of terminal alkynes.

We have developed a copper-catalyzed hydroalkylation of terminal alkynes using alkyl triflates as coupling partners and (Me(2)HSi)(2)O as a hydride donor. The hydroalkylation proceeds with excellent anti-Markovnikov regioselectivity and provides exclusively (E)-alkenes. We have demonstrated that both alkyl- and aryl-substituted alkynes can be used as substrates, together with 1° alkyl and benzylic triflates.

Catalytic anti-Markovnikov hydrobromination of alkynes.

We have developed the first catalytic method for anti-Markovnikov hydrobromination of alkynes. The reaction affords terminal E-alkenyl bromides in high yield and with excellent regio- and diastereoselectivity. Both aryl- and alkyl-substituted terminal alkynes can be used as substrates.

Asymmetric synthesis of trisubstituted allenes: copper-catalyzed alkylation and arylation of propargylic phosphates.

Asymmetric synthesis of trisubstituted allenes is accomplished by copper-catalyzed alkylation and arylation of propargylic phosphates using organoboron nucleophiles. Excellent chirality transfer and regioselectivity, together with good functional group compatibility, were observed in reactions with both alkyl boranes and arylboronic esters.