Use of Green Solvents in Metallaphotoredox Cross-Electrophile Coupling Reactions Utilizing a Lipophilic Modified Dual Ir/Ni Catalyst System

Translation of Nickel-Catalyzed C(sp2)-C(sp3) Cross-Electrophile Coupling to Non-Amide Solvents

The cross-electrophile coupling of organobromides is widely utilized in organic synthesis but generally requires undesirable amide solvents (e.g., DMF, DMA, and NMP). We report that the combination of a strongly donating, bidentate nitrogen ligand, LiI, and 4-picoline enables coupling in a variety of alcohol, ester, and ethereal solvents at up to 50 g scale. An improved synthesis of the optimal ligand, 4,4'-bis(dimethylamino)-2,2'-bipyridine, is also reported on the basis of the reductive homocoupling of 4-dimethylamino-2-chloropyridine.

The main factor that determines the formation-efficiencies of photochemically derived one-electron-reduced species

While the quantum yields of photosensitiser-derived one-electron-reduced species (OERSs) significantly impact the overall efficiencies of various redox-photosensitised photocatalytic reactions, the primary factors that influence them remain unclear. In this study, we systematically compared the photochemical formation quantum yields for OERSs associated with Ru(ii) and Os(ii) tris-diimine, cis, trans-[ReI(diimine)(CO)2(PR3)2]+, and cyclometalated Ir(iii) complexes in the presence of the same 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) reductant. The reduction potentials of the excited metal complexes, the heavy-atom effects of the central metal ions, and the oxidation potentials and charges of their OERSs were examined, which reveals that the driving force for photoinduced electron-transfer is the most important factor that determines the quantum yields associated with photochemical OERS formation. For complexes with higher oxidation power in their excited states, the formation quantum yield of OERSs divided by the quenching efficiency of the excited state by BIH is greater. This finding suggests that a higher photoinduced electron-transfer exergonicity promotes electron transfer over larger excited-complex/BIH distances, which in turn enables more-efficient separation of the resulting OERSs and one-electron-oxidised BIH species.

Cross-Electrophile Coupling: Principles, Methods, and Applications in Synthesis

Cross-electrophile coupling (XEC), defined by us as the cross-coupling of two different σ-electrophiles that is driven by catalyst reduction, has seen rapid progression in recent years. As such, this review aims to summarize the field from its beginnings up until mid-2023 and to provide comprehensive coverage on synthetic methods and current state of mechanistic understanding. Chapters are split by type of bond formed, which include C(sp3)-C(sp3), C(sp2)-C(sp2), C(sp2)-C(sp3), and C(sp2)-C(sp) bond formation. Additional chapters include alkene difunctionalization, alkyne difunctionalization, and formation of carbon-heteroatom bonds. Each chapter is generally organized with an initial summary of mechanisms followed by detailed figures and notes on methodological developments and ending with application notes in synthesis. While XEC is becoming an increasingly utilized approach in synthesis, its early stage of development means that optimal catalysts, ligands, additives, and reductants are still in flux. This review has collected data on these and various other aspects of the reactions to capture the state of the field. Finally, the data collected on the papers in this review is offered as Supporting Information for readers.

Amine-Borane-Mediated, Nickel/Photoredox-Catalyzed Cross-Electrophile Coupling between Alkyl and Aryl Bromides

Nickel/photoredox catalysis has emerged as a powerful platform for exploring nontraditional and challenging cross-couplings. Herein, a metallaphotoredox catalytic protocol has been developed on the basis of a tertiary amine-ligated boryl radical-induced halogen atom transfer process under blue-light irradiation. A wide variety of aryl and heteroaryl bromides featuring different functional groups and pharmaceutical moieties were facilely coupled to rapidly install C(sp3)-enriched aromatic scaffolds. The compatibility of Lewis base-ligated borane with nickel catalysis was well exemplified to extend the chemical space for Ni-catalyzed cross-electrophile coupling.

CdS Quantum Dots for Metallaphotoredox-Enabled Cross-Electrophile Coupling of Aryl Halides with Alkyl Halides

Semiconductor quantum dots (QDs) offer many advantages as photocatalysts for synthetic photoredox catalysis, but no reports have explored the use of QDs with nickel catalysts for C-C bond formation. We show here that 5.7 nm CdS QDs are robust photocatalysts for photoredox-promoted cross-electrophile coupling (40 000 TON). These conditions can be utilized on small scale (96-well plate) or adapted to flow. NMR studies show that triethanolamine (TEOA) capped QDs are the active catalyst and that TEOA can displace native phosphonate and carboxylate ligands, demonstrating the importance of QD surface chemistry.

Picolinamide Ligands: Nickel-Catalyzed Reductive Cross-Coupling of Aryl Bromides with Bromocyclopropane and Beyond

The arylcyclopropane motif as the combination of aryl and cyclopropyl ring systems can be found in an increasing amount of approved and investigational drugs. Herein, we have developed a mild, efficient nickel-catalyzed reductive cross-coupling protocol, featuring a simple Ni(II) precatalyst and a novel picolinamide NN₂ pincer ligand. A variety of (hetero)aryl bromides could successfully couple with cyclopropyl bromide to furnish the valued arylcyclopropanes in good to excellent yields. This method is applicable to other alkyl bromides as well. Notably, the reaction is tolerant of a broad range of functionalities including free amines. Furthermore, the synthesis of several significant intermediates of bioactive molecules was achieved in grams, proving the practicability of this method.