Redox-Induced Aromatic C–H Bond Functionalization in Metal Complex Catalysis from the Electrochemical Point of View

This review generalizes and specifies the oxidizing ability of a number of oxidants used in palladium (Pd)-catalyzed aromatic C–H functionalizations. The redox potentials have been analyzed as the measure of oxidant strength and applied to the reasoning of the efficiency of known reactions where catalytic cycles include cyclometalated palladium complexes (and other organopalladium key intermediates)

Exploring Mechanisms in Ni Terpyridine Catalyzed C-C Cross-Coupling Reactions-A Review

In recent years, nickel has entered the stage for catalyzed C-C cross-coupling reactions, replacing expensive palladium, and in some cases enabling the use of new substrate classes. Polypyridine ligands have played an important role in this development, and the prototypical tridentate 2,2':6',2 ''-terpyridine (tpy) stands as an excellent example of these ligands. This review summarizes research that has been devoted to exploring the mechanistic details in catalyzed C-C cross-coupling reactions using tpy-based nickel systems

Non-Noble-Metal Mono and Bimetallic Composites for Efficient Electrocatalysis of Phosphine Oxide and Acetylene C-H/P-H Coupling under Mild Conditions

The present work describes an efficient reaction of electrochemical phosphorylation of phenylacetylene controlled by the composition of catalytic nanoparticles based on non-noble-metals. The sought-after products are produced via the simple synthetic protocol based on room temperature, atom-economical reactions, and silica nanoparticles (SNs) loaded by one or two d-metal ions as nanocatalysts. The redox and catalytic properties of SNs can be tuned with a range of parameters, such as compositions of the bimetallic systems, their preparation method, and morphology. Monometallic SNs give phosphorylated acetylene with retention of the triple bond, and bimetallic SNs give a bis-phosphorylation product. This is the first example of acetylene and phosphine oxide C-H/P-H coupling with a regenerable and recyclable catalyst

Morpholine Radical in the Electrochemical Reaction with Quinoline <i>N</i>-Oxide

An electrochemical reaction between quinoline N-oxides and morpholine was developed by using Cu(OAc)2 as a catalyst, generating products of 4-aminoquinoline N-oxides in CH2Cl2 or 2-aminoquinoline N-oxides in CH3CN in good yields. With an increase in the amount of electricity passed, the product deoxygenates with the formation of aminoquinolines. The advantages of the reaction are mild conditions, room temperature, the use of morpholine rather than its derivatives, and the ability to control the process when the electrolysis conditions change. Bisubstituted quinoline has also been obtained. The redox properties of both individual participants of C–H/N–H cross-coupling and multicomponent systems were established by voltammetry and EPR methods. For the first time, the EPR spectrum of the morpholine radical was recorded at room temperature, and its magnetic resonance parameters were determined in CH2Cl2. Mechanisms for the catalytic reaction have been proposed. This is a simple and easy-to-perform method for introducing a morpholine substituent, important in medicinal chemistry and other fields, by C–H/N–H cross-coupling

Mechanism-Driven Development of <i>N</i>‑(Quinolin-8-yl)-benzamide Coupling Reactions via C–H or N–H Activation

The mechanistic details of the oxidative coupling of compounds with a number of different redox centers are investigated using N-(quinolin-8-yl)-benzamide (L) as a model substrate. The control of the chemical or electrooxidation parameters in the absence or presence of a cobalt catalyst makes it possible to obtain regioselectively different oxidative coupling products (ortho- vs para-C–H/C–H vs C–H/N–H vs N–H/N–H). The results indicate that the operative mechanism depends on the type of oxidized reaction center and the oxidant nature. Oxidation affects the para-C–H bond in quinoline or the N–H fragment or the ortho-C–H bond in the benzene substituent in the molecule. The intermediate Co(II)[L–H]2 complex and C–H-activated CoIII metallacycle with benzamide ligands, which are shown to oxidize at close potentials, have been isolated and characterized by various techniques, including X-ray diffraction and voltammetry. The strength of the oxidizing agent affects the formation of a particular product, though not acting as the determining factor. Two-electron oxidation of Co(II)[L–H]2 yields to C–N coupling, but one-electron oxidation of Co(III) leads to ortho-C–C coupling. All electrochemical reactions are performed under mild conditions at room temperature without adding special reagents (oxidants, halides, phosphines, etc.)

Electrochemical Ortho Functionalization of 2‑Phenylpyridine with Perfluorocarboxylic Acids Catalyzed by Palladium in Higher Oxidation States

The electochemical oxidation of palladium acetate or palladium perfluoroacetate in the presence of 2-phenylpyridine promotes catalytic ortho C–H substitution reactions. As possible intermediates, Pd­(II) metallacycles with Pd-bound acetate, perfluoroacetate, and perfluoroheptanoate substituents have been isolated and characterized: binuclear [(PhPy)­Pd­(μ-OAc)]₂ and [(PhPy)­Pd­(μ-TFA)]₂ and mononuclear [(PhPy)­Pd­(TFA)]­(CH₃CN), [(PhPy)­Pd­(TFA)]­(PhPy), and [(PhPy)­Pd­(PFH)]­(PhPy). The fluorinated derivatives were found to exist in solvent-dependent equilibria between mononuclear and binuclear forms. Cyclic voltammetry was used to elucidate redox properties of the palladacycles and the oxidation route to the final products