Alkylation of the α-amino C-H bonds of anilines photocatalyzed by a DMEDA-Cu-benzophenone complex: reaction scope and mechanistic studies

Photogeneration of Chlorine Radical from a Self-Assembled Fluorous 4CzIPN•Chloride Complex: Application in C-H Bond Functionalization

The chlorine radical is a strong HAT (Hydrogen Atom Transfer) agent that is very useful for the functionalization of C(sp3)-H bonds. Albeit highly attractive, its generation from the poorly oxidizable chloride ion mediated by an excited photoredox catalyst is a difficult task. We now report that 8Rf8-4CzIPN, an electron-deficient fluorous derivative of the benchmark 4CzIPN photoredox catalyst belonging to the donor-acceptor carbazole-cyanoarene family, is not only a better photooxidant than 4CzIPN, but also becomes an excellent host for the chloride ion. Combining these two properties ultimately makes the self-assembled 8Rf8-4CzIPN•Cl- dual catalyst highly reactive in redox-neutral Giese-type C(sp3)-H bond alkylation reactions promoted by the chlorine radical. Additionally, because of its fluorous character, the efficient separation/recovery of 8Rf8-4CzIPN could be envisioned.

Transition-metal-catalyzed C-H bond alkylation using olefins: recent advances and mechanistic aspects

Transition metal catalysis has contributed immensely to C-C bond formation reactions over the last few decades, and alkylation is no exception. The superiority of such methodologies over traditional alkylation is evident from minimal reaction steps, shorter reaction times, and atom economy while also allowing control over regio- and stereo-selectivity. In particular, hydrocarbonation of alkenes has grabbed increased attention due its fundamental ability to effectively and selectively synthesise a wide range of industrially and pharmaceutically relevant moieties. This review attempts to provide a scientific viewpoint and a systematic analysis of the recent developments in transition-metal-catalyzed alkylation of various C-H bonds using simple and activated olefins. The key features and mechanistic studies involved in these transformations are described briefly.

Dual Photoredox Ni/Benzophenone Catalysis: A Study of the NiII Precatalyst Photoreduction Step

The combination of Ni^IIX₂ salts with a bipyridine-type ligand and aromatic carbonyl-based chromophores has emerged as a benchmark precatalytic system to efficiently conduct cross-couplings mediated by light. Mechanistic studies have led to two scenarios in which Ni⁰ is proposed as the catalytic species. Nonetheless, in none of these studies has a Ni^II to Ni⁰ photoreduction been evidenced. By exploiting UV-visible, nuclear magnetic resonance, resonance Raman, electron paramagnetic resonance, and dynamic light scattering spectroscopies and also transmission electron microscopy, we report that, when photolyzed by UVA in alcohols, the structurally defined [Ni^II₂(μ-OH₂)(dtbbpy)₂(BPCO₂)₄] complex 1 integrating a benzophenone chromophore is reduced into a diamagnetic Ni^I dimer of the general formula [Ni^I₂(dtbbpy)₂(BPCO₂)₂]. In marked contrast, in THF, photolysis led to the fast formation of Ni⁰, which accumulates in the form of metallic ultrathin Ni nanosheets characterized by a mean size of ∼100 nm and a surface plasmon resonance at 505 nm. Finally, it is shown that 1 combined with UVA irradiation catalyzes cross-couplings, that is, C(sp³)-H arylation of THF and O-arylation of methanol. These results are discussed in light of the mechanisms proposed for these cross-couplings with a focus on the oxidation state of the catalytic species.