In situ copper photocatalysts triggering halide atom transfer of unactivated alkyl halides for general C(sp3)-N couplings.

Direct reduction of unactivated alkyl halides for C(sp3)-N couplings under mild conditions presents a significant challenge in organic synthesis due to their low reduction potential. Herein, we introduce an in situ formed pyridyl-carbene-ligated copper (I) catalyst that is capable of abstracting halide atom and generating alkyl radicals for general C(sp3)-N couplings under visible light. Control experiments confirmed that the mono-pyridyl-carbene-ligated copper complex is the active species responsible for catalysis. Mechanistic investigations using transient absorption spectroscopy across multiple decades of timescales revealed ultrafast intersystem crossing (260 ps) of the photoexcited copper (I) complexes into their long-lived triplet excited states (>2 µs). The non-Stern-Volmer quenching dynamics of the triplets by unactivated alkyl halides suggests an association between copper (I) complexes and alkyl halides, thereby facilitating the abstraction of halide atoms via inner-sphere single electron transfer (SET), rather than outer-sphere SET, for the formation of alkyl radicals for subsequent cross couplings.

B(C6F5)3-Catalyzed Dehydrogenation of Pyrrolidines to Form Pyrroles.

Pyrroles are important N-heterocycles found in medicines and materials. The formation of pyrroles from widely accessible pyrrolidines is a potentially attractive strategy but is an underdeveloped approach due to the sensitivity of pyrroles to the oxidative conditions required to achieve such a transformation. Herein, we report a catalytic approach that employs commercially available B(C6F5)3 in an operationally simple procedure that allows pyrrolidines to serve as direct synthons for pyrroles. Mechanistic studies have revealed insights into borane-catalyzed dehydrogenative processes.

Radical metallacyclopropene: synthesis, structure and aromaticity.

Metallaaromatics are an important class of aromatic compounds, showing diverse and interesting aromatic properties. Radical rhenabenzofurans 1-3 with a fused metallacyclopropene unit are reported, containing d1 Re centers. Computational studies show that the three-membered rhenacyclopropene ring is σ-aromatic, while the rhenafuran ring is nonaromatic. These complexes represent the first radical metallacyclopropenes. α-Metallabenzofuran complexes 4-5 with d0 Re centers and 6 with a d2 Re center are also synthesized. α-Metallabenzofurans 1-6 have adjacent oxidation states (Re(III), Re(IV), and Re(V)). Both the structure and aromatic nature of these metallacycles are affected by the change of oxidation states of the metal center.

Regioselective coupling of benzyl chlorides with allyl and allenyl boronates catalysed by a bidentate phosphine ligand/palladium catalyst.

A palladium-catalysed aromative benzylic allylation and allenylation of benzyl chlorides with allyl and allenyl pinacolborates is described for the first time. The reactions proceed smoothly in the presence of a bidentate phosphine ligand to afford normal cross-coupling products in good yields. This novel synthetic procedure exhibits good tolerance for various electron-withdrawing and -donating functional groups linked to aromatic rings and is also well tolerant of sensitive functional groups such as NO2, CF3, CN, and COOMe. The utilisation of a bidentate ligand and heating are essential to transformation. The DFT calculation results reveal that wide-bite-angle bidentate ligands are beneficial to the formation of an η1-benzyl-η1-allylpalladium intermediate and that the normal coupling is thermodynamically favourable.

A Small Organic Molecular Catalyst with Efficient Electron Accumulation for Near-unity CO2 Photoreduction.

Molecular catalysis is of great interest to CO2 photoreduction. Various transition metal complexes have been developed as efficient molecular catalysts. However, it remains a challenge to catalyze CO2 reduction by a small organic molecular photocatalyst, as the accumulation of multiple electrons in a small organic molecule is normally difficult for CO2 reduction. We report herein a small organic molecular catalyst can be used for selective reduction of CO2 to CO under visible light irradiation. The turnover number (TON) of CO formation is found to be 400±26 with near 100% selectivity in DMF/H2 O medium. UV-Vis absorption spectroscopy, density functional theory (DFT) calculations, and spectroelectrochemical studies demonstrate that the organic molecular catalyst is capable of accumulating electrons through a 2e- reduced product which shows good stability and is responsible for interacting with CO2 . These findings elucidate an accessible way to develop purely organic molecular catalysts for CO2 reduction by strengthening the electron accumulation.