Jian-Ji Zhong

A Cascade Cross-Coupling Hydrogen Evolution Reaction by Visible Light Catalysis

Cross-dehydrogenative-coupling reaction has long been recognized as a powerful tool to form a C-C bond directly from two different C-H bonds. Most current processes are performed by making use of stoichiometric amounts of oxidizing agents. We describe here a new type of reaction, namely cross-coupling hydrogen evolution (CCHE), with no use of any sacrificial oxidants, and only hydrogen (H2) is generated as a side product. By combining eosin Y and a graphene-supported RuO2 nanocomposite (G-RuO2) as a photosensitizer and a catalyst, the desired cross-coupling products and H2 are achieved in quantitative yields under visible light irradiation at room temperature.

A Highly Efficient and Selective Aerobic Cross‐Dehydrogenative‐Coupling Reaction Photocatalyzed by a Platinum(II) Terpyridyl Complex

Thanks to the superior redox potential of platinum(II) complex compared with that of Ru(bpy)3(2+) in the excited state, an efficient and selective visible-light-induced CDC reaction has been developed by using a catalytic amount (0.25 %) of 1. With the aid of FeSO4 (2 equiv), the corresponding amide could not be detected under visible-light irradiation (λ=450 nm), but the desired cross-coupling product was exclusively obtained under ambient air conditions. A spectroscopic study and product analysis revealed that the CDC reaction is initiated by photoinduced electron-transfer from N-phenyltetrahydroisoquinoline to the complex. An EPR (electron paramagnetic resonance) experiment provides direct evidence on the generation of superoxide radical anion (O2(-·)) rather than singlet oxygen ((1)O2) under irradiation of the reaction system, in contrast to that reported in the literature. Combined, the photoinduced electron-transfer and subsequent formation of superoxide radical anion (O2(-·)) results in a clean and facile transformation.

Cross-coupling hydrogen evolution reaction in homogeneous solution without noble metals.

A highly efficient noble-metal-free homogeneous system for a cross-coupling hydrogen evolution (CCHE) reaction is developed. With cheap, earth-abundant eosin Y and molecular catalyst Co(dmgH)2Cl2, good to excellent yields for coupling reactions with a variety of isoquinolines and indole substrates and H2 have been achieved without any sacrificial oxidants. Mechanistic insights provide rich information on the effective, clean, and economic CCHE reaction.

Cobalt-Catalyzed Cross-Dehydrogenative Coupling Reaction in Water by Visible Light

By using catalytic amount of CoCl2 with dmgH (dimethylglyoxime) as ligand to form a photosensitizer in situ, a highly selective, efficient, and environmentally benign visible light mediated cross-dehydrogenative coupling (CDC) reaction has been developed in aqueous medium. The desired cross-coupling C-C bonds that involve Csp3 with Csp, Csp2, and Csp3, respectively, were achieved exclusively in high yields without formation of any other byproduct.

Graphene-supported RuO2 nanoparticles for efficient aerobic cross-dehydrogenative coupling reaction in water.

A cross-dehydrogenative coupling (CDC) reaction between tertiary amines and nitroalkanes has been realized under an oxygen atmosphere in water simply by using graphene-supported RuO(2) as the catalyst, which was made from water-soluble graphene with sulfonic groups and RuCl(3)·nH(2)O to form RuO(2)·nH(2)O nanocomposites in situ. In contrast to RuCl(3)·nH(2)O and RuO(2)·nH(2)O, the graphene-supported RuO(2) nanoparticles exhibited higher activity and stability for the aerobic CDC reaction in water.

A unique 1,2-acyl migration for the construction of quaternary carbon by visible light irradiation of platinum(II) polypyridyl complex and molecular oxygen.

A unique 1,2-acyl migration for the construction of quaternary carbon in a one-pot reaction under visible light is described. By irradiating a platinum(II) polypyridyl complex with visible light, enamine 1 is able to react with alcohol 2 to yield compound 3 featuring a quaternary carbon via 1,2-acyl migration and concurrent esterification. Studies on the mechanism reveal that the platinum(II) complex is able to generate singlet oxygen ((1)O2) that is responsible for this unprecedented intramolecular 1,2-acyl migration transformation.

Visible Light-Induced Synthesis of 3,4-Diarylthiophenes from 3,4-Diaryl-2,5-dihydrothiophenes

Using a catalytic amount of platinum(II) terpyridyl complex 3, 3,4-diarylthiophenes (2a-f) could be synthesized from 3,4-diaryl-2,5-dihydrothiophenes (1a-f) under visible light (λ > 450 nm) irradiation in degassed CH(3)CN. Spectroscopic study and product analysis reveal that the reaction is initiated by photoinduced electron transfer from 3,4-diaryl-2,5-dihydrothiophenes to platinum(II) complex 3, leading to the formation of 3,4-diarylthiophenes.

Identifying key intermediates generated in situ from Cu(II) salt–catalyzed C–H functionalization of aromatic amines under illumination

Cu(II) salts can activate C–H bonds of aromatic amines or imines to construct C–C bonds in air without external photosensitizer. Copper compounds involved in photocatalysis have recently spurred considerable interest for their novel transformations. However, mechanistic investigations are still in infancy. We find a new type of reaction, that is, Cu(II) salt–catalyzed C–H functionalization of aromatic amines triggered by visible light irradiation. An array of mechanistic observations, including high-resolution mass spectrometry, ultraviolet-visible absorption spectrum, electron spin resonance, x-ray absorption near-edge structure, and density functional theory calculation, have identified the key intermediates generated in situ in the transformation. Integration of single-electron transfer, singlet oxygen (1O2), and new absorption species, intermediate I and intermediate II formed in situ from Cu(II) salts and substrate amines or imines, respectively, is responsible for the N–H and C–H bond activation of secondary amines to couple with nucleophiles in air, thereby leading to the formation of quinoline, indolo[3,2-c]quinoline, β-amino acid, and 1,4-dihydropyridine derivatives in moderate to good yields under visible light irradiation at room temperature.