The increasing global energy and environmental crises make it urgent to find and use renewable, clean, and environmentally benign new energy resources. New energy conversion schemes based on small molecule activation reactions, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR), have been proposed. For example, catalytic water splitting provides a promising way to convert solar energy to chemical energy, which is stored as the hydrogen fuel. Hydrogen oxidation in fuel cells is an energy-releasing process to generate electric energy and water as the only product. Although such a hydrogen-based new energy scheme is appealing, its viability is dependent on highly efficient and robust catalysts for these small molecule activation reactions. Recently, a variety of metal corroles have been demonstrated to be efficient in catalyzing HER, OER, and ORR. The redoxactive trianionic corrole ligands can afford a rigid four-coordinated square-planar molecular structure and are very effective in stabilizing high-valent metal centers. These features make metal corroles very attractive to serve as catalysts for these processes. More importantly, the structure of metal corroles can be systematically modified, which provides an ideal system to investigate the structure−reactivity relationship with aims to obtain fundamental knowledge on catalyst design and also catalytic mechanism. In this review, we summarize recently reported metal corrole catalysts for HER, OER, and ORR, as well as pay particular attention to the structure effects on these reactions.

Cobalt complexes have been extensively explored in catalyzing the oxygen reduction reaction (ORR), which is the cathode reaction in fuel cells. Although they show high activities, mononuclear Co complexes typically mediate the 2e reduction of O 2 to H 2 O 2 , and two Co sites are generally required to catalyze the 4e reduction of O 2 to H 2 O. Herein we report the significantly improved efficiency of covalently grafted Co corroles on carbon nanotubes (CNTs) for the 4e ORR. Azide-containing Co corroles can be attached to alkyne-modified CNTs via azide−alkyne cycloaddition. This attachment can avoid the formation of dimeric face-to-face Co corroles. The resulted hybrid catalyzes the 4e ORR in 0.5 M H 2 SO 4 aqueous solutions with a half-wave potential at 0.78 V versus reversible hydrogen electrode (RHE). This performance makes this hybrid one of the most efficient Co-based molecular ORR electrocatalysts. Control studies using Co corrole analogues loaded on CNTs via noncovalent interactions give ORR half-wave potentials at 0.68−0.61 V versus RHE. This work is significant in demonstrating that with proper covalent bond interactions to CNTs mononuclear Co corroles can become intrinsically active for the 4e ORR with significantly improved efficiency.

Electrodes for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are required in energy conversion and storage technologies. An assembly strategy involves covalently grafting Co corrole 1 onto Fe3O4 nanoarrays grown on Ti mesh. The resulted electrode shows significantly improved activity and durability for OER and ORR in neutral media as compared to Fe3O4 alone and with directly adsorbed 1. It also displays higher atom efficiency (at least two magnitudes larger turnover frequency) than reported electrodes. Using this electrode in a neutral Zn‐air battery, a small charge–discharge voltage gap of 1.19 V, large peak power density of 90.4 mW cm−2, and high rechargeable stability for >100 h are achieved, opening a promising avenue of molecular electrocatalysis in a metal–air battery. This work shows a molecule‐engineered electrode for electrocatalysis and demonstrates their potential applications in energy conversion and storage.

To investigate the effect of trans axial ligand on the oxygen reduction reaction (ORR), Co corroles with axial pyridine (py) and triphenylphosphine (PPh 3 ) ligands were examined. Two methods were used to immobilize these Co corroles on carbon nanotubes (CNTs): Co 5,15-bis(pentafluorophenyl)-10-( 4)-(1azido)phenylcorrole (1) was grafted on CNTs via covalent bonds, whereas Co tris(pentafluorophenyl)corrole (2) was directly loaded through simple physical adsorption. When examined in alkaline media, covalently grafted Co corroles displayed much higher electrocatalytic ORR efficiency than simply adsorbed analogues. ORR half-wave potential at 0.85 V versus reversible hydrogen electrode was achieved by using grafted Co corroles with PPh 3 axial ligand, which represents the state-of-the-art performance for molecular catalysis under alkaline conditions. Remarkably, 1 with PPh 3 ligand outperforms 1 with py ligand in terms of anodically shifted half-wave potential by 130 mV, but 2 with either PPh 3 or py axial ligand displays almost identical efficiency. These results show that (1) improved ORR performance can be achieved by using axial ligand of stronger electron-donating ability but (2) immobilization method may weaken catalyst design for molecular electrocatalysis. Therefore, caution should be paid when analyzing structural effects of molecular catalysts that are loaded on supporting materials.

A new [3+2] cycloaddition strategy for the direct synthesis of highly substituted pyrroles from the readily available α‐acylketene dithioacetals (or related substrates) and commercially available propargylamines under mild metal‐free conditions has been developed. In this reaction, the acyl group plays a critical role in driving the conjugate addition of propargylamine and further cyclization to give pyrroles. Furthermore, the wide scope was confirmed by the preparation of 1,2,3,4‐tetrasubstituted pyrroles (60–70% yields) via a formal 1,2‐acyl migrating [3+2] cycloaddition pathway with N‐methylprop‐2‐yn‐1‐amine as the secondary amine component.