Boron subphthalocyanines with chloride and fluoride axial ligands and three antimony complexes chelated by corroles that differ in size and electron-richness were examined as electrocatalysts for reduction of protons to hydrogen. Experiment- and computation-based investigations revealed that all redox events are ligand-centered and that the meso-C of the corroles and the peripheral N atoms of the subphthalocyanines are the largely preferred proton-binding sites.

Corroles are synthetic porphyrin analogs that contain one meso carbon atom lesser and bear a trianionic N4 metal-chelating core. They require in-depth preparative chemistry, demonstrate unique coordination chemistry and have impressive and diverse physical properties, and these are commonly compared to their respective porphyrins. The corrole's macrocyclic system is inherently electron rich and chelates metal ions in a more compact, less symmetric tetranitrogen cavity compared to that of porphyrins. Herein, we cover the highlights of the corrole research through the decades by first reviewing, in a chronological sense, multi-step syntheses; some routes have since been discontinued. This is followed by describing post-functionalization of already formed corroles via reactions performed on either the macrocycle's periphery or the inner nitrogen atoms or on the existing substituents. We do also mention milestones in literature reviewing, publication of encyclopedias, and the creation of professional organizations and conferences (ICPP) which make up the corrole/porphyrin research landscape. Also highlighted are still existing challenges and future perspectives.

meta -BPDM is a new type of discrete conjugated porphyrinoid system and shows tremendous properties related to fluorescence and different behaviors with substituents on the sp 3 meso carbons.

Global energy needs the development of non-polluting and renewable sources. Hydrogen is most attractive as such, it has high energy density of 140 MJ/Kj and water as a byproduct.1 Despite the “simplicity” of the H-H bond, a catalyst is required to make its formation process efficient and economic.2 Although platinum group metal (PGM) are the best catalysts for the Hydrogen Evolution Reaction (HER) to date, they are rare and expensive.3 Conventional HER catalysis employs a transition metal with the ability to accommodate several oxidation states for the two-electron hydride transfer associated with hydrogen evolution. Emerging interest is being shown in the utilization of redox-active ligands that open alternative HER pathways, such as ligand-assisted metal-centered,4 ligand-centered,5and metal-assisted ligand-centered reactivity.6 Antimony corroles7 and two boron subphthalocyanines8 are reported as HER electrocatalysts. For that, two new corroles with electron donating and electron withdrawing meso-substituents were fully characterized X-ray crystallography, NMR, electronic spectra, and electrochemistry. All the complexes were studied under homogeneous conditions (CH3CN solvent and TFA as proton source), which revealed that catalysis relies on ligand reduction, in contrast with ordinary transition metal complexes. It revealed that the electron withdrawing substituents are best for homogeneous catalysis and the most electron rich substituents are best in heterogeneous catalysis in terms of onset potential and faradaic efficiency due to secondary sphere. References: (1) Beyene, B. B.; Hung, C. H. Recent Progress on Metalloporphyrin-Based Hydrogen Evolution Catalysis. Coord. Chem. Rev. 2020, 410, 213234. https://doi.org/10.1016/j.ccr.2020.213234. (2) Bullock, R. M.; Appel, A. M.; Helm, M. L. Production of Hydrogen by Electrocatalysis: Making the H-H Bond by Combining Protons and Hydrides. Chem. Commun. 2014, 50 (24), 3125–3143. https://doi.org/10.1039/c3cc46135a. (3) Karunadasa, H. I.; Chang, C. J.; Long, J. R. A Molecular Molybdenum-Oxo Catalyst for Generating Hydrogen from Water. Nature 2010, 464 (7293), 1329–1333. https://doi.org/10.1038/nature08969. (4) Jurss, J. W.; Khnayzer, R. S.; Panetier, J. A.; El Roz, K. A.; Nichols, E. M.; Head-Gordon, M.; Long, J. R.; Castellano, F. N.; Chang, C. J. Bioinspired Design of Redox-Active Ligands for Multielectron Catalysis: Effects of Positioning Pyrazine Reservoirs on Cobalt for Electro- and Photocatalytic Generation of Hydrogen from Water. Chem. Sci. 2015, 6 (8), 4954–4972. https://doi.org/10.1039/c5sc01414j. (5) Haddad, A. Z.; Garabato, B. D.; Kozlowski, P. M.; Buchanan, R. M.; Grapperhaus, C. A. Beyond Metal-Hydrides: Non-Transition-Metal and Metal-Free Ligand-Centered Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation. J. Am. Chem. Soc. 2016, 138 (25), 7844–7847. https://doi.org/10.1021/jacs.6b04441. (6) Sherbow, T. J.; Fettinger, J. C.; Berben, L. A. Control of Ligand PKa Values Tunes the Electrocatalytic Dihydrogen Evolution Mechanism in a Redox-Active Aluminum(III) Complex. Inorg. Chem. 2017, 56 (15), 8651–8660. https://doi.org/10.1021/acs.inorgchem.7b00230. (7) Luobeznova, I.; Raizman, M.; Goldberg, I.; Gross, Z. Synthesis and Full Characterization of Molybdenum and Antimony Corroles and Utilization of the Latter Complexes as Very Efficient Catalysts for Highly Selective Aerobic Oxygenation Reactions. Inorg. Chem. 2006, 45 (1), 386–394. https://doi.org/10.1021/ic051483g. (8) Mizrahi, A.; Bukuroshi, E.; Vestfrid, J.; Bender, T. P.; Gross, Z. Axial/Peripheral Chloride/Fluoride-Substituted Boron Subphthalocyanines as Electron Acceptors. Inorg. Chem. 2020, 59 (5), 2641–2645. https://doi.org/10.1021/acs.inorgchem.9b03529.

Current technologies for the mass production of hydrogen gas, needed for fuel cells, the synthesis of ammonia, and many other purposes, have an enormous carbon footprint. Less than 5% of H-2 is manufactured by the much cleaner water electrolysis process, mainly because electrodes are based on precious platinum. In line with the worldwide effort of replacing platinum by earth-abundant metals, this study focused on electrocatalytic proton reduction by cobalt. A series of cobalt(III) corroles that greatly varies in the electronic and steric effects of the meso-C substituents was fully characterized for investigating how the complexes differ in terms of their reduction potentials and as electrocatalysts for proton reduction to hydrogen gas. The smallest and most electron-rich derivative, with H atoms rather than larger and more electron-withdrawing substituents on the macrocycle, displayed the most interesting catalytic activity. Despite of its most negative Co-II/Co-I reduction potential in the absence of acid, catalysis by this complex was characterized by the lowest overpotential and the largest faradaic efficiency, as well as an activity that was almost as good as that of platinum under heterogeneous conditions. Mechanism-of-action investigations via experimental and computational analyses exposed that the superior performance of the most electron-rich complex is attributable to its capability of reducing protons by singly (rather than doubly) reduced cobalt.

A novel one-pot synthetic method to produce crystalline tri-octylphosphine (TOP) capped iron phosphide nanoparticles is reported here. Standard method of synthesizing FeP includes preparation of a precursor, sodium phosphide, which is finally reacted with ferric chloride (FeCl3).The methods for synthesizing iron phosphide (FeP), reported so far, rely on the use of toxic red or yellow phosphorus to generate the precursor, Sodium phosphide (Na3P). In present investigation, instead of red or yellow phosphorus, a relatively less toxic substance TOP and sodium metal (Na) have been used to yield Na3P. The synthesized nanoparticles were fully characterized by X-ray diffraction pattern (XRD), Infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID) analyses. The results showed that the synthesized FeP nanoparticles have the characteristic orthorhombic crystal structures, with the size similar to 10 nm and the coercivity 70 Oe at RT.