There have recently been significant developments in the applications of metal-organic frameworks (MOFs). We have developed new applications of MOFs as catalysts, as supports for metal nanoparticles and as templates/precursors for functional materials synthesis. Metal nanoparticles (NPs) have been encapsulated into MOFs by a variety of approaches, especially the double-solvents method, which exhibit excellent catalytic performances. We have developed a from-MOF-to-carbon approach to synthesize carbon materials using MOFs as templates/precursors, which has distinguished advantages of morphology control and heteroatom doping. The resultant carbon materials and carbon composites with metal species, including metal single atoms, clusters and nanoparticles, display excellent functionalities as electrode materials for energy storage and conversion and as catalysts for a variety of reactions. We have proposed ʻʻquasi-MOFsʼʼ formed through controlled deligandation, which partially keep the porosity and highly expose the metal nodes of MOFs, leading to dramatically enhanced catalytic performances.

Researchers in the authorʼs laboratory have investigated small-molecule activation reactions using low-coordinate early transition-metal complexes supported by sterically demanding N-hydrocarbyl anilide ligands. Such complexes are potent one, two, or three-electron reducing agents, and early on the focus was on small molecules including N2, NO, and N2O with metalligand multiply bonded systems formed as products of the bond activation reactions. Reactions with P4 (white phosphorus) and As4 led respectively to complexes with metal-phosphorus or metal-arsenic triple bonds. This led to the notion of element or molecule activation using transition metals, to be followed by atom or group transfer to organic molecules. Phosphorus transfer was achieved in a novel phosphaalkyne synthesis method involving transfer of a P4-derived phosphorus atom using a niobium complex. Next, diphosphorus transfer was achieved using first a niobium and then an anthracene-based platform, the latter culminating in a synthesis of diphosphatriazolate, P2N3 −. Triphosphorus group transfer was harnessed in a synthesis of AsP3. This was echoed by the synthesis of HCP3. Anthracene emerged as a privileged two-electron platform for the construction of molecular precursors to reactive intermediates including HCP, P2, and phosphorus mononitride, PN. This account thus describes an arc from the activation of kinetically inert small molecules to the synthesis, transfer, or transient generation of reactive ones.

In aerobic organisms, a variety of metalloproteins regulate reactions involving molecular oxygen (O₂). These include O₂-transport proteins such as hemoglobin (Hb) and hemocyanin (Hc), electron transfer proteins and cytochrome c oxidase involved in mitochondrial oxidative phosphorylation, and various metalloproteins such as oxygenases and oxidases that catalyze selective oxidation of alkanes, alkenes, aromatics, and various natural products. These reactions involve the coordination of oxygen species such as O₂, O₂^-•, and H₂O₂ to the metal and their activation. Since these processes involve redox reactions, redox-active metals such as iron and copper are present in the active center. Various highly functional metal complexes have been synthesized to understand these reactions and reaction mechanisms from the viewpoint of bioinorganic chemistry, and to develop practical catalysts and other practically useful compounds. In this Accounts, the authorʼs research in relation to them is summarized as follows: (1) development of dicopper complexes that reproduce the reversible O₂-binding function at the dicopper site of hemocyanin, (2) development of diiron complexes that reproduce O₂-activation at the diiron site of soluble methane monooxygenase and related selective oxidation of alkanes, alkenes, and various organic compounds.

Metal−ligand cooperation, in which both metal and ligand participate in bond cleavage and formation, is gathering great attention in recent years. While many types of complexes have been employed in metal–ligand cooperative heterolytic cleavage of H–H bond, a cyclopentadienone–hydroxycyclopentadienyl-based metal complex, originally reported by Shvo, has a unique character, that is, red/ox activity of the metal center along with the heterolytic bond cleavage. To date, various transition-metal complexes (M = Ru, Fe, Re, Mo, Ir, Rh, Pt, etc.) having cyclopentadienone/ hydroxycyclopentadienyl ligands are reported to show catalytic reactions utilizing the heterolytic cleavage/formation of H–H bond. On the other hand, there are substantial efforts to expand the scope of the bond to be cleaved other than the H−H bond. This article summarizes our recent progress in the metal−ligand cooperative cleavages of C–H, B–H and Si−H bonds by cyclopentadienone metal complexes with introduction of the historical background.

This study explores the selective oxidation of inert hydrocarbons employing transition-metal complexes bearing reactive oxygen ligand, inspired by metalloenzyme mechanisms. We developed oxidation systems enabling hydroxylation of unactivated alkanes and arenes under mild conditions, focusing on direct observation of catalytic active species. Using iron-porphyrin complexes, we established a system stabilizing the Compound I model species even near room temperature, overcoming previous limitations from its extreme reactivity. This allowed for quantitative analysis of C–H hydroxylation, revealing new structure–reactivity correlations, including the roles of axial ligand of Compound I and bond “hardness” of the substrate. We also designed redox-active ligand frameworks to facilitate alkane oxidation through a concerted mechanism, and fluorocarbon-phase catalysts that selectively hydroxylate alkanes while suppressing overoxidation of alcohols via product-phase separation. In parallel, we investigated arene hydroxylation catalyzed by nickel complexes supported by multidentate amine ligands, achieving high selectivity and proposing a di(μ-oxido)dinickel(III) complex as the active intermediate. Overall, this research provides new insights into hydrocarbon activation via well-defined high-valent metal–oxido species, with implications for catalyst design.

Here in this manuscript, 30-year history of group-10 metal catalyzed copolymerization of olefins with polar monomers are reviewed focusing on roles played by unsymmetric bidentate ligands. Nickel and palladium are the metal of choice and ligands consists of combination of a strong s-donor such as a phosphine or a carbenes and a stable oxygen anion such as sulfonate, phenoxide, etc have been used for the copolymerization affording linear polyethylenes or head-to-tail polypropylenes incorporating polar monomers. Certain steric-demand is essential for giving high molecular-weight polymers as are discussed in the mechanistic considerations.

Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University Kazuhiro Uemura Although many one-dimensional chain complexes bridged by halide ions or organic molecules have been reported, relatively few are extended by direct metal–metal bonds, and the metals involved are limited to Rh, Pd, Ir, and Pt. In this paper, several one-dimensional complexes in which two or three metals are regularly aligned with metal–metal bonds will be shown, utilizing the HOMO–LUMO interaction at the σ* orbitals between two types of complexes. The obtained single crystals of the heterometallic one-dimensional complexes exhibit an attractive color with a metallic luster. In addition, while one-dimensional complexes consisting of a single species have a partially oxidized σ-type orbital as the HOMO, heterometallic one-dimensional complexes can exhibit an unusual electronic structure in which another metal orbital is inserted between the σ-type valence and conduction bands as the HOMO, enabling paramagnetism and band gap modulation. Our research group has also found that these complexes exhibit strong magnetic interactions via metal–metal bonds.