Inorganic reaction mechanisms

The Dalton Division of the Royal Society of Chemistry has seven interest groups in the field of inorganic chemistry and one of those is the inorganic reaction mechanism discussion group (IRMG). These discussion groups bring the community together and organise scientific meetings, workshops and summer schools in their area of research. Furthermore, the discussion groups provide valuable opportunities for young academics and students to network and disseminate results. In particular, the IRMG is one of the lead discussion groups behind the highly successful biennial Dalton20xx conferences.

The IRMG was founded in 1970 by Martin Tobe and Geoff Sykes (among others) and has been a thriving community ever since. Since its foundation, regular meetings have been organised that have advanced research in the area of inorganic reaction mechanisms. This themed collection celebrates 50 years of the IRMG and shows that it has expanded its topics and borders. Innovations in computational techniques and analytical instrumentation have allowed for studies of unparalleled scope and accuracy. As such we are pleased to see contributions from experimental and computational research groups in areas ranging from transition metal catalysis, enzymology and biomimetic chemistry. Much of the work highlighted in this issue could barely have been conceived of in 1970. Below we highlight some examples of inorganic reaction mechanism studies contributed to this themed collection.

The experimental studies by Banse et al. (DOI: 10.1039/C9DT03487K) on biomimetic iron complexes in their reaction with hydrogen peroxide led to the trapping and characterization of several short-lived intermediates during the reaction cycle, namely iron(IV)-oxo and iron(III)-hydroperoxo species. These kinetic and spectroscopic studies give insight into how enzymes and synthetic catalysts activate dioxygen or hydrogen peroxide on an iron centre. In line with these studies, Martínez et al. (DOI: 10.1039/C9DT03557E) studied the effect of pH on the oxygen activation reaction by an iron bis-thiosemicarbazone complex and established kinetics pathways and reaction rates that give insight into its catalytic reaction mechanism. Further biomimetic iron(IV)-oxo complexes and their kinetic reaction mechanism were reported by Comba and co-workers (DOI: 10.1039/C9DT04578C) using an iron-bispidine type complex. The work highlighted the importance and the effect of the equatorial ligand on the charge and spin distributions in the system that determine the catalytic efficiency of the oxidant.

In catalysis research, Davies et al. (DOI: 10.1039/C9DT04581C) report the cyclometallation on the Rh/Ir centre of 2-phenylpyridines with different electron donating and withdrawing groups, which gives changes in hydrogen atom transfer kinetics and kinetic isotope effects. Using catalytic Rh pincer complexes, Macgregor and Weller and co-workers (DOI: 10.1039/C9DT03358K) studied the dehydrocoupling reaction and found kinetic and computational evidence of a neutral hydride as a reaction intermediate. The direct benzene coupling reaction on a Pt centre was studied by Abu Omar et al. (DOI: 10.1039/C9DT04261J) and kinetic profiles with supporting density functional theory studies give insight into the details of the reaction mechanism.

The broad spectrum of different topics is highlighted by the inclusion of several biochemical studies in this themed collection. Worrall et al. (DOI: 10.1039/C9DT04583J) describe the hydrogen peroxide reactivity in peroxidases using a combination of X-ray absorption spectroscopy, stopped-flow kinetics, deuterium kinetic isotope effect studies and electron paramagnetic resonance spectroscopy. They show that the changes in the active site pocket affect the proton delivery system and the biosynthesis of its active species. Studies on the diiron enzyme ferritin by Le Brun et al. (DOI: 10.1039/C9DT03570B) focus on crystallography studies of the wildtype and variants, and insights into iron entrance and exit channels of the protein were obtained. Computational studies of Tahsini et al. (DOI: 10.1039/D0DT00007H) on the nonheme iron dioxygenase AlkB investigated various dealkylation pathways of alkylated DNA bases. It was found that a high-valent iron(IV)-oxo enzymatic intermediate can rapidly react with aliphatic groups and olefins through either hydroxylation or epoxidation reactions that can initiate the dealkylation process. An analogous enzyme, namely fumitremorgin B endoperoxidase, was studied by Borowski and Miłaczewska (DOI: 10.1039/C9DT02581B). It catalyses endoperoxide formation as part of the biosynthesis of verruculogen. A combination of molecular dynamics simulations and density functional studies of cluster models gave insight into the mechanistic features of this biosynthesis process.

Vanadium(IV)-oxo and vanadium(V)-oxo porphyrin complexes and their reaction with peroxides for the hydroxylation and epoxidation of cyclohexene were studied by de Visser and Mubarak (DOI: 10.1039/C9DT03048D). It was found that an anionic ligand trans to the oxo group in the presence of H₂O₂ forms the highly reactive vanadium-peroxo complex. Reaction mechanisms for various pathways were calculated. In related peroxidase chemistry Baik and co-workers (DOI: 10.1039/D0DT00042F) studied a cobalt(III)-peroxo complex and investigated the dioxygenation of nitriles using computational methods, establishing the ligand effects in the reaction mechanism. Deoxygenative hydrosilation of carbon dioxide on a scandium centre was reported by the Piers group (DOI: 10.1039/C9DT04323C). Synthesis and crystallographic characterisation of several intermediates in the reaction cycle gave insight into the chemical reaction mechanism. The Waterman group (DOI: 10.1039/C9DT04870G) investigated an iron cyclopentadienyl dicarbonyl complex that, through photoactivation, triggers a heterodehydrocoupling reaction and established the factors that determine the catalytic reaction mechanism.

These and several more papers contribute to this themed collection on inorganic reaction mechanisms and highlight the diversity in topics, research interests and general appeal. We are looking forward to the next 50 years of inorganic reaction mechanisms research and hope Dalton Transactions will continue to support us, as a natural home for the publication of research from this community!

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