Front Cover: Synthesis of Cytotoxic Iron‐Containing Macrocycles Through Unexpected C(sp2)−C(sp2) Bonds Formation (Eur. J. Inorg. Chem. 23/2023)
Carolina Torres‐GutiérrezAldo S. Estrada‐MontañoChristophe OrvainGeorg MellitzerChristian GaiddonRonan Le Lagadec
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The Front Cover shows a representation of stomach cancer cells being destroyed by an iron(II) complex bearing a tetradentate ligand. Gastric cancer is associated with a high mortality rate and high lethality and is frequently resistant to standard chemotherapies and immunotherapy. A cutting-edge reaction between Fe3(CO)12 and brominated or mercurated pincer derivatives promotes the formation of carbon−carbon bonds, and a 16-electron iron(II) complex with a tetradentate ligand originating from the dimerization of 6-phenyl-2,2′-bipyridine and a protonated 14-membered macrocycle from 2,6-diphenyl-pyridine were obtained. These new compounds are cytotoxic towards stomach cancer cells. Thanks to the presence of the iron center, the biological activity dramatically increased, and the complex was 5-fold more toxic than cisplatin on AGS cells. The cover was designed by Carolina Torres-Gutiérrez (the first author) and Hortensia Segura Silva. More information can be found in the Research Article by R. Le Lagadec and co-workers.Keywords:
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Protonation states of amino and hydroxyl phosphoroorganic derivatives have been studied. Based on the presented calculations we can state that mono- and di-protonated species on nitrogen are dominating states in solution. The protonation on phosphoryl oxygen occurs only as an effect of dynamic equilibrium between protonated species. The double and tripple protonation lead to very strong acid and thus such states are rather not present even in strong acidic media.
Brønsted–Lowry acid–base theory
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Terphenyl
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Metalation
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Phosphinite
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Iron complexes containing pincer ligands that incorporate N-heterocyclic carbene (NHC) moieties are of significant interest in organometallic catalysis in order to generate more oxidatively robust complexes that may exhibit novel catalytic properties. In order to define the effect that introducing NHC moieties into pincer ligands has on electronic structure and bonding in iron(II)-pincer complexes, MCD and DFT studies of (iPrCDA)FeBr2, (iPrPDI)FeBr2, and (iPrCNC)FeBr2 were performed. These studies quantify the electronic structures and bonding interactions as a function of pincer ligand variation. They also demonstrate that the observed ligand fields (and, hence, spin states) directly correlate to the increased Fe–C bonding and pincer-donating abilities that result from introducing NHC moieties into the pincer ligand. However, the net donor abilities of the pincers and the strength of the Fe-pincer interaction do not directly correlate to the number of NHC moieties present, but instead are determined to be due to differences in Fe–C and overall Fe-pincer bonding as a result of the position of the NHC moieties in the pincer ligand and the overall geometric constraints of the pincer architecture.
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The ECE-pincer ligand framework contains several positions that are readily functionalized and by doing so offer a wealth of possibilities to modify and fine-tune the structural and electronic properties of the metal centre in ECE-pincer metal complexes. Many ECE-type pincer metal complexes show remarkable catalytic performances in a number of catalytic reactions. With the aim to achieve enantioselective transformations, the development of chiral pincer metal complexes has been an integral part of pincer chemistry. The development of ECE’-type (E≠=/=E’) pincer metal complexes is a relatively new aspect of pincer chemistry. In such ECE’-type pincer complexes, the combination and cooperation of two different types of donor atom groups, E and E’, could lead to very interesting electronic and structural properties of the metal centers, which in turn could lead to improved catalytic performances. This thesis reports about a novel series of PCN- and PCS-pincer Pd- and Pt-complexes, phosphite P’CP’-pincer Pd-complexes, C,P-cyclometalated Pd- and Pt-complexes, and P-chiral phosphoramidite-pincer Pd-complexes. It provides an overview of the fine-tuning of the geometrics and electronic properties of these phosphorus-based pincer metal complexes through appropriate organic transformations of the pincer ligand. The newly reported pincer complexes were found to be active catalysts in C-P cross coupling, homoallylation, tandem catalytic, and aza-Michael addition reactions. Several aspects of this study deserve special attention. First of all, the development of new P-chiral pincer complexes derived from readily available chiral amino alcohols provide access to a library of new P-chiral phosphoramidite pincer metal complexes with great potential in enantioselective catalysis. Moreover, the synthetic protocol toward a series of electronically and structurally fine-tuned PCE-pincer metal complexes (E = N and S) using isovanillin as the common intermediate holds a great promising for the synthesis of new tailor-made ECE’-type pincer metal complexes. The combination and possible cooperativity of different E-donors has proven potential to alter the catalytic activities of pincer complexes. The further development of PCE-pincer metal complexes could, therefore, provide a stepping stone to improve and extend their application in homogeneous catalysis.
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Abstract Review: synthesis, characterization, properties, and catalytic applications of trianionic pincer metal complexes;171 refs.
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Abstract The gas‐phase basicities (GBs) of 12 nicotinoids were calculated for the two potential sites of protonation, the sp 2 pyridine and the sp 3 amino nitrogen atoms, at the B3LYP/6–311 + G(3df,2p)//B3LYP/6–31G(d,p) level and estimated from substituent effects on the GBs of 2‐substituted pyrrolidines and N ‐methylpyrrolidines. It was found that, in contrast to the Nsp 3 protonation in water, nicotinoids with a secondary amino nitrogen (substituted nornicotines, anabasine, anatabine) are protonated on the pyridine nitrogen. Nicotinoids with a tertiary amino nitrogen (substituted nicotines, N ‐methylanabasine, N ‐methylanatabine) are protonated on either the pyridine or the amino nitrogen, depending on the electronic effects of the substituents and the strength of an intramolecular CH···Nsp 3 hydrogen bond. Copyright © 2005 John Wiley & Sons, Ltd.
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