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The synthesis of cyclometalated osmium complexes is usually more complicated than of other transition metals such as Ni, Pd, Pt, Rh, where cyclometalation reactions readily occur via direct activation of C-H bonds. It differs also from their ruthenium analogs. Cyclometalation for osmium usually occurs under more severe conditions, in polar solvents, using specific precursors, stronger acids, or bases. Such requirements expand reaction mechanisms to electrophilic activation, transmetalation, and oxidative addition, often involving C-H bond activations. Osmacycles exhibit specific applications in homogeneous catalysis, photophysics, bioelectrocatalysis and are studied as anticancer agents. This review describes major synthetic pathways to osmacycles and related compounds and discusses their practical applications.
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http://dx.doi.org/10.3390/molecules26061563 | DOI Listing |
Chemistry
August 2025
CNRS, L2CM, Université de Lorraine, Nancy, 54000, France.
Two Ru(II) and Os(II) homoleptic complexes based on a phenanthroline-pyridylidene tridentate ligand have been designed to reach NIR emission by combining strong σ-donation, provided by the unconventional N-heterocyclic carbene (NHC) pyridylidene moiety, with the low-lying π-accepting phenanthroline scaffold. Detailed experimental and computational investigations of the photophysical properties of this novel family of cyclometallated complexes reveal emission squarely falling in the NIR domain peaking at λ = 790 nm for the Os(II) complex, while emission is hypsochromically shifted at λ = 747 nm for the Ru(II) homologue in deaerated CHCN solution at room temperature. Despite the triplet metal-to-ligand charge transfer (MLCT) nature that characterizes the excited state in both complexes, density functional theory (DFT) calculations allow to ascribe the remarkable optical shift observed in the latter to the larger spin-orbital coupling (SOC) effects exerted by the heavier metal.
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January 2025
Department of Chemistry, Indian Institute of Technology Guwahati, 781039, Guwahati, Assam, India.
Oxidative cleavage of olefins is a useful reaction in organic synthesis. The most well-known catalytic system is the osmium based Lemieux-Johnson catalyst, which generally requires high catalyst loading and tends to suffer from rapid overoxidation to produce the acid predominantly. Hence, the development of a mild, general, and selective method toward the oxidative cleavage of alkenes to carbonyl compounds is highly desired.
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March 2024
Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Straße 42, 1090 Vienna, Austria.
In this contribution we report the synthesis, characterization and anticancer activity of novel cyclometalated 4-phenylthiazole-derived ruthenium(II) (2a-e) and osmium(II) (3a-e) complexes. Formation and sufficient purity of the complexes were unambigiously confirmed by H-, C- and 2D-NMR techniques, X-ray diffractometry, HRMS and elemental analysis. The binding preferences of these cyclometalates to selected amino acids and to DNA models including G-quadruplex structures were analyzed.
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June 2023
Departament de Química Inorgànica i Orgànica, Facultat de Química, Secció de Química Inorgànica, Universitat de Barcelona, Martí i Franquès, 1-11, 08028 Barcelona, Spain.
Inorg Chem
April 2023
Czech Academy of Sciences, Institute of Biophysics, CZ-61200 Brno, Czech Republic.
We present the synthesis and characterization of six new heteroleptic osmium(II) complexes of the type [Os(C^N)(N^N)]OTf (N^N = 2,2'-bipyridine and dipyrido[3,2-:2',3'-]quinoxaline; C^N = deprotonated methyl 1-butyl-2aryl-benzimidazolecarboxylate) with varying substituents in the R3 position of the phenyl ring of the cyclometalating C^N ligand. The new compounds are highly kinetically inert and absorb a full-wavelength range of visible light. An investigation of the antiproliferative activity of the new compounds has been performed using a panel of human cancer and noncancerous 2D cell monolayer cultures under dark conditions and green light irradiation.
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