Selective Preparation of a Heteroleptic Cyclometallated Ruthenium Complex Capable of Undergoing Photosubstitution of a Bidentate Ligand

Abstract

Cyclometallated ruthenium complexes typically exhibit red‐shifted absorption bands and lower photolability compared to their polypyridyl analogues. They also have lower symmetry, which sometimes makes their synthesis challenging. In this work, the coordination of four N,S bidentate ligands, 3‐(methylthio)propylamine (mtpa), 2‐(methylthio)ethylamine (mtea), 2‐(methylthio)ethyl‐2‐pyridine (mtep), and 2‐(methylthio)methylpyridine (mtmp), to the cyclometallated precursor [Ru(bpy)(phpy)(CH 3 CN) 2 ] + (bpy=2,2′‐bipyridine, Hphpy=2‐phenylpyridine) has been investigated, furnishing the corresponding heteroleptic complexes [Ru(bpy)(phpy)(N,S)]PF 6 ([ 2 ]PF 6 –[ 5 ]PF 6 , respectively). The stereoselectivity of the synthesis strongly depended on the size of the ring formed by the Ru‐coordinated N,S ligand, with [ 2 ]PF 6 and [ 4 ]PF 6 being formed stereoselectively, but [ 3 ]PF 6 and [ 5 ]PF 6 being obtained as mixtures of inseparable isomers. The exact stereochemistry of the air‐stable complex [ 4 ]PF 6 was established by a combination of DFT, 2D NMR, and single‐crystal X‐ray crystallographic studies. Finally, [ 4 ]PF 6 was found to be photosubstitutionally active under irradiation with green light in acetonitrile, which makes it the first cyclometallated ruthenium complex capable of undergoing selective photosubstitution of a bidentate ligand.

Theoretical Study of the Full Photosolvolysis Mechanism of [Ru(bpy)3]2+: Providing a General Mechanistic Roadmap for the Photochemistry of [Ru(N^N)3]2+-Type Complexes toward Both Cis and Trans Photoproducts

“…Bidentate ligand photorelease has been explored in recent years in view of biological applications. − A two-step mechanism was inferred from early spectroscopic observations invoking an intermediate containing a monocoordinated bidentate ligand (Scheme ). ,,,− Structural characterization of such κ 1 intermediate photoproducts has been provided by 1 H NMR spectroscopy − and X-ray diffraction studies .…”

Intracellular Photophysics of an Osmium Complex bearing an Oligothiophene Extended Ligand

“…Only PDT has been approved clinically, and its underlying mechanism of action involves the generation of cytotoxic singlet oxygen ( 1 O 2 ) and other reactive oxygen species (ROS) [13–15] . PCT has focused on avoiding this oxygen dependence mainly through photoinduced ligand loss and subsequent covalent modification of biomolecules as an alternate mechanism [16–25] . While the Ru II systems that have been investigated for PDT and PCT absorb visible light, many cannot be activated with wavelengths in the so‐called biological window (650–850 nm) that are desirable for deeper tissue penetration.…”

“…[13][14][15] PCT has focused on avoiding this oxygen dependence mainly throughp hotoinducedl igand loss and subsequentc ovalentm odification of biomolecules as an alternate mechanism. [16][17][18][19][20][21][22][23][24][25] While the Ru II systems that have been investigated for PDT and PCT absorb visiblel ight, many cannotb ea ctivatedw ith wavelengthsi n the so-called biological window (650-850 nm) that are desirable for deeper tissue penetration.…”

Stimuli-responsive platinum and ruthenium complexes for lung cancer therapy

“…The Bonnet group have explored thioether ligand-chelating Ru(II) complexes as PACT agents. The softness of thioether-Ru coordination bonds enhances their photolability ( Van Rixel et al, 2016 ; Cuello-Garibo et al, 2019 ; Meijer and Bonnet, 2019 ). A methylthiomethyl pyridine chelating Ru-complex 42 was designed ( Chen et al, 2022 ) and its photocytotoxicity and cellular uptake were evaluated in A549 cells.…”