Diastereoselective Synthesis and Two-Step Photocleavage of Ruthenium Polypyridyl Complexes Bearing a Bis(thioether) Ligand

Abstract

Thioethers are good ligands for photoactivatable ruthenium(II) polypyridyl complexes, as they form thermally stable complexes that are prone to ligand photosubstitution. Here, we introduce a novel symmetric chelating bis(thioether) ligand scaffold, based on 1,3-bis(methylthio)-2-propanol ( 4 ) and report the synthesis and stereochemical characterization of the series of novel ruthenium(II) polypyridyl complexes [Ru(bpy) 2 (L)](PF 6 ) 2 ([ 1 ]–[ 3 ](PF 6 ) 2 ), where L is ligand 4 , its methyl ether, 1,3-bis(methylthio)-2-methoxypropane ( 5 ), or its carboxymethyl ether, 1,3-bis(methylthio)-2-(carboxymethoxy)propane ( 6 ). Coordination of ligands 4 – 6 to the bis(bipyridine)ruthenium center gives rise to 16 possible isomers, consisting of 8 possible Λ diastereoisomers and their Δ enantiomers. We found that the synthesis of [ 1 ]–[ 3 ](PF 6 ) 2 is diastereoselective, yielding a racemic mixture of the Λ-( S )-eq-( S )-ax-OH eq -[ Ru ] 2+ and Δ-( R )-ax-( R )-eq-OH eq -[ Ru ] 2+ isomers. Upon irradiation with blue light in water, [ 1 ]–[ 3 ](PF 6 ) 2 selectively substitute their bis(thioether) ligands for water molecules in a two-step photoreaction, ultimately producing [Ru(bpy) 2 (H 2 O) 2 ] 2+ as the photoproduct. The relatively stable photochemical intermediate was identified as cis -[Ru(bpy) 2 (κ 1 -L)(H 2 O)] 2+ by mass spectrometry. Global fitting of the time evolution of the UV–vis absorption spectra of [ 1 ]–[ 3 ](PF 6 ) 2 was employed to derive the photosubstitution quantum yields (Φ 443 ) for each of the two photochemical reaction steps separately, revealing very high quantum yields of 0.16–0.25 for the first step and lower values (0.0055–0.0093) for the second step of the photoreaction. The selective and efficient photochemical reaction makes the photocleavable bis(thioether) ligand scaffold reported here a promising candidate for use in e.g. ruthenium-based photo-activated chemotherapy.

Xanthoepocin, a photolabile antibiotic of Penicillium ochrochloron CBS 123823 with high activity against multiresistant gram-positive bacteria

“…A xanthoepocin solution in methanol was prepared with an OD of approximately 0.1 at the detection wavelength of λ = 450 nm. The visible light emission of xanthoepocin and the near-infrared emission of singlet oxygen was detected at λ = 1270 nm as previously reported [ 46 ]. An absorbance measurement (200–800 nm) before and after excitation was recorded to assure the stability of xanthoepocin.…”

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

“…[Ru(bpy) 2 (bthmp)] 2+ (Figure 6), reveals rapid photochemical conversion to ligand loss intermediates [Ru(bpy) 2 (κ 1 -bthmp)(solvent)] 2+ followed by a much slower photochemical release of the monodentate bthmp ligand. 95 The high degree of conformational flexibility of the [Ru(bpy)(κ 2 -btz)(κ 1 -btz)(NCMe)] 2+ , with final photochemical loss of the κ 1 -btz ligand being slow. 110 Due to the trans arrangement of the monodentate btz and acetonitrile ligands, the 3 MC state responsible for elongation of the Ru-N bond to the former will also elongate the corresponding bond to the latter.…”

796 nm Activation of a Photocleavable Ruthenium(II) Complex Conjugated to an Upconverting Nanoparticle through Two Phosphonate Groups

“…The potential isomers of this class of ruthenium thioether complexes were described by us recently. 56 According to 1D and 2D 1 H NMR, which showed only a single set of 16 aromatic proton signals originating from the bipyridine ligands, both complexes [ 1 ](PF 6 ) 2 and [ 6 ](PF 6 ) 2 were obtained as single diastereoisomers.…”

“…This two-step photoreactivity is strictly similar to that reported previously for the complex [Ru(bpy) 2 (bmtp)](PF 6 ) 2 , where bmtp = 1,3-bis(methylthio)propanol. 56 The quantum efficiencies of the two photochemical steps were derived using global fitting of the time evolution of the UV–vis absorption spectra, using the Glotaran software package. 57 The photosubstitution quantum yields were found to be 0.12 for the first step and 0.0051 for the second one ( Table 1 and Figure S9 ).…”