Diastereoselective Synthesis and Two-Step Photocleavage of Ruthenium Polypyridyl Complexes Bearing a Bis(thioether) Ligand.
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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)](PF6)2 ([1]-[3](PF6)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 ? diastereoisomers and their ? enantiomers. We found that the synthesis of [1]-[3](PF6)2 is diastereoselective, yielding a racemic mixture of the ?-(S)-eq-(S)-ax-OHeq-[Ru]2+ and ?-(R)-ax-(R)-eq-OHeq-[Ru]2+ isomers. Upon irradiation with blue light in water, [1]-[3](PF6)2 selectively substitute their bis(thioether) ligands for water molecules in a two-step photoreaction, ultimately producing [Ru(bpy)2(H2O)2]2+ as the photoproduct. The relatively stable photochemical intermediate was identified as cis-[Ru(bpy)2(?1-L)(H2O)]2+ by mass spectrometry. Global fitting of the time evolution of the UV-vis absorption spectra of [1]-[3](PF6)2 was employed to derive the photosubstitution quantum yields (?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.
SUBMITTER: Meijer MS
PROVIDER: S-EPMC6724527 | biostudies-literature | 2019 Sep
REPOSITORIES: biostudies-literature
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