Photochemical Oxidation of Pt(IV)Me3(1,2-diimine) Thiolates to Luminescent Pt(IV) Sulfinates

Synthesis, Luminescence, and Electrochemistry of Tris-Chelate Platinum(IV) Complexes with Cyclometalated N-Heterocyclic Carbene Ligands and Aromatic Diimines

Dicationic, C2-symmetrical, tris-chelate Pt(IV) complexes of general formula [Pt(trz)2(N∧N)](OTf)2, bearing two cyclometalated 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene (trz) ligands and one aromatic diimine [N∧N = 2,2'-bipyridine (bpy, 2), 4,4'-di-tert-butyl-2,2'-bipyridine (dbbpy, 3), 4,4'-dimethoxi-2,2'-bipyridine (dMeO-bpy, 4), 1,10-phenanthroline (phen, 5), 4,7-diphenyl-1,10-phenanthroline (bphen, 6), dipyrido[3,2-a:2',3'-c]phenazine (dppz, 7), or 2,3-diphenylpyrazino[2,3-f][1,10]phenanthroline (dpprzphen, 8)] are obtained through chloride abstraction from [PtCl2(trz)2] (1) using AgOTf in the presence of the corresponding diimine. Complexes 2-4 show long-lived phosphorescence from 3LC excited states involving the diimine ligand, with quantum yields that reach 0.18 in solution and 0.58 in the solid matrix at room temperature for 3. Derivatives with more extended aromatic systems show dual phosphorescent/fluorescent emissions (5, 6) or mainly fluorescence (7, 8) in solution. Comparisons with similar complexes bearing cyclometalated 2-arylpyridines instead of aryl-N-heterocyclic carbenes indicate that the {Pt(trz)2} subunit is crucial to enable efficient emissions from diimine-centered excited states. It is also shown that the introduction of protective bulky substituents on the diimine, such as the tert-butyl groups in 3, is a key strategy to reach higher emission efficiencies. The new compounds represent rare examples of luminescent Pt(IV) complexes that show quasi-reversible one-electron reductions, indicating an unusually high redox stability.

Preparation and Ground-State Electronic Structure of Heterobimetallic Yb-PtIV-Alkyl Complexes

This article focuses on the synthesis of heterobimetallic complexes of lanthanide and platinum. It describes the synthesis of the Cp*Yb(bipym)PtMe2 complex and its characterization, followed by its reactivity with oxidants, giving access to various Pt + IV compounds of trismethyl (PtMe3) and tetramethyl (PtMe4) fragments. Characterization of the electronic properties of the complexes by magnetic measurements demonstrated that the tetramethyl complex possesses a singlet ground state. The trismethyl fragments, on the other hand, have a ground state that evolves as a function of the ligand saturating the coordination sphere: a singlet for triflate and pyridine and a triplet for iodine, demonstrating the capacity for simple tuning of the electronic structure of these complexes. While the addition of B(C6F5)3 to the platinum + II bis methyl complex leads to FLP-like reactivity triggering THF opening, reactivity with [Ph3C]+[BPh4]- leads to oxidation of the bipym ligand. Furthermore, the light reactivity of the tetramethyl complex indicated the possible transfer of a methyl group, leading to functionalization of the bridging bipym ligand.

Rhenium fac-Tricarbonyl Bisimine Chalcogenide Complexes: Synthesis, Photophysical Studies, and Confocal and Time-Resolved Cell Microscopy

We describe the preparation, characterization, and imaging studies of rhenium carbonyl complexes with a pyta (4-(2-pyridyl)-1,2,3-triazole) or tapy (1-(2-pyridyl)-1,2,3-triazole)-based heteroaromatic N∧N ligand and thiolate or selenoate X ligand. The stability and photophysical properties of the selenolate complexes are compared with parent chloride complexes and previously described analogues with benzenethiolate ligands. Two complexes were imaged in A549 cells upon excitation at 405 nm. Colocalization studies suggest a lysosomal accumulation, while one parent chloride complex was described to localize at the Golgi apparatus. Preliminary fluorescence lifetime measurements and imaging demonstrate potential for application in time-resolved microscopy techniques due to the long and variable lifetimes observed in cellular environments, including an increase in lifetime between the solution and solid state many times larger than previously reported.

Singlet Oxygen Generation, Quenching, and Reactivity with Metal Thiolates

Metal thiolate complexes can act as photosensitizers for the generation of singlet oxygen, quenchers of singlet oxygen, and they may undergo chemical reactions with singlet oxygen leading to oxidized thiolate ligands. This review covers all of the chemical reactions of thiolate ligands with singlet oxygen (through early 2021). Since some of these reactions are self-sensitized photooxidations, singlet oxygen generation by metal complexes is also discussed. Mechanistic features such as the effects of protic vs. aprotic conditions are presented and compared with the comparatively well-understood photooxidation of organic sulfides. In general, the total rate of singlet oxygen removal correlates with the nucleophilicity of the thiolate ligand which in turn can be influenced by the metal. Some interesting patterns of reactivity have been noted as a result of this survey: Metal thiolate complexes bearing arylthiolate ligands appear to exclusively produce sulfinate (metal-bound sulfone) products upon reaction with singlet oxygen. In contrast, metal thiolate complexes bearing alkylthiolate ligands may produce sulfinate and/or sulfenate (metal-bound sulfoxide) products. Several mechanistic pathways have been proposed for these reactions, but the exact nature of any intermediates remains unknown at this time.