Labilizing the Photoinert: Extraordinarily Facile Photochemical Ligand Ejection in an [Os(N^N)₃]²⁺ Complex

Abstract

Whilst [Os(N^N)3 ](2+) complexes are supposed to be photochemically inert to ligand loss, the complex [Os(btz)3 ](2+) (btz=1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl) undergoes unprecedented photolytic reactivity to liberate free btz (Φ363 ≈1.2 %). Further, both cis and trans isomers of the photodechelated ligand-loss solvento intermediate [Os(κ(2) -btz)2 (κ(1) -btz)(NCMe)](2+) are unambiguously observed and characterized by NMR spectroscopy and mass spectrometry.

Metal Complexes of Click-Derived Triazoles and Mesoionic Carbenes: Electron Transfer, Photochemistry, Magnetic Bistability, and Catalysis

“…[27b] It was also proven that bond activation takes place at the axial positions of the octahedron (with bpy in the equatorial plane). A similar reactivity pattern was recently observed for the osmium complex [Os( L4 ) 3 ] 2+ ( 32 2+ ) . Notably, this was the first time that photoinduced ligand dissociation was observed for a metal ion like osmium(II) that is known to have rather inert metal‐ligand bonds.…”

“…Notably, this was the first time that photoinduced ligand dissociation was observed for a metal ion like osmium(II) that is known to have rather inert metal‐ligand bonds. [28a]…”

Towards Water Soluble Mitochondria-Targeting Theranostic Osmium(II) Triazole-Based Complexes

“…These absorption and emission bands at wavelengths closer to the red in comparison to those of common iridium(III) complexes, and therefore in a more biologically transparent region of the spectrum, will also enable greater depth of penetration for excitation and imaging. Complexes of osmium(II) are also typically highly inert to ligand photosubstitution making them highly robust [34] (although the unprecedentedly facile ligand photoejection in the complex [Os(btz)3] 2+ was recently reported [35]). The intensity of phosphorescence is, however, sensitive to the presence of oxygen resulting in quenching through conversion of ground state 3 O2 to reactive 1 O2, thus enabling exploitation in photodynamic therapy (PDT) [36].…”

Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

“…The emission lifetimes for compounds 1-3 were recorded in aerated acetonitrile solutions and interestingly show reversed ordering to expectations based on energy-gap law considerations. In ruthenium(II) [40][41][42][43][44] and even osmium(II) [45,46] complexes, the presence of a 1,2,3-triazole-based chelate ligand can result in the quenching of The complexes are luminescent in aerated acetonitrile solutions and exhibit broad featureless bands at significantly longer wavelengths than their 1 MLCT absorption bands, indicative of emission from 3 MLCT states ( Figure 4a and Table 2). The emission spectra follow the same trend for the electronic absorption spectra with red-shifting of the 3 MLCT bands in the order 1 (540 nm) < 2 (572 nm) < 3 (638 nm).…”

“…The emission lifetimes for compounds 1-3 were recorded in aerated acetonitrile solutions and interestingly show reversed ordering to expectations based on energy-gap law considerations. In ruthenium(II) [40][41][42][43][44] and even osmium(II) [45,46] complexes, the presence of a 1,2,3-triazole-based chelate ligand can result in the quenching of luminescence and promotion of photochemical reactivity through increased accessibility of 3 MC states from the photoexcited 3 MLCT state. Indeed, the rhenium(I) complex [Re(btz)(CO) 3 (Cl)] is non-emissive in fluid solution [47].…”