Triazole-based osmium(II) complexes displaying red/near-IR luminescence : antimicrobial activity and super-resolution imaging

Cellular uptake, luminescence imaging and antimicrobial activity against clinically relevant methicillin-resistant S. aureus (MRSA) bacteria are reported. The osmium(ii) complexes [Os(N^N)(3)](2+) (N^N = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (1(2+)); 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (2(2+)); 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (3(2+))) were prepared and isolated as the chloride salts of their meridional and facial isomers. The complexes display prominent spin-forbidden ground state to triplet metal-to-ligand charge transfer ((3)MLCT) state absorption bands enabling excitation as low as 600 nm for fac/mer-3(2+) and observation of emission in aqueous solution in the deep-red/near-IR regions of the spectrum. Cellular uptake studies within MRSA cells show antimicrobial activity for 1(2+) and 2(2+) with greater toxicity for the meridional isomers in each case and mer-1(2+) showing the greatest potency (32 μg mL(−1) in defined minimal media). Super-resolution imaging experiments demonstrate binding of mer- and fac-1(2+) to bacterial DNA with high Pearson's colocalisation coefficients (up to 0.95 using DAPI). Phototoxicity studies showed the complexes exhibited a higher antimicrobial activity upon irradiation with light

Photophysical and Cellular Imaging Studies of Brightly Luminescent Osmium(II) Pyridyltriazole Complexes

The series of complexes [Os(bpy)3- n(pytz) n][PF6]2 (bpy = 2,2'-bipyridyl, pytz = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole, 1 n = 0, 2 n = 1, 3 n = 2, 4 n = 3) were prepared and characterized and are rare examples of luminescent 1,2,3-triazole-based osmium(II) complexes. For 3 we present an attractive and particularly mild preparative route via an osmium(II) η6-arene precursor circumventing the harsh conditions that are usually required. Because of the high spin-orbit coupling constant associated with the Os(II) center the absorption spectra of the complexes all display absorption bands of appreciable intensity in the range of 500-700 nm corresponding to spin-forbidden ground-state-to-3MLCT transitions (MLCT = metal-to-ligand charge transfer), which occur at significantly lower energies than the corresponding spin-allowed 1MLCT transitions. The homoleptic complex 4 is a bright emitter (λmaxem = 614 nm) with a relatively high quantum yield of emission of ∼40% in deoxygenated acetonitrile solutions at room temperature. Water-soluble chloride salts of 1-4 were also prepared, all of which remain emissive in aerated aqueous solutions at room temperature. The complexes were investigated for their potential as phosphorescent cellular imaging agents, whereby efficient excitation into the 3MLCT absorption bands at the red side of the visible range circumvents autofluorescence from biological specimens, which do not absorb in this region of the spectrum. Confocal microscopy reveals 4 to be readily taken up by cancer cell lines (HeLa and EJ) with apparent lysosomal and endosomal localization, while toxicity assays reveal that the compounds have low dark and light toxicity. These complexes therefore provide an excellent platform for the development of efficient luminescent cellular imaging agents with advantageous photophysical properties that enable excitation and emission in the biologically transparent region of the optical spectrum

The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C5R4(CH2)2PR2] (R = Et, R = H or Me, R = Ph, R = Me), have been prepared from the reaction of spirohydrocarbons C5R4(C2H4) with LiPR2. C5Et4HSiMe2CH2PMe2, was prepared from reaction of Li[C5Et4] with Me2SiCl2 followed by Me2PCH2Li. The lithium salts were reacted with [RhCl(CO)2]2, [IrCl(CO)3] or [Co2(CO)8] to give [M(C5R4(CH2)2PR2)(CO)] (M = Rh, R = Et, R = H or Me, R = Ph, R = Me; M = Ir or Co, R = Et, R = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of CO for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp(CH2)2PEt2)(CO)] (Cp = C5Me4), the most electron rich of the complexes. [Rh(C5Et4SiMe2CH2PMe2)(CO)] may be a dimer. [Co2(CO)8] reacts with C5H5(CH2)2PEt2 or C5Et4HSiMe2CH2PMe2 (L) to give binuclear complexes of the form [Co2(CO)6L2] with almost linear PCoCoP skeletons. [Rh(Cp(CH2)2PEt2)(CO)] and [Rh(Cp(CH2)2PPh2)(CO)] are active for methanol carbonylation at 150 °C and 27 bar CO, with the rate using [Rh(Cp(CH2)2PPh2)(CO)] (0.81 mol dm–3 h–1) being higher than that for [RhI2(CO)2]– (0.64 mol dm–3 h–1). The most electron rich complex, [Rh(Cp(CH2)2PEt2)(CO)] (0.38 mol dm–3 h–1) gave a comparable rate to [Cp*Rh(PEt3)(CO)] (0.30 mol dm–3 h–1), which was unstable towards oxidation of the phosphine. [Rh(Cp(CH2)2PEt2)I2], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp(CH2)2PEt2)(CO)]. Neither of [M(Cp(CH2)2PEt2)(CO)] (M = Co or Ir) was active for methanol carbonylation under these conditions, nor under many other conditions investigated, except that [Ir(Cp(CH2)2PEt2)(CO)] showed some activity at higher temperature (190 °C), probably as a result of degradation to [IrI2(CO)2]–. [M(Cp(CH2)2PEt2)(CO)] react with MeI to give [M(Cp(CH2)2PEt2)(C(O)Me)I] (M = Co or Rh) or [Ir(Cp(CH2)2PEt2)Me(CO)]I. The rates of oxidative addition of MeI to [Rh(C5H4(CH2)2PEt2)(CO)] and [Rh(Cp(CH2)2PPh2)(CO)] are 62 and 1770 times faster than to [Cp*Rh(CO)2]. Methyl migration is slower, however. High pressure NMR studies show that [Co(Cp(CH2)2PEt2)(CO)] and [Cp*Rh(PEt3)(CO)] are unstable towards phosphine oxidation and/or quaternisation under methanol carbonylation conditions, but that [Rh(Cp(CH2)2PEt2)(CO)] does not exhibit phosphine degradation, eventually producing inactive [Rh(Cp(CH2)2PEt2)I2] at least under conditions of poor gas mixing. The observation of [Rh(Cp(CH2)2PEt2)(C(O)Me)I] under methanol carbonylation conditions suggests that the rhodium centre has become so electron rich that reductive elimination of ethanoyl iodide has become rate determining for methanol carbonylation. In addition to the high electron density at rhodiu

A near-infrared luminescent Cr(III) N-heterocyclic carbene complex

Photoluminescent coordination complexes of Cr(III) are of interest as near-infrared spin-flip emitters. Here, we explore the preparation, electrochemistry, and photophysical properties of the first two examples of homoleptic N-heterocyclic carbene complexes of Cr(III), featuring 2,6-bis(imidazolyl)pyridine (ImPyIm) and 2-imidazolylpyridine (ImPy) ligands. The complex [Cr(ImPy)3]3+ displays luminescence at 803 nm on the microsecond time scale (13.7 μs) from a spin-flip doublet excited state, which transient absorption spectroscopy reveals to be populated within several picoseconds following photoexcitation. Conversely, [Cr(ImPyIm)2]3+ is nonemissive and has a ca. 500 ps excited-state lifetime