Os Complexes Research Articles

Synthesis and Characterization of New Os2 5+ and Os2 6+ Azido Complexes

Reaction of Os2(OAc)4Cl2 with an excess of HDPhF (HDPhF = N,N′-diphenylformamidine) gives a high yield of Os2(DPhF)4Cl2 (1), which can be converted to its azido analog, Os2(DPhF)4(N3)2 (3), by treatment with NaN3. We report a major improvement on the preparation of Os2(chp)4Cl (2; Hchp = 2-chloro-6-hydroxypyridine) by synthesizing the compound in the reducing solvent ethanol. Reaction of 2 with NaN3 affords the azido complex Os2(chp)4N3 (4). Compound 3 has been examined by X-ray crystallography, and has an Os–Os bond distance of 2.45 A, suggesting a (π*)2 ground state for the molecule.

Chloridotris(pentafluorobenzenethiolato-κS)[tris(4-fluorophenyl)phosphine-κP]osmium(IV)

The title complex, [Os(C6F5S)3Cl(C18H12F3P)], displays a trigonal-bipyramidal OsIV coordination geometry with the S atoms of three thiol­ate ligands occupying the equatorial positions. The thiol­ate penta­fluoro­phenyl substituents are all placed above the equatorial plane, forming a claw-like cavity which accommodates the chloride ligand with a normal Os—Cl bond length. The phosphine ligand trans to the chloride ligand reveals a short Os—P bond length compared to other chloride–phosphine OsIV complexes (average = 2.40 Å). This strong bonding indicates that the inductive effect of the F atoms in the phosphine does not affect significantly its basicity, compared to triphenyl­phosphine. This feature is also consistent with the known poor trans influence of Cl−. The crystal packing involves π–π contacts between inversion-related thiol­ate C6F5 rings, with a centroid–centroid separation of 3.659 (8) Å.

Oxidation of alkanes and alcohols with hydrogen peroxide catalyzed by complex Os3(CO)10(µ‐H)2

AbstractTrinuclear carbonyl hydride cluster, Os3(CO)10(µ‐H)2, catalyzes oxidation of cyclooctane to cyclooctyl hydroperoxide by hydrogen peroxide in acetonitrile solution. The hydroperoxide partly decomposes in the course of the reaction to afford cyclooctanone and cyclooctanol. Selectivity parameters obtained in oxidations of various linear and branched alkanes as well as kinetic features of the reaction indicated that the alkane oxidation occurs with the participation of hydroxyl radicals. A similar mechanism operates in transformation of benzene into phenol and styrene into benzaldehyde. The system also oxidizes 1‐phenylethanol to acetophenone. The kinetic study led to a conclusion that oxidation of alcohols does not involve hydroxyl radicals as main oxidizing species and apparently proceeds with the participation of osmyl species, ‘OsO’. Copyright © 2010 John Wiley & Sons, Ltd.

Asymmetric Ruthenium(II) and Osmium(II) Complexes with New Bidentate Polyquinoline Ligands. Synthesis and NMR Characterization

A series of Ru(II) and Os(II) tris-chelate complexes with new bidentate 2-pyridylquinoline ligands have been synthesized and fully characterized by EA,1H-NMR and FAB-MS techniques. The new ligands are: L1 = 4-p-methoxyphenyl-6-bromo-2-(2′-pyridyl)quinoline (mphbr-pq) and L2 = 4-p-hydroxyphenyl-6-bromo-2-(2′-pyridyl)- quinoline (hphbr-pq). The complexes studied are: [Ru(bpy)2L1](PF6)2 (C1), [Ru(bpy)2L2](PF6)2 (C2), [Os(bpy)2L1](PF6)2 (C3), [Os(bpy)2L2](PF6)2 (C4) (bpy = 2,2′-bipyridine), [Ru(dmbpy)2L1](PF6)2 (C5), [Ru(dmbpy)2L2](PF6)2 (C6), [Os(dmbpy)2L1](PF6)2 (C7), and [Os(dmbpy)2L2](PF6)2 (C8) (dmbpy = 4,4′-dimethyl-2,2′-bipyridine). Moreover, new functionalized complexes C9-C12 were obtained by the base-catalyzed direct alkylation of C2, C4, C6, and C8 with 6-bromo-1-hexene. The complete assignment of the 1H-NMR spectra for the two new ligands (L1 and L2), and their Ru(II) or Os(II) complexes has been accomplished using a combination of one- and two-dimensional NMR techniques. The JH,H values have been determined for the majority of the resonances.

Electronic structures and spectroscopic properties of promising highly efficient red phosphorescent Os(II)(LR)2(PH3)2 complexes: a theoretical exploration

The red phosphorescent osmium(II) complexes [Os(LR)2(PH3)2] (L = 2-pyridyltriazole (ptz): R = H (1a), CF3 (1b), t-Bu (1c)); L = 2-pyridylpyrazole (ppz): R = H (2a), CF3 (2b), t-Bu (2c)); L = 2-phenylpyridine (ppy): R = H (3a)) were explored using density functional theory (DFT) methods. The ground- and excited-state geometries of the complexes were optimized at the B3LYP/LANL2DZ and UB3LYP/LANL2DZ levels, respectively. The absorption and phosphorescence of the complexes in CH2Cl2 media were calculated based on the optimized ground- and excited-state geometries using time-dependent density functional theory method with the polarized continuum model. The optimized geometry structural parameters of the complexes in the ground state agree well with the corresponding experimental values. The lower-lying unoccupied molecular orbitals of the complexes are dominantly localized on the L ligand, while the higher-lying occupied ones are composed of Os(II) atom and L ligand. The low-lying metal-to-ligand and intraligand charge transfer (MLCT/ILCT) transitions and high-lying ILCT transitions are red-shifted with the increase in the π-donating ability of the L ligand and the π electron-donating ability of R substituent. The calculation revealed that the phosphorescence originated from 3MLCT/3ILCT excited state. However, the complex 3a displayed different types of MLCT/ILCT excited state compared with that of 1a–2c, and the different types of transition were also found in the absorption. In addition, we found that the phosphorescence quantum efficiency of Os(II) complexes is related to the metal composition in the high-energy occupied molecular orbitals, it will be helpful to designing highly efficient phosphorescent materials.

A browser-based operating systems project

This paper presents one educator's experience with a browser-based project for an upper-level/graduate Operating Systems course. The author explains the project goals, why the browser in general and JavaScriptin particular are so well suited for this task, challenges andtheir solutions, the incremental assignments that ultimately result in a fairly complex OS simulation by the end of the semester, the response to the project, and some ideas about where to go next.

Synthesis of an osmafuran from photochemical hydrolysis of OsCl2(CHC(PPh3)C(O)-η2-CHCH2)(PPh3)2

The η 2 -alkene coordinated α,β-unsaturated ketone complex 1 which is very stable even at elevated temperature can be converted to the corresponding osmafuran 2 almost quantitatively by ultraviolet irradiation. This new highly efficient method for the preparation of osmafurans via photochemically assisted hydrolysis of η 2 -α,β-unsaturated ketone complexes, presents an addition to previous synthetic approaches. The η 2 -alkene coordinated α,β-unsaturated ketone complex Os(CH C(PPh 3 )C(O)-η 2 -CH CH 2 )Cl 2 (PPh 3 ) 2 ( 3 ) is very stable even at elevated temperature due to the strong steric hindrance effect of PPh 3 ligands. However, compound 3 in a chloroform solution can be almost quantitatively converted into the corresponding osmafuran [OsCl(CO)(PPh 3 ) 2 (CHC(PPh 3 )C(CH 3 )O)]Cl ( 6 ) via hydrolysis of the η 2 -coordinated olefin under photochemical conditions. Osmafuran 6 has been characterized by single crystal X-ray diffraction analysis, NMR spectroscopy and elemental analysis data. The UV-induced reaction provides a new highly efficient method for preparation of osmafurans by hydrolysis of η 2 -α,β-unsaturated ketone complexes.

High-color-rendering pure-white phosphorescent organic light-emitting devices employing only two complementary colors

We report successful fabrication of high-color-rendering pure-white phosphorescent organic light-emitting devices (OLEDs) by employing a true-blue iridium complex Ir(dfbppy)(fbppz)2 and a wide-bandwidth yellow emitting osmium complex Os(bptz)2(dppee). The two-component phosphorescent white OLED exhibited a high color rendering index (CRI) of 81 and CIEx,y coordinates close to the ideal white emission (0.33, 0.33). By doping the yellow phosphors into the hole-transport layer and the electron-transport layer adjacent to the blue-emitting layer and thereby forming a triple-emitting-layer device structure, we obtained WOLED which exhibited rather stable colors at different biases/brightnesses. Such high-CRI pure-white two-component WOLEDs yielded EL efficiencies of up to 9.5%, 22.9 cd/A, and 20 lm/W for the forward directions.

Unusual Ru(III) Chloro Complexes Containing Bis-dentate Ligands

Figure 1. Molecular structure of trans-[Ru(depe)2Cl2][PF6] in the crystals. Displacement ellipsoids are shown at the 50% probability level. Hydrogen atoms have been omitted for clarity. Redox chemistry of oxo and nitrido Ru or Os complexes containing polypyridine, Schiff base, or porphyrin ligands has been extensively studied. Especially the polypyridyl complexes of ruthenium have been known as excellent photosensizers in the use of photovoltaic cells based on nanocrystalline TiO2 films as well. Multiple bonding with O and/or N atoms of the oxo/nitrido ligands bonded to the metal stabilizes oxidants and promotes the conversion of organic and inorganic substrates via electron transfer, oxygen or nitrogen atom transfer, hydride transfer, and proton-coupled electron transfer pathways. Many researchers have endeavored to find out other sources of chelating ligands. We have been developed the synthetic chemistry of the reactive complexes of the diphosphine ligands coordinated to the ruthenium metal. One of general methods for the preparation of reactive Ru-oxo complexes is using the oxidation of the corresponding Ru-aqua complexes, which can be obtained from the reaction of Ru-chloro complexes with Ag in water. We applied it to the synthesis of the Ru-dioxo complexes surrounded by the diphosphine ligands. [Ru(dmpe)2Cl2] and [Ru(depe)2Cl2] complexes were isolated by the reactions of [Ru(PPh3)3Cl2] with dmpe (1,2-bis(dimethylphosphino)ethane) and depe (1,2-bis(diethylphosphino)ethane), respectively, in acetone under refluxing, then aquated the corresponding Ru-dichloro complexes by AgClO4 in H2O. We tried to prepare Ru(II) diaqua complexes, which have been known as the precursor to lead to Ru-dioxo complexes, however it turned out to be unsuccessful.

In vivo tumour and metastasis reduction and in vitro effects on invasion assays of the ruthenium RM175 and osmium AFAP51 organometallics in the mammary cancer model

We have compared the organometallic arene complexes [(eta(6)-biphenyl)M(ethylenediamine)Cl](+) RM175 (M=Ru(II)) and its isostructural osmium(II) analogue AFAP51 (M=Os(II)) for their ability to induce cell detachment resistance from fibronectin, collagen IV and poly-l-lysine, and cell re-adhesion after treatment, their effects on cell migration and cell viability, on matrix metalloproteinases production, and on primary tumour growth of MCa mammary carcinoma, the effect of human serum albumin on their cytotoxicity. There are differences between ruthenium and osmium. The Os complex is up to 6x more potent than RM175 towards highly-invasive breast MDA-MB-231, human breast MCF-7 and human epithelial HBL-100 cancer cells, but whereas RM175 was active against MCa mammary carcinoma in vivo and caused metastasis reduction, AFAP51 was not. Intriguingly the presence of human serum albumin in the growth medium enhanced the cytotoxicity of both compounds. RM175 increased the resistance of MDA-MB-231 cells to detachment from substrates and both compounds inhibited the production of MMP-2. These data confirm the key role of ruthenium itself in anti-metastatic activity. It will be interesting to explore the activity of osmium arene complexes in other tumour models and the possibility of changing the non-arene ligands to tune the anticancer activity of osmium in vivo.

Making Oxygen with Ruthenium Complexes

Mastering the production of solar fuels by artificial photosynthesis would be a considerable feat, either by water splitting into hydrogen and oxygen or reduction of CO(2) to methanol or hydrocarbons: 2H(2)O + 4hnu --> O(2) + 2H(2); 2H(2)O + CO(2) + 8hnu --> 2O(2) + CH(4). It is notable that water oxidation to dioxygen is a key half-reaction in both. In principle, these solar fuel reactions can be coupled to light absorption in molecular assemblies, nanostructured arrays, or photoelectrochemical cells (PECs) by a modular approach. The modular approach uses light absorption, electron transfer in excited states, directed long range electron transfer and proton transfer, both driven by free energy gradients, combined with proton coupled electron transfer (PCET) and single electron activation of multielectron catalysis. Until recently, a lack of molecular catalysts, especially for water oxidation, has limited progress in this area. Analysis of water oxidation mechanism for the "blue" Ru dimer cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(OH(2))(bpy)(2)](4+) (bpy is 2,2'-bipyridine) has opened a new, general approach to single site catalysts both in solution and on electrode surfaces. As a catalyst, the blue dimer is limited by competitive side reactions involving anation, but we have shown that its rate of water oxidation can be greatly enhanced by electron transfer mediators such as Ru(bpy)(2)(bpz)(2+) (bpz is 2,2'-bipyrazine) in solution or Ru(4,4'-((HO)(2)P(O)CH(2))(2)bpy)(2)(bpy)(2+) on ITO (ITO/Sn) or FTO (SnO(2)/F) electrodes. In this Account, we describe a general reactivity toward water oxidation in a class of molecules whose properties can be "tuned" systematically by synthetic variations based on mechanistic insight. These molecules catalyze water oxidation driven either electrochemically or by Ce(IV). The first two were in the series Ru(tpy)(bpm)(OH(2))(2+) and Ru(tpy)(bpz)(OH(2))(2+) (bpm is 2,2'- bipyrimidine; tpy is 2,2':6',2''-terpyridine), which undergo hundreds of turnovers without decomposition with Ce(IV) as oxidant. Detailed mechanistic studies and DFT calculations have revealed a stepwise mechanism: initial 2e(-)/2H(+) oxidation, to Ru(IV)=O(2+), 1e(-) oxidation to Ru(V)=(3+), nucleophilic H(2)O attack to give Ru(III)-OOH(2+), further oxidation to Ru(IV)(O(2))(2+), and, finally, oxygen loss, which is in competition with further oxidation of Ru(IV)(O(2))(2+) to Ru(V)(O(2))(3+), which loses O(2) rapidly. An extended family of 10-15 catalysts based on Mebimpy (Mebimpy is 2,6-bis(1-methylbenzimidazol-2-yl)pyridine), tpy, and heterocyclic carbene ligands all appear to share a common mechanism. The osmium complex Os(tpy)(bpy)(OH(2))(2+) also functions as a water oxidation catalyst. Mechanistic experiments have revealed additional pathways for water oxidation one involving Cl(-) catalysis and another, rate enhancement of O-O bond formation by concerted atom-proton transfer (APT). Surface-bound [(4,4'-((HO)(2)P(O)CH(2))(2)bpy)(2)Ru(II)(bpm)Ru(II)(Mebimpy)(OH(2))](4+) and its tpy analog are impressive electrocatalysts for water oxidation, undergoing thousands of turnovers without loss of catalytic activity. These catalysts were designed for use in dye-sensitized solar cell configurations on TiO(2) to provide oxidative equivalents by molecular excitation and excited-state electron injection. Transient absorption measurements on TiO(2)-[(4,4'((HO)(2)P(O)CH(2))(2)bpy)(2)Ru(II)(bpm)Ru(II)(Mebimpy)(OH(2))](4+), (TiO(2)-Ru(II)-Ru(II)OH(2)) and its tpy analog have provided direct insight into the interfacial and intramolecular electron transfer events that occur following excitation. With added hydroquinone in a PEC configuration, APCE (absorbed-photon-to-current-efficiency) values of 4-5% are obtained for dehydrogenation of hydroquinone, H(2)Q + 2hnu --> Q + H(2). In more recent experiments, we are using the same PEC configuration to investigate water splitting.

Amide Linkage Isomerism As an Activity Switch for Organometallic Osmium and Ruthenium Anticancer Complexes

We show that the binding mode adopted by picolinamide derivatives in organometallic Os(II) and Ru(II) half-sandwich complexes can lead to contrasting cancer cell cytotoxicity. N-Phenyl picolinamide derivatives (XY) in Os(II) (1, 3-5, 7, 9) and Ru(II) (2, 6, 8, 10) complexes [(eta(6)-arene)(Os/Ru)(XY)Cl](n+), where arene = p-cymene (1-8, 10) or biphenyl (9), can act as N,N- or N,O-donors. Electron-withdrawing substituents on the phenyl ring resulted in N,N-coordination and electron-donating substituents in N,O-coordination. Dynamic interconversion between N,O and N,N configurations can occur in solution and is time- and temperature- (irreversible) as well as pH-dependent (reversible). The neutral N,N-coordinated compounds (1-5 and 9) hydrolyzed rapidly (t(1/2) <or= min), exhibited significant (32-70%) and rapid binding to guanine, but no binding to adenine. The N,N-coordinated compounds 1, 3, 4, and 9 exhibited significant activity against colon, ovarian, and cisplatin-resistant ovarian human cancer cell lines (3 >> 4 > 1 > 9). In contrast, N,O-coordinated complexes 7 and 8 hydrolyzed slowly, did not bind to guanine or adenine, and were nontoxic.

Hydrogen Atoms Location in Os3(μ-H)(CO)9(μ3, η2-C2H) from Accurate X-Ray Data at 100 K

The structure of the complex Os3(μ-H)(CO)9(μ3, η2-C2H) has been determined using X-ray data collected at low temperature (100 K); all hydrogen atoms have been located. The asymmetric unit is formed by two molecules joined through hydrogen bonds involving the hydrogen atoms of C2H moiety and the oxygen atoms of carbonyl groups. The complex crystallizes in the monoclinic space group P21/c with a = 12.94040(2), b = 15.4705(2), c = 16.0164(2) A, β = 106.0860(10)°, and V = 3,080.85(7) A3, Z = 8. A molecule is formed by a triangular Os3 cluster, with metal atoms bearing terminal CO groups. The acetylenic residual is formally π-bonded to two Os atoms in a perpendicular mode and σ-linked to the third Os atom. A bridging hydride atom completes the coordination. An high resolution X-ray analysis at 100 K has allowed the location of hydrogen atoms in the Os3(μ-H)(CO)9(μ3, η2-C2H) complex; C–H···O hydrogen bonds connect the molecules in the crystal.

Voltammetry of Os(VI)‐Modified Polysaccharides at Carbon Electrodes

AbstractWe show that polysaccharides (PSs, such as dextran and mannan) can be chemically modified by Os(VI) complexes, yielding electroactive adducts. Os(VI) complexes with different ligands (e.g., temed and 2,2′‐bipyridine) produced at pyrolytic graphite electrodes redox couples at different potentials suitable for “multicolor” labeling of PSs and for studies of ligand exchange kinetics. PS‐Os(VI)L adducts can be determined not only in their purified forms but also in the reaction mixtures.

Concerted proton-coupled electron transfers in aquo/hydroxo/oxo metal complexes: Electrochemistry of [Os II (bpy) 2 py(OH 2 )] 2+ in water

Kinetic analysis of the successive oxidative cyclic voltammetric responses of [Os(II)(bpy)(2)py(OH(2))](2+) in buffered water, together with determination of H/D isotope effects, has allowed the determination of the mechanisms of the successive proton-coupled electron transfers that convert the Os(II)-aquo complex into the Os(III)-hydroxo complex and the later into the Os(IV)-oxo complex. The stepwise pathways prevail over the concerted pathway in the first case. However, very large concentrations of a base, such as acetate, trigger the beginning of a concerted reaction. The same trend appears, but to a much larger extent, when high local concentration of carboxylates are attached close to the Os complex. The Os(III)-hydroxo/Os(IV)-oxo couple is globally much slower and concerted pathways predominate over the stepwise pathways. Water is, however, not an appropriate proton acceptor in this respect. Other bases, such as citrate or phosphate, are instead quite effective for triggering concerted pathways. Here, we suggest factors causing these contrasting behaviors, providing a practical illustration of the prediction that concerted processes are an efficient way of avoiding high-energy intermediates. Observation of a strong decelerating effect of inactive ions together with the positive role of high local concentrations of carboxylates to initiate a concerted route underscores the variety of structural and medium factors that may operate to modulate and control the occurrence of concerted pathways. These demonstrations and analyses of the occurrence of concerted pathways in an aquo-hydroxo-oxo series are expected to serve as guidelines for studies in term of methodology and factor analysis.

Efficient microwave syntheses of the compounds Os 3(CO) 11L, L = NCMe, py, PPh 3

The results of simple microwave-assisted ligand substitution reactions of Os 3(CO) 12 are reported. In a remarkably short period of time, the labile complex Os 3(CO) 11(NCMe) is prepared in high yield without the need for a decarbonylation reagent such as trimethylamine oxide. Microwave irradiation of Os 3(CO) 12 in a relatively small amount of acetonitrile is shown to be a useful first step in two-step, one-pot syntheses of the cluster complexes Os 3(CO) 11(py) and Os 3(CO) 11(PPh 3).

Transformations of allylamine and N-allylacetamide on triosmium cluster complexes with hemilabile ligands

The cluster complexes (μ-H)Os 3(μ-O CR)(СО) 10 (R = Me ( 1); R = Ph ( 2)) catalyze the allylic rearrangement of N-allylacetamide at room temperature. Microwave irradiation greatly (by more than several thousand-fold) accelerates the reaction between the solution of 2 and allylacetamide. The interaction of cluster 2 with allylamine both at room and elevated temperatures results in cleavage of the C–N bond and coordination of the allylic fragment to one of the osmium atoms with the formation of Os 3(CO) 9(μ,η 2-O C-Ph)(η 3-C 3H 5) ( 4) cluster.

Synthesis and reactivity of osmium (VI) nitrido complexes containing pyridine-carboxylato ligands

A series of osmium(VI) nitrido complexes containing pyridine-carboxylato ligands Os VI(N)(L) 2X (L = pyridine-2carboxylate ( 1), 2-quinaldinate ( 2) and X = Cl ( a), Br ( 1b and 2c) or CH 3O ( 2b)) and [Os VI(N)(L)X 3] − (L = pyridine-2,6-dicarboxylate ( 3) and X = Cl ( a) or Br ( b)) have been synthesised. Complexes 1 and 2 are electrophilic and react readily with various nucleophiles such as phosphine, sulfide and azide. Reaction of Os VI(N)(L) 2X ( 1 and 2) with triphenylphosphine produces the osmium(IV) phosphiniminato complexes Os VI(NPPh 3)(L) 2X ( 4 and 5). The kinetics of nitrogen atom transfer from the complexes Os VI(N)(L) 2Br ( 2c) (L = 2-quinaldinate) with triphenylphosphine have been studied in CH 3CN at 25.0 °C by stopped-flow spectrophotometric method. The following rate law is obtained: −d[Os(VI)]/d t = k 2[Os(VI)][PPh 3]. Os VI(N)(L) 2Cl (L = 2-quinaldinate) ( 2a) reacts also with [PPN](N 3) to give an osmium(III) dichloro complex, trans-[PPN][Os III(L) 2Cl 2] ( 6). Reaction of Os VI(N)(L) 2Cl (L = 2-quinaldinate) ( 2a) with lithium sulfide produces an osmium(II) thionitrosyl complex Os II(NS)(L) 2Cl ( 7). These complexes have been structurally characterised by X-ray crystallography.

Syntheses and structures of Osmium(II) and Osmium(VI) meso-tetra(benzo-15-crown-5)porphyrinates according to the spectral data

The reaction of meso-tetra(benzo-15-crown-5)porphyrin (H2TCP) with the osmium carbonyl complex Os3(CO)12 yieds the corresponding osmium(II) porphyrinate OsTCP(CO). The oxidation of OsTCP(CO) with air oxygen and hydrogen peroxide in neutral and acidic media was studied. A preparative method for the synthesis of osmium(VI) meso-tetra(benzo-15-crown-5)porphyrinate (OsO2) TCP by the oxidation of OsTCP(CO) with 50% hydrogen peroxide in acetic acid was developed. The structures of new osmium porphyrinates were determined by IR, 1H NMR, and UV/Vis spectroscopies.

Electrochemiluminescence studies of phosphine chelated osmium(II) complexes

The electrochemiluminescence (ECL) properties of five different yellow/orange emissive osmium(II) complexes of general formula Os(L 2L’) with three different kinds of bidentate phosphine ligands L’ have been studied in acetonitrile/dioxane 1:1 solution by means of the triple-potential-step technique. The investigated complexes contain either two substituted pyrazolate or triazolate ligands L. The obtained ECL results have been interpreted in terms of the ligands nature, showing that the efficiency of ECL seems to be sensitive to the π-acidity of the phosphine ligand. To the authors’ best knowledge, the reported ECL efficiencies are the highest found for Os(II) complexes under similar conditions to date, that are at maximum five times higher than that of the famous Ru ( bipy ) 3 2 + based ECL systems.