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PubMed1983

Cytochemical demonstration of phosphatases in the rat liver by a cerium-based method in combination with osmium tetroxide and potassium ferrocyanide postfixation.

Acid phosphatase, alkaline phosphatase, glucose-6-phosphatase, Mg-activated adenosine triphosphatase and 5'nucleotidase were demonstrated in the rat liver using a cerium-based method. This method can be applied routinely and yields better results than the lead-based method. The tissue was postfixed in osmium tetroxide and potassium ferrocyanide which considerably enhances the membrane contrast in comparison with solely osmium tetroxide postfixation. This facilitates the precise localization of the reaction product.

Acid Phosphatase↗
PubMed1986

A technique for the electron microscopic autoradiography of Al adenosine receptors in brain tissue. Ligand-receptor fixation by osmium tetroxide.

A procedure for the electron microscopic autoradiography of Al adenosine receptors is described. Fresh tissue slices from rat hippocampus were incubated with the radioactive adenosine analogs: Cyclohexyl[3H]adenosine, 5'-N-ethylcarboxamido[3H]adenosine or or [125I]-iodohydroxyphenylisopropyladenosine. Various fixation agents were tested with respect to the retention of these ligands by the tissue. While most of the ligands were lost in aldehyde fixation they were retained by osmium tetroxide probably via a crosslinking reaction. The final method of choice was an aldehyde prefixation (in the case of [125I]-iodohydroxyphenylisopropyladenosine with 4% buffered paraformaldehyde) during which more than 90% of the nonspecifically bound ligands were washed out while 40% of the specifically bound ligands remained. Subsequent fixation with osmium tetroxide (1%) allowed a standard protocoll for dehydration and embedding to be used with only minimal (less than 5%) further loss of the ligands. Electron microscopic autoradiography provided evidence for a specific distribution of the binding sites for [125I]-iodohydroxyphenylisopropyladenosine.

Animals↗
PubMed2004

Voltammetric behavior of DNA modified with osmium tetroxide 2,2'-bipyridine at mercury electrodes.

Osmium tetroxide complexes with nitrogen ligands (L) are probes of DNA structure and electroactive labels of DNA. Here adducts of single-stranded (ss) DNA with osmium tetroxide 2,2'-bipyridine (DNA-Os,bipy) were studied by cyclic voltammetry for the first time. It was found that at neutral pH DNA-Os,bipy produces three redox couples in the potential range between 0 and -1 V (peaks I-III) and a cathodic peak at about -1.3 V (peak IV). The latter peak decreased with increasing scan rate, and peaks arising from the forward and reverse scans exhibited the same direction, suggesting catalytic nature of the electrode process. We concluded that this peak corresponds to the known differential pulse voltammetric (polarographic) peak of DNA-Os,L adducts for which catalytic hydrogen evolution is responsible. In contrast, currents of cathodic peaks II and III increased almost linearly with increasing scan rate, suggesting involvement of adsorption in the electrode processes. Adsorptive stripping square-wave voltammetry was used to analyze the DNA-Os,bipy at low concentrations. It was shown that at neutral pH, peak III can offer sensitivity in the ppb range, which is only little lower than that reached by catalytic peak IV. The latter peak is, however, superior in sensitivity at acid pH values.

2,2'-Dipyridyl↗
PubMed1984

Osmium ferricyanide fixation improves microfilament preservation and membrane visualization in a variety of animal cell types.

Using a fixation formula which includes adding potassium ferricyanide (K3Fe(CN)6) to the osmium step and an en bloc aqueous uranyl acetate step before dehydration we have looked at cells from mammals, birds, amphibia, algae, and higher plants and we have collaborated in fixing cells of teleost fish. In every cell type except the algae and higher plants the final EM image was improved by the OsFeCN-uranium method. The most common improvement was an increase in the membrane contrast but more significantly, some cells show improved preservation of microfilaments. We conclude that the OsFeCN adds contrast to all classes of membrane and does not destroy microfilaments to the extent that osmium alone does. Adding uranyl acetate to the cells may protect delicate filamentous structures from collapse during dehydration and embedding. We have preliminary evidence in PtK1 cells that addition of tannic acid after OsFeCN may function in a similar manner. This method is recommended for any animal cell type where improved visualization of membranes and filaments is required.

Animals↗
PubMed2005

The transillumination possibility of imidazole-osmium postfixed tissue and its consequences for the handling of tissue samples.

Osmium postfixation is established as a routine procedure for transmission electron microscopy (TEM). On the one hand, this routine procedure leads to good results for TEM, but on the other hand results in blackened tissue samples that do not allow examination of any structures within the embedded tissue sample by a light microscope. Equivalent fixation results for TEM are achieved with imidazole-osmium postfixation, and with this postfixation method tissue is not blackened and can be transilluminated with point light sources. This allows easier recognition of histological details within tissue samples and makes it possible to screen embedded samples for appropriate ultrastructural processing. Jejunum is used to demonstrate the method.

Animals↗
PubMed2000

Oxo complexes of osmium(IV) formed via dioxygen activation. X-ray structures of [OsX(dcpe)2]PF6 (X = Cl, Br), [OsCl(eta 2-O2)(dcpe)2]BPh4, and [OsCl(O)(dcpe)2]BPh4 (dcpe = 1,2-bis(dicyclohexylphosphino)ethane).

Dioxygen addition to the 16-electron complexes [OsX(P-P)2]+ (3) gives the dioxygen adducts [OsCl(eta 2-O2)(P-P)2]+ (3), which in turn react with HCl gas to give the novel osmium(IV) oxo complexes trans-[OsX(O)(P-P)2]+ (5) (X = Cl, Br; P-P = 1,2-bis(dicyclohexylphosphino)ethane (dcpe), 1,2-bis(diethylphosphino)ethane (depe), 1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene (Me-duphos)). The complexes [OsX(dcpe)2]+ (X = Cl, Br) (3) are studied by X-ray crystallography and are shown to have a "Y-shaped" coordination geometry in the equatorial plane. The X-ray structural analysis of [OsCl(eta 2-O2)(dcpe)2]+ (4a) reveals an exceptionally short O-O bond (1.315(5) A). trans-[OsCl(O)(dcpe)2]+ (5a), the first oxo complex of osmium(IV) investigated crystallographically, exhibits a long Os-O distance of 1.834(3) A. The reactivity of 4 and 5 as oxidants is described. The dioxygen complex 4a transfers one oxygen atom to PPh3 (to give Ph3PO) or oxidizes iodide ions to triiodide ions in the presence of anhydrous HCl. In both reactions, the corresponding oxo species 5a is quantitatively formed as the only metal-containing product. Oxo complexes 5 are surprisingly stable and unreactive toward standard reducing agents such as phosphines.

Journal Article↗
PubMed2001

Regular and inverse secondary kinetic enthalpy effects (KHE) for the rate of inversion of thioether and 1,1'-biisoquinoline complexes of ruthenium and osmium.

Thioether complexes with the formula Delta/Lambda-chloro(thioether)bis(2,2'-bipyridine)metal(II) (M = Ru, Os; thioether = dimethyl sulfide (3a(+)), diethyl sulfide (3b(+)), and tetrahydrothiophene (3c(+))) have been synthesized. The rates of inversion at the sulfur atom of the thioether ligands have been measured by spin-inversion transfer and line-shape NMR methods. In every case, the ruthenium derivative exhibits a faster inversion frequency at a given temperature than the corresponding osmium derivative. In contrast, similar complexes with the formula chloro(delta/lambda-1,1'-biisoquinoline)(2,2':6',2"-terpyridine)metal(II), 4(M=Ru,Os)(+), undergo atropisomerization of the misdirected 1,1'-biisoquinoline (1,1'-biiq) ligand with rates that are faster for osmium than ruthenium. As a result of the lanthanide contraction effect and the similar metric parameters associated with the structures of second-row and third-row transition metal derivatives, steric factors associated with the isomerizations are presumably similar for the Ru and Os derivatives of these compounds. Since third-row transition metal complexes tend to have larger bond dissociation enthalpies (BDE) than their second-row congeners, we conclude the difference in reactivities of 3(M=Ru)(+) versus 3(M=Os)(+) and 4(M=Ru)(+) versus 4(M=Os)(+) are attributed to electronic effects. For 3, the S3p lone pair of the thioether, the principal sigma donor orbital, is orthogonal to the metal sigma acceptor orbital in the transition state of inversion at sulfur and the S 3s orbital is an ineffective sigma donor. Thus, a regular relationship between the kinetic and thermodynamic stabilities of 3(M=Ru)(+) and 3(M=Os)(+) is observed for the directed <==> [misdirected] <==> directed (DMD) isomerization (the more thermodynamically stable bond is less reactive). In contrast, atropisomerization of 4(+) involves redirecting (strengthening) the M-N bonds of the misdirected 1,1'-biiq ligand in the transition state. Therefore, an inverse relationship between the kinetic and thermodynamic stabilities of 4(M=Ru)(+) and 4(M=Os)(+) is observed for the misdirected <==> [directed] <==> misdirected (MDM) isomerization (the more thermodynamically stable bond is more reactive). The rates obtained for 4(+) are consistent with the rates of atropisomerization of Delta/Lambda-(delta/lambda-1,1'-biisoquinoline)bis(2,2'-bipyridine)metal(II), 1(M=Ru,Os)(2+), and (eta(6)-benzene) Delta/Lambda-(delta/lambda-1,1'-biisoquinoline)halometal(II), 2(M=Ru,Os;halo=Cl,I)(+), that we reported previously. We term the relative rates of reaction of second-row versus third-row transition metal derivatives kinetic element effects (KEE = k(second)/k(third)). While the KEE appears to be generally useful when comparing reactions of isostructural species (e.g. the relative rates of 1(M=Ru)(2+), 1(M=Os)(2+), and 1(M=Ir)(3+)), different temperature dependencies of reactions prevent the comparison of related reactions between species that have different structures (e.g., the 1,1'-biiq atropisomerization reactions of 1(M=Ru,Os)(2+) versus 2(M=Ru,Os;halo=Cl,I)(+) versus 4(M=Ru,Os)(+)). This problem is overcome by comparing entropies of activation and kinetic enthalpy effects (KHE = DeltaH(third)/DeltaH(second)). For a given class of 1,1'-biiq complexes, we observe a structure/reactivity relationship between DeltaH and the torsional twist of the 1,1'-biiq ligands that are measured in the solid state.

Journal Article↗
PubMed2002

Photoinduced and chemical oxidation of coordinated imine to amide in isomeric osmium(II) complexes of N-arylpyridine-2-carboxaldimines. Synthesis, characterization, electron transfer properties, and structural studies.

The reaction of N-arylpyridine-2-carboxaldimine [C(5)H(4)NC(H)NC(6)H(4)R] (HL) with ammonium hexabromoosmate (NH(4))(2)[OsBr(6)] in boiling 2-methoxyethanol afforded a violet solution from which two geometrical isomers of [OsBr(2)(HL)(2)] (1 and 2) were isolated. These are characterized by analytical and spectroscopic data. (1)H NMR spectral data were used for the identification of the isomers. The blue-violet isomer, 1 (designated as ctc), has a 2-fold symmetry axis and gave rise to resonances for only one coordinated HL. The geometry of the ctc-isomer was, however, revealed from the X-ray structure determination of a representative example. The red-violet isomer (2, designated as ccc), on the other hand, is unsymmetrical and gave rise to a large number of proton resonances. The isomeric complexes, [OsBr(2)(HL)(2)], showed intense MLCT transitions in the visible region. This transition, in the ccc-isomer, is slightly (10 nm) red shifted in comparison to the ctc-isomer. These diimine complexes showed one metal based reversible oxidation assignable to the Os(III)/Os(II) process followed by two irreversible oxidations at more anodic potentials (>1.4 V). In addition to these, the complexes also showed two irreversible ligand reductions at high cathodic potentials (<-1.4 V). An unusual type of photochemical transformation of the azomethine function of coordinated HL in osmium compounds 1 is studied. When an air equilibrated acetonitrile solution of 1 was exposed to a xenon lamp, it underwent oxidation affording the mixed ligand, amido complexes of general formula [OsBr(2)(HL)(LO)], 3 (LO = C(5)H(4)NC(O)-N-C(6)H(4)R), in an excellent yield (>95%). This transformation (1 --> 3) was achieved chemically when H(2)O(2) was used as an oxidant. Notably, the chemical oxidation with H(2)O(2) also led to the formation of a tetravalent complex, [OsBr(2)(LO)(2)], 4, as a minor product. Compound 3 was characterized by various spectroscopic and analytical techniques. The room temperature magnetic moment of 3 corresponds to a t(2)(5) configuration for the osmium(III) center. EPR spectra of the amido complexes were recorded at 77 K in 1:1 dichloromethane-toluene glass, and they were anisotropic in nature. FAB mass spectra of 3 displayed intense peaks due to parent molecular ions. For example, the complex [OsBr(2)(HL(1))(L(1)O)], 3a, showed a strong peak at m/z 729 amu. The electronic spectrum of compound 3 consisted of a broad LMCT transition (ca. 525 nm; epsilon, 3000 M(-1) cm(-1)). The cyclic voltammogram of compound 3 consisted of two responses, one each on the positive and negative side of SCE, corresponding to Os(IV)/Os(III) (ca. 0.8V) and Os(III)/Os(II) (ca. -0.3V) couples, respectively. There has been a large cathodic shift of potential for the Os(III)/Os(II) couple in 3 in comparison to that in the parent complex, 1. The diamido compound [OsBr(2)(LO)(2)], 4, is diamagnetic and insoluble in common solvents. The X-ray structure determination of a representative sample, 4a, is reported. The molecule contains a C(2)-symmetry axis with bromide ions in relative cis positions. The Os-N(amide) bond lengths are considerably shorter than the Os-N(pyridine) lengths. All other bond lengths and angles fall within the expected range.

Journal Article↗
PubMed2002

Structural systematics for o-C(6)H(4)XY ligands with X,Y= O, NH, and S donor atoms. o-iminoquinone and o-iminothioquinone complexes of ruthenium and osmium.

The structural features of quinone ligands are diagnostic of charge. The o-benzoquinone, radical semiquinonate, and catecholate electronic forms have C-O bond lengths and a pattern of ring C-C bond lengths that point to a specific mode of coordination. This correlation between ligand charge and structure has been extended to iminoquinone and iminothioquinone ligands, giving a charge-localized view of electronic structure for complexes of redox-active metal ions. The radical semiquinonate form of these ligands has been found to be a surprisingly common mode of coordination; however, the paramagnetic character of the radical ligand is often obscured in complexes containing paramagnetic metal ions. In this report, diamagnetic iminosemiquinonate (isq) and iminothiosemiquinonate (itsq) complexes of ls-d(5) Ru(III) with related complexes of osmium are reported. With osmium, the Os(IV)-amidophenolate (ap) redox isomer is formed. Electrochemical and spectral properties are described for Ru(PPh(3))(2)(isq)Cl(2), Ru(PPh(3))(2)(itsq)Cl(2), Os(PPh(3))(2)(ap)Br(2), Os(PPh(3))(2)(atp)Br(2), and Os(PPh(3))(2)(ap)H(2). Crystallographic characterization of Ru(PPh(3))(2)(isq)Cl(2), Ru(PPh(3))(2)(itsq)Cl(2), and Os(PPh(3))(2)(ap)H(2) was used to assign charge distributions.

Journal Article↗
PubMed2003

Osmium phosphiniminato complexes: synthesis, protonation, structure, and redox-coupled hydrolytic scission of N-p bonds.

The osmium(VI) nitrido complex TpOs(N)Cl(2) [1, Tp = hydrotris(1-pyrazolyl)borate] reacts with triarylphosphines to afford the Os(IV) phosphiniminato complexes TpOs(NPAr(3))Cl(2) [Ar = p-tolyl (tol) (2a), phenyl (2b), p-CF(3)C(6)H(4) (2c)] in nearly quantitative yield. Protonation of 2a-c with 1 equiv of HOTf in MeCN occurs at the phosphiniminato nitrogen to give [TpOs(IV)(NHPAr(3))Cl(2)]OTf (3a-c) in 68-80% yield. Solutions of 2a-c in CH(2)Cl(2) react with excess H(2)O over 1 week to form the disproportionation products 1 (28%), TpOs(III)(NHPAr(3))Cl(2) (4a-c) (60%), and OPAr(3) (35%). Treatment of solutions of 3a-c with H(2)O also affords 1, 4a-c, and OPAr(3). X-ray structures of 2b, 3b, and 4b are presented. Cyclic voltammograms of compounds 2a-c exhibit Os(V)/Os(IV) and Os(IV)/Os(III) couples at approximately 0.3 and -1 V versus Cp(2)Fe(+/0). Protonation to give 3 makes reduction easier by approximately 1.2 V, so that these compounds show Os(IV)/Os(III) and Os(III)/Os(II) couples. In the hydrolytic disproportionation of 2a-c, labeling studies using (18)O-enriched O(2) and H(2)O establish water as the source of the oxygen atom in the OPAr(3) product. The conversions are accelerated by HOTf and inhibited by NaOD. The relative rates of hydrolytic disproportionation of 2a-c vary in the order tol > Ph > p-CF(3)C(6)H(4). The data indicate that protonation of the phosphiniminato nitrogen is required for hydrolysis. The mechanism of the hydrolytic disproportionation is compared to that of the related reaction of the osmium(IV) acetonitrile complex [TpOs(NCMe)Cl(2)](+).

Journal Article↗
PubMed2003

4,4'-dithiodipyridine as a bridging ligand in osmium and ruthenium complexes: the electron conductor ability of the -S-S- bridge.

The compounds [Ru(NH(3))(5)(dtdp)](TFMS)(3), [Os(NH(3))(5)(dtdp)](TFMS)(3), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](TFMS)(6), [(NH(3))(5)Os(dtdp)Ru(NH(3))(5)](TFMS)(3)(PF(6))(2), and [(NH(3))(5)Os(dtdp)Fe(CN)(5)] (dtdp = 4,4'-dithiodipyridine, TFMS = trifluoromethanesulfonate) have been synthesized and characterized by elemental analysis, cyclic voltammetry, electronic, vibrational, EPR, and (1)H NMR spectroscopies. Changes in the electronic and voltammetric spectra of the ion complex [Os(NH(3))(5)(dtdp)](3+) as a function of the solution pH enable us to calculate the pK(a) for the [Os(NH(3))(5)(dtdpH)](4+) and [Os(NH(3))(5)(dtdpH)](3+) acids as 3.5 and 5.5, respectively. The comparison of the above pK(a) data with that for the free ligand (pK(1) = 4.8) provides evidence for the -S-S- bridge efficiency as an electron conductor between the two pyridine rings. The symmetric complex, [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](6+), is found to exist in two geometric forms, and the most abundant form (most probably trans) has a strong conductivity through the -S-S- bridge, as is shown by EPR, which finds it to have an S = 1 spin state with a spin-spin interaction parameter of 150-200 G both in the solid sate and in frozen solution. Further the NMR of the same complex shows a large displacement of unpaired spin into the pi orbitals of the dttp ligand relative to that found in [Os(NH(3))(5)(dtdp)](3+). The comproportionation constant, K(c) = 2.0 x 10(5), for the equilibrium equation [Os(II)Os(II)] + [Os(III)Os(III)] right harpoon over left harpoon 2[Os(II)Os(III)] and the near-infrared band energy for the mixed-valence species (MMCT), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](5+) (lambda(MMCT) = 1665 nm, epsilon = 3.5 x 10(3) M(-)(1) cm(-)(1), deltanu(1/2) = 3.7 x 10(3) cm(-)(1), alpha = 0.13, and H(AB) = 7.8 x 10(2) cm(-)(1)), are quite indicative of strong electron delocalization between the two osmium centers. The electrochemical and spectroscopic data for the unsymmetrical binuclear complexes [(NH(3))(5)Os(III)(dtdp)Ru(II)(NH(3))(5)](5+) (lambda(MMCT) = 965 nm, epsilon = 2.2 x 10(2) M(-)(1) cm(-)(1), deltanu(1/2) = 3.0 x 10(3) cm(-)(1), and H(AB) = 2.2 x 10(2) cm(-)(1)) and [(NH(3))(5)Os(III)(dtdp)Fe(II)(CN)(5)] (lambda(MMCT) = 790 nm, epsilon = 7.5 x 10 M(-)(1) cm(-)(1), deltanu(1/2) = 5.4 x 10(3) cm(-)(1), and H(AB) = 2.0 x 10(2) cm(-)(1)) also suggest a considerable electron delocalization through the S-S bridge. As indicated by a comparison of K(c) and energy of the MMCT process in the iron, ruthenium, and osmium complexes, the electron delocalization between the two metal centers increases in the following order: Fe < Ru < Os.

Journal Article↗
PubMed2005

Dual room-temperature fluorescent and phosphorescent emission in 8-quinolinolate osmium(II) carbonyl complexes: rationalization and generalization of intersystem crossing dynamics.

A new series of quinolinolate osmium carbonyl complexes were synthesized and characterized by spectroscopic methods. Single-crystal X-ray diffraction studies indicate that these complexes consist of an octahedral ligand arrangement with one chelating quinolinolate, one tfa or halide ligand, and three mutually orthogonal terminal CO ligands. Variation of the substituents on quinolinolate ligands imposes obvious electronic or structural effects, while changing the tfa ligand to an electron-donating iodide slightly increases the charge density on the central osmium atom. These Os(II) complexes show salient dual emissions consisting of fluorescence and phosphorescence, the spectral properties and relaxation dynamics of which have been studied comprehensively. The results, in combination with the theoretical approaches, lead us to propose that the emission mainly originates from the quinolinolate pi pi* state. Both experimental and theoretical approaches generalize various types of intersystem crossing versus those of the tris(quinolinolate) iridium Ir(Q)3, and their relative efficiencies were accessed on the basis of the associated frontier orbital configurations. Our results suggest that [1d(pi)pi* absolute value(H(so))3 pi pi*] (or [3d(pi)pi* absolute value(H(so))1 pi pi*]) in combination with a smaller deltaE(S1-T1) gap (i.e., increasing the MLCT (d(pi)pi*) character) is the main driving force to induce the ultrafast S1 --> T1 intersystem crossing in the third-row transition metal complexes, giving the strong phosphorescent emission.

Journal Article↗
PubMed2006

Where is the limit of highly fluorinated high-oxidation-state osmium species?

The structures and stabilities of various osmium fluorides and oxyfluorides in high oxidation states have been studied by quantum-chemical calculations at DFT (B3LYP), MP2, CCSD, and CCSD(T) levels. The calculations indicate that the homoleptic fluorides all the way up to OsF8 may exist, even though OsF8 will be difficult to prepare. The last missing osmium oxyfluoride, OsOF6, is computed to be thermochemically stable against mononuclear gas-phase elimination reactions. The problem with the nonexistence of such highly fluorinated complexes appears thus to be mainly in difficult synthetic access under typical condensed-phase conditions. Matrix-isolation techniques might provide a means to characterize the highly fluorinated OsVIII and OsVII species.

Journal Article↗
PubMed1996

Oxidative Addition of Group 14 Element Hydrido Compounds to OsH(2)(eta(2)-CH(2)=CHEt)(CO)(P(i)Pr(3))(2): Synthesis and Characterization of the First Trihydrido-Silyl, Trihydrido-Germyl, and Trihydrido-Stannyl Derivatives of Osmium(IV).

The dihydrido-olefin complex OsH(2)(eta(2)-CH(2)=CHEt)(CO)(P(i)Pr(3))(2) (2) reacts with H(2)SiPh(2) to give OsH(3)(SiHPh(2))(CO)(P(i)Pr(3))(2) (3). The molecular structure of 3 has been determined by X-ray diffraction (monoclinic, space group P2(1)/c with a = 16.375(2) Å, b = 11.670(1) Å, c =18.806(2) Å, beta = 107.67(1) degrees, and Z = 4) together with ab initio calculations on the model compound OsH(3)(SiH(3))(CO)(PH(3))(2). The coordination geometry around the osmium center can be rationalized as a heavily distorted pentagonal bipyramid with one hydrido ligand and the carbonyl group in the axial positions. The two other hydrido ligands lie in the equatorial plane, one between the phosphine ligands and the other between the SiHPh(2) group and one of the phosphine ligands. Complex 3 can also be prepared by reaction of OsH(eta(2)-H(2)BH(2))(CO)(P(i)Pr(3))(2) (4) with H(2)SiPh(2). Similarly, the treatment of 4 with HSiPh(3) affords OsH(3)(SiPh(3))(CO)(P(i)Pr(3))(2) (5), while the addition of H(3)SiPh to 4 in methanol yields OsH(3){Si(OMe)(2)Ph}(CO)(P(i)Pr(3))(2) (6). Complex 2 also reacts with HGeR(3) and HSnR(3) to give OsH(3)(GeR(3))(CO)(P(i)Pr(3))(2) (GeR(3) = GeHPh(2) (7), GePh(3) (8), GeEt(3) (9)) and OsH(3)(SnR(3))(CO)(P(i)Pr(3))(2) (R = Ph (10), (n)Bu (11)), respectively. In solution, compounds 3 and 5-11 are fluxional and display similar (1)H and (31)P{(1)H} NMR spectra, suggesting that they possess a similar arrangement of ligands around the osmium atom.

Journal Article↗
PubMed1996

Osmium Complexes of 1,4,7-Triazacyclononane (tacn) and 1,4,7-Trimethyl-1,4,7-triazacyclononane (Me(3)tacn) and the X-ray Crystal Structure of [(Me(3)tacn)Os(eta(6)-C(6)H(5)BPh(3))]BPh(4).CH(3)CN.

The complexes of osmium with tacn (1,4,7-triazacyclononane) and Me(3)tacn (1,4,7-trimethyl-1,4,7-triazacyclononane), [LOs (eta(6)-C(6)H(6))](PF(6))(2) (L = tacn) and LOsCl(3) (L = tacn, Me(3)tacn), have been prepared by substitution of L on [Os(eta(6)-C(6)H(6))Cl(2)](2) or [Os(2)Cl(8)](2)(-), respectively. Reaction of LOsCl(3) with neat triflic acid leads to partial replacement of chloride and formation of the binuclear Os(III)-Os(III) complexes [LOs(&mgr;-Cl(3))OsL](PF(6))(3) (L = tacn, Me(3)tacn). The binuclear nature was established by NMR spectroscopy and elemental analysis and, for L = tacn, a partially refined X-ray crystal structure which shows the Os-Os separation to be 2.667 Å, indicative of significant metal-metal bonding. Reduction of [LOs(&mgr;-Cl(3))OsL](3+) over zinc amalgam in either aqueous or non-aqueous solution yields the intensely colored Os(II)-Os(III) mixed-valence ions [LOs(&mgr;-Cl(3))OsL](2+). Electrochemical measurements on [LOs(&mgr;-Cl(3))OsL](3+) in CH(3)CN reveal the reversible formation of the mixed valence ions. These are further reduced at lower potential to the Os(II)-Os(II) binuclear species, reversibly for L = Me(3)tacn. (Me(3)tacn)OsCl(3) is oxidized by persulfate ion to give [(Me(3)tacn)OsCl(3)](+); zinc amalgam reduction in an aqueous solution at high concentration produces the binuclear complex [(Me(3)tacn)Os(&mgr;-Cl(3))Os(Me(3)tacn)](3+) or, at low concentration, a solution containing an air sensitive osmium(II) species. Addition of BPh(4)(-) results in the eta(6)-arene zwitterion [(Me(3)tacn)Os(eta(6)-C(6)H(5)BPh(3))](+), which was characterized by X-ray diffraction on the BPh(4)(-) salt. The compound crystallizes in the triclinic space group P1 with a = 11.829(2) Å, b = 12.480(3) Å, c = 17.155(4) Å, alpha = 84.42(2) degrees, beta = 83.52(2) degrees, gamma = 71.45(2) degrees, V = 2380(2) Å(3), Z = 2, and R = 7.62%, and R(w) = 7.39%.

Journal Article↗
PubMed1997

Osmium-Promoted Oxidative Dimerization of Aminoarenes to N-Aryl-o-arenoquinone Diimines (L). Synthesis, Structure, Electrochemistry, and Reactivity of OsBr(2)L(2).

A family of o-arenoquinone diimine chelates, OsBr(2)L(2) (1, L = N-aryl-o-arenoquinone diimine), were isolated from the reaction of (NH(4))(2)OsBr(6) and primary aromatic amines, Ar-NH(2). These complexes constitute the first examples of osmium compounds of the o-benzoquinone diimine family. The above oxidative dimerization reaction of Ar-NH(2) was authenticated by the X-ray structure determination of a representative example. The X-ray structure of OsBr(2)L(2) (R = H) revealed a cis geometry with respect to two coordinated bromides. The bond length trends within the chelate as well as the aromatic rings are consistent with a diimine character of the ligand bound to osmium in its bivalent oxidation state. The complexes showed multiple transitions in near-IR and visible regions. These are electroactive and undergo multiple electron transfer. Three successive voltammetric responses, two oxidative and one reductive, were observed. The potential range was +1.7 to -0.8 V vs SCE in CH(3)CN solution (Pt electrode). The potentials of the above responses for differently substituted compounds depend on the Hammett summation operatorsigma(p) parameters of the substitution on L. The EPR spectrum of the electrogenerated 1-electron-oxidized complex 1a(+) is described. The electrode potentials of 1 are compared with those of related systems. A qualitative correlation between Os-N bond distances and Os(III)/Os(II) formal potentials for the Os(II) compounds of three different N,N donors is noted. The synthesis of a mixed-ligand tris chelate, [Os(bpy)L(2)](ClO(4))(2).H(2)O, is described, involving the reaction of 1 equiv of 1 with 2 equiv of Ag(bpy)(2)(+). The redox properties of the tris complex are reported. Crystal data for OsBr(2)L(2) (R = H) are as follows: empirical formula C(24)H(20)Br(2)N(4)Os; crystal system triclinic, space group P&onemacr;; a = 10.464(6) Å, b = 11.778(6) Å, c = 12.595(10) Å; alpha = 103.86(5) degrees, beta = 112.72(6) degrees, gamma = 107.79(4) degrees; V = 1245.3(10) Å(3); Z = 2; R = 4.46%; R(w) = 5.21%.

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PubMed1997

Heterometallic Osmium-Mercury Chain Structures Linking Two {Os(3)(CO)(10)(&mgr;-X)} Subunits (X = Cl, Br, I): Syntheses and Molecular Structures of [{Os(3)(CO)(10)(&mgr;-X)}(2)(&mgr;(4)-Hg)] (X = Cl, I), [{Os(3)(CO)(10)(&mgr;-Cl)}(2){&mgr;-HgOs(CO)(4)}(2)], and cis-[Os(CO)(4){(&mgr;-Hg)Os(3)(CO)(10)(&mgr;-Cl)}(2)].

Treatment of RHgCl (R = Me, Et, Ph, Fc) with the activated cluster [Os(3)(CO)(10)(NCMe)(2)] produces the osmium-mercury mixed-metal clusters [{Os(3)(CO)(10)(&mgr;-Cl)}(2)(&mgr;(4)-Hg)] (1a) and [{Os(3)(CO)(10)(&mgr;-Cl)}(2){&mgr;-HgOs(CO)(4)}(2)] (2a) in low yields. Cluster 1a bears a central wingtip mercury atom simultaneously bridging two {Os(3)(CO)(10)(&mgr;-Cl)} units. Cluster 2a comprises an unprecedented decanuclear osmium-mercury framework in which there is a central linear "Hg-{Os(CO)(4)}(2)-Hg" molecular backbone with the two Os(CO)(4) fragments arranged in a staggered conformation. Cluster 2a is thermally unstable and converts slowly to cis-[Os(CO)(4){(&mgr;-Hg)Os(3)(CO)(10)(&mgr;-Cl)}(2)] (4a) via the extrusion of an Os(CO)(4) moiety under ambient conditions. Cluster 4a comprises two {(&mgr;-Hg)Os(3)(CO)(10)(&mgr;-Cl)} subcluster units bonded to a central Os(CO)(4) moiety in a cis configuration. Similar reactions with PhHgBr and MeHgI have also been investigated. Cluster 1a crystallizes in the triclinic space group P&onemacr; with a = 9.112(2) Å, b = 12.314(2) Å, c = 15.501(4) Å, alpha = 84.92(2), degrees beta = 88.26(3), degrees gamma = 79.52(2) degrees and Z = 2. Cluster 2a crystallizes in the triclinic space group P&onemacr; with a = 13.306(2) Å, b = 20.768(5) Å, c = 9.771(4) Å, alpha = 96.36(3), degrees beta = 90.50(2), degrees gamma = 98.81(2) degrees and Z = 2. Cluster 4a crystallizes in the triclinic space group P&onemacr; with a = 18.356(2) Å, b = 19.100(3) Å, c = 14.478(2) Å, alpha = 89.783(2), degrees beta = 113.19(2), degrees gamma = 113.70(2) degrees and Z = 4.

Journal Article↗
PubMed2002

Divalent osmium complexes: synthesis, characterization, strong red phosphorescence, and electrophosphorescence.

We report new divalent osmium complexes that feature strong red metal-to-ligand-charge-transfer (MLCT) phosphorescence and electrophosphorescence. The general formula of the complexes is Os(II)(N-N)(2)L-L, where N-N is either a bipyridine or a phenanthroline and L-L is either a phosphine or an arsine. New polypyridyl ligands synthesized are 4,4'-di(biphenyl)-2,2'-bipyridine (15) and 4,4'-di(diphenyl ether)-2,2'-bipyridine (16), and the 1,10-phenanthroline derivatives synthesized are 4,7-bis(p-methoxyphenyl)-1,10-phenanthroline (17), 4,7-bis(p-bromophenyl)-1,10-phenanthroline (18), 4,7-bis(4'-phenoxybiphen-4-yl)-1,10-phenanthroline (19), and 4,7-bis(4-naphth-2-ylphenyl)-1,10-phenanthroline (20). 4,4'-Diphenyl-2,2'-bipyridine (21) and 4,7-diphenyl-1,10-phenanthroline (22) were also used in these studies. Strong pi-acid ligands used were 1,2-bis(diphenylarseno)ethane (23), cis-1,2-bis(diphenylphosphino)ethylene (24), and cis-1,2-vinylenebis(diphenylarsine) (25). Ligand 25 is used for the first time in these types of luminescent osmium complexes. These compounds feature strong MLCT absorption bands in the visible region and strong red phosphorescent emission ranging from 611 to 651 nm, with quantum efficiency up to 45% in ethanol solution at room temperature. Red organic light-emitting diodes (OLEDs) were successfully fabricated by doping the Os(II) complexes into blend of poly(N-vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD). Brightness over 1400 cd/m(2) for a double-layer device has been reached, with a turn-on voltage of 8 V. The maximum external quantum efficiency was 0.64%. Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (x, y) of the red electrophosphorescence from the complexes are (0.65, 0.34), which indicates pure red emission.

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