Osmium Clusters Research Articles

MgO-supported bimetallic catalysts consisting of segregated, essentially molecular rhodium and osmium species

A family of supported bimetallic samples was prepared by the reactions of Rh(C2H4)(acac) (acac = acetylacetonate) and Os3(CO)12 with MgO. The samples were characterized by infrared and extended X-ray absorption fine structure spectroscopies, before and after various treatments with hydrogen at temperatures up to 393 K. The spectra identify the following combinations of supported species: (a) [Os3(CO)11](2-) + Rh(C2H4)2, (b) [Os3(CO)11](2-) + Rh(CO)2, and (c) [Os3(CO)11](2-) + rhodium clusters containing approximately 4 to 6 atoms each, on average. No bimetallic clusters formed. The triosmium frame remained intact while the rhodium surface species were reduced in the presence of H2. The samples were tested as catalysts for ethylene hydrogenation at 298 K, and the catalytic activity matched that of the rhodium complexes alone; evidently the rhodium complexes were responsible for all the catalysis, with the osmium clusters remaining inactive because of the presence of the carbonyl ligands on them.

The structural and electronic properties of small osmium clusters (2–14): A density functional theory study

The ground state structures and several isomers of osmium clusters of up to 14 atoms were obtained from the basin-hopping algorithm within a density functional theory. The small Os clusters favor cubic-based configurations which are similar to those found in Ru clusters. In contrast, Os clusters show much higher binding energy and stability than Ru clusters, which suggests that Os clusters have the potential to be better catalysts than Ru clusters. Magnetic property of small Os clusters also studied. These results provide an elementary understanding of small osmium clusters and provide a catalyst alternative to other group VIII clusters.

Microwave preparation of osmium clusters with anticancer activity; rapid syntheses of Os6(CO)18, Os3(CO)10(acetonitrile)2, and Os3(μ-H)(μ-OH)(CO)10

Microwave-assisted syntheses of the osmium cluster synthons Os6(CO)18, Os3(CO)10(NCMe)2, and Os3(μ-H)(μ-OH)(CO)10 are reported. Microwave irradiation of Os3(CO)12 in a small amount of 1,2-dichlorobenzene is shown to be a superior method of preparing Os6(CO)18 that produces a relatively high yield in only 35 min of heating instead of many days of pyrolysis. In a simple two-step method requiring less than 1 h, the labile complex Os3(CO)10(NCMe)2 is prepared in excellent yield (over 90%). This preparation is accomplished without the need to exclude air from the reaction vessel, and with one-tenth as much solvent and one-half as much trimethylamine-N-oxide as the standard method of synthesis. The cluster Os3(μ-H)(μ-OH)(CO)10 is also conveniently prepared with a small amount of solvent by heating a mixture of Os3(CO)12, silica gel, toluene and water in a microwave reactor for 2 h.

Coordination Behavior and Transformations of Thienyl-Substituted Diacetylenes upon Coordination to Os3H2(CO)10

The reaction between 2- and 3-thienyl-substituted 1,3-butadiynes and the electron-deficient osmium cluster Os3H2(CO)10 yields trinuclear coordination products, associated with transformations of the diacetylene ligands. Depending on the heteroaryl end groups, osmium clusters with both a closed and open Os-triangle core were formed. The reaction between Os3H2(CO)10 and 1,4-bis(2-thienyl)butadiyne yielded [Os3(μ-H)(CO)10{(μ-η-(C4H3S)(C8H4S)}] (1) and [Os3(μ-H)(CO)10{(μ3-η2-η1-η1-(SC7H4)C(SC4H3)}] (2), whereas in the analogous case of 1,4-bis(3-thienyl)butadiyne the main coordination product was found to be [Os3(μ-H)(CO)10{(μ-η-(C4H3S)(C8H4S)}] (3). Compounds 1–3 were stable in air, but lost carbon monoxide upon prolonged heating. Thermal decarbonylation of 1 under N2 yielded a mixture of [Os3(μ-H)(CO)9{(μ3-η3-(C4H3S)(C8H4S)}] (4) and [Os3(μ-H)2(CO)9{(μ3-η1-η1-(C4H3S)(C8H3S)}] (5). Thermal decarbonylation of 2 yielded [Os3(μ-H)(CO)9{(μ3-η3-(C4H3S)(C8H4S)}] (6), while thermal decarbonylation of 3 yielded [Os3(μ-H)(CO)9{(μ3-η3-(C4H3S)(C8H4S)}] (7). A reaction involving 3 with CF3COOH affords as the main cluster product the known cluster [Os3(μ-H)(CO)10(O2CF3)] (8) and, unusually, permits the isolation and characterization of the novel organic molecule [(C4H3S)(C8H4S)(OCF3)] (9) cleaved from the parent cluster. The structures of the new compounds were established by single-crystal X-ray studies and spectroscopic methods and supported by density functional theory.

Theoretical study of geometry structures and stability of OsnN0,±(n=1—6) clusters

The possible geometrical and electronic structures of (OsnN)0, ±(n=1—6) clusters are optimized by using the density functional theory (B3LYP) at the LANL2DZ level. For the ground state structures of (OsnN)0,±(n=1—6) clusters, the average binding energies, second finite differences, dissociation energies and energy gaps are analyzed. The calculated results show that there are many different isomerides in (OsnN)0,±(n=1—6) clusters. With the increase of number of atoms, the N atom tend to the peripheral endpoint; the clusters show "odd - even" oscillation and "magic number" effect. The cluster is more stable when the number of atoms is even than odd. It was found that the Os3N+ and Os5N+ clusters are the most stable and n=4 clusters is the least stable, yet the stability of (OsnN)0,±(n=1—6) clusters have increased significantly than pure osmium clusters.

Osmium−Bismuth Complexes from the Reaction of Os3(CO)11(NCMe) with BiPh3

Five new compounds were obtained from the reaction of Os(3)(CO)(11)(NCMe), 1, with BiPh(3) in hexane solution at reflux. These have been identified as Os(2)(CO)(8)(mu-BiPh), 2, Os(CO)(4)Ph(2), 3, Os(4)(CO)(14)(mu-eta(3)-O=CC(6)H(5))(mu(4)-Bi), 4, Os(4)(CO)(15)Ph(mu(4)-Bi), 5, and Os(5)(CO)(19)Ph(mu(4)-Bi), 6. Cleavage of the phenyl groups from the BiPh(3) was the dominant reaction pathway. Fragmentation of the original triosmium cluster was accompanied by reaggregation processes that were facilitated by the naked bismuth to yield the higher nuclearity osmium cluster complexes containing spiro-bridging bismuth ligands. Compound 6 was photo-decarbonylated to yield the compound HOs(5)(CO)(18)(mu-eta(2)-C(6)H(4))(mu(4)-Bi), 7, formed by ortho-CH activation of the sigma-bonded phenyl ring in 6 to form a bridging eta(2)-benzyne ligand. Compounds 2- 7 were each characterized structurally by a single-crystal X-ray diffraction analysis.

Synthesis, Structure and Reactivity of Electron Deficient Triosmium Cluster Bearing 2,6-Dimethylbenzothiazolide Ligand

Reaction of [Os3(CO)10(NCMe)2] with 2,6-dimethylbenzothiazole at room temperature affords [Os3(CO)10(μ-H){μ-η 2-C7H2NS(Me)2}] (1) in 45% yield. Decarbonylation of 1 in refluxing toluene furnishes the electron-deficient cluster [Os3(CO)9(μ-H){μ 3-η 2-C7H2NS(Me)2}] (2) in almost quantitative yield. Treatment of 2 with PPh3 at 40 °C gives the addition product [Os3(CO)9(PPh3)(μ-H){μ-η 2-C7H2NS(Me)2}] (3) in 85% in which the PPh3 ligand is coordinated to the rear osmium atom. A similar treatment of 2 with P(OMe)3 gives [Os3(CO)9{P(OMe)3}(μ-H){μ-η 2-C7H2NS(Me)2}] (4) in 60% yield with P(OMe)3 ligand also coordinated to the rear metal. Compounds 3 and 4 differ by the disposition of the hydride ligands. In compound 4 both the hydride and the heterocyclic ligands simultaneously bridge the same metal–metal edge whereas they bridge different metal–metal edges in 3. Compounds 1–4 have been characterized by a combination of elemental analysis, infrared, NMR and mass spectral data together with single crystal X-ray diffraction studies for 3. Compound 3 crystallizes in the monoclinic space group P21/n with a = 9.2659(10), b = 23.643(2), c = 16.382(3) A, β = 91.324(12)°, Z = 4 and V = 3,587.8(8) A3. Synthesis and reactivity of electron-deficient 2,6-dimethylbenzothiazole osmium cluster [Os3(CO)9(μ-H){μ 3-η 2-C7H2NS(Me)2}] (2) are described. Reaction of 2 with PR3 (R = Ph, OMe) furnishes [Os3(CO)9(PR3)(μ-H){μ-η 2-C7H2NS(Me)2}] (3, R = Ph; 4, R = OMe) in which the PR3 ligand is coordinated to the rear osmium atom.

NHC Complexes of Osmium Clusters: A Structural and Reactivity Study

A carbene transfer agent, 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene-silver(I)chloride ([IMes]AgCl), was treated with various osmium clusters. Reaction of ([IMes]AgCl) with [Os3(μ-H)2(CO)10] gave [Os3(μ-H)(μ-Cl)(CO)9(IMes)] (1), an osmium N-heterocyclic carbene complex. The reaction of ([IMes]AgCl) with the cluster [Os3(CO)10(CH3CN)2] yielded two products, [Os3(μ-Cl)(CO)10(μ-Ag(IMes)] (2) and [(IMes-H)][Os3(μ-Cl)(CO)10](μ4-Ag)[Os3(μ-Cl)(CO)10] (3). Compound (2) is a heterobimetallic carbene complex resulting from the complete incorporation of ([IMes]AgCl). Transmetalation using [(IMes)AgCl] and the cluster [Os4(μ-H)4(CO)12] in the presence of trimethylamine-N-oxide resulted in the formation of [Os4(μ-H)4(CO)11(n·IMes)] (4), where (n denotes normal carbene bonding, i.e., through C2). [Os4(μ-H)4(CO)10(IMes)2] (5) was formed using the activated cluster [Os4(μ-H)4(CO)10(CH3CN)2] and [(IMes)AgCl]. Compound (5) was found to be sensitive to silica gel column chromatography in the presence of dichlorometha...

The deposition of osmium carbonyl clusters onto inorganic oxide surfaces: A ToF-SIMS and IR spectroscopic study of the surface species

The interaction between the osmium clusters [Os 3(CO) 12], [Os 3(CO) 10(μ-H) 2], [Os 3(CO) 10(μ-H)(μ-OH)], and a series containing a free functional group, viz., [Os 3(CO) 10(μ-H)(μ- S ∧ EH )] (where = alkyl ∧ chain or an aromatic ring, E = COO, S or O), with SiO 2, ZnO and In 2O 3, was examined by ToF-SIMS and IR spectroscopy. While the interaction with the silica surface is mostly via an O atom or the functional group, the interaction with the ZnO and In 2O 3 surfaces is more complex.

An open-channel architecture assembly from the [Os3(CO)8{µ-η3-ONCPh(NC5H4)}2] cluster

A novel osmium cluster with an open-channel structure has been synthesised and characterised by X-ray diffraction.

Microwave-assisted synthesis of dimolybdenum tetracarboxylates and a decanuclear osmium cluster

An improved method for the synthesis of dimolybdenum tetracarboxylates has been developed. The standard procedure for the preparation of these compounds involves extended reflux (up to 20 h) of a mixture of Mo(CO) 6 and the appropriate carboxylic acid, along with its anhydride, under an inert atmosphere. Using a microwave reactor and a closed vessel, Mo 2(acetate) 4, Mo 2(propionate) 4 and Mo 2(benzoate) 4 have been prepared in superior yields in less than 1 h. Furthermore, this new method does not require the use of the acid anhydride or the use of an inert gas. An improved method for the preparation of [N(PPh 3) 2] 2[Os 10C(CO) 24] directly from Os 3(CO) 12 has also been developed. The published synthesis of this osmium cluster calls for the pyrolysis of Os 3(CO) 11(py) for 64 h. Microwave irradiation of a mixture of Os 3(CO) 12 and diglyme in a closed vessel yields the desired product in just over 1 h.

Normal and Abnormal NHC Coordination in [Os4(μ-H)4(CO)11(IMes)] and Exhaustive Dehydrogenation of an IMes Methyl Group

The osmium cluster [Os4(μ-H)4(CO)11(IMes)] (1·nIMes) was prepared by treatment of IMesAgCl with [Os4(μ-H)4(CO)12]. The product of this reaction is believed to be the first tetranuclear NHC cluster compound. Thermolysis of this complex in benzene at reflux resulted in exhaustive dehydrogenation of an o-methyl group on IMes, partial dehydrogenation of benzene, and subsequent coupling of the two unsaturated fragments to produce 2. The abnormal NHC complex (1·aIMes) was also isolated. All compounds were characterized by spectroscopic studies and confirmed by X-ray crystallography.

Facile Activation of Hydrogen by an Unsaturated Platinum−Osmium Cluster Complex

The electronically unsaturated platinum−osmium complex Pt2Os3(CO)10(PtBu3)2, 3, has been obtained from the reaction of Os3(CO)10(NCMe)2 with Pt(PtBu3)2. Compound 3 adds hydrogen at 0 °C to yield the dihydrido complex Pt2Os3(CO)10(PtBu3)2(μ-H)2, 4 (93% yield) within 10 min and subsequently the tetrahydrido complex Pt2Os3(CO)10(PtBu3)2(μ-H)4, 5, in 70% yield within 60 min. Compound 3 contains a trigonal bipyramidal cluster of five metal atoms having the two platinum atoms in the apical sites. With the addition of each equivalent of hydrogen, the trigonal bipyramidal cluster opens by series of Pt−Os bond cleavages that result in sequential shifts of the Pt groups to edges of the Os3 triangle. The hydrogen addition process can be reversed partially at 25 °C by purging solutions of 5 with nitrogen.

Non-classical NHC transfers from the reaction of (IMes)AgCl with osmium carbonyl clusters

N-Heterocyclic carbene transfer reactions were attempted using IMesAgCl and two osmium clusters. The products isolated from these reactions suggest that NHC transfers can be unpredictable.

The series Os4(µx-η2-C2Ph2)(CO)14–n(n = 0, 1, 2;x = n+ 2) — Models for site-specific surface catalysts

The cluster Os4(µ-η2-C2Ph2)(CO)14(1) has been prepared from the reaction of Os4(CO)14and C2Ph2in CH2Cl2at 25 °C. Other minor products include the known clusters Os3(µ3-η2-C2Ph2)(CO)10and Os3(µ-η4-C4Ph4)(CO)9. The structure of 1 reveals an approximately planar C2Os4skeleton with a dimetallacyclobutene ring (C—C = 1.32(4) Å) and a flat butterfly Os4unit (Os—Os range = 2.859(2)–2.916(2) Å). The13C{1H} NMR spectrum of 1 indicates the carbonyl ligands are rigid at room temperature. Stirring 1 in CH2Cl2for 2 days (ambient temperature) afforded Os4(µ3-η2-C2Ph2)(CO)13(2). The Os atoms in 2 also have an almost flat butterfly arrangement (Os—Os range = 2.7392(7)–2.8947(6) Å) with the alkyne ligand located over one of the Os3triangles. The13C NMR data for 2 are consistent with rapid rotation on the NMR timescale of the hinge Os(CO)3units at 21 °C, but slow rotation at –50 °C. Heating 2 at 40 °C gave Os4(µ4-η2-C2Ph2)(CO)12(3) after 2 days. Cluster 3 has the common butterfly arrangement of Os atoms with the C2Ph2bound to all four metal atoms (Os—Os range = 2.7457(5)–2.8742(5) Å). The13C{1H} NMR spectra of 3 at 21 and 90 °C indicate there is rapid CO exchange of the carbonyls of the two types of Os(CO)3units, but not between the units. The spectrum at –90 °C indicates one of the rotations (presumed to be that involving the carbonyls of the wingtip Os(CO)3units) is slowed on the NMR timescale. Compounds 1–3 form a unique series of clusters that have an alkyne ligand bound to two, three, and four metal atoms. Compound 1 is a model for a corner, compound 2 for a planar surface, and compound 3 a step site, in site-specific surface catalysts.Key words: osmium cluster, diphenylacetylene, dimetallacyclobutene, carbonyl exchange, surface catalysis.

Synthesis and structural characterization of mesitylphosphinidene-capped ruthenium and osmium clusters

Thermal reaction of [Ru 3(CO) 12] with PH 2Mes (Mes = mesityl) in refluxing toluene afforded mesitylphosphinidene-capped ruthenium carbonyl clusters, [Ru 3(CO) 9(μ-H) 2(μ 3-PMes)] ( 1), [Ru 3(CO) 8(PH 2Mes)(μ-H) 2(μ 3-PMes)] ( 2), [Ru 3(CO) 9(μ 3-PMes) 2] ( 3), [Ru 4(CO) 10(μ-CO)(μ 4-PMes) 2] ( 4), and [Ru 5(CO) 10H 2(μ 4-PMes)(μ 3-PMes) 2] ( 5). All products were fully characterized and structurally confirmed by X-ray crystal structure analysis. Complexes 2– 4 were also obtained in high yields by stepwise reaction starting from 1. Fluxional behavior of carbonyl groups was observed in case of 4. Complex 5 reveals a new type of skeletal structure, bicapped-octahedron having μ 3- and μ 4-phosphinidene ligands at the capping positions. Similar reaction of [Os 3(CO) 12] with PH 2Mes yielded a phosphido-bridged osmium cluster [Os 3(CO) 10(μ-H)(μ-PHMes)] ( 6) and a phosphinidene-capped cluster [Os 3(CO) 9(μ-H) 2(μ 3-PMes)] ( 7).

The synthesis of heteronuclear clusters containing cyclopentadienyl- or pentamethylcyclopentadienyliridium and ruthenium or osmium

The reaction of Cp*Ir(CO) 2 or CpIr(CO) 2 with Ru 3(CO) 12 under a hydrogen atmosphere afforded the heterometallic clusters Cp*IrRu 3(μ-H) 2(CO) 10 and CpIrRu 3(μ-H) 2(CO) 10, respectively, in moderate yields. In the former reaction, the tetrahydrido cluster Cp*IrRu 3(μ-H) 4(CO) 9 was also formed in trace amounts, although this cluster can be obtained in high yields by the hydrogenation of Cp*IrRu 3(μ-H) 2(CO) 10; the Cp analogue was not obtainable. The reaction of Os 3(μ-H) 2(CO) 10 with Cp*Ir(CO) 2 afforded the osmium analogue Cp*IrOs 3(μ-H) 2(CO) 10 in 70% yield, along with a trace amount of the pentanuclear cluster Cp*IrOs 4(μ-H) 2(CO) 13. Hydrogenation of Cp*IrOs 3(μ-H) 2(CO) 10 afforded Cp*IrOs 3(μ-H) 4(CO) 9 in excellent yield. The reaction of Cp*Ir(CO) 2 with Os 3(CO) 10(CH 3CN) 2 afforded the known trinuclear cluster Cp*IrOs 2(CO) 9 and the novel cluster Cp*IrOs 3(CO) 11. Solution-state NMR studies show that the hydrides in the iridium–ruthenium clusters are highly fluxional even at low temperatures while those in the iridium–osmium clusters are less so.

Triphenylphosphine-substituted selenido and sulfido clusters of osmium derived from Ph 3P [dbnd]Se or Ph 3P [dbnd

Cleavage of P Se bonds occurs readily in the room-temperature treatment of [Os 3(CO) 10(MeCN) 2] with Ph 3P Se to give three new compounds, [Os 3(μ 3-Se) 2(CO) 8(PPh 3)] ( 2), [Os 3(μ 3-Se)(μ 3-CO)(CO) 7(PPh 3) 2] ( 5) and [Os 3(μ-OH) 2(CO) 8(PPh 3) 2] ( 6), respectively, and three known compounds, [Os 3(μ 3-Se) 2(CO) 9] ( 1), [Os 3(μ 3-Se)(μ-CO) 2(CO) 7(PPh 3)] ( 3), and 1,2-[Os 3(CO) 10(PPh 3) 2] ( 4).No evidence for any product containing a co-ordinated Ph 3P Se ligand was obtained.The analogous reaction between [Os 3(CO) 10(MeCN) 2] and Ph 3P S produces five new compounds [Os 3(μ 3-S) 2(CO) 8(PPh 3)] ( 7), [Os 3(μ 3-S)(μ-CO) 2(CO) 7(PPh 3)] ( 8), [Os 3(μ 3-S)(μ 3- CO)(CO) 7(PPh 3) 2] ( 9), [Os 3(μ 3-) 2(CO) 7(PPh 3) 2] ( 11) and compound 6 in addition to the known compound 4. Treatment of 2 with Me 3NO at 50 °C gives the trinuclear cluster [Os 3(μ 3-Se) 2(CO) 7(PPh 3)(NMe 3)] ( 13) and the hexanuclear cluster [Os 6(μ 3-Se) 4(CO) 14(PPh 3) 2] ( 12). Treatment of compound 1 with PPh 3 and Me 3NO at room temperature gives [Os 3(μ 3-Se) 2(CO) 7(PPh 3) 2] ( 10). Compound 2 reacts with PPh 3 similarly to give 10. Compound 3 reacts with elemental selenium at 110 °C to give 2. The new compounds 2, 5, 6 and 8 were characterized by single-crystal X-ray diffraction. The compounds 3, 5, 8 and 9 contain Os 3(μ 3-S) or Os 3(μ 3-Se)cluster cores with three metal–metal bonds while 2, 7, 10, 11 and 12 contain Os 3(μ 3-S) 2or Os 3(μ 3-Se) 2 cores two metal–metal bonds. The two hydroxy ligands in the triosmium cluster 6 bridging the open osmium-osmium edge and are probably derived from water. A study of the dynamic exchange of PPh 3 ligands in 5 is also reported.

Growth of the metal framework in linear ruthenium and osmium carbonyls

Formation of the linear chain ruthenium and osmium carbonyls by successive linkage of mononuclear [M(CO) 4Cl 2] units and by opening trinuclear clusters [M 3(CO) 12] and [FeM 2(CO) 12] (M = Ru, Os) with chlorine gas have been studied by computational DFT methods. Energetically the formation of dinuclear [M 2(CO) 8Cl 2] from [M(CO) 4Cl 2] units is the most demanding step. The following chain growth by adding new mononuclear units proceeds more easily with nearly constant energy per step. Cluster opening by chlorine gas to obtain trinuclear [M 3(CO) 12Cl 2] is a facile reaction for both ruthenium and osmium clusters as well as for mixed metal clusters. Mixed metal clusters [FeOs 2(CO) 12] and [FeRu 2(CO) 12] open preferably between iron–osmium or iron–ruthenium bonds producing linear trinuclear Fe–M–M-type of compound. In the case of mixed metal Os–Ru clusters, the cleavage of Os–Ru bond is not clearly preferred. Fragmentation of the cluster to shorter units cis(Cl)-[M(CO) 4Cl 2] or [M 2(CO) 8Cl 2] with equatorial chlorides is highly favorable and competes with the cluster opening. No preferences on the bond type (Os–Ru, Os–Os, or Ru–Ru) that are broken can be found in the case of mixed metal Os–Ru clusters.

Activation of Metal-Carbonyl Clusters by their Encapsulation Within Alumina Sol-Gel Matrices

Entrapment of Ru3(CO)12 and Os3(CO)12 within alumina sol-gel matrices, (obtained by hydrolysis and polycondensation of a THF solution of aluminum isopropoxide) converts these clusters into highly active, leach-proof and recyclable hydrogen transfer catalysts. Likewise Rh2Co2(CO)12 which, in its silica sol-gel entrapped form, neither promotes the isomerization of allylbenzene nor the disproportionation of dihydroarenes, becomes upon its entrapment in an alumina sol-gel matrix, an efficient and recyclable catalyst for these reactions. While the entrapped osmium cluster promotes at 100–110∘C and 20 bar only the hydrogenation of alkenes, the ruthenium analog catalyzes also the saturation of the aromatic C–C bonds. The hydrogenations take place via the hydride mechanism. XPS and TEM studies revealed that the carbonyl clusters do not decompose to give detectable amounts of (entrapped) metal particles during the encapsulation as well as during the catalytic processes.