Tetranuclear Osmium Research Articles

Anticancer activity of osmium metalla-rectangles

A series of cationic metalla-rectangles of the general formula [(p-cymene)(4)Os(4)(OO[intersection]OO)(2)(N[intersection]N)(2)](4+) have been obtained in methanol from the dinuclear arene osmium precursors [(p-cymene)(2)Os(2)(OO[intersection]OO)(2)Cl(2)] (OO[intersection]OO = 2,5-dioxydo-1,4-benzoquinonato (dhbq), 2,5-dichloro-1,4-benzoquinonato (dcbq)) by reaction with bipyridine linkers (N[intersection]N = 4,4'-bipyridine, 1,2-bis(4-pyridyl)ethylene) in the presence of AgCF(3)SO(3). All complexes were isolated as triflate salts and characterised by NMR, IR and UV-visible spectroscopy. The cytotoxicities of the dinuclear and tetranuclear osmium complexes were established using ovarian A2780 cancer cell lines. The most active metalla-rectangle, [(p-cymene)(4)Os(4)(dhbq)(2)(4,4'-bipyridine)(2)](4+), shows an IC(50) value of 5.7 microM (comparable to cisplatin) against A2780 cancer cells and 7.5 microM against the cisplatin resistant A2780cisR cells.

Synthesis and structure of two tetranuclear osmium carbonyl isotopomers: a crystallographic isotope effect

A synthetic route to [Os4(mu-H)(mu-OH)(mu-CO)(CO)12] ( 1) has been devised through the activation of [Os4(CO)14] with Me3NO. The pyrolysis and photolysis of the reactant in the presence of a trace amount of water produces 1 in low yield. The solid-state structure of [Os4(mu-H)(mu-OH)(mu-CO)(CO)12 x H2O] (1 x H2O) reveals a butterfly Os4 skeleton with bridging H, OH and CO ligands as well as hydrogen-bonded molecules of water in the crystal lattice. A low-temperature 13C{1H} NMR spectroscopic study revealed a merry-go-round exchange of CO ligands around the Os3 plane containing the asymmetric bridging CO. The exposure of 1 x H2O to D2O yielded [Os4(mu-H)(mu-OD)(mu-CO)(CO)12]2. Although the solid-state, intramolecular structure of 2 closely matched that of 1 x H2O, the intermolecular structure did not: its crystal lattice contained no water of crystallization, a previously unreported crystallographic isotope effect.

Homoleptic tetranuclear osmium carbonyls: from the rhombus via the butterfly to the tetrahedron

The structures of the tetranuclear osmium carbonyl derivatives Os4(CO)n (n = 16, 15, 14, 13, 12) have been investigated using the density functional theory method MPW1PW91 with the SDD effective core potential basis set, found to be effective in previous work for the study of Os3(CO)12. The Os4 clusters in the lowest energy structures for Os4(CO)16, Os4(CO)15, and Os4(CO)14 are found to be rhombi, butterflies, and tetrahedra with four, five, and six Os-Os bonds, respectively, in accord with structures determined by X-ray diffraction as well as the 18-electron rule. The fluxionality of tetrahedral Os4(CO)14, suggested by experimental work of Johnston, Einstein, and Pomeroy, is confirmed by our DFT studies, which find four Os4(CO)14 structures within 1.5 kcal mol-1 of each other with similar tetrahedral Os4 frameworks but with different arrangements of bridging and semibridging carbonyl groups. The lowest energy structures for the more unsaturated Os4(CO)13 and Os4(CO)12 are also based on Os4 tetrahedra but with shorter Os-Os edge lengths than in Os4(CO)14 suggesting delocalized multiple bonding in the more highly unsaturated systems. Thus the global minimum for Os4(CO)12 is predicted to have tetrahedral symmetry, with all terminal carbonyl groups analogous to the experimentally known structure of (mu3-H)4Re3(CO)12, but without the face-bridging hydrogen atoms.

Synthesis, characterization and crystal structures of osmium–rhodium mixed-metal clusters containing pentamethylcyclopentadienyl ligand: [Os 3Rh(μ-CO) 2(CO) 9(η 5-Cp*)], [Os 3Rh 2(μ-H)(μ-CO) 2(CO) 8(η 5-Cp*)(μ 2-η 5,η 1-CH 2C 5Me 4)] and [Os 3Rh(μ 3-H)(μ-Cl)(μ-CO)(CO) 9(η 5-Cp*)

Treatment of the anionic triosmium cluster [N(PPh 3) 2][Os 3(μ-H)(CO) 11] with one equivalent of [RhCp*(MeCN) 3][{PF 6} 2] [Cp*=pentamethylcyclopentadiene] yielded three Cp*-containing clusters including [Os 3Rh(μ-H) 2(μ-CO)(CO) 9(η 5-Cp*)] 1, [Os 3Rh(μ-CO) 2(CO) 9(η 5-Cp*)] 2 and [Os 3Rh 2(μ-H)(μ-CO) 2(CO) 8(η 5-Cp*)(μ 2-η 5,η 1-CH 2C 5Me 4)] 3. Solid state vacuum pyrolysis of 2 gave 1 in moderate yield via the replacement of a bridging carbonyl by two bridging hydrides. The coupling reaction of [N(PPh 3) 2][Os 3(μ-H)(CO) 11] with the monocationic complex, [RhCp*(dppe)Cl][PF 6] [dppe=bis(diphenylphosphino)ethane] afforded the tetranuclear cluster [Os 3Rh(μ 3-H)(μ-Cl)(μ-CO)(CO) 9(η 5-Cp*)] 4 in a moderate yield. Clusters 2– 4 have been fully characterized by both spectroscopic and crystallographic methods. The X-ray structure analysis shows that 3 comprises an edge-bridging tetrahedron in which one of the pentamethylcyclopentadienyl units adopts a novel μ 2-η 5,η 1-bonding mode across a Os–Rh bond. Cluster 4 is a tetranuclear osmium–rhodium mixed-metal cluster containing a chloride, bridging across the wing-tips of the butterfly core.

Tert-Butylimido complexes of osmium-(VIII), -(VII) and -(VI). X-Ray crystal structures of [(ButN)2Os(µ-NBut)2Os(NBut)(µ-O)]2, [Os(NBut)2(µ-NBut)]2and [Os(NBut)2(µ-NBut)]2[BF4]2

The interaction of OsO4 with neat NHBut(SiMe3) gives the first homoleptic osmium(VIII) imido compound, Os(NBut)41, together with the tetranuclear osmium(VI) oxo-imido complex [(ButN)2Os(µ-NBut)2Os(NBut)(µ-O)]22. Complex 1 can be reduced to the osmium(VI) dimer, [Os(NBut)2(µ-NBut)]23, by triphenylphosphine or by sodium amalgam in tetrahydrofuran; with trimethyloxonium tetrafluoroborate an unusual reduction reaction leads to the osmium(VII) dimeric cationic complex [Os(NBut)2(µ-NBut)]2[BF4]24. The syntheses of Os(NR)3, R = 2,6-Me2C6H35, or 2,6-Pri2C6H36, by interaction of OsO4 with NHR(SiMe3) are reported. The X-ray crystal structures of 2, 3 and 4 have been determined. Compound 2 has a chain tetrameric structure with two (ButN)2Os(µ-NBut)2Os(NBut)(µ-O) units linked by a dioxo bridge. The outer Os atoms are four-co-ordinate, distorted tetrahedral, the inner Os atoms five-co-ordinate, square pyramidal. The bridging Os–N distances to the inner, five-co-ordinate osmiums are shorter than those to the outer osmiums; the terminal Os–N distances are essentially the same for both types of osmium. Compound 3 and the cation in 4 are dimers with imido bridges. The main difference between them is a significant shortening in the Os…Os distance in the osmium(VIII) compound as a result of Os–Os single bond formation. This also results in a slight shortening of the Os–N bridge distances in 4 as compared to the neutral molecule 3.

Synthesis, structure, and fluxional properties of the novel tetranuclear osmium clusters Os4(CO)n(PMe3) (n = 15, 14, 13)

Os 4 (CO) 15 (PMe 3 ) cristallise dans le systeme triclinique, groupe d'espace P1 et sa structure est affinee jusqu'a R=0,0367. Os 4 (CO) 14 (PMe 3 ) cristallise dans le systeme monoclinique, groupe d'espace P2 1 /a avec R=0,0385. Os 4 (CO) 13 (PMe 3 ) cristallise dans P2 1 /c avec R=0,0470

Synthesis, reactivity, and spectroscopic studies of some tetranuclear osmium clusters. Structural characterization of [Os4H(CO)12{µ3-NC(O)Me}{M(PPh3)}](M = Au or Cu) and [N(PPh3)2][Os4H2(CO)12I

The interaction of [Os4H3(CO)12(NCMe)2][BF4](1) with [N(PPh3)2][X](X = NO2, Cl, Br, or l) affords the species [N(PPh3)2][Os4H(CO)12{µ3-NC(O)Me}](2)(X = NO2), [Os4H3(CO)12(µ-X)][X = Cl (6), Br (7), or l (8)], and [N(PPh3)2][Os4H2(CO)12X][X = Cl (9), Br (10), or l (11)] which were characterized by i.r. and 1H n.m.r. spectroscopy. The reaction of complex (1) with nitrite ion results in a novel interaction which involves oxygen transfer from the nitrite ion and conversion of a co-ordinated NCMe ligand into an amido group on the cluster surface. The anionic species (2) reacts with [M(PPh3)]+ to yield the neutral mixed-metal clusters [Os4H(CO)12{µ3NC(O)Me}{M(PPh3)}][M = Au (3) or Cu (4)] which have been structurally characterized by single-crystal X-ray diffractometry. This shows that they possess a butterfly metal framework capped by the heterometallic fragment and µ3-bridged by the four-electron-donor amido group. Complexes (3) and (4) are isomorphous, monoclinic, with space group C2/c and Z= 8: (3), a= 25.681(7), b= 16.069(1), c= 18.265(2)Å, and β= 90.90(1)°(4)a= 25.318(6), b= 15.964(5), c= 18.347(7)Å, and β= 91.80(2)°. Spectroscopic data suggest that compounds (6) and (7) also possess a butterfly metal framework with a bridging, three-electron-donor, halide ligand, while the anionic species (11) possesses a tetrahedral arrangement of metal atoms with a terminally co-ordinated iodide ligand, as shown by X-ray diffractometry: monoclinic, space group P21/a, Z= 8, a= 16.841(2), b= 20.699(1), c= 29.249(3), and β= 90.91(2)°. Protonation of (11) yields the neutral species [Os4H3(CO)12(µ-l)], showing that facile reversible tetrahedral–butterfly interconversion is assisted by a change in co-ordination mode and electron donation of the l atom. The reaction of compound (11) with CF3SO3R (R = Me or Et) was monitored by 1H n.m.r. spectroscopy and the results explained in terms of the formation of alkyl iodide derivatives.

ChemInform Abstract: Homogeneous Catalysis by Metal Clusters. Part 2. Tetranuclear Osmium Complexes as Catalyst Precursors in the Hydrogenation of Styrene.

AbstractThe hydrogenation of styrene to ethylbenzene in decalin is efficiently catalyzed by the clusters (I)‐(IV) at 140 °C and 800 torr of H2.

Homogeneous catalysis by metal clusters. 2. Tetranuclear osmium complexes as catalyst precursors in the hydrogenation of styrene

Homogeneous catalysis by metal clusters. 2. Tetranuclear osmium complexes as catalyst precursors in the hydrogenation of styrene

Molecular organoosmium chemistry and catalysis on the basic magnesium oxide surface

The complex (H/sub 2/Os(CO)/sub 4/) is deprotonated upon adsorption on the basic surface of magnesia. The resulting (HOs(CO)/sub 4/)/sup -/ is held strongly to the surface by a localized carbonyl-Mg/sup 2 +/ interaction analogous to the contact anion ion pairing observed for (Na)(HOs(CO)/sub 4/) in THF. The surface-bound complex is the precursor of surface species that are catalytically active for CO hydrogenation to give methane and higher hydrocarbons at 275 /sup 0/C and 10 atm. During catalysis, the mononuclear anion is transformed into the stable (H/sub 3/Os/sub 4/(CO)/sub 12/)/sup -/ and (Os/sub 10/C(CO)/sub 24/)/sup 2 -/, which become the only surface species detected by infrared spectroscopy and by extraction of surface-bound anions. The chemistry of the molecular condensation reactions of osmium carbonyls on the basic magnesia surface closely parallels that of osmium carbonyls in basic solution. The tetranuclear osmium cluster is suggested to be involved in the CO hydrogenation catalysis. 51 references, 12 figures, 1 table.

Systematic synthesis of tetranuclear osmium clusters by the reaction of trinuclear clusters with [OsH2(CO)4]; crystal structure of [Os4H3Br(CO)13

The complex [OsH2(CO)4] reacts with the clusters [Os3(CO)12–n(MeCN)n](n= 1 or 2) to afford the tetranuclear species [Os4H2(CO)15](1) and [Os4H2(CO)14(MeCN)](2), respectively. The pyrolysis of [Os4H2(CO)14(MeCN)](2) leads to the formation of [Os4H2(CO)13]via the intermediate [Os4H2(CO)14]. The acetonitrile ligand of complex (2) is readily displaced by P(OMe)3 to give [Os4H2(CO)14{P(OMe)3}](3) along with small quantities of [Os3(CO)14{P(OMe)3}2] and [Os3(CO)9{P(OMe)3}3]. With PPh3 the reaction is so slow that fragmentation occurs and the only product isolated is [Os3(CO)10(PPh3)2]. The hydride-coupling reaction also occurs between [OsH2(CO)4] and [Os3H(X)(CO)9(NMe3)](X = Cl, Br, or I) and the complexes obtained [(4)–(6) respectively] have been fully characterised. These complexes decompose in solution via loss of HX to afford [Os4H2(CO)13]. The reaction between [Os3H(OR)(CO)9(MeCN)] and [OsH2(CO)4] proceeds smoothly for R = Me (7) or Ph (8) but for R = H the major product isolated is [Os3H(OH)(CO)10]. All the products were characterised by i.r., 1H and 13C n.m.r. spectroscopy and structural assignments made. The structure of the cluster [Os4H3Br(CO)13](5) was confirmed by an X-ray analysis and shown to consist of an OS3 triangle with a pendant OsH(CO)4 unit co-ordinated to it. One edge of the triangle is bridged by both a hydride and a bromide ligand while another edge is bridged by a hydride.

Tetranuclear osmium clusters from the reactions of H 4 Os 4 (CO) 12 with alkenes

Organotetraosmium cluster compounds of the general formulae H 3 Os 4 (CO) 11HC 2HR and H 2 Os 4 (CO) 11HC 2 R (where R = H, Ph or t-Bu) have been prepared from reactions of H 4 Os 4 (CO) 12. with the appropriate alkene.