Cluster [Os3 Research Articles

Osmium and ruthenium carbonyl clusters containing arsine, arsenide, and arsinidene ligands

The reactivity of trimetallic clusters [Os3(CO)10(NCMe)2], [M3(CO)10(µ-dppm)] [M = Os, Ru; dppm = bis(diphenylphosphino)methane] and [Os3(CO)8{µ3-Ph2PCH2PPh(C6H4)}(µ-H)] with triphenylarsine (AsPh3) has been investigated. The labile [Os3(CO)10(NCMe)2] reacts with AsPh3 at room temperature to give 1,2-[Os3(CO)10(AsPh3)2] (1) in good yield. Thermolysis of 1 in refluxing toluene affords the known clusters [Os3(CO)11(AsPh3)] (2), [Os3(CO)9(µ-AsPh2)(µ3,η2-C6H4)(µ-H)] (3) and [Os3(CO)7(µ-AsPh2)2(µ3,η2-C6H4)] (4). Treatment of [Os3(CO)10(µ-dppm)] with AsPh3 in refluxing toluene affords [Os3(CO)9(AsPh3)(µ-dppm)] (5) as the major product together with [Os3(CO)7(AsPh3){µ3-Ph2PCH2PPh(C6H4)}(µ-H)] (6). Control experiment shows that 5 is a precursor of 6 as the former converts to the latter under similar experimental conditions. The same reaction affords 5 as the sole product when it is carried out in refluxing benzene. Cluster 5 and 6 can also be obtained in similar yield by treating [Os3(CO)8{µ3-Ph2PCH2PPh(C6H4)}(µ-H)] with AsPh3 at room temperature. On the other hand, the reaction of [Ru3(CO)10(µ-dppm)] with AsPh3 in refluxing toluene furnishes only [Ru4(CO)8(µ-CO)(μ4-AsPh)(µ4,η2-C6H4)(µ-dppm)] (7) in low yield. Cluster 7 can also be obtained by heating [Ru3(CO)9(AsPh3)(µ-dppm)] in refluxing toluene. It contains a phenylarsinidene and a benzyne ligands that were formed by AsC bond cleavage during the reaction. The molecular structures of all the new products have been established by X-ray crystallography.

Tri and hexaosmium clusters bearing saccharinate and diphosphine ligands: Synthesis, structure and fluxionality

The reactivity of saccharinate-bridged triosmium cluster [Os3(CO)10(μ-H)(μ-sac)] (1) with two diphosphines namely bis(diphenylphosphino)methane (dppm) and 1,1′-bis(diphenylphosphino)ferrocene (dppf) have been investigated. Cluster 1 reacts with dppm in refluxing toluene to yield triosmium [Os3(CO)9(κ1-dppm)(μ-H)(μ-sac)] (2), [Os3(CO)9(κ1-dppm)(μ-H)(μ-sac)] (3) and [Os3(CO)8(µ-dppm)(μ-H)(µ-sac)] (4) along with the hexaosmium [{Os3(CO)9(μ-H)(µ-sac)}2(κ2-dppm)] (5). The dppm ligand acts as a monodentate ligand in 2 and 3 by coordinating to a single osmium, while it bridges an osmium-osmium edge in 4 and connects to triosmium units in 6. A similar reaction with dppf furnishes [Os3(CO)9(κ1-dppf)(μ-H)(μ-sac)] (6), [Os3(CO)8(µ-dppf)(μ-H)(μ-sac)] (7) and [{Os3(CO)9(μ-H)(µ-sac)}2(κ2-dppf)] (8) which are dppf analogues of 3–5, respectively. Control experiments confirms that 3 is the precursor of 4 and 5, while 6 is the precursor of 7 and 8. All the products are formed via substitution of carbonyl by the diphosphine, and have been characterized by analytical and spectroscopic data. The molecular structures of 2 and 4–7 have been determined by X-ray crystallography. Cluster 7 shows fluxional behavior in solution at room temperature, and its fluxionality has been probed by VT NMR experiments.

Triosmium cluster bearing a metalated dibenzylideneacetone ligand: Synthesis, structure, redox and electronic properties

Dibenzylideneacetone (DBA) reacts with [Os3(CO)10(NCMe)2] in boiling benzene to afford the triosmium cluster [Os3(CO)10{κ2-(C,O)-C17H13O}(µ-H)] (1) formed through activation of one of the β-C–H bonds of the DBA ligand after initial coordination of the ketonic oxygen. The molecular structure of 1 has been determined unequivocally by single crystal X-ray diffraction analysis which reveals that the metalated DBA ligand formed a five-membered osmacycle by coordinating to a single osmium atom using its both donor atoms. Cluster 1 exhibits two closely spaced irreversible reduction peaks at –1.20 V and –1.30 V, respectively, together with an irreversible oxidation peak at 0.57 V. DFT calculations reveals the frontier orbitals are primarily either metal-based (HOMO) or ligand-based (LUMO) which suggests that the oxidation occurs from the metallic core while the first reduction is ligand-centered. Cluster 1 displays two absorption peaks at 337 nm and 477 nm in the UV-visible absorption spectrum. The lowest energy absorption at 477 nm can be attributed to the transition from HOMO to LUMO (MLCT) based on its frontier orbitals.

Reactivity of [Os3(CO)9(μ3-η1,κ1-C9H6N)(μ-H)] towards Ph3EH (E = Si, Ge, Sn): Synthesis and structure of triosmium clusters bearing a Ph3E ligand

The reactions of quinoline-capped triosmium cluster [Os3(CO)9(μ3-η1,κ1-C9H6N)(μ-H)] (1) with Ph3EH (E = Si, Ge, Sn) have been investigated. Cluster 1 reacts with Ph3EH in refluxing benzene to afford [Os3(CO)9(EPh3)(μ-η1,κ1-C9H6N)(µ-H)2] (2a, E = Si; 2b, E = Ge; 2c, E = Sn) and [Os3(CO)8(EPh3)(μ3-η1,κ1-C9H6N)(µ-H)2] (3a, E = Si; 3b, E = Ge; 3c, E = Sn). Control experiments confirm that 2 is a precursor of 3. Cluster 2 is formed via oxidative-addition of E–H bond to 1 whose decarbonylation leads to the formation of 3. The molecular structures of all the new clusters (except 3c) have been determined by X-ray crystallography. Both 2 and 3 exist as a pair of isomers in solution, and their fluxionality in solution has been probed by VT NMR experiments.

Reactions of diphosphine-stabilized Os3 clusters with triphenylantimony: syntheses and structures of new antimony-containing Os3 clusters via Sb-Ph bond cleavage.

The reactivity of the trimetallic clusters [Os3(CO)10(μ-dppm)] [dppm = bis(diphenylphosphino)methane] and [HOs3(CO)8{μ3-Ph2PCH2PPh(C6H4-μ2,σ1)}] with triphenylantimony (SbPh3) has been examined. [Os3(CO)10(μ-dppm)] reacts with SbPh3 in refluxing toluene to yield three new triosmium clusters [Os3(CO)9(SbPh3)(μ-dppm)] (1), [HOs3(CO)7(SbPh3){μ3-Ph2PCH2PPh(C6H4-μ2,σ1)}] (2), and [HOs3(CO)7(SbPh3)(μ-C6H4)(μ-SbPh2)(μ-dppm)] (3). [HOs3(CO)8{μ3-Ph2PCH2PPh(C6H4-μ2,σ1)}] reacts with SbPh3 (excess) at room temperature to afford [Os3(CO)8(SbPh3)(η1-Ph)(μ-SbPh2)(μ-dppm)] (4) as the sole product. A series of control experiments have also been conducted to establish the relationship between the different products. The molecular structure of each product has been determined by single-crystal X-ray diffraction analysis, and the bonding in these new clusters has been investigated by electronic structure calculations.

Bimodal substitution behavior in the reaction of N,N’-diisopropylformamidine with [Os3(CO)10(NCMe)2]: Kinetics and molecular structures of the formamidinate-substituted clusters HOs3(CO)9[μ-C(O)NPriC(H)NPri], HOs3(CO)10[μ-NPriC(H)NPri], and HOs3(CO)9[μ3-NPriC(H)NPri

The dinitrogen donor N,N’-diisopropylformamidine [PriN=C(H)NHPri] reacts with the triosmium cluster Os3(CO)10(NCMe)2 at room temperature to yield the isomeric clusters HOs3(CO)9[μ-C(O)NPriC(H)NPri] (1) and HOs3(CO)10[μ-NPriC(H)NPri] (2) in a 1:2.8 ratio. 1 contains an edge-bridging iminocarbamoyl ligand, while 2 contains a bridging formamidinate ligand. Thermolysis of 1 yields 2 plus the face-capped cluster HOs3(CO)9[μ3-NPriC(H)NPri] (3). The decarbonylation of 2 to 3 + CO confirms the molecularity of the observed reaction steps. The three products have been fully characterized in solution by IR and NMR spectroscopies, and the solid-state structures for 1-3 have been determined by X-ray crystallography. The kinetics for the thermolysis reaction were investigated over the temperature range 342–383 K, and the concentration versus time profiles for the conversion of 1 → 2 → 3 + CO have been successfully modeled using two consecutive, irreversible first-order reactions. The bonding in clusters 1-3 have been examined by DFT, and these data support cluster 1 as the kinetic substitution product and cluster 2 as the thermodynamically favored isomer.

Discovery of an Antibiotic-Related Small Protein of Biocontrol Strain Pseudomonas sp. Os17 by a Genome-Mining Strategy.

Many root-colonizing Pseudomonas spp. exhibiting biocontrol activities produce a wide range of secondary metabolites that exert antibiotic effects against other microbes, nematodes, and insects in the rhizosphere. The expression of these secondary metabolites depends on the Gac/Rsm signal transduction pathway. Based on the findings of a previous genomic study on newly isolated biocontrol pseudomonad strains, we herein investigated the novel gene cluster OS3, which consists of four genes (Os1348–Os1351) that are located upstream of putative efflux transporter genes (Os1352–Os1355). Os1348 was predicted to encode an 85-aa small precursor protein, the expression of which was under the control of GacA, and an X-ray structural analysis suggested that the Os1348 protein formed a dimer. The mutational loss of the Os1348 gene decreased the antibiotic activity of Pseudomonas sp. Os17 without changing its growth rate. The Os1349–1351 genes were predicted to be involved in post-translational modifications. Intracellular levels of the Os1348 protein in the deficient mutant of each gene differed from that in wild-type cells. These results suggest that Os1348 is involved in antibiotic activity and that the structure or expression of this protein is under the control of downstream gene products.

Towards understanding the mode of action of the cytotoxic triosmium carbonyl cluster Os3(CO)10(NCCH3)2: Its reactivity with amino acids and oligopeptides

The reactions of the triosmium carbonyl cluster Os3(CO)10(NCCH3)2 (1) with a number of protected amino acids, tri- and pentapeptides were examined. The results show that reaction with the side chains follow the order: -SH > -COOH > -CONH2, and there is a slight preference for the longer side chain of glutamic acid over aspartic acid. The trends observed are retained under physiological conditions and in the peptides.

Inhibition of Thioredoxin Reductase by Triosmium Carbonyl Clusters.

Tumor cells are characterized by increased reactive oxygen species production in parallel with an enhanced antioxidant system to avoid oxidative damage. The inhibition of antioxidant systems is an effective way to kill cancer cells, and the thioredoxin system or, more specifically, the cytosolic selenocysteine-containing enzyme thioredoxin reductase (TrxR) has become an interesting target for cancer therapy. We show here that the known cytotoxic and apoptosis-inducing osmium carbonyl cluster Os3(CO)10(NCCH3)2 (1) is a nonsubstrate inhibitor of mammalian TrxR, with an IC50 of 5.3 ± 0.9 μM. It inhibits TrxR selectively over the closely related glutathione reductase (GR) and in the presence of excess reduced glutathione (GSH). This inhibition has also been demonstrated in cell lysates, suggesting that TrxR inhibition is a potential apoptotic pathway for 1.

Reactions of [Os3(CO)10(μ-H)2] and [Os3(CO)8{µ3-Ph2PCH2P(Ph)C6H4}(μ-H)] with pymS‒SnPh3 (pymS = pyrimidine-2-thiolate): Synthesis and Structure of Triosmium Clusters Containing pymS Ligand

Reactivity of pymS‒SnPh3 (pymS = pyrimidine-2-thiolate) towards two unsaturated triosmium clusters [Os3(CO)10(μ-H)2] and [Os3(CO)8{µ3-Ph2PCH2P(Ph)C6H4}(μ-H)] are investigated. Reaction of pymS‒SnPh3 with [Os3(CO)10(μ-H)2] affords [Os3(CO)10(µ-pymS)(µ-H)] (1) and [Os3(CO)9(µ3-pymS)(µ-H)] (2), while with [Os3(CO)8{µ3-Ph2PCH2P(Ph)C6H4}(μ-H)] leads to the isolation of only [Os3(CO)8(μ-pymS)(μ-H)(μ-dppm)] (3). In both reactions, the products are formed via incorporation of the thiolate part (pymS) of pymS‒SnPh3 into the parent clusters through Sn‒S bond cleavage. Clusters 1–3 have been characterized by a combination of analytical and spectroscopic data together with single crystal X-ray diffraction analysis. Reactions of pymS‒SnPh3 with two unsaturated triosmium clusters have been investigated which resulted in the isolation and characterization of three triosmium clusters containing a pymS ligand.

QTAIM View of Os–Os Bonding in Triosmium Cluster [Os3(CO)9(µ-ɳ2-C7H3(2-CH3)NS)(µ-CH2)CH3

The topological features of the triosmium cluster [Os3(CO)9(µ-ɳ2-C7H3(2-CH3)NS)(µ-CH2)CH3], containing carbonyl and 2-methylbenzothiazol ide ligands, has been examined using density functional theory (DFT) and QTAIM-based Quantum Theory Atoms in Molecules. The topological parameters of the electron density in the cluster have been calculated. The QTAIM analysis of the topological features demonstrated that the core part Os3C1 in the cluster is significantly absence a bond critical point and its bond path between Os1-Os3. Whereas, the analysis Os1-Os2 and Os2-Os3 interactions revealed the occurrence of bond paths and bond critical points between these atoms. A multicenter 4c–5e interaction for the Os3C1 core has been proposed. The topological parameters calculation show that the interactions in the bridging 2-methylbenzothiazolide Ligand are a typical for shared shell with the existence of some double-bond character.

Reactions of the lightly-stabilized triosmium cluster Os3(CO)8{μ3-Ph2PCH(Me)P(Ph)C6H4}(μ-H) with two-electron donor ligands

Reactions of the lightly-stabilized Os3(CO)8{μ3-Ph2PCH(Me)P(Ph)C6H4}(μ-H) (1) with dihydrogen and representative 2-electron donor ligands, PPh3 and P(OMe)3, are described. With PPh3, the phosphine-adduct Os3(CO)8(PPh3){μ3-Ph2PCH(Me)P(Ph)C6H4}(μ-H) (2) is initially formed but this reacts further via three separate pathways: adding a second equivalent of PPh3 to yield Os3(CO)8(PPh3)2{μ-Ph2PCH(Me)PPh2} (5), losing a CO ligand with concomitant phosphine migration to afford Os3(CO)7(PPh3){μ3-Ph2PCH(Me)P(Ph)C6H4}(μ-H) (3) or adding a CO ligand to yield Os3(CO)9(PPh3){μ-Ph2PCH(Me)PPh2} (4). In contrast, reaction with P(OMe)3 leads to the simple stepwise formation of the mono- and bis-phosphite adducts, Os3(CO)8{P(OMe)3}{μ3-Ph2PCH(Me)P(Ph)C6H4}(μ-H) (6) and Os3(CO)8{P(OMe)3}2{μ-Ph2PCH(Me)PPh2} (7), respectively. Addition of dihydrogen to 1 cleanly affords the unsaturated 46-electron cluster Os3(CO)8{μ-Ph2PCH(Me)PPh2}(μ-H)2 (8). All the new clusters have been spectroscopically characterized together with single crystal X-ray diffraction studies of 2, 3 and 8.

Double activation of the diphosphinite pincer proligand by a triosmium carbonyl cluster

The reaction between 1,3-bis(diphenylphosphinite)-benzene and Os3(CO)10(MeCN)2 affords complex Os3(CO)10[1,3-(PhPO)2C6H4]. A thermolysis of this cluster in refluxing toluene results in the activation of O–PPh2 and C–H bonds and the formation of unsaturated triosmium cluster Os3(μ-H)(μ-PPh2)(CO)7[(C6H3(O)(OPPh2)] that possesses a remarkable structure with the pseudo-pincer ligand containing a bridging μ-η1-aryl group.

Facile Os-Os bond cleavage in the reactions of [Os3(CO)10(NCMe)2] and [Os3(CO)10(μ-H)2] with tetramethylthiuram disulfide (tmtd): Syntheses and crystal structures of new polynuclear osmium carbonyl complexes containing a dimethyldithiocarbamate ligand(s)

The reaction of the labile triosmium cluster [Os3(CO)10(NCMe)2] with tetramethylthiuram disulfide [(Me2NCS2)2, tmtd] has been investigated at room temperature. Conducting the reaction under mild conditions has permitted the isolation of the three new polynuclear osmium complexes [Os3(CO)10{κ2(S,S)-S2CNMe2}2] (1), [Os4(CO)12{κ2(S,S)-S2CNMe2}2{μ3-η1(C),κ2(O,O)-CO2)}(μ3-S)] (2) and [Os3(CO)9{μ3-η1(C),κ1(S)-SCNMe2}{μ-κ1(S)-SC(O)NMe2}] (3) in 20, 16 and 10% yield, respectively, in addition to the known mononuclear complex [Os(CO)2{κ2(S,S)-S2CNMe2}2] (4) in 10% yield. The triosmium complex 1 has a linear arrangement of osmium atoms with each terminal osmium center containing a chelating Me2NCS2 ligand. The tetraosmium complex 2 also possesses a μ3-CO2 ligand in addition to capping sulfido and chelating Me2NCS2 ligands. Complex 3 contains an open triosmium core with the open Os···Os edge bridged by a Me2NC(O)S ligand and a capping Me2NCS ligand. A similar reaction between the unsaturated cluster [Os3(CO)10(μ-H)2] and [(Me2NCS2)2] yielded the triosmium complexes [Os3(CO)10{μ-κ1(S)-S2CNMe2}(μ-H)] (5) and [Os3(CO)9{μ3-κ2(S,S)-S2CNMe2}(μ-H)] (6) in addition to compounds 1 and 4 and the known hydroxyl cluster [Os3(CO)10(μ-OH)(μ-H)] (7) in 7, 14, 14, 10, and 6% yield, respectively. Both 5 and 6 possess a triosmium core, and the Me2NCS2 ligand acts in edge-bridging capacity in the former while it serves as a face-capping ligand in the latter. All new complexes have been characterized by combustion analyses and IR and NMR spectroscopies, and the solid-state structures of 1–3, and 6 have been established by X-ray crystallography. The bonding in clusters 1-3 and 6 has been examined by electronic structure calculations, and the thermodynamics for the formation of 1 and MeCN (two equiv) from [Os3(CO)10(MeCN)2] and tmtd, relative to other chelated and bridged isomers of [Os3(CO)10(tmtd)] are discussed.

A new synthetic route for the preparation of [Os3(CO)10(μ-OH)(μ-H)] and its reaction with bis(diphenylphosphino)methane (dppm): syntheses and X-ray structures of two isomers of [Os3(CO)8(μ-OH)(μ-H)(μ-dppm)] and [Os3(CO)7(μ3-CO)(μ3-O)(μ-dppm)

The triosmium cluster [Os3(CO)10(μ-OH)(μ-H)] containing bridging hydride and hydroxyl groups at a common Os–Os edge was obtained in good yield (ca. 75%) from the hydrolysis of the labile triosmium cluster [Os3(CO)10(NCMe)2] in THF at 67 °C. [Os3(CO)10(μ-OH)(μ-H)] reacts with dppm at 68 °C to afford the isomeric clusters 1 and 2 with the general formula [Os3(CO)8(μ-OH)(μ-H)(μ-dppm)] that differ by the disposition of bridging dppm ligand. Cluster 1 is produced exclusively from the reaction of [Os3(CO)10(μ-OH)(μ-H)] with dppm in CH2Cl2 at room temperature in the presence of added Me3NO. Heating cluster 1 at 81 °C furnishes 2 in a process that likely proceeds by the release of one arm of the dppm ligand, followed by ligand reorganization about the cluster polyhedron and ring closure of the pendent dppm ligand. The oxo-capped [Os3(CO)7(μ3-CO)(μ3-O)(μ-dppm)] (3) has been isolated starting from the thermolysis of either 1 or 2 at 139 °C. Reactions of [Os3(CO)10(μ-dppm)] with ROH (R = Me, Et) in the presence of Me3NO at 80 °C furnish [Os3(CO)8(μ-OH)(μ,η1,κ1-OCOR)(μ-dppm)] (4, R = Me; 5, R = Et). Clusters 1–5 have been characterized by a combination of analytical and spectroscopic studies, and the molecular structure of each product has been established by X-ray crystallography. The bonding in these products has been examined by electronic structure calculations, and cluster 1 is confirmed as the kinetic product of substitution, while cluster 2 represents the thermodynamically favored isomer.

Carboxylated Chalcone and Benzaldehyde Derivatives of Triosmium Carbonyl Clusters: Synthesis, Characterization and Biological Activity Towards MCF-7 Cells

The activated cluster Os3(CO)10(CH3CN)2 (1) reacts readily with a number of carboxylated chalcones and benzaldehydes (2a−j) to afford products with the general formula Os3(CO)10(µ-H)(µ-O2CR) (3a–j). The structures of all the novel clusters have been characterized by IR and 1H NMR spectroscopy, as well as mass spectrometry and elemental analysis. Single-crystal X-ray diffraction analysis has also been carried out for one of the carboxylated chalcones and two of the derivatized clusters. The activity of some of the derivatized clusters against the ER+ breast carcinoma MCF-7 cancer cell line has also been evaluated.

Reactions of [Os3(CO)10(μ-dppm)] and [HOs3(CO)8{μ3-Ph2PCH2P(Ph)C6H4}] with Bu3GeH: Ge–H and Ge–C bond cleavage at triosmium centers

The reactivity of the triosmium clusters [Os3(CO)10(μ-dppm)] [dppm = bis(diphenylphosphino)methane] and [HOs3(CO)8{μ3-Ph2PCH2P(Ph)C6H4}] with tributylgermanium hydride (Bu3GeH) has been investigated. Oxidative addition of Bu3GeH to [Os3(CO)10(μ-dppm)] at 110 °C affords [HOs3(CO)9(GeBu3)(μ-dppm)] (1) which undergoes further decarbonylation upon prolonged heating to yield [H2Os3(CO)7(GeBu3){μ3-Ph2PCH2P(Ph)C6H4}] (2) and [HOs3(CO)8(GeBu3)(μ-GeBu2)(μ-dppm)] (3). Control experiments confirm the bimodal formation of 2 and 3 from 1 during thermolysis. Cluster 2 reacts with additional Bu3GeH at 140 °C to give [Os3(CO)6(μ-GeBu2)2{μ3-PhP(C6H4)CH2P(Ph)C6H4}] (4), a thermolysis product also produced from 3. In contrast, oxidative addition of Bu3GeH to [HOs3(CO)8{μ3-Ph2PCH2P(Ph)C6H4}] occurs at room temperature to afford [H2Os3(CO)8(GeBu3){μ3-Ph2PCH2P(Ph)C6H4}] (5), which decarbonylates at 110 °C to yield 4. All new clusters have been characterized by elemental analyses and spectroscopic methods, and the molecular structures established by X-ray crystallography. Electronic structure calculations on the different hydride isomers based on 1 and 5 are reported.

Activation of thiosaccharin at a polynuclear osmium cluster

The reaction of thiosaccharin (tsacH) with the triosmium cluster [Os3(CO)10(NCMe)2] furnishes the decacarbonyl isomers [HOs3(CO)10(μ-S-tsac)] (1) and [HOs3(CO)10(μ-N,S-1,3-tsac)] (2) in a 3:1 ratio at room temperature. These isomers differ by the coordination mode displayed by tsac ligand. The tsac moiety functions as an edge-bridging ligand via the sulfur atom in 1 while in 2 the bridging of adjacent osmium centers is achieved through the sulfur and nitrogen groups. The ancillary hydride in both products shares the OsOs edge that is bridged by the heterocyclic ligand. Heating 1 at 80 °C affords 2 and demonstrates that the former cluster is the product of kinetic control. The conversion of 1 → 2 has been investigated by DFT and the isomerization pathway elucidated. The DFT calculations confirm cluster 2 as the thermodynamically preferred isomer in this pair of products. Thermolysis of 2 in refluxing toluene affords the hexanuclear cluster [H2Os6(CO)17(μ-C,N-1,2-C6H4CNSO2)2(μ3-S)(μ4-S)] (3) via carbon-sulfur bond scission and subsequent capture of the extruded sulfur by the cluster core. The molecular structures for the three new clusters have been determined by single-crystal X-ray diffraction analyses.

Accurate Description of Low-Lying Excited States in a Series of Photoreactive Clusters [Os3(CO)10(α-diimine)] by DFT Calculations

Density functional theory (DFT) calculations were performed on clusters [Os3(CO)10(α-diimine)], for α-diimine = 2,2'-bipyridine (BPY), N-isopropyl 2-iminomethylpyridine (IMP), and N, N'-diisopropyl-l,4-diaza-1,3-butadiene (DAB), together with their spectroscopic study. This important family of clusters is known to convert upon irradiation with visible light into short-lived biradicals and long-lived zwitterions from a σπ* (SBLCT) excited state that has not been described accurately thus far by quantum mechanical calculations. On the basis of the combined DFT, UV-vis absorption, and resonance Raman data, the lowest-lying visible absorption band is assigned to a σ(Os1-Os3)-to-π*(α-diimine) CT transition, for α-diimine = bpy and IMP, and to a strongly delocalized σ(Os1-Os3)π*-to-σ*(Os1-Os3)π* transition for conjugated nonaromatic α-diimine = DAB. The DFT calculations rationalize the experimentally determined characteristics of this electronic transition in the studied series: (i) The corresponding absorption band is the dominant feature in the visible spectral region. (ii) The CT character of the electronic excitation declines from α-diimine = bpy to IMP and vanishes for DAB. (iii) The excitation energies decrease in the order α-diimine = DAB > BPY > IMP. (iv) The oscillator strength shrinks in the order α-diimine = DAB > IMP > BPY. Reference photoreaction quantum yields measured accurately for the formation of a cluster zwitterion from [Os3(CO)10(IMP)] in strongly coordinating pyridine demonstrate that the optical population of the lowest-energy 1σπ* and relaxed 3σπ* excited states in the DFT model scheme is still capable of inducing the initial homolytic Os1-Os3 σ-bond splitting, although less efficiently than the optical excitation into neighbor higher-lying electronic transitions due to a higher potential barrier for the reaction from a dissociative (σσ*) state.

Reaction of electron-deficient 6-methoxyquinolinate-substituted cluster [Os3(CO)9{μ3-η1,κ1-C9H5N(6-OMe)}(μ-H)] with PPh3: Thermally induced ligand isomerization, decarbonylation and orthometallation

Abstract The reaction of the electron-deficient 6-methoxyquinolinate-substituted triosmium cluster [Os3(CO)9{μ3-η1,κ1-C9H5N(6-OMe)}(μ-H)] (1) with PPh3 proceeds readily at room temperature to afford the electron-precise adduct [Os3(CO)9(PPh3){μ-η1,κ1-C9H5N(6-OMe)}(μ-H)] (2), in which the PPh3 ligand is bound to the osmium that serves as the coordination site for the hydride and the metallated-carbon atom of the benzoheterocycle. This reaction also leads to a change in the hapticity of the 6-methoxyquinolinate ligand from μ3-η1,κ1 to μ-η1,κ1 as confirmed by X-ray crystallography. Thermolysis of 2 in boiling toluene furnishes five new triosmium clusters (3–7) as a result of ligand isomerization, decarbonylation and orthometallation of the ancillary PPh3 ligand. Clusters 3 and 4 are isomers of 2 and the location of the metal-bound hydride and PPh3 with respect to 6-methoxyquinolinate moiety is the only difference between these isomers. Control experiments show that 5 is a decarbonylation product of 4 which converts into 6 as a result of further decarbonylation with concomitant orthometallation of one of the phenyl rings of the coordinated PPh3 ligand, whilst 7 is formed from 6 through replacement of an equatorial carbonyl of the nitrogen-bound osmium by PPh3 ligand. All the new clusters have been characterized by a combination of analytical and spectroscopic methods as well as by X-ray crystallography in the case of 2, 3, 6 and 7.