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The 13C NMR spectrum of Ru6(μ6-C)(μ-CO)(CO)16 (1) in solution at − 125 °C indicates that the CO ligands of the equatorial Ru4(μ6-CO)(CO)10 unit are undergoing ultra-fast exchange estimated to be ≳ 3 × 107 s− 1. The variable temperature solution IR spectra of 1 shows bands that are attributed to the Ru4(μ6-CO)(CO)10 unit at − 58 °C that broaden and collapse almost to the baseline in the spectrum at + 70 °C. On the other hand, two of the three strong CO stretches of the Ru(CO)3 units of 1 observed in the low temperature spectra coalesce to a sharp signal typical of a C3v fac-L3M(CO)3 grouping. These results are interpreted in terms of the carbonyls of the equatorial Ru4(μ-CO)(CO)10 unit undergoing exchange on the IR timescale (~ 1012 s− 1) at room temperature, consistent with DFT calculations.

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 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.

The cluster Os4(µ-η2-C2Ph2)(CO)14 (1) has been prepared from the reaction of Os4(CO)14 and C2Ph2 in CH2Cl2 at 25 °C. Other minor products include the known clusters Os3(µ3-η2-C2Ph2)(CO)10 and Os3(µ-η4-C4Ph4)(CO)9. The structure of 1 reveals an approximately planar C2Os4 skeleton with a dimetallacyclobutene ring (C—C = 1.32(4) Å) and a flat butterfly Os4 unit (Os—Os range = 2.859(2)–2.916(2) Å). The 13C{1H} NMR spectrum of 1 indicates the carbonyl ligands are rigid at room temperature. Stirring 1 in CH2Cl2 for 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 Os3 triangles. The 13C NMR data for 2 are consistent with rapid rotation on the NMR timescale of the hinge Os(CO)3 units 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 C2Ph2 bound to all four metal atoms (Os—Os range = 2.7457(5)–2.8742(5) Å). The 13C{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)3 units, 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)3 units) 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.

The cluster Os7(CO)20(CNBu t ) (1) has been prepared in ∼25% yield by the reaction of Os6(CO)18 with Me3NO and Os(CO)4(CNBu t ) at −78°C. The crystal structure of 1 reveals the expected capped octahedral arrangement of metal atoms with the noncarbonyl ligand attached to the capping Os atom. The OsOs lengths in the two independent molecules in the unit cell are in the range 2.823(1)–2.922(1) A, with the longer bonds associated with the Os3 triangle farthest from the capping Os atom. The 13C NMR spectrum of 1 in solution at room temperature has a 3:3:1 pattern that is consistent with rotation of the individual Os(CO)2(L) (L=CO or CNBu t ) groups in the cluster. This in turn supports the idea that the capping Os(CO)2(CNBu t ) unit binds to the central Os6 via a centrally directed MO plus two tangential molecular orbitals.

Addition of Re(CO) 5 (H) to Os 4 (CO) 1 4 in solution at room temperature affords ReOs 4 (μ-H)-(CO) 1 9 (1). Careful pyrolysis of 1 in hexane at 85 °C initially yields ReOs 4 (μ-H)(μ-CO)(CO) 1 7 (2), which on further heating gives ReOs 4 (μ-H)(CO) 1 6 (3). There was no evidence for ReOs 4 -(μ-H)(CO) 1 7 . The four osmium atoms in 1 have a planar kite arrangement with the Re(CO) 5 in an equatorial site, that is, a spiked kite metal skeleton. The H ligand is believed to bridge the OsOs bond (length 2.892(1), 2.904(1) A; two independent molecules) that is cis to the Re atom, rather than one of the longer OsOs bonds. Cluster 2 has a distorted tetrahedral Os 4 nucleus with the Re(CO) 5 again acting as a spike ligand (i.e., a spiked tetrahedral metal skeleton). Compound 3 has the expected trigonal bipyramidal core of metal atoms with the Re(CO) 4 unit in the equatorial plane. The structures of 1-3 are compared to those of the analogous Os 5 (CO) n (n = 19, 18, 16) clusters. The solution behavior of the new clusters was also investigated by variable-temperature 1 3 C NMR spectroscopy.

The complexes (OC)4(CNBut)ReOs(CO)3(CNBut)Os(CO)3(CNBut)Re(CNBut)(CO)4 (A) and (OC)3(CNBut)2ReOs(CO)4Os(CO)3(CNBut)Re(CNBut)(CO)4 (B) have been isolated in low yield from the reaction of Os(CO)3(CNBut)2 with Re2(μ-H)(μ-η-C2H3)(CO)8 in hexane at room temperature. Both compounds have approximately linear ReOs2Re chains. The Re–Os lengths are in the range 2.9311(7)–2.952(1) A the Os–Os lengths are 2.875(1) (A) and 2.8759(7) A (B).

Complexes of formula (X)[Os(CO)3(CN-t-Bu)]nMn(CO)5 (X = Cl, Br, I; n = 1, 2, 3) have been prepared by the reaction of Os(CO)4(CN-t-Bu) with Mn(CO)5(X) in hexane at room temperature. The characterization of the complexes included the crystal structures of compounds with X = I, n = 1, 3 and X = Cl, Br, n = 2 (2ClA and 2BrB). The trinuclear products were isolated as two isomers. The major isomer (2XA) has an isocyanide ligand attached to each osmium atom, whereas the minor isomer (2XB) has both of these ligands bound to the terminal Os atom. The structures contain OsnMn chains with unbridged Os—Mn bonds (range of lengths are 2.870(1)–2.9245(8) Å) and for compounds with n = 2 or 3 Os—Os bonds (range of lengths are 2.8812(4)–2.8928(5) Å). The mechanism of formation is believed to involve replacement of a CO ligand with the 18e- ligand Os(CO)4(CN-t-Bu) at the metal with the coordinated halide, followed by a rearrangement in which the halide ligand migrates to the donor Os atom with concomitant migration in the reverse direction of a carbonyl ligand. The preparation of (OC)4(t-BuNC)OsMn(CO)4(Cl) with an Os–Mn dative bond is also reported along with the (OC)4(t-BuNC)OsRe(CO)4(X) analogues.Key words: manganese–osmium, rhenium–osmium, dinuclear, metal chain, dative metal–metal bond.

Complexes of formula (X)Os3(CO)12Os(CO)3(L)(X) and (X)(L)(OC)3OsOs3(CO)12Os(CO)3(L)(X) (L = CNBut; X = Cl, Br, I) have been prepared by the addition of Os(CO)4(L) to Os3(CO)12(X)2 in solution at 60...

Os5(μ-X)2(CO)16(L)2 (X=Cl, 1, Br; L=CNBut) clusters have been prepared by the reaction of Os3(μ-X)2(CO)10 with Os(CO)4(L) at a 1:2 molar ratio in solution at 60°C. The crystal structure of the chloro compound reveals that the Os3(μ-Cl)2 fragment present in the precursory cluster is maintained in 1 with a coordination site cis to the Cl ligands occupied by the unusual Os(CO)4Os(CO)3(L)2 unit. The resulting “hook” arrangement of the Os5 skeleton has not been observed previously. The OsOs lengths are in the range 2.8384(6)–2.8999(6)A. The OsOs bonds associated with the pendant fragment are both considered dative bonds.

In what is a new metal-chain forming reaction, (X)[Os(CO)3(CNBut)]3Mn(CO)5 (X=Cl, Br, I) complexes have been prepared by the successive addition of Os(CO)4(CNBut) to Mn(CO)5(X) in hexane. The crystal structure of the iodo derivative reveals it to contain an approximately linear Os3 Mn chain of metal atoms.

The structures of Os3(CO)11(PR3) with R=F, OPh, Et, p-C6H4Me, o-C6H4Me, p-C6H4(CF3) and C6H11, and with PR3=P(OCH2)3CMe have been determined. The Os–Os bond lengths in these compounds are compared to the Os–Os lengths for the other structures of Os3(CO)11(PR3) clusters reported in the literature. In most cases, the Os–Os bond length remote from the P ligand [range, 2.8666(4)–2.9044(4) A] and that in the pseudo-trans position [range, 2.8712(5)–2.900(1) A] show little variation as the steric and electronic properties of the P ligand are varied. The Os–Os length cis to PR3 shows more variation [range, 2.879(1)–2.9429(4) A] and is sensitive to both the size and the σ-donor/π-acceptor properties of the PR3 ligand: larger or better donor PR3 ligands cause an increase in the Os–Os bond length. The Os–P distances [range, 2.15(2)–2.478(1) A] show a similar dependence on the steric and electronic properties of the PR3 ligand.

The following complexes, in which CpIr(CO)2 acts as a 2e donor ligand, have been prepared: Cp(OC)2IrW(CO)5 (1), Cp(OC)2IrRu(CO)3(SiCl3)2, Cp(OC)2IrOs(CO)3(GeCl3)(Cl) (2), Cp(OC)2IrOs(CO)3(X)2 (X = Cl, Br (3), I). The characterization of the complexes included the crystal structures of 1, 2, and 3, which reveal that all contain an unbridged metal-metal bond. The carbonyl ligands of 1 in solution undergo exchange on the NMR time scale above -40°C. With the exception of 2, all the complexes dissociate in solution at room temperature, some rapidly so. Only in the case of 3 is an equilibrium with the dissociation products established. The results indicate that CpIr(CO)2 is a weak ligand.Key words: tungsten, osmium, iridium, binuclear.

Complexes of formula (R3P)(OC)4MRu(CO)3(SiCl3)2 (M = Ru, Os) and (OC)3(ButNC)2MRu(CO)3(SiCl3)2 (M = Fe, Ru, Os) have been prepared from the reaction of cis-Ru(CO)4(SiCl3)2 and the appropriate donor molecule in solution at room temperature. The characterization of the complexes included the crystal structures of (Me3P)(OC)4MRu(CO)3(SiCl3)2 (M = Ru, 1Ru; Os, 1Os) and the three M(CO)3(CNBut)2 derivatives (3Fe, 3Ru, 3Os). All five structures reveal molecules with unbridged metal−metal bonds. The PMe3 ligand is trans to the metal bond in 1M, whereas the isocyanide ligands are cis to this bond in 3M. The ButNC substituents have a cis configuration in 3Fe and 3Ru, but a trans arrangement in 3Os. Complexes 3Fe, 1Ru, and 3Ru are rare examples of structurally characterized compounds in which a first-row or second-row transition metal acts as the donor atom in a molecule containing an unbridged dative bond between two transition metals. The (OC)3(ButNC)2FeRu(CO)3(SiCl3)2 derivative is unstable both in solution and t...

The clusters Os3(CO)11(PR3) (R = p-C6H4F, 1; But, 2) have been prepared by the addition of PR3 to Os3(CO)11(CH3CN), and their structures determined. There are yellow and red forms of 1 (1y and 1r, ...

This paper reports the characterization of the fac-Os(CO)3(PME3)Cl2 (fac-2) product that is formed when (Me3P)(OC)4OsW(CO)5 (1; a complex with a dative OsW bond) is irradiated (λ > 400 nm) in the presence of CCl4. In an attempt to independently synthesize fac-2), Os3(CO)9(PMe3)3 was allowed to react with Cl2. The product, however, was mer-cis-Os(CO)3(PMe3)Cl2 (mer-cis-2). The mer-cis isomer is converted to the fac isomer (fac-2) by stirring under nitrogen in THF for nine days. The stereochemistry of each compound was confirmed by infrared and NMR spectroscopy and by X-ray crystallography. The [Os(CO)2(PMe3)(Cl)(μ-Cl)]2 compound (3) was also formed as a minor product in the conversion of mer-cis-Os(CO)3(PMe3)Cl2 to fac-Os(CO)3(PMe3)Cl2. Irradiation (λ > 400 nm) of Os(CO)4(PMe3) in benzene in the presence of CCl4 gave a product tentatively identified as fac-Os(CO)3(PMe3)(CCl3)Cl (4), which results from the oxidative-addition of CCl4 to OS(CO)3(PMe3).

Complexes of formula (η6-C6H6-xRx)Fe(CO)(SiCl3)2 have been prepared from the reaction of Fe(CO)4(SiCl3)2 and the appropriate arene at 210 °C. The characterization of the complexes included the crystal structures of the 1,4-C6H4Pri2 and C6Me6 derivatives. As ascertained by variable-temperature 1H NMR spectroscopy, the (η6-1,4-C6H4R2)Fe(CO)(SiCl3)2 (R = Me, Et, Pri) compounds exhibit restricted rotation of the arene ring about the iron atom. Line-shape analyses of the NMR spectra reveal the barriers to the rotation in the three compounds are approximately the same (ΔG⧧298 = 9.6−10.8 kcal mol-1). This finding is rationalized in terms of gearing of the R and SiCl3 groups with the rotation. The 1,3,5-C6H3Me3 and C6Me6 derivatives do not show restricted rotation of the arene ring by 1H NMR spectroscopy to −120 °C. It is concluded from these observations that both ground-state and transition-state effects are important in determining the barrier to rotation of the arene ring in organometallic molecules.

The photochemistry of (Me3P)(OC)4OsW(CO)5 (1), a molecule with a dative covalent metal−metal bond, was investigated. The results indicate that the photoprocess is heterolytic cleavage of the metal−metal bond, rather than homolytic cleavage as is found in compounds with nondative covalent metal−metal bonds. The principal evidence for heterolysis comes from the irradiation (λ > 400 nm) of 1 in benzene in the presence of PPh3. The major products were Os(CO)4(PMe3), Os(CO)3(PMe3)(PPh3), and W(CO)5(PPh3). These products are consistent with a pathway that involves initial heterolysis to form Os(CO)4(PMe3) and W(CO)5 followed by trapping of the coordinatively unsaturated W(CO)5 species with PPh3. (Control experiments showed that Os(CO)3(PMe3)(PPh3) forms from Os(CO)4(PMe3) and PPh3 under the reaction conditions.) Primary photoprocesses involving either M−CO bond dissociation or Os−W bond homolysis are incompatible with the results of other experiments. For example, when the irradiation of 1 was carried out under...

Derivatives of formula (arene)M(CO)2(SiCl3) (M = Mn, Re) have been prepared in moderate to good yield by the reaction of M(CO)5(SiCl3) and the appropriate arene (with heptane in those cases where the arene was a solid) in an evacuated sealed tube at 230–260 °C for 12–24 h, depending on the arene and the metal. Carefully purified reagents were necessary to obtain satisfactory yields. The (η6-1,4-C6H4tBu2)M(CO)2(SiCl3) complexes in solution exhibit free rotation of the arene ring about the metal atom to −120 °C as ascertained by 1H NMR spectroscopy. The manganese compound did show the onset of decoalescence of two of the signals due to the arene ligand in the 13C{1H} NMR spectrum in CD2Cl2, solution below −90 °C. This, however, is interpreted in terms of restricted rotation of the tert-butyl substituent rather than restricted rotation of the arene ring. Keywords: arene, manganese, rhenium, restricted rotation.

The compound [Os(CO)4(SnPh2)]6 (1) has been isolated as one product from the reaction of Na2[Os(CO)4] and Ph2SnCl2 in THF. The X-ray structure of 1 reveals it possesses an approximately planar 12-membered ring of alternating tin and osmium atoms. Carbon-13 NMR spectroscopy indicates there is free rotation about the Os−Sn bonds in 1 in solution so as to render all the carbonyl ligands equivalent.

The molecular structure of the chloro-bridged tetraosmium cluster, dodecacarbonyl-1κ3C,2κ3C,3κ3C,4κ3C-μ-chloro-3:4κ2Cl-tris-μ-hydrido-1:2κ2H;1:3κ2H;2:4κ2H-tetraosmium(5Os—Os), [Os4(μ-Cl)(μ-H)3(CO)12], consists of a `butterfly' arrangement of Os atoms, just as in the iodo analogue. The chloro bridge in the tetraosmium cluster is symmetric, whereas in the pentaosmium cluster, tetradecacarbonyl-1κ3C, 2κ2C,3κ3C,4κ3C,5κ3–μ-chloro-2:5κ2Cl-tris-μ-hydrido-1:2κ2H;2:3κ2H;2:4κ2H-pentaosmium(8 Os—Os), [Os5(μ-Cl)(μ-H)3(CO)14], it is distinctly asymmetric. This asymmetry is attributed to the trans influence of a carbonyl ligand, which lengthens the trans-Os—Cl bond.

High-resolution variable-energy photoelectron spectra of Os(CO)5 and Os(CO)4PMe3 are reported. Using variable-energy synchrotron radiation, both the metal 5p → 5d resonance and the Cooper minimum effect are observed on the osmium 5d orbitals, and they have been successfully used to assign the osmium 5d-based bands. The Xα-SW calculation for Os(CO)5 is used to assign the valence level molecular orbitals. Experimental branching ratios of Os(CO)5 agree well with the theoretical results from both Xα-SW and Gelius methods. The electronic structure of Os(CO)5 from the present study is shown to be similar to that of Fe(CO)5, both of which have a trigonal-bipyramidal structure. The binding energies of the Os 5p core level have been determined, which are shown to be important in the observation of 5p → 5d resonances. Both vibrational and ligand field splittings are shown to be important in the line broadening in the high-resolution Os 4f core level spectra. The chemical shifts of valence and core levels for Os(CO)...

The complexes [(OC)4Os(PbMe2)]2 (3) and [(OC)4OsSnBu 2 ′ ]2 (4) have been prepared from be reaction of Na2[Os(CO)4] with Me2PbCl2 and Bu 2 ′ SnCl2, respectively, in THF and their X-ray crystal structures determined. The red derivative,3, was light-sensitive in solution. The reactions or [(OC)4 Os(SnMe2)]2 (2), or its decarbonylated derivative [Os3(CO)7(SnMe2)2]2 (7), with olefins or phosphorus donor ligands have also been investigated, and the structures of two derivatives, viz. [Os2(CO)7(SnMe2)2(C2H4)] (5a) and [Os2(CO)7(SnMe2)2(PMe3)] (6a), have been determined; the noncarbonyl ligand occupies an equatorial site in each case. The X-ray crystal structures of all these compounds, like those of [(OC)4Os(EMe2)]2 (E=Ge (1), Sn (2)) which have been reported previously, show leaning of the axial carbonyl ligands toward the metal tetracycle, i.e., an “umbrella” effect. Crystallographic data for compound3: space group, P21/a;a=13.4404(13) A,b=10.7494(14) A,c=148967(18) A,β=98.204(9)°,R=0.035, 1983 observed reflections. For compound4: space group,P1;a=9.016(1) A,b=9.370(1),c=11.334(1) A, α=103.67(1)°,β=100.30(1)°, γ=115.03(1)°, R=0.046, 2026 observed reflections. For compound5a: space group,P1;a=9.2933(11)A,b=9.7181(3),c=12.2508(15) A, α=89.21(1)°,β=87.61(1)°, γ=86.13(1)°,R=0.038, 2770 observed reflections. For compound6a space groupP1:a=8.7244(9)A,b=10.9318(6),c=13.2560(13) A, α=87.815(6)°,β=83.655(8)°, γ=82.343(6)°, R=0.030, 3497 observed reflections.

Pyrolysis a the cluster Os3(µ-H h (CO)10 (SnMe2 H) produced an as yet unidentified purple duster, which upon reaction with PEt2Ph at room temperature, gave essentially a quantitative yield of the cluster Os3(µ-H)3(CO)9(µ3-Sn) Os3(µ-H)(CO)10(PEt2Ph), 4. The X-ray structure of 4 (as the toluene solvate) shows that it consists Or two Os, triangles linked through a µ4-Sn unit, such that one of the Os3 triangle is µ3-bonded to the Sn atom (Os-Sn range 2.689(2)–2.707(2) A) and the other is bonded via a single covalent bond (Os-Sn = 2.643(2) A). The phosphine ligand occupies the equatorial site on a second osmium atom a be latter Os3 moiety that is syn to the Sn atom; the unique bridging hydride ligarid is believed to occupy a site that Acis to both the P and Sn atoms. Crystallographic data for compound4. 0.5C7H8: space group,P\(\bar 1\); ca= 11862(4) A,b = 12.940(4) A,c = 16.513(5) A, α=68.96(3),β=80.60(3)°,γ=62.49(2).R=0.029, 4118 observed reflections.

The high resolution valence level photoelectron spectra of Os(CO) 4 PMe 3 using He I and He II laboratory sources and synchrotron radiation, are reported. The binding energies of the osmium 5p core orbitals have also been determined. The metal 5p → 5d resonances were observed using variable synchrotron radiation, and have been successfully used to assign the osmium 5d valence orbitals.

Pyrolysis of [(OC)4Os(SnMe2)]2 (1) at 170 °C gave [(OC)3Os(SnMe2)]3 (2) as the major product. The structure of 2 reveals a planar triangulated (raftlike) Os3Sn3 unit (6 crystallographic symmetry, with Os−Os = 2.974(1) A and Os−Sn = 2.667(1) and 2.673(1) A). UV irradiation of 1 in hexane provided the yellow, insoluble Os4(SnMe2)4(CO)14(3). The structure of 3 shows an essentially planar Os4Sn4 skeleton comprised of a central rhomboidal Os2Sn2 unit with each Os atom part of two outer Os2Sn triangles. The Os−Sn bonds of the Os2Sn2 unit at 2.760(1) and 2.780(1) A are significantly longer than the corresponding bonds of the Os2Sn groups (2.678(1) and 2.727(1) A); the Os−Os bonds in 3 are long at 3.0414(5) A. From the treatment of 1 in solution with Me3NO, Os4(μ3-O)2(SnMe2)4(CO)14 (4) was isolated in low yield. The structure of 4 has a central six-membered (OsOSn)2 ring to which are fused two OsOSnOs rings such that each outer ring shares a common OsO edge with the central ring. The outer rings of 4 are planar,...

The complex [(OC)4Os(GeMe2)]2 (1) has been prepared from Na2[Os(CO)4] and Me2GeCl2 in THF. Photolysis of 1 in hexane affords the known [(OC)3Os(GeMe2)]3 (4) as the major product, along with the new clusters Os3(GeMe2)2(CO)11 (3) and Os4(GeMe2)4(CO)12 (5). Pyrolysis of 1, in hexane at 100 °C, gives the same compounds except that Os2(GeMe2)3(CO)6 (2) was also isolated, albeit in low yield. The structures of 1−5 have been determined; the configurations of 1, 2, and 4 are analogous to those previously found for group 8−group 14 congeners. The skeleton of 3 consists of two Os2Ge triangles that share a common osmium atom, that is, a “bow-tie” arrangement; the Os−Os lengths in 3 are crystallographically equivalent at 2.981(1) A, and the Os−Ge lengths are 2.520(1) and 2.522(1) A. The framework of 5 consists of a central triangulated (raftlike) Os3Ge3 unit (similar to that in 4) to one Os atom of which is bound an (OC)4Os(GeMe2) fragment so as to give an Os2Ge triangle that lies in the plane of the other metal ato...

The binary carbonyl Os4(CO)15, 1, has been prepared by the addition of Os(CO)5 to Os3(CO)10(cyclooctene)2 at −15 °C. The related clusters Os4(CO)13(PMe3)[P(OMe)3], 2, and Os4(CO)14(CNBu′), 3, have been synthesized from Os4(CO)13(PMe3) and Os4(CO)15(CNBu′), respectively. The crystal structures of 1, 2, and 3 reveal similar planar metal skeletons with short (2.774 (1) − 2.793 (2) Å) and long (2.978 (2) − 3.019 (2) Å) peripheral Os—Os bonds; the hinge Os—Os bond in 1–3 ranges in length from 2.936 (2) to 2.948 (1) Å. The variable temperature 13C nuclear magnetic resonance spectra of 1 and 3 show that both are highly nonrigid in solution even at −120 °C. The mechanism of nonrigidity is believed to be an all-equatorial, merry-go-round carbonyl exchange. The variable temperature 13C nmr spectra of 2 indicate it is rigid on the nmr time scale in solution at −45 °C. Carbonyl exchange is, however, observed in the spectrum at −6 °C. From the mode of collapse of the signals it is believed that the lowest energy exchange processes in 3 involve axial-equatorial, merry-go-round CO exchanges in the two planes that each contain a short Os—Os bond. Crystallographic data for compound 1: space group C2/c; a = 12.802 (3) Å, b = 10.217 (3) Å, c = 16.380 (5) Å, β = 91.39 (2)°; R = 0.044, 1204 observed reflections. For compound 2: space group P21/c; a = 11.106 (7) Å, b = 16.931 (5) Å, c = 16.481 (5) Å, β = 97.71 (5)°; R = 0.051, 2117 observed reflections. For compound 3: space group P21/n; a = 11.747 (3) Å, b = 18.009 (5) Å, c = 12.448 (2) Å, β = 92.65 (2)°; R = 0.054, 2131 observed reflections. Keywords: osmium, carbonyl, cluster, nonrigidity.

The new binary metal carbonyl Os5(CO)18 has been prepared by pyrolysis of Os5(CO)19 and shown by X-ray crystallography to have a planar metal skeleton.

Clusters of the type (OC) 5 M[Os(CO) 3 (PR 3 )] 2 (M=Cr, Mo, W; R=Me, OMe; R 3 =(OCH 2 ) 3 CMe) have been obtained (30-40% yield) by ultraviolet irradiation of (R 3 P)(CO) 4 OsM(CO) 5 complexes in C 6 F 6 . The crystal structures of (CO) 5 Cr[Os(CO) 3 (PMe 3 )] 2 , (OC) 5 Mo{Os(CO) 3 [P(OMe) 3 ]} 2 cocrystallized in a 1:1 ratio with [(MeO) 3 P](OC) 4 OsMo(CO) 5 , and (CO) 5 W[Os(CO) 3 (PMe)] 2 have been determined by X-ray crystallography.

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.

Clusters of the type Os 4 (CO) 15 (L) have been prepared by the reaction of L with Os 4 (CO) 14 at or below room temperature. The structures of Os 4 (CO) 16 (1), Os 4 (CO) 15 (PF 3 ) (2), and Os 4 (CO) 15 [P(OCH 2 ) 3 CMe] (3) (the last compound as the CH 2 Cl 2 solvate) have been determined by X-ray crystallography: Compound 1 crystallizes in the space groupe P1

Osmium forms more neutral binary carbonyls than any other metal; before 1987, nine were known with one to eight osmium atoms. There were, however, no tetranuclear binary carbonyls of osmium known before this data. This review describes the synthesis of Os4(CO)14 (1), Os4(CO)15 (2) and Os4(CO)16 (3) along with various derivatives of these clusters. Addition of Os(CO)5 to Os3(CO)10(C8H14)2 in hexane affords 2 in good yield. The crystal structure of 2 reveals it to have an unusual planar structure with short (2.775 A) and long (2.998 A) peripheral Os—Os bonds (the hinge Os—Os bond length of 2.948 A is more typical of an Os—Os single bond). The unusual metal—metal bond lengths are rationalized in terms of three-center, two-electron metal—metal bonds so that the short bonds have a bond order of 1.5 and the long bonds an order of 0.5. In this way each osmium atom achieves an 18-electron configuration. Several clusters with essentially the same arrangement of metal atoms have also been synthesized (e.g., Os4(CO)14(PMe3) (4), (η5- C5Me5)IrOs3(CO)12). The variable temperature 13C NMR spectra of 2 and 4 indicate that rapid CO-exchange in the equatorial plane occurs in these compounds. Other 62-electron clusters prepared in this study were Os4(μ-H)(CO)14(SnMe3) (8) and Os4(μ-H)2(CO)13(PMe3) (9); whereas 8 has a planar metal skeleton, 9 adopts the more common butterfly arrangement. For these clusters, the planar configuration is adopted when at least one of the metal atoms in the hinge position has four terminal ligands. Refluxing 2 in hexane yields Os4(CO)14 (1), which as expected from polyhedral skeletal electron pair theory has a tetrahedral metal core. Evidence is presented which indicates that in solution the carbonyl ligands in 1 undergo exchange on the infrared time scale. Treatment of 2 in CH2Cl2 at 0 ° C with CO (1 atm) gives Os4(CO)16 (3) in essentially quantitative yield. The crystal structure of 3 reveals it to have a cyclobutane-like Os4 core; the Os—Os bonds are long and range in length from 2.979 to 3.000 A. In solution at room temperature, 3 readily decomposes to give mainly Os3(CO)12. The much greater stability of the trinuclear cluster suggests that the metal—metal bonding in this cluster should be described in terms of a centrally directed molecular orbital plus edge-bridging molecular orbitals, rather than in terms of two-center, two-electron metal—metal bonds. The structures of Os4(CO)15(L) (L = PF3, PMe3, P(OCH2)3CMe, CNBut) have been determined. Only the PF3 derivative has a puckered square arrangement of metal atoms (with long Os—Os bonds) like 3; the other derivatives have a spiked triangular arrangement of metal atoms. The Os—Os bond lengths in the latter clusters range from 2.849 to 2.938 A. From this study it is concluded that it is the electronic properties of L that dictate which structure a cluster of the type Os4(CO)15(L) adopts. The nonrigid properties of 3 and the Os4(CO)15(L) clusters are also briefly discussed. t001 . The neutral binary carbonyls of osmium known before 1987 Formula Structure Ref. Os(CO)5 trigonal bipyramidal (D3h) 1 Os2(CO)9 single carbonyl bridge (C2v) a 2 Os3(CO)12 triangular Os3 (D3h) 3 Os5(CO)16 trigonal bipyramidal Os5 4 Os5(CO)19 “bow-tie” Os5 5 Os6(CO)18 capped trigonal bipyramidal Os6 6 Os6(CO)21 planar, “raft-like” Os6 b 7 Os7(CO)21 capped octahedral Os7 9 Os8(CO)23 bicapped octahedral Os8 c a Probable structure. b Probable structure based on the structures of Os6(CO)21-x[P(OMe)3]x (x = 1−4) [18,81]. c B.F.G. Johnson, personal communication.

Rapid heating of HOs 3 (μ)-H)(CO) 10 )(CNBu t ) in hexane produces Os 3 (μ-H) 2 (CO) 9 (CNBu t ) as the green isomer. The structure has been determined by X-ray crystallography: space group P2 1 /n with a=11.341 (2) A, b=12.106 (2) A, c=16.225 (2) A, β=108.43 (1) o , V=2113.3 A 3 , Z=4: R=0.034 for 2044 reflections

The cluster Os 4 (CO) 15 (CNBu t ) has been prepared by the addition of Bu t NC to OS 4 (CO) 15 in CH 2 Cl 2 at 0 o C. The structure has been solved by X-ray crystallography: space group P2/a with a=15.946 (2) A, b=11.465 (2) A, c=16.776 (2) A, β=92.09 (1) o , V=3064.8 A 3 , Z=4; R 1 =0.51, R 2 =0.057 for 2163 observed reflections; there is a partial molecule of CH 2 Cl 2 that is disordered

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.

Bromination of the substituted triosmium clusters Os3(CO)11(EPh3) (E = P, Sb) yielded two trimetallic chain compounds, viz., (Br)2Os(CO)3Os(CO)4Os(CO)4(EPh3) and (Br)(OC)4OsOs(CO)4Os(CO)3(Br)(EPh3). The former contains two donor−acceptor metal−metal bonds in tandem.

The title compound, octacarbonyl-1κ4C, 2κ4C-dihydrido-1κH, 2κH-bis(phenyl­3κ4C)germaniumdiosmium(2 Ge—Os), [Os2(H)2 (CO)8{Ge(C6H5)2}], is the first cluster containing a single Os—E—Os (E = Ge, Sn, Pb) chain to be structurally characterized. The molecule possesses approximate C2 symmetry. The Os—Ge—Os metal chain is bent and the Os—Ge bonds [2.599 (2) and 2.614 (2) A] are the longest yet known.

The title compound, hexadecacarbonyl-1k 3 C,2k 3 C,3k 3 C,4k 4 C,5k 3 C-di-μ-hydrido-1:2k 2 H;1:3k 2 H-pentaosmium(8 Os-Os), has been crystallized in a different crystal form from that reported previously [Guy & Sheldrick (1978). Acta Cryst. B34, 1725-1727]. The form reported here has crystallographic mirror symmetry and the packing arrangement in the crystal exhibits a different relative orientation of the molecules from the earlier structure.

Fourier transform infrared and Raman spectroscopy have been used to investigate a number of metal carbonyl clusters involving bonds between osmium and other transition metals. The distinction of covalent and dative metal-metal bonds is discussed with an emphasis on the polarization techniques used in this analysis. The application of permutation theory in the spectroscopic analysis of LM(CO) 5 complexes and its use in this analysis are presented.