Osmium–Germanium and Osmium–Germanium–Gold Carbonyl Cluster Complexes: Syntheses, Structures, Bonding, and Reactivity

Reactions of Os3(CO)10(NCMe)2 with HGePh3 have yielded the compounds Os3(CO)10(NCMe)(GePh3)(μ-H) (1) and Os3(CO)10(GePh3)2(μ-H)2 (2) by the sequential replacement of the NCMe ligands and the oxidative addition of the GeH bonds of one and two HGePh3 molecules, respectively, to the osmium atoms of the cluster. Compound 2 exists as two isomers in solution at low temperatures which interconvert rapidly on the H NMR time scale at room temperature. When it was heated, 1 was transformed into the pentaosmium complex Os5(CO)17(μ-GePh2) (3), which exhibits a planar raft structure with one bridging GePh2 ligand. Compound 1 reacts with the compound PhAu(PPh3) to yield the compound Os3(CO)8(μ-CO)(μ-OCPh)(μ-GePh2)(μ-AuPPh3) (4), which contains a bridging OCPh ligand and a Au(PPh3) group that bridges an Os−Ge bond. A minor product, Os(CO)4(GePh3)(AuPPh3) (5), was also obtained in this reaction. Compound 4 was also obtained from the reaction of 1 with CH3Au(PPh3). Compound 4 reacted with PhC2Ph to yield the complex Os3(CO)7(μGePh2)(μ-AuPPh3)[μ-(O)CPhCPhCPh)] (6), which contains a novel bridging oxametallacycle formed by the coupling of PhC2Ph to the bridging OCPh ligand in 4 and is another example of a Au(PPh3) group that bridges an Os−Ge bond. The bonding of the bridging Au(PPh3) group to the Os−Ge bonds in 4 and 6 was investigated by DFT computational analyses. ■ INTRODUCTION Germanium and tin are well-known to be valuable modifiers for heterogeneous transition-metal catalysts. It has been shown that transition metal−tin complexes can serve as precursors to excellent biand multimetallic supported heterogeneous catalysts. The reactions of Ir3(CO)9(μ-Bi) with HGePh3 and HSnPh3 have yielded the tris-EPh3 (E = Ge, Sn) triiridium trihydrido carbonyl complexes Ir3(CO)6(μ-Bi)(EPh3)3(μ-H)3, which were converted to the tris-germylene-bridged and tris-stannylenebridged triiridiium complexes Ir3(CO)6(μ-Bi)(μ-EPh2)3, upon mild heating (eq 1). The complexes Ru3(CO)9(EPh3)(μ-H)3 also eliminate 3 equiv of benzene when heated to yield the tris-EPh2 complexes Ru3(CO)9(μ-EPh2)3 (E = Ge, Sn) (eq 2). 5,6 It has recently been shown by a computational analysis that the α-cleavage of a phenyl group from a GePh3 ligand occurs at a single iridium atom in the transformation of the triiridium complex Ir3(CO)6(μ-CO)(μ-GePh2)2(GePh3)3 to the complex Ir3(CO)6(η -Ph)(μ-GePh2)3(GePh3)2 (eq 3). 7 Received: November 8, 2012 Published: December 11, 2012 Article pubs.acs.org/Organometallics © 2012 American Chemical Society 8639 dx.doi.org/10.1021/om301074w | Organometallics 2012, 31, 8639−8646 D ow nl oa de d by T E X A S A & M U N IV C O L G S T A T IO N o n A ug us t 3 0, 2 01 5 | h ttp :// pu bs .a cs .o rg P ub lic at io n D at e (W eb ): D ec em be r 11 , 2 01 2 | d oi : 1 0. 10 21 /o m 30 10 74 w We have now investigated the reactions of Os3(CO)10(NCMe)2 with HGePh3 and have obtained the new compounds Os3(CO)10(NCMe)(GePh3)(μ-H) (1) and Os3(CO)10(GePh3)2(μ-H)2 (2). Compound 1 contains a labile NCMe ligand, and this complex was found to react readily with the organogold phosphine compounds RAu(PPh3) (R = CH3, Ph) to yield the gold− osmium−germylene complex Os3(CO)8(μ-CO)(μ-OCPh)(μ-GePh2)(μ-AuPPh3) (4), which also contains a bridging benzoyl ligand and an AuPPh3 group that bridges an Os−Ge bond. Compound 4 reacts with PhC2Ph to yield the complex Os3(CO)7(μ-GePh2)(μ-AuPPh3)[μ-(O)CPhCPhCPh)] (6), which contains a novel bridging oxametallacycle formed by the coupling of PhC2Ph to the bridging benzoyl ligand. The results of these studies are reported herein. ■ EXPERIMENTAL SECTION General Data. Reagent-grade solvents were dried by the standard procedures and were freshly distilled prior to use. Unless indicated otherwise, all reactions were performed under an atmosphere of nitrogen. Infrared spectra were recorded on a Thermo Nicolet Avatar 360 FT-IR spectrophotometer. H NMR spectra were recorded on a Varian Mercury 300 spectrometer operating at 300.1 MHz. Variable temperature H NMR spectra for 2 were recorded on a Varian Mercury 400 spectrometer operating at 399.9 MHz. P{H} NMR were recorded on a Bruker Avance/DRX 400 NMR spectrometer operating at 162.0 MHz. Mass spectral (MS) measurements were performed by a direct-exposure probe using either electron impact ionization (EI) or electrospray techniques (ES) on a VG 70S instrument. Os3(CO)12 and CH3AuPPh3 were purchased from STREM. HGePh3 was purchased from Aldrich and was used without further purification. Os3(CO)10(NCMe)2 8 and PhAuPPh3 9 were prepared according to previously reported procedures. Product separations were performed by TLC in open air on Analtech 0.25 or 0.5 mm silica gel 60 Å F254 glass plates. Reactions of Os3(CO)10(NCMe)2 with HGePh3. (a). Synthesis of Os3(CO)10(NCMe)(GePh3)(μ-H) (1). A 29.5 mg (0.0316 mmol) amount of Os3(CO)10(NCMe)2 was dissolved in 30 mL of methylene chloride in a 100 mL three-neck flask. To this solution was added 9.60 mg (0.0315 mmol) of HGePh3, and the mixture was stirred at room temperature until the IR spectra showed that no Os3(CO)10(NCMe)2 was remaining in the solution (approximately 15 min). Since the reagent Os3(CO)10(NCMe)2 and the osmium products are air stable, samples can be removed from the reaction solution in order to follow the reaction by IR spectroscopy. The solvent was then removed in vacuo, and the product was isolated by TLC by using a 6/1 hexane/ methylene chloride elution solvent mixture to yield 31.2 mg of yellow Os3(CO)10(NCMe)(GePh3)(μ-H) (1; 64% yield). Spectral data for 1 are as follows. IR νCO (cm −1 in methylene chloride): 2102 (m), 2065 (vs), 2040 (s), 2019 (s), 2002 (s), 1987 (m), 1962 (sh). H NMR (CD2Cl2, δ in ppm) at 25 °C: δ 7.25−7.57 (m, 15H, Ph), 2.31 (s, 3H, CH3), −16.10 (s, hydride). ES+/MS: m/z 1197 (M). (b). Synthesis of Os3(CO)10(GePh3)2(μ-H)2 (2). A 10.2 mg (0.0109 mmol) amount of Os3(CO)10(NCMe)2 was dissolved in 20 mL of methylene chloride in a 50 mL three-neck flask. To this solution was added 8.3 mg (0.0272 mmol) of HGePh3, and the mixture was stirred at room temperature until the IR spectra showed no Os3(CO)10(NCMe)2 was remaining in the solution (approximately 2 h). Since the reagent Os3(CO)10(NCMe)2 and the osmium product 2 are air stable, samples can be removed from the reaction solution in order to follow the reaction by the IR spectroscopy. The solvent was then removed in vacuo, and the product was isolated by TLC by using a 6/1 hexane/methylene chloride elution solvent mixture to yield 15.9 mg of yellow Os3(CO)10(GePh3)2(μ-H)2 (2; 71% yield). Spectral data for 2 are as follows. IR νCO (cm −1 in CH2Cl2): 2127 (w), 2099 (m), 2056 (m), 2044 (vs), 2029 (m), 1977 (w). H NMR (CD2Cl2, δ in ppm) at 25 °C: 7.58−7.26 (m, 30H, Ph), −17.05 (s, hydride); the hydride resonances reveal the presence of two isomers assigned as 2 and 2′ at −80 °C, for isomer 2 −17.121 (d, JH−H = 1.32 Hz), −17.162 (d, JH−H = 1.32 Hz), for isomer 2′ −17.231 (s) and −17.704 (s); the ratio of 2/2′ is 2.3/1 at −80 °C. ES+/MS: m/z 1501 (M + K). Synthesis of Os3(CO)10(GePh3)2(μ-H)2 (2) from 1. A 25.3 mg (0.0211 mmol) of 1 was added to a 100 mL three-neck flask with a solution of 6.4 mg (0.0210 mmol) of HGePh3 in 30 mL of CH2Cl2. The mixture was then stirred at room temperature until the IR spectrum showed no 1 remaining in the solution (approximately 30 min). The solvent was then removed in vacuo, and the product was isolated by TLC by using a 6/1 hexane/methylene chloride elution solvent mixture to yield a yellow band of 2 (10.8 mg, 35% yield). Synthesis of Os5(CO)17(μ-GePh2) (3). A 10.7 mg (0.0089 mmol) amount of 1 was dissolved in 30 mL of hexane in a 100 mL three-neck flask. The solution was heated to reflux for 4 h. After cooling, the solvent was removed in vacuo, and the product was then isolated by TLC by using a 6/1 hexane/methylene chloride elution solvent mixture to yield a purple band of Os5(CO)17(μ-GePh2) (3; 1.06 mg, 9.3% yield) plus traces of a few uncharacterizable products. Spectral data for 3 are as follows. IR νCO (cm −1 in CH2Cl2): 2125 (w), 2095 (w), 2080 (m), 2063 (m), 2043 (vs), 2004 (m), 1991 (m). H NMR (CD2Cl2, δ in ppm) at 25 °C: 7.24−7.46 (m, 10H, Ph). EI/MS: m/z 1654 (M). Synthesis of Os3(CO)8(μ-CO)(μ-OCPh)(μ-GePh2)(μ-AuPPh3) (4). A 19.5 mg (0.0163 mmol) amount of 1 was dissolved in 30 mL of hexane in a 100 mL three-neck flask. To this solution was added 7.9 mg (0.0166 mmol) of CH3Au(PPh3), and the mixture was heated to reflux for 2 h. The solution changed from pale yellow to dark yellow. After cooling, the solvent was removed in vacuo, and the product was isolated by TLC by using a 3/1 hexane/methylene chloride elution solvent mixture to yield a dark yellow band of Os3(CO)8(μ-CO)(μ-O CPh)(μ-GePh2)(μ-AuPPh3) (4; 18.4 mg, 70% yield). Spectral data for 4 are as follows. IR νCO (cm −1 in CH2Cl2): 2098 (w), 2073 (s), 2033 (vs), 2027 (vs), 1995 (vs), 1975 (s), 1877 (vw). H NMR (CD2Cl2, δ in ppm) at 25 °C: 7.87−7.06 (m, 30H, Ph). P{H} NMR (CD2Cl2, 25 °C, 85% ortho-H3PO4): δ 60.30 (s, 1P). ES+/MS: m/z 1614 (M ). Reaction of 1 with PhAuPPh3. A 19.2 mg (0.0160 mmol) amount of 1 was dissolved in 30 mL of hexane in a 100 mL three-neck flask. To this solution was added 9.8 mg (0.0183 mmol) of PhAu(PPh3), and the mixture was heated to reflux for 1.5 h. The solution changed from pale yellow to orange. After cooling, the solvent was then removed in vacuo, and the products were separated by TLC by using a 3/1 hexane/methylene chloride solvent mixture to yield, in order of elution, 0.6 mg of pale yellow Os(CO)4(GePh3)(AuPPh3) (5; 1% yield) and 12.4 mg of dark yellow 4 (47% yield). Spectral data for 5 are as follows. IR νCO (cm −1 in CH2Cl2): 2075 (m), 1990 (vs). P{H} NMR (CD2Cl2, 25 °C, 85% ortho-H3PO4): δ 53.77 (s, 1P, P−Au). ES+/MS: m/z 1105 (M). Synthesis of Os3(CO)7(μ-GePh2)(μ-AuPPh3)[μ-(O)CPhCPhCPh)] (6). An 18.5 mg (0.0115 mmol) amount of 4 was dissolved in 30 mL of heptane in a 100 mL three-neck flask. To this solution was added 3.1 mg (0.0174 mmol) of PhC2Ph, and the mixture was heated to reflux for 10 h. The color changed from orange to deep red. After cooling, the solvent was then removed in vacuo, and the product was isolated by TLC by using a 4/1 hexane/methylene chloride elution solvent mixture to yield a yellow band of unreacted 4 (7.7 mg) followed by a red band of Os3(CO)7(μ-GePh2)(μ-AuPPh3)[μ-(O)CPhCPhCPh)] (6; 3.2 mg, 28% yield). Spectral data for 6 are as follows. IR νCO (cm −1 in hexane): 2063 (w), 2031 (vw), 2006 (s), 1996 (vs), 1985 (s), 1965 (w), 1946 (m), 1935 (m). H NMR (CD2Cl2, δ in ppm) at 25 °C: 7.80−6.81 (m, 40H, Ph). P{H} NMR (CD2Cl2, 25 °C, 85% ortho-H3PO4): δ 61.32 (s,1P, P−Au). ES+/MS: 1736 (M). Crystallographic Analyses. Yellow crystals of 1 suitable for X-ray diffraction analyses were obtained by slow evaporation of solvent from solutions in pure benzene solvent at room temperature. Yellow crystals of 2 and orange crystals of 4−6 suitable for X-ray diffraction analyses were obtained by slow evaporation of solvent from solutions in hexane/methylene chloride solvent mixtures at room temperature. Green crystals of 3 suitable for X-ray diffraction analyses were obtained by slow evaporation of solvent from a hexane solution at room temperature. Each data crystal was glued onto the end of a thin glass fiber. X-ray diffraction intensity data were measured by using a Bruker SMART APEX CCD-based diffractometer by using Mo Kα radiation Organometallics Article dx.doi.org/10.1021/om301074w | Organometallics 2012, 31, 8639−8646 8640 D ow nl oa de d by T E X A S A & M U N IV C O L G S T A T IO N o n A ug us t 3 0, 2 01 5 | h ttp :// pu bs .a cs .o rg P ub lic at io n D at e (W eb ): D ec em be r 11 , 2 01 2 | d oi : 1 0. 10 21 /o m 30 10 74 w (λ = 0.71073 Å). The raw data frames were integrated with the SAINT+ program by using a narrow-frame integration algorithm. Corrections for Lorentz and polarization effects were also applied with SAINT+. An empirical absorption correction based on the multiple measurement of equivalent reflections was applied using the program SADABS. All structures were solved by a combination of direct methods and difference Fourier syntheses and refined by full-matrix least squares on F by using the SHELXTL software package. All non-hydrogen atoms were refined with anisotropic thermal parameters. All hydride ligands in the complexes were refined with isotropic thermal parameters. Crystal data, data collection parameters, and results of these analyses are given in Table S1 (see the Supporting Information). Computational Details. All density functional theory (DFT) calculations were performed with the Amsterdam Density Functional (ADF) suite of programs by using the hybrid (B3LYP) and metaGGA (M06-L) functionals for compounds 4 and 6, respectively, with valence quadruple-ζ + 4 polarization function, relativistically optimized (QZ4P) basis sets for gold, osmium, and germanium atoms, and double-ζ (DZ) basis sets for phosphorus, carbon, oxygen, and hydrogen atoms with no frozen cores. The molecular orbitals and their energies were determined by single-point calculations based on the molecular structures of the compounds as established by the crystal structure analyses. ■ RESULTS AND DISCUSSION Reactions of Os3(CO)10(NCMe)2 with HGePh3 have yielded the compounds Os3(CO)10(NCMe)(GePh3)(μ-H) (1) and Os3(CO)10(GePh3)2(μ-H)2 (2) by the sequential replacement of the NCMe ligands and the oxidative addition of the GeH bonds of one and two HGePh3 molecules to the osmium atoms of the cluster. The yield of 2 was increased by using an excess of HGePh3. Compound 1 was converted to 2 by reaction with an additional quantity of HGePh3. Both products were characterized by IR, H NMR, mass spectra, and single-crystal X-ray diffraction analyses. An ORTEP diagram of the molecular structure of 1 is shown in Figure 1. The structure of compound 1 consists of a closed triangular cluster of three osmium atoms. There is one GePh3 ligand coordinated to Os(1). The Os−Ge distance (Os(1)−Ge(1) = 2.5301(6) Å) is slightly longer than the Os−Ge distance (2.4933(9) Å) to the GePh3 ligand in the complex PtOs3(CO)7(PBu t 3)(μ-PBu t 2)(μ4-CHCMeCH)(GePh3)(μ-H). The GePh3 ligand lies in an equatorial position, in the plane of the Os3 triangle. There is one hydride ligand that bridges the Os(1)−Os(2) bond and one NCMe ligand that occupies an axial coordination site on Os(2) (Os(2)−N(1) = 2.107(5) Å). As expected, the hydride-bridged Os−Os bond (Os(1)−Os(2) = 3.0163(3) Å) is significantly longer, than the other two Os−Os bonds (Os(1)−Os(3) = 2.8972(3) Å and Os(2)−Os(3) = 2.8883(4) Å). The Os−Os bond distance found in Os3(CO)12 is 2.877(3) Å. The position of the hydride ligand was located and refined in the analysis (Os(1)−H(1) = 1.74(6) Å and Os(2)−H(1) = 1.76(6) Å). The hydride ligand exhibits a highfield shift in the H NMR spectrum (δ −16.10). An ORTEP diagram of the molecular structure of 2 is shown in Figure 2. Like 1, the structure of compound 2 consists of a closed triangular cluster of three osmium atoms, but it has two GePh3 ligands on adjacent osmium atoms and two hydrido ligands that bridge neighboring Os−Os bonds. Both GePh3 ligands occupy equatorial positions, in the plane of the Os3 triangle, coordinated to Os(1) and Os(2) (Os(1)−Ge(1) = 2.5634(8) Å and Os(2)−Ge(2) = 2.5292(8) Å). The two hydride-bridged Os−Os bonds (Os(1)−Os(2) = 3.0636(4) Å and Os(1)−Os(3) = 3.0884(4) Å) are significantly longer than the Os−Os bond that does not have a bridging hydride ligand (Os(2)−Os(3) = 2.9165(5) Å). Pomeroy reported a similar bis-(SnMe3)Os3 complex, Os3(CO)10(SnMe3)2(μ-H)2, that was obtained from the reaction of Os3(CO)10(μ-H)2 with HSnMe3. 16 The H NMR spectrum of 2 exhibits a single high-field resonance for the two inequivalent hydride ligands at room temperature at δ −17.05, which is inconsistent with the solidstate structure. Suspecting dynamic activity, we performed a variable-temperature NMR study. H NMR spectra of 2 at Figure 1. ORTEP diagram of the molecular structure of Os3(CO)10(NCMe)(GePh3)(μ-H) (1) showing thermal ellipsoids at the 30% probability level. Selected interatomic bond distances (Å) are as follows: Os(1)−Os(2) = 3.0163(3), Os(1)−Os(3) = 2.8972(3), Os(2)−Os(3) = 2.8883(4), Os(1)−Ge(1) = 2.5301(6), Os(2)−N(1) = 2.107(5), Os(1)− H(1) = 1.74(6), Os(2)−H(1) = 1.76(6). Figure 2. ORTEP diagram of the molecular structure of Os3(CO)10(GePh3)2(μ-H)2 (2) showing thermal ellipsoids at the 30% probability level. Selected interatomic bond distances (Å) are as follows: Os(1)−Os(2) = 3.0636(4), Os(1)−Os(3) = 3.0884(4), Os(2)− Os(3) = 2.9165(5), Os(1)−Ge(1) = 2.5634(8), Os(2)−Ge(2) = 2.5292(8), Os(1)−H(1) = 1.77(6), Os(3)−H(1) = 1.70(6), Os(1)−H(2) = 1.77(6), Os(2)−H(2) = 1.80(5). Organometallics Article dx.doi.org/10.1021/om301074w | Organometallics 2012, 31, 8639−8646 8641 D ow nl oa de d by T E X A S A & M U N IV C O L G S T A T IO N o n A ug us t 3 0, 2 01 5 | h ttp :// pu bs .a cs .o rg P ub lic at io n D at e (W eb ): D ec em be r 11 , 2 01 2 | d oi : 1 0. 10 21 /o m 30 10 74 w various temperatures in the high-field region are shown in Figure 3. These spectra reveal that not only are the two hydride resonances of the isomer found in the solid state averaged but also there is a second isomer present in solution at low temperatures which also exhibits two separate hydride resonances. The two isomers observed at −80 °C shall be called 2 (the major isomer) and 2′, respectively. For isomer 2, δ −17.121 (d) and −17.162 (d), and for isomer 2′, δ −17.231 (s) and −17.704 (s); the ratio 2/2′ is 2.3/1 at −80 °C. The first two resonances are mutually coupled doublets (JH−H = 1.32 Hz); the latter two (2′) are broad singlets. In addition, it was found that the two isomers are interconverting rapidly on the NMR time scale at intermediate temperatures. This was confirmed by a 2D NOESY spectrum recorded at −80 °C, which showed magnetization transfer not only between the resonances of the two different isomers but also between the two resonances of the major isomer (at −40 °C) (see the Supporting Information). These spectral changes can be explained by either of two mechanisms, which differ depending on the identity and structure of the unknown minor isomer. Mechanism 1 involves hydride positional isomers. Without repositioning any of the non-hydride ligands, three isomers of 2 can be created by repositioning the hydride ligands about the three Os−Os bonds. These structures are represented by 2, 2′, and 2′′, as shown in Scheme 1. It is presumed that structure 2, which is that found in the solid state, is the major isomer in solution. The spectra show the presence of only one other isomer in solution at low temperatures. The structure of 2′ is tentatively assigned as shown in Scheme 1. This isomer is probably more stable than 2′′, because 2′ retains one hydride on the Os−Os bond between the two electron-rich GePh3 ligands. The isomerization between 2 and 2′ could occur by simply shifting the hydride ligand H2 back and forth between the two Os−Os bonds involving the Os(CO)4 group (process A). Low-energy migration of hydride ligands between the metal−metal bonds in other trinuclear metal cluster complexes has been observed previously. The barrier to the exchange of the hydrides H1 and H2 within isomer 2 itself is a higher energy process, because it is still not rapid on the NMR time scale at −20 °C. Without putting two hydride ligands onto the same Os−Os bond, a minimum of three hydride shifts must occur in order to complete the exchange of H1 and H2 in 2. To do this, it is proposed to invoke the third isomer, presumably 2′′, which was not observed directly in the solutions. Isomer 2′′ can be accessed from isomer 2 by process B shown in Scheme 1 or by process C from isomer 2′. The H1−H2 exchange is completed by shifting atom H2 to the bond between the two GePh3-substituted Os atoms. This can be achieved in one step from 2′, shown on the right of Scheme 1, and in two steps from 2′′, shown on the left of Scheme 1. Mechanism 2 involves GePh3 ligand positional isomers. Isomers of 2 could also be formed by repositioning the GePh3 ligands and could be interconverted dynamically via polytopal rearrangements. We have recently observed examples of this in the compounds Ir3(CO)6(μ-Bi)(EPh3)3(μ-H)3 (E = Ge, Sn), but the temperatures required for those rearrangements are higher than those observed for the isomerization and hydride ligand exchange processes observed in 2. Two plausible GePh3 ligand positional isomers of 2 are shown in Scheme 2. One is the observed solid-state structure of 2; the other isomer, 2*, could be formed by repositioning the GePh3 ligand on one of the Os atoms. There are other possible isomers, but isomers that have the bulky GePh3 ligand in equatorial positions should be energetically more favorable for steric reasons. The two isomers 2 and 2* can be interconverted by polytopal ligand rearrangements involving the GePh3 ligands. Similar processes have been described for the bis-phosphine complex Os3(CO)10(PMe2Ph)2. 18 However, the process shown in Scheme 2 does not allow for the observed exchange of the hydride ligands within a given isomer. To explain that observation, either additional hydride shift processes (e.g. Scheme 1) or perhaps a Ge−H “reductive elimination” coupled with a polytopal rearrangement Figure 3. Variable-temperature H NMR spectra for compound 2 in CD2Cl2 solvent recorded in the high-field region of the spectrum. Scheme 1 Scheme 2 Organometallics Article dx.doi.org/10.1021/om301074w | Organometallics 2012, 31, 8639−8646 8642 D ow nl oa de d by T E X A S A & M U N IV C O L G S T A T IO N o n A ug us t 3 0, 2 01 5 | h ttp :// pu bs .a cs .o rg P ub lic at io n D at e (W eb ): D ec em be r 11 , 2 01 2 | d oi : 1 0. 10 21 /o m 30 10 74 w without dissociation of the HGePh3 ligand would have to be invoked. These processes cannot be distinguished with the available data. When a solution of 1 in hexane solvent was heated to reflux for 4 h, the higher nuclearity compound Os5(CO)17(μ-GePh2) (3) was obtained in low yield (9.3%). Compound 3 was characterized by a single-crystal X-ray diffraction analysis, and an ORTEP diagram of its molecular structure is shown in Figure 4. Compound 3 contains five osmium atoms arranged in a planar raftlike structure with one GePh2 ligand that bridges the Os(1)−Os(2) bond (Os(1)−Os(2) = 2.8691(7) Å). The six other Os−Os bonds are similar in length (Os(1)−Os(3) = 2.8713(8) Å, Os(1)−Os(4) = 2.8536(7) Å, Os(2)−Os(4) = 2.8376(8) Å, Os(2)−Os(5) = 2.8531(8) Å, Os(3)−Os(4) = 2.8631(7) Å, and Os(4)−Os(5) = 2.8804(7) Å). The metal cluster in 3 is structurally similar to that found in the two related Os5 raft cluster complexes Os5(CO)17(μ-CO) 19 and Os5(CO)16(PMe3)(μ-CO), 20 both of which have a bridging CO ligand at the site corresponding to the GePh2 ligand in 3. The Os−Ge bond distances (Os(1)−Ge(1) = 2.5115(16) Å and Os(2)−Ge(1) = 2.5286(16) Å) are similar to those found to the edge-bridging GePh2 ligands in the complexes Os4(CO)9(μ4-GePh)2(μ-GePh2)3 and Os4(CO)8(μ4-GePh)2(μ-GePh2)4. 21 Overall, compound 3 contains a total of 76 valence electrons on the metal atoms, which is in accord with the 18-electron rule for a cluster of 5 metal atoms having 7 metal−metal bonds. We have recently shown that organogoldphosphines of the type PhAu(PPh3) (R = Ph, naphthyl) react with Os3(CO)10(NCMe)2 by displacement of the NCMe ligand and oxidative addition of the Au−C bond of the gold complexes to yield the (organo)(goldphosphine)triosmium carbonyl complexes Os3(CO)10(μ-AuPPh3)[μ-R]. 22 Compound 1 was found to react with the compounds RAu(PPh3) (R = CH3, Ph) by loss of its NCMe ligand and oxidative addition of the Au−C bond of the gold complexes to yield the compound Os3(CO)8(μCO)(μ-OCPh)(μ-GePh2)(μ-AuPPh3) (4; 70% yield). One minor product, Os(CO)4(GePh3)(AuPPh3) (5; 1% yield), was obtained when PhAu(PPh3) was used as the gold reagent. The molecular structures of both products were established by single-crystal X-ray diffraction analyses. An ORTEP diagram of the molecular structure of 4 is shown in Figure 5. Compound 4 contains a triangular cluster of three osmium atoms, one Au(PPh3) group, one bridging GePh2 ligand, and one bridging benzoyl ligand (OCPh). There are two long Os−Os bonds (Os(1)−Os(2) = 2.8671(5) Å, Os(1)− Os(3) = 2.8822(5) Å) and one that is significantly shorter (Os(2)−Os(3) = 2.7643(5) Å); the latter contains the bridging benzoyl ligand (Os(2)−O(1) = 2.162(5) Å and Os(3)−C(1) = 2.066(8) Å) and also a bridging CO ligand, which could explain the shortness of that Os−Os bond. The GePh2 ligand bridges the Os(1)−Os(2) bond, and the Os−Ge bond distances are significantly different (Os(1)−Ge(1) = 2.5021(9) Å, Os(2)− Ge(1) = 2.6107(9) Å); the latter is similar to the Os−Ge bond distances in 3. The Au(PPh3) group is primarily bonded to Os(1) (Os(1)−Au(1) = 2.6757(5) Å), but the Au atom does have a significant bridging/semibridging interaction to the germanium atom (Au(1)−Ge(1) = 2.7618(10) Å). There are only a few examples of Au−Ge bonds among the known complexes containing Au(PPh3) groups. These are Au(GeCl3)(P-o-tolyl3) (Au−Ge = 2.376(1) Å) and Au(GeCl3)(PPh3)3, (Au−Ge = 2.563(1) Å and [2.536(1)] Å), and for both of these compounds, the Ge group has three strongly electron withdrawing Cl atoms. We are unaware of any previous examples of complexes having Au(PPh3) groups bridging transition-metal−Ge bonds, but some years ago Ruiz did report the compound [Mn2(CO)6(dppm)(μ-SnCl2){AuP(p-tol)3}2], which was shown to have AuP(p-tol)3 groups bridging each of the Mn−Sn bonds to the bridging SnCl2 ligand. 25 There are a few examples of hydrogen atoms bridging M−Ge bonds in polynuclear metal complexes. The phenyl group on the benzoyl ligand must have originated from the phenyl group that was cleaved from the GePh3 ligand in the course of the formation of the GePh2 ligand and not from the PhAu(PPh3) reagent, because the same ligand (benzoyl not acetyl) was formed when the CH3Au(PPh3) was used as the reagent. Compound 4 contains nine carbonyl ligands and a total Figure 4. ORTEP diagram of the molecular structure of Os5(CO)17(μGePh2) (3) showing thermal ellipsoids at the 30% probability level. Selected interatomic bond distances (Å) are as follows: Os(1)−Os(2) = 2.8691(7), Os(1)−Os(3) = 2.8713(8), Os(1)−Os(4) = 2.8536(7), Os(2)−Os(4) = 2.8376(8), Os(2)−Os(5) = 2.8531(8), Os(3)− Os(4) = 2.8631(7), Os(4)−Os(5) = 2.8804(7), Os(1)−Ge(1) = 2.5115(16), Os(2)−Ge(1) = 2.5286(16). Figure 5. ORTEP diagram of the molecular structure of Os3(CO)8(μCO)(μ-OCPh)(μ-GePh2)(μ-AuPPh3) (4) showing thermal ellipsoids at the 30% probability level. Selected interatomic bond distances (Å) are as follows: Os(1)−Os(2) = 2.8671(5), Os(1)−Os(3) = 2.8822(5), Os(2)−Os(3) = 2.7643(5), Os(1)−Au(1) = 2.6757(5), Os(1)−Ge(1) = 2.5021(9), Os(2)−Ge(1) = 2.6107(9), Au(1)−Ge(1) = 2.7618(10), Au(1)−P(1) = 2.284(2), Os(2)−O(1) = 2.162(5), Os(3)−C(1) = 2.066(8), O(1)−C(1) = 1.293(9). Organometallics Article dx.doi.org/10.1021/om301074w | Organometallics 2012, 31, 8639−8646 8643 D ow nl oa de d by T E X A S A & M U N IV C O L G S T A T IO N o n A ug us t 3 0, 2 01 5 | h ttp :// pu bs .a cs .o rg P ub lic at io n D at e (W eb ): D ec em be r 11 , 2 01 2 | d oi : 1 0. 10 21 /o m 30 10 74 w of 48 valence electrons (the Au(PPh3) group is a one electron donor); thus, each osmium atom achieves the conventional 18-electron configuration. To investigate the character of the Au−Ge interaction further, geometry-optimized DFT molecular orbital calculations were performed on the structures of compound 4 by using the B3LYP functional of the Amsterdam Density Functional program library. A significant Au−Ge interaction was confirmed by a significant orbital component found between the Au and Ge atoms in the highest occupied molecular orbital (HOMO) of 4 as shown in Figure 6. There is also a significant orbital component between the Au atom and the associated Os atom, Os(1). An ORTEP diagram of the molecular structure of 5 is shown in Figure 7. Compound 5 contains only one osmium atom, in an Os(CO)4 group, and a Au(PPh3) group and one GePh3 ligand. Compound 5 is clearly the result of a cluster fragmentation process. The Os atom has an octahedral geometry, and the Au(PPh3) and GePh3 groups occupy cis coordination sites (Au(1)− Os(1)−Ge(1) = 89.47(2)°). However, unlike the case for 4, there does not appear to be any significant bonding interaction between the Au and Ge atoms (Ge(1)···Au(1) = 3.6833(8) Å). The Os−Au bonding distance (Os(1)−Au(1) = 2.6574(5) Å) is slightly shorter than that in 4. The Os−Ge distance (Os(1)− Ge(1) = 2.5750(8) Å) is very slightly longer than those in 1 and 2. The osmium atom in 5 has an 18-electron configuration. To investigate the reactivity of compound 4 further, it was treated with PhC2Ph in a heptane solution at reflux for 10 h. From this solution, the compound Os3(CO)7(μ-GePh2)(μAuPPh3)[μ-(O)CPhCPhCPh)] (6) was obtained in 28% yield. An ORTEP diagram of the molecular structure of 6 is shown in Figure 8. Compound 6 contains a triangular cluster of three osmium atoms, one Au(PPh3) group, one bridging GePh2 ligand, and one bridging η-OCPhCPhCPh ligand. The last group was formed by the addition and coupling of one molecule of PhC2Ph to the carbon atom of the bridging benzoyl ligand in 4. As in 4, the Au(PPh3) group bridges one of the Os−Ge bonds to the GePh2 ligand (Au(1)−Ge(1) = 2.7846(12) Å and Os(1)−Au(1) = 2.6803(6) Å). The Os−Ge bond distances (Os(1)−Ge(1) = 2.5143(12) Å and Os(2)−Ge(1) = 2.5992(11) Å) are similar to those in 4. The η-OCPhCPhCPh ligand formed a metallacycle by coordination of its two terminal atoms O(1) and C(64) to the metal atom Os(2) (Os(2)−O(1) = 2.108(7) Å and Os(2)−C(64) = 2.046(10) Å). All four atoms of the OC3 chain are π-bonded to Os(3) (Os(3)−C(1) = 2.260(10) Å, Os(3)−O(1) = 2.217(6) Å, Os(3)−C(64) = 2.277(9) Å, and Os(3)−C(65) = 2.292(9) Å). The formation of bridging metallacycles by the coupling of alkynes is well established, but the formation of heteroatom metallacycles such as that found in 6 is very rare; in fact, we have not been able to find any other examples of the coupling of an alkyne to a bridging acyl ligand to form an oxametallacycle. However, there have been some examples of the insertion coupling of alkynes to terminally coordinated acyl ligands and η-acyl ligands. The nature of the Au−Ge bonding in 6 was also investigated by DFT MO calculations. The HOMO and HOMO-2 of 6 are shown in Figure 9. As seen in 4, there is a significant orbital interaction Figure 6. Highest occupied molecular orbital of compound 4 (Iso = 0.03), showing that a significant component of the orbital is derived from a direct interaction between the Au and Ge atoms. Figure 7. ORTEP diagram of the molecular structure of Os(CO)4(GePh3)(AuPPh3) (5) showing thermal ellipsoids at the 30% probability level. Selected interatomic bond distances (Å) and angles (deg) are as follows: Os(1)−Au(1) = 2.6574(5), Os(1)−Ge(1) = 2.5750(8), Au(1)−P(1) = 2.292(2), Ge(1)···Au(1) = 3.6833(8); Au(1)− Os(1)−Ge(1) = 89.47(2). Figure 8. ORTEP diagram of the molecular structure of Os3(CO)7(μGePh2)(μ-AuPPh3)[μ-OCPhCPhCPh)] (6) showing thermal ellipsoids at the 20% probability level. Selected interatomic bond distances (Å) are as follows: Os(1)−Os(2) = 2.8170(6), Os(1)−Os(3) = 2.7731(6), Os(2)−Os(3) = 2.7025(7), Os(1)−Au(1) = 2.6803(6), Os(1)−Ge(1) = 2.5143(12), Os(2)−Ge(1) = 2.5992(11), Au(1)−Ge(1) = 2.7846(12), Au(1)−P(1) = 2.305(3), Os(2)−O(1) = 2.108(7), Os(2)−C(64) = 2.046(10), Os(3)−C(1) = 2.260(10), Os(3)−O(1) = 2.217(6), Os(3)− C(64) = 2.277(9), Os(3)−C(65) = 2.292(9), O(1)−C(1) = 1.374(12), C(1)−C(65) = 1.414(13), C(65)−C(64) = 1.451(13). Organometallics Article dx.doi.org/10.1021/om301074w | Organometallics 2012, 31, 8639−8646 8644 D ow nl oa de d by T E X A S A & M U N IV C O L G S T A T IO N o n A ug us t 3 0, 2 01 5 | h ttp :// pu bs .a cs .o rg P ub lic at io n D at e (W eb ): D ec em be r 11 , 2 01 2 | d oi : 1 0. 10 21 /o m 30 10 74 w