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Organometallics 2010, 29, 4346–4353 DOI: 10.1021/om1006424
Iridium-Germanium and -Tin Carbonyl Complexes Richard D. Adams* and Eszter Trufan Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208 Received July 2, 2010
The new compound Ir(COD)(CO)2GePh3, 1, was obtained when a solution containing [Ir(COD)Cl]2 and HGePh3 was treated with a solution of BuLi under a purge with CO. The tin homologue Ir(COD)(CO)2SnPh3, 2, was obtained similarly by replacing the HGePh3 reagent with HSnPh3. The reaction of [Ir(COD)Cl]2 with HGePh3 and CO in the absence of BuLi yielded the compound HIr(CO)3(GePh3)2, 3. When 3 was heated to reflux in toluene solvent, three new compounds were formed: Ir2(CO)6(GePh3)2(μ-GePh2), 4; H2Ir2(CO)4(GePh3)2(μ-GePh2)2, 5; and Ir2(CO)8[μ-Ph2Ge(OH)GePh2](μ-GePh2)(GePh3)2(μ-H), 6. The yield of 5 was increased when the reaction was performed under an atmosphere of hydrogen, and the yield of 4 was increased when the reaction was performed under an atmosphere of CO. The reaction of 4 with H2GePh2 yielded 5, 6, and the new compound H2Ir2(CO)4(μ-GePh2)(GePh2H)2, 7. Compounds 1-7 were fully characterized by IR, 1H NMR, and single-crystal X-ray diffraction analyses. Molecular orbital calculations on compounds 5 and 7 were performed and compared.
Introduction The catalytic properties of iridium have been of interest ever since it was discovered that bimetallic platinumiridium clusters provided performance superior to that of pure platinum in petroleum reforming processes.1,2 Later it was shown that the addition of germanium to these catalysts improved the selectivity for the desirable aromatization, isomerization, and hydrocracking reactions even further.2 Polynuclear iridium carbonyl cluster complexes have been shown to serve as good catalysts for the hydrogenation of toluene and olefins when activated on suitable supports.3,4 Germanium has been shown to be a valuable modifier of rhodium for the selective catalytic hydrogenation of citral and other unsaturated hydrocarbons.5 Accordingly, we have recently turned our attention to the syntheses of polynuclear *To whom correspondence should be addressed. E-mail: Adams@ mail.chem.sc.edu. (1) (a) Sinfelt, J. H. Sci. Am. 1985, 253, 90–98. (b) Sinfelt, J. H. Bimetallic Catalysts. Discoveries, Concepts and Applications; Wiley: New York, 1983. (c) Sinfelt, J. H.; Via, G. H. J. Catal. 1979, 56, 1–11. (d) Rasser, J. C.; Beindorff, W. H.; Scholten, J. J. F. J. Catal. 1979, 59, 211–222. (2) (a) Macleod, N.; Fryer, J. R.; Stirling, D.; Webb, G. Catal. Today 1998, 46, 37–54. (b) Ponec, V. Bond, G. C. In Catalysis by Metals and Alloys, Studies in Surfure Science Catalysis; Elsevier: Amsterdam, 1998; Vol. 95, Chapter 13. (3) Gates, B. C. Chem. Rev. 1995, 95, 511–522. (4) (a) Argo, A. M.; Odzak, J. F.; Goellner, J. F.; Lai, F. S.; Xiao, F.-S.; Gates, B. C. J. Phys. Chem. B 2006, 110, 1775–1786. (b) Argo, A. M.; Odzak, J. F.; Gates, B. C. J. Am. Chem. Soc. 2003, 125, 7107–7115. (c) Xu, Z.; Xiao, F.-S.; Purnell, S. K.; Alexeev, O.; Kawi, S.; Deutsch, S.; Gates, B. C. Nature 1994, 372, 346–348. (d) Li, F.; Gates, B. C. J. Phys. Chem. C 2007, 111, 262–267. (e) Moura, F. C. C.; dos Santos, E. N.; Lago, R. M.; Vargas, M. D.; Araujo, M. H. J. Mol. Catal. A: Chem. 2005, 226, 243–251. (5) (a) Ekou, T.; Vicente, A.; Lafaye, G.; Especel, C.; Marecot, P. Appl. Catal., A 2006, 314, 73–80. (b) Lafaye, G.; Micheaud-Especel, C.; Montassier, C.; Marecot, P. Appl. Catal., A 2002, 230, 19–30. (c) Lafaye, G.; Micheaud-Especel, C.; Montassier, C.; Marecot, P. Appl. Catal., A 2004, 257, 107–117. pubs.acs.org/Organometallics
Published on Web 09/07/2010
complexes of the platinum group metals containing germanium ligands for possible use as selective hydrogenation catalysts.6-8 There are very few examples of polynuclear iridium carbonyl complexes containing organogermanium ligands. We have recently made some of the first examples of tri- and tetrairidium carbonyl cluster complexes containing phenylgermyl ligands by the reaction of tetrairidium dodecacarbonyl with triphenylgermane, e.g., eqs 1 and 2.9
The compound Ir3(CO)5(GePh3)(μ-H)(μ-GePh2)(μ3-GePh) contains a terminal triphenylgermyl ligand, a triply bridging (6) Adams, R. D.; Captain, B.; Trufan, E. J. Cluster Sci. 2007, 18, 642–659. (7) Adams, R. D.; Trufan, E. Inorg. Chem. 2009, 48, 6124–6129. (8) Adams, R. D.; Trufan, E. Inorg. Chem. 2010, 49, 3029–3034. (9) Adams, R. D.; Captain, B.; Smith, J. L., Jr. Inorg. Chem. 2005, 44, 1413–1420. r 2010 American Chemical Society
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phenylgermylyne ligand, and three edge-bridging diphenylgermylene ligands all in the same triiridium complex. The complex H4Ir4(CO)4(μ-GePh2)4(μ4-GePh)2 contains two quadruply bridging phenylgermylyne ligands. The germylene and germylyne ligands in these complexes were formed by the cleavage of phenyl groups from the germanium atom of the HGePh3 reagent. We have recently obtained the trigonal-bipyramidal complex Rh(CO)4(GePh3) from the reaction of [Rh(CO)2Cl]2 with [GePh3]- in the presence of a CO atmosphere.8 We have now obtained a series of new iridium-germanium and iridium-tin complexes from the reactions of [Ir(COD)Cl]2, COD = 1,5-cyclooctadiene, with HGePh3 and HSnPh3. The results of our studies of these reactions are reported here.
Experimental Section General Data. All reactions were performed under a nitrogen atmosphere unless otherwise specified. Reagent-grade solvents were dried by the standard procedures and were freshly distilled prior to use. Infrared spectra were recorded on a ThermoNicolet Avatar 360 FT-IR spectrophotometer. 1H NMR spectra were recorded on a Mercury 300 spectrometer operating at 300.1 MHz. Mass spectrometric (MS) measurements performed by a direct-exposure probe using electron impact ionization (EI) were made on a VG 70S instrument. Product separations were performed by TLC in air on Analtech 0.5 mm silica gel 60 A˚ F254 glass plates. [Ir(COD)Cl]2 was purchased from Strem Chemicals, Inc. HGePh3 and butyllithium were purchased from Aldrich and were used without further purification. Synthesis of Ir(COD)(CO)2GePh3. A 20.0 mg (0.030 mmol) amount of [Ir(COD)Cl]2 was dissolved in 15 mL of hexane in a 100 mL three-neck flask under nitrogen. To this solution was added 19.2 mg (0.063 mmol) of HGePh3 followed by the addition of 0.25 mL of a 1.6 M BuLi solution in hexane. The reaction mixture was stirred under CO for 15 min while the color of the solution turned pale yellow and a precipitate formed. The solvent was then evaporated and the residue was separated by TLC using a 4:1 hexane-methylene chloride solvent mixture to yield 9.0 mg of Ir(COD)(CO)2GePh3, 1 (23% yield). Spectral data for Ir(COD)(CO)2GePh3: IR νCO (cm-1 in hexane): 2020 (s), 1971(vs). 1H NMR (CDCl3, δ in ppm): 7.16-7.7.49 (m, 15H, Ph), 4.20 (s, 4H, CH), 2.38-2.58 (br, 8H, CH2). Mass spectrum: EI-MS showed the parent ion at m/z 660. Synthesis of Ir(COD)(CO)2SnPh3, 2. A 20.5 mg (0.030 mmol) amount of [Ir(COD)Cl]2 was dissolved in 15 mL of hexane in a 100 mL three-neck flask and stirred. To this solution was added 63.4 mg (0.181 mmol) of HSnPh3 followed by the addition of 0.35 mL of a 1.6 M BuLi solution in hexane. The reaction mixture was then stirred under CO for 5 min. During this time, the color of the solution turned pale orange and a precipitate formed. The solvent was then removed in vacuo, and the residue was separated by TLC using a 4:1 hexane-methylene chloride solvent mixture to yield 5.4 mg of Ir(COD)(CO)2SnPh3, 2 (13% yield). Spectral data for 2: IR νCO (cm-1 in hexane): 2015 (s), 1970 (vs). 1H NMR (CDCl3, δ in ppm): 7.12-7.80 (m, 15H, Ph), 4.39 (s, 4H, CH), 2.37-2.52 (br, 8H, CH2). Mass spectrum: EI-MS showed the parent ion at m/z = 700. Synthesis of HIr(CO)3(GePh3)2, 3. A 20.2 mg (0.030 mmol) amount of [Ir(COD)Cl]2 was dissolved 15 mL of hexane in a 100 mL three-neck flask. To this solution was added 50.0 mg (0.164 mmol) of HGePh3, and the reaction mixture was stirred for 20 min under N2. Then, CO was slowly purged through the solution for 2 h. The solvent was then removed, and the residue was separated by TLC using a 4:1 hexane-methylene chloride solvent mixture to yield 24.4 mg of 3 (46% yield). Spectral data for 3: IR νCO (cm-1 in hexane): 2058 (vs), 2041 (w). 1H NMR (CDCl3, in ppm): δ 6.60-8.18 (m, 30H, Ph), -11.82 (s, 1H, CH). Mass spectrum: EI-MS showed the parent ion at m/z = 886.
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Synthesis of 3 from Reaction of 1 with HGePh3. An 11.7 mg (0.018 mmol) amount of 1 was dissolved in 1 mL of d6-benzene in an NMR tube. To this solution was added 16.5 mg (0.054 mmol) of HGePh3, and the tube was purged with CO and allowed to react for 48 h at room temperature. The solvent was then removed, and the residue was separated by TLC using a 4:1 hexane-methylene chloride solvent mixture to yield 4.3 mg of HIr(CO)3(GePh3)2, 3 (27% yield), and 2.1 mg of unreacted 1 (18%). Thermal Decomposition of 3. A 31.3 mg (0.035 mmol) amount of HIr(CO)3(GePh3)2 was dissolved in 15 mL of toluene in a 100 mL three-neck flask. The solution was refluxed for 3.5 h under N2. The solvent was then removed, and the residue was separated by TLC using a 4:1 hexane-methylene chloride solvent mixture to yield in order of elution 1.6 mg of unreacted 3 (5%), 7.7 mg of colorless Ir2(CO)6(GePh3)2(μ-GePh2), 4 (31% yield), 0.4 mg of H2Ir2(CO)4(GePh3)2(μ-GePh2)2, 5 (0.4%), and 1.1 mg of orange Ir2(CO)8[μ-Ph2Ge(OH)GePh2](GePh2)(GePh3)2(μ-H), 6 (4% yield). Spectral data for 4: IR νCO (cm-1 in CH2Cl2): 2102 (w), 2047 (m), 2029 (vs). 1H NMR (CDCl3, in ppm): δ 6.60-8.18 (m, 30H, Ph). Mass spectrum: ESMS showed the parent ion at m/z 1387. Spectral data for 5: IR νCO (cm-1 in CH2Cl2): 2071 (w), 2031 (vs). 1H NMR (CDCl3, in ppm): δ 6.89-7.59 (m, 50H, Ph), -8.59 (s, 2H, hydride). Mass spectrum: EI-MS showed the parent ion at m/z 1560. Spectral data for 6: IR νCO (cm-1 in CH2Cl2): 2085 (vw), 2035 (w), 2014 (vs), 1978 (m). 1H NMR (CDCl3, in ppm): δ 6.89-7.59 (m, 50H, Ph), 4.36 (s, 1H, OH), -9.74 (s, 1H, hydride). Mass spectrum: Negative ion MS showed the parent ion Mþ at m/z = 1803. Thermal Decomposition of 3 under H2. A 44.7 mg (0.050 mmol) amount of 3 was dissolved in 12 mL of toluene in a 100 mL three-neck flask. The solution was refluxed for 3 h under H2. The solvent was then removed, and the residue was separated by TLC using a 4:1 hexane-methylene chloride solvent mixture to yield in order of elution 7.5 mg of unreacted 3 (17%) and 10.8 mg of colorless 5 (27%). Thermal Decomposition of 3 under CO. A 47.0 mg (0.053 mmol) amount of 3 was dissolved in 12 mL of toluene in a 100 mL three-neck flask. The solution was refluxed for 10 h under a CO atmosphere. The solvent was then removed, and the residue was separated by TLC using a 4:1 hexane-methylene chloride solvent mixture to yield in order of elution 3.3 mg of unreacted 3 (7%), 14.8 mg of colorless 4 (40% yield), 0.4 mg of 5 (0.1%), and 1.5 mg of orange 6 (3%). Reaction of 4 with H2GePh2. An 11.7 mg (0.008 mmol) amount of Ir2(CO)6(μ-GePh2)(GePh3)2 was dissolved in benzene in a 100 mL three-neck flask. To this solution was added 3.2 mg (0.0139 mmol) of H2GePh2, and the solution was refluxed for 10 h under N2. The solvent was then removed in vacuo, and the residue was separated by TLC using a 4:1 hexane-methylene chloride solvent mixture to yield in order of elution 1.4 mg of H2Ir2(CO)4(μ-GePh2)(GePh2H)2, 7 (12% yield), 1.0 mg of 5 (8%), and 1.4 mg of 6 (9%). Spectral data for 7: IR νCO (cm-1 in CH2Cl2): 2075 (w), 2036 (vs). 1H NMR (CDCl3, in ppm): δ 7.14-7.50 (m, 40H, Ph), 5.78 (s, 2H, GeH), -9.24 (s, 2H, hydride). Crystallographic Analyses. Colorless single crystals of 1 and 5 and pale yellow crystals of 3 suitable for X-ray diffraction were obtained by slow evaporation of solvent from solutions in methylene chloride-hexane solvent mixtures at room temperature. Single crystals of the colorless 2, 4, and 7 and yellow 6 suitable for X-ray diffraction were obtained by slow evaporation of solvent from solutions in methylene chloride-hexane solvent mixtures at -20 °C. Each data crystal was glued onto the end of a thin glass fiber. X-ray intensity data were measured using a Bruker SMART APEX CCD-based diffractometer using Mo KR radiation (λ = 0.71073 A˚). The raw data frames were integrated with the SAINTþ program using a narrow-frame integration algorithm.10 Corrections for Lorentz and polarization (10) SAINTþ, version 6.2a; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2001.
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Table 1. Crystallographic Data for Compounds 1-7
empirical formula fw cryst syst lattice params a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) space group Z value Fcalc (g/cm3) μ(Mo KR) (mm-1) temperature (K) 2θmax (deg) no. obsd (I > 2σ(I)) no. params goodness of fit GOFa max. shift in cycle residualsa: R1; wR2 absorp corr max./min. largest peak in final diff map (e-/A˚3) 4
1
2
3
IrGeO2C28H27 660.29 monoclinic
IrSnO2C28H27 706.39 monoclinic
IrGe2O3C39H31 885.02 triclinic
9.1269(4) 15.9576(7) 16.6473(7) 90.00 94.507(1) 90.00 2417.07(18) P21/n 4 1.814 6.766 294(2) 56.64 6033 397 1.065 0.004 0.0173, 0.0413 multiscan 1.000/0.600 0.638
9.3637(7) 15.9094(12) 16.8632(13) 90.00 94.597(2) 90.00 2504.0(3) P21/n 4 1.874 6.328 294(2) 43.76 6217 289 1.032 0.001 0.0443, 0.0741 multiscan 1.000/0.630 1.399
10.3420(9) 12.6458(11) 14.4925(13) 71.546(2) 75.118(2) 82.052(2) 1734.2(3) P1 (#2) 2 1.695 5.585 293(2) 87.82 8556 410 1.069 0.019 0.0512, 0.0822 multiscan 1.000/0.645 1.025
5
6
7
empirical formula Ir2Ge3O6C54H40 Ir2Ge4O4C64H52 Ir2Ge5O5C76H62 3 2CH2Cl2 3 H2O Ir2Ge4O4C52H44 fw 1471.96 1559.82 1989.47 1407.63 cryst syst monoclinic triclinic triclinic monoclinic lattice params a (A˚) 14.2765(9) 9.9572(9) 14.2370(12) 10.3589(7) b (A˚) 21.9011(14) 11.2423(10) 14.3558(12) 20.6075(14) c (A˚) 17.2919(11) 13.4482(12) 20.2408(17) 12.0951(8) R (deg) 90.00 76.579(2) 106.007(2) 90.00 β (deg) 98.102(1) 74.859(2) 91.639(2) 102.470(2) γ (deg) 90.00 87.433(2) 106.752(2) 90.00 5352.7(6) 1413.3(2) 3781.4(5) 2521.0(3) V (A˚3) P1 (#2) P1 (#2) P21/n (#14) space group P21/c (#14) Z value 4 1 2 2 1.827 1.833 1.747 1.854 Fcalc (g/cm3) 6.767 6.837 5.656 7.654 μ (Mo KR) (mm-1) temperature (K) 294(2) 294(2) 294(2) 294(2) 56.54 56.58 56.56 56.42 2θmax (deg) no. obsd (I > 2σ(I)) 10 950 7001 18 742 5150 no. params 613 338 872 288 1.128 1.125 1.035 1.191 goodness of fit GOFa max. shift in cycle 0.002 0.001 0.002 0.002 a 0.0377, 0.0884 0.0455, 0.1031 0.0409, 0.1048 0.0448, 0.0995 residuals : R1; wR2 absorption multiscan multiscan multiscan multiscan correction, max./min. 1.000/0.640 1.000/0.670 1.000/0.632 1.000/0.636 1.449 2.976 3.698 1.950 largest peak in - ˚ 3 final diff map (e /A ) P P P P P a R1 = hkl(||Fobs| - |Fcalc||)/ hkl|Fobs|; wR2 = [ hklw(|Fobs| - |Fcalc|)2/ hklwFobs2]1/2, w = 1/σ2(Fobs); GOF = [ hklw(|Fobs| - |Fcalc|)2/ (ndata - nvari)]1/2.
effects were also applied with SAINTþ. 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 leastsquares on F2 using the SHELXTL software package.11 All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms on the ligands were placed in geometrically idealized positions and included as standard riding atoms during the least-squares refinements. Crystal data, data collection parameters, and results of the analyses are listed in Table 1. (11) Sheldrick, G. M. SHELXTL, version 6.1; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 1997.
Compounds 1, 2, and 7 crystallized in the monoclinic crystal system. The systematic absences in the intensity data identified the unique space group P21/n. The crystals of 1 and 2 contain one independent formula equivalent of the complex in the asymmetric unit. For compound 1 all the hydrogen atoms were crystallographically located (diff Fourier). The crystal of 7 contains one-half formula equivalent of the complex in the asymmetric unit. The hydride ligand was located (diff Fourier) and refined in the analysis, and the other hydrogen atoms were included as standard riding atoms. Compound 4 crystallized in the monoclinic crystal system. The systematic absences in the intensity data identified the unique space group P21/c. For this compound there is one formula equivalent of the complex with one molecule of CH2Cl2 from the crystallization solvent included in the asymmetric unit. Compounds 3, 5, and
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7 crystallized in the triclinic crystal system. The space group P1 was assumed and confirmed by the successful refinement and solution of the structures. For 3 there is one formula equivalent of the complex present in the asymmetric unit. The hydride ligand was located (diff Fourier) and refined in the analysis. For compound 5, the molecule lies positioned on a crystallographic center of symmetry; only one-half formula equivalent of the complex is present in the asymmetric unit. The one independent hydride was located (diff Fourier) and refined in the analysis. The positions of the other hydrogen atoms were calculated on the basis of idealized geometry and included as standard riding atoms. For compound 6, the asymmetric unit contains one complete formula equivalent of the molecule with two formula equivalents of CH2Cl2 from the crystallization solvent and one molecule of H2O. The hydrogen atoms in the H2O molecule were included as standard riding atoms, and they were refined on their positional parameters with fixed isotropic thermal parameters and geometric restraints (i.e., the O-H bond distances were fixed at 0.80 A˚). Molecular Orbital Calculations. All molecular orbital calculations reported herein were performed using the Fenske-Hall method.12 The calculations were performed utilizing a graphical user interface developed13 to build inputs and view outputs from stand-alone Fenske-Hall and MOPLOT2 binary executables.14 Contracted double-ζ basis sets were used for the Ir 4d, Ge 4p, and C and O 2p atomic orbitals. The Fenske-Hall scheme is a nonempirical approximate method that is capable of calculating molecular orbitals for very large transition metal systems. For these calculations, the input structures were obtained from the positional parameters from the crystal structure analyses. The structures were not optimized in these calculations. The phenyl groups on the GePh3 and GePh2 ligands were replaced by hydrogen atoms to give GeH3 and GeH2 ligands in the model.
Results and Discussion When a solution containing [Ir(COD)Cl]2 and HGePh3 in hexane solvent was treated with a solution of BuLi under a purge of CO for 15 min, the new compound Ir(COD)(CO)2GePh3, 1, was formed in 23% yield. Compound 1 was characterized by a combination of IR, 1H NMR, and singlecrystal X-ray diffraction analyses. An ORTEP diagram of the molecular structure of 1 is shown in Figure 1. The iridium atom in 1 is pentacoordinate with four ligands. The stucture can be viewed as a trigonal bipyramid. The COD ligand is bidentate; one of the olefinic groups is coordinated in one of the equatorial sites of the trigonal bipyramid; the other olefinic group is coordinated in one of the axial sites. There are two linear terminal carbonyl ligands that occupy the two remaining equatorial sites, and there is one GePh3 ligand that occupies the second axial site. A trigonal-bipyramidal structure was also observed for the compound Rh(CO)4(GePh3).8 The Ir(1)-Ge bond distance, Ir1-Ge1 = 2.4693(2) A˚, is very similar to the Ir-Ge bond distances in the pentacoordinate anionic complex [Ir(CO)3(GePh3)2]-, 2.4922(8) and (12) (a) Hall, M. B.; Fenske, R. F. Inorg. Chem. 1972, 11, 768–775. (b) Webster, C. E.; Hall, M. B. In Theory and Applications of Computational Chemistry: The First Forty Years; Dykstra, C., Ed.; Elsevier, Amsterdam, 2005; Chapter 40, pp 1143-1165. (13) Manson, J.; Webster, C. E.; Hall, M. B. JIMP, development version 0.1.v117 (built for Windows PC and Redhat Linux); Department of Chemistry, Texas A&M University: College Station, TX; http://www.chem. tamu.edu/jimp/, accessed July 2004. (14) MOPLOT2 for orbital and density plots from linear combinations of Slater or Gaussian type orbitals, version 2.0; Lichtenberger, D. L., Department of Chemistry, University of Arizona: Tucson, AZ, 1993. (15) Allen, J. M.; Brennessel, W. W.; Buss, C. E.; Ellis, J. E.; Minyaev, M. E.; Pink, M.; Warnock, G. F.; Winzenburg, M. L.; Young, V. G., Jr. Inorg. Chem. 2001, 40, 5279–5284.
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Figure 1. ORTEP diagram of the molecular structure of Ir(CO)2(COD)(GePh3), 1, showing 30% thermal ellipsoid probability. Selected bond distances (A˚) and angles (deg) are as follows: Ir1-Ge1 = 2.4693(2), Ir1-C12 = 1.904(2), Ir1-C11 = 1.913(3), Ir1-C17 = 2.182(2), Ir1-C18 = 2.193(2), Ir1-C13 = 2.325(2), Ir1-C14 = 2.345(2); C12-Ir1-C11 = 107.50(12), C12-Ir1Ge1 = 85.42(7), C11-Ir1-Ge1 = 87.28(8).
2.4932(8) A˚,15 and also similar to that found in the cluster compounds Ir4(CO)8(GePh3)2(μ-GePh2)4, 8, 2.5246(11) A˚, and Ir3(CO)5(GePh3)(μ-H)(μ-GePh2)3(μ3-GePh), 9, 2.4850(8) A˚.9 The iridium atom in 1 has a þ1 oxidation state and has an 18-electron configuration. The analogous tin compound Ir(COD)(CO)2SnPh3, 2, was obtained in 13% yield when a mixture of [Ir(COD)Cl]2 and HSnPh3 in a solution in hexane solvent was treated with BuLi under a purge of CO. Compound 2 was also characterized crystallographically. The structure of 2 is virtually identical to that of 1 except for the replacement of the germanium atom of 1 with a tin atom. The Ir-Sn bond distance of 2.6216(5) A˚ is significantly longer than the Ir-Ge distance in 1, but is slightly shorter than the Ir-Sn distances, 2.6736(9), 2.6981(11), 2.6888(10) A˚, found to the three SnPh3 ligands in the triiridium cluster complex Ir3(CO)6(SnPh3)3(μ-SnPh2)3.16 When [Ir(COD)Cl]2 and HGePh3 were allowed to mix with CO in the absence of BuLi, the compound HIr(CO)3(GePh3)2, 3, was obtained instead in 46% yield. Compound 3 was characterized crystallographically, and an ORTEP diagram of its molecular structure is shown in Figure 2. Compound 3 contains six ligands, one hydride, three carbonyls, and two GePh3 groups, arranged in an octahedral-type geometry. The bulky GePh3 ligands lie trans to one another, Ge2-Ir1-Ge1 = 169.26(2)o. The Ir-Ge bond distances, Ir1-Ge1 = 2.5381(7) A˚, Ir1-Ge2 = 2.5361(7) A˚, are slightly longer than that found in 1 and in [Ir(CO)3(GePh3)2]-.15 The hydride ligand was located and refined in the analysis, Ir(1)-H(1) = 1.54(6) A˚. This distance is shorter than the Ir-H distance, 1.72(8) A˚, found in the iridium-germylene complex [Ir{ GeCl(NR2)N(R)SiMe2CH2}(CO)2H{Ge(NR2)2}] (R = SiMe3),17 but the errors are large in both measurements and the difference is probably not significant. The hydride ligand exhibits the usual high-field resonance shift in the 1H NMR (16) Adams, R. D.; Captain, B.; Smith, J. L., Jr.; Hall, M. B.; Beddie, C. L.; Webster, C. E. Inorg. Chem. 2004, 43, 7576–7578. (17) Hawkins, S. M.; Hitchcock, P. B.; Lappert, M. F.; Rai, A. K. J. Chem. Soc., Chem. Commun. 1986, 1689–1690.
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Figure 2. ORTEP diagram of the molecular structure of HIr(CO)3(GePh3)2, 3, showing 30% thermal ellipsoid probability. Selected bond distances (A˚) and angles (deg) are as follows: Ir1-Ge1 = 2.5381(7), Ir1-Ge2 = 2.5361(7), Ir1-C11 = 1.901(7), Ir1-C13 = 1.915(7), Ir1-C12 = 1.937(7), Ir1-H1 = 1.54(6); Ge2-Ir1-Ge1 = 169.26(2).
spectrum, δ = -11.82. Compound 3 was also obtained in 27% yield from the reaction of 1 with HGePh3 in the presence of CO in 48 h at room temperature. The oxidation state for the iridium atom is formally þ3 in 3, and it has an 18-electron configuration. The increase in the oxidation state is brought about by the formal oxidation-addition of one equivalent of the HGePh3 to the iridium atom. When a solution of 3 in toluene solvent was heated to reflux (110 °C) for 3.5 h under nitrogen, three new compounds were formed: Ir2(CO)6(GePh3)2(μ-GePh2), 4 (31% yield); H2Ir2(CO)4(GePh3)2(μ-GePh2)2, 5 (0.4% yield); and Ir2(CO)8[μPh2Ge(OH)GePh2](GePh2)(GePh3)2(μ-H), 6 (4% yield). The yield of 5 was increased to 27% when the thermal treatment was performed under an atmosphere of hydrogen, and the yield of 4 was increased to 40% when the thermal treatment was preformed under an atmosphere of CO. All three compounds were characterized by a combination of IR, 1H NMR, and singlecrystal X-ray diffraction analyses. An ORTEP diagram of the molecular structure of 4 is shown in Figure 3. Compound 4 contains two mutually bonded iridium atoms that are bridged by a GePh2 ligand. The Ir-Ir bond distance, 2.9005(3) A˚, is similar to the GePh2-bridged Ir-Ir distances, 2.9344(4), 2.8971(4), and 2.9135(4) A˚, found in the triiridium complex Ir3(CO)6(GePh3)3(μ-GePh2)3, 10.9 Each iridium atom contains three linear terminal carbonyl ligands and one GePh3 ligand. The GePh3 ligands lie approximately trans to the Ir-Ir bond, Ge1-Ir1-Ir2=159.520(18)o, Ge3-Ir2Ir1 = 165.413(18)o. The Ir-Ge bond distances to the GePh3 ligands, Ir1-Ge1 = 2.5232(7) A˚, Ir2-Ge3 = 2.5233(7) A˚, are slightly longer than those to the bridging GePh2 ligand, Ir1-Ge2 = 2.5066(7) A˚, Ir2-Ge2 = 2.5076(7) A˚. The iridium atoms in 3 have a formal þ2 oxidation state. Both iridium atoms have 18-electron configurations. Compound 4 is structurally analogous to the related rhodium compound Rh2(CO)6(GePh3)2(μ-GePh2), which we recently obtained from the reaction of Rh(CO)4GePh3 with HGePh3.8 The metal-metal bonding in Rh2(CO)6(GePh3)2(μ-GePh2) was analyzed by the Fenske-Hall method.8 In the solid state, compound 5 lies on a crystallographic center of symmetry; thus the molecular structure is rigorously centrosymmetric. An ORTEP diagram of the molecular structure of 5 is shown in Figure 4. Compound 5 contains two
Adams and Trufan
Figure 3. ORTEP diagram of the molecular structure of Ir2(CO)6(GePh3)2(μ-GePh2), 4, showing 30% thermal ellipsoid probability. Selected bond distances (A˚) and angles (deg) are as follows: Ir1-Ir2 = 2.9005(3), Ir1-Ge2 = 2.5066(7), Ir1Ge1 = 2.5232(7), Ir2-Ge2 = 2.5076(7), Ir2-Ge3 = 2.5233(7); Ge1-Ir1-Ir2 = 159.520(18), Ge3-Ir2-Ir1 = 165.413(18).
Figure 4. ORTEP diagram of the molecular structure of H2Ir2(CO)4(GePh3)2(μ-GePh2)2, 5, showing 30% thermal ellipsoid probability. Selected bond distances (A˚) and angles (deg) are as follows: Ir1-Ge1 = 2.4739(7), Ir1-Ge2 = 2.4975(7), Ir1Ge1 = 2.5504(7), Ir1-Ir1 = 2.9257(5), Ir1-H1 = 1.74(4), Ge1 3 3 3 H1 = 2.16(4); Ge1-Ir1-Ge2 = 114.29(2), Ge1-Ir1Ge1* = 108.79(2), Ge2-Ir1-Ge1* = 136.91(2), Ge2-Ir1Ir1* = 169.90(2).
mutually bonded iridium atoms that are bridged by two GePh2 ligands. The Ir-Ir bond distance, 2.9257(5) A˚, is slightly longer than that in 4. Each iridium atom contains two trans-positioned linear terminal carbonyl ligands and one GePh3 ligand that lies approximately trans to the Ir-Ir bond, Ge2-Ir1-Ir1* = 169.90(2)o. The Ir-Ge bond distance to the GePh3 ligands, Ir1-Ge2 = 2.4975(7) A˚, is slightly longer than those to the GePh3 ligands in 1 and 4. The Ir-Ge distances to the bridging GePh2 ligand are significantly different, Ir1-Ge1 = 2.4739(7) A˚, Ir1-Ge1* = 2.5504(7) A˚. The difference is probably due to the presence of a hydride ligand H(1) on the iridium atom that lies in the Ir2Ge2 plane and makes a close approach to the bridging GePh2 ligand. In fact, the hydride ligand could be described as a semibridging ligand to the germanium atom, Ir1-H1 = 1.74(4) A˚, Ge1* 3 3 3 H1 = 2.16(4) A˚. It is known that bridging hydride ligands generally increase the length of
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Figure 5. ORTEP diagram of the molecular structure of Ir2(CO)8[μ-Ph2Ge(OH)GePh2](GePh2)(GePh3)2(μ-H) 3 H2O, 6 3 H2O, showing 30% thermal ellipsoid probability. Selected bond distances (A˚) and angles (deg) are as follows: Ir1-Ge1 = 2.4974(6), Ir1Ge2 = 2.4930(9), Ir1-Ge5 = 2.4525(6), Ir1-Ir2 = 2.9682(3), Ir2Ge4 = 2.4608(6), Ir2-Ge3 = 2.5088(6), Ir2-Ge2 = 2.5935(9), Ir2-H1 = 2.04(8), Ge2-H1 = 2.01(8), Ge4-O1 = 1.908(4), Ge5-O1 = 1.911(4), O1-H2 = 0.73(6); Ge4-O1-Ge5 = 130.7(2), O1-Ge4-Ir2 = 108.62(12), O1-Ge5-Ir1 = 103.32(11).
the associated metal-metal bonds.18 We have also observed a significant lengthening of the hydride-bridged Ir-Ge bond to the triply bridging GePh ligand in compound 9.9 As expected, the hydride ligand exhibits a high-field resonance shift, δ = -8.59, in the 1H NMR spectrum of 5. An ORTEP diagram of the molecular structure of 6 is shown in Figure 5. Compound 6 is similar to 5, but it contains a bridging Ph2GeOHGePh2 ligand in place of one of the hydride ligands and one of the bridging GePh2 ligands. We recently observed and structurally characterized a similar Ph2GeOHGePh2 ligand in the complex Re2(CO)8[μPh2GeO(H)GePh2](μ-H).19 Each germanium atom in 6 is bonded to one iridium atom to form a five-membered heterocyclic ring. There is an OH group positioned between the two GePh2 groups in this ligand, Ge4-O1 = 1.908(4) A˚, Ge5-O1 = 1.911(4) A˚, Ge4-O1-Ge5 = 130.7(2)o. The hydrogen atom H(2) on the oxygen atom O(1) was located and refined in the structural analysis, O1-H2 = 0.73(6) A˚, and a resonance at δ = 4.36 (s, 1H) in the 1H NMR spectrum is attributed to this hydrogen atom. The Ir-Ir bond distance, 2.9682(3) A˚, is slightly longer than the Ir-Ir distance found in 5, which contains two GePh2 bridging ligands. Each iridium atom contains two linear terminal carbonyl ligands and one GePh3 ligand. There is one GePh2 bridging ligand and one hydride ligand H(1) in 6. The hydride ligand in 6 is slightly closer to the germanium atom Ge(2) than those in 5, Ge2-H1 = 2.01(8) A˚, and we have formulated it as a bridge across the Ir(2)-Ge(2) bond, Ir2-H1 = 2.04(8) A˚. This hydride ligand exhibits the classical high-field resonance shift in the 1H NMR spectrum, δ = -9.74 (s, 1H). As in 5, the H(1)-bridged Ir-Ge bond is longer, Ir2-Ge2 = 2.5935(9) A˚, than the unbridged Ir-Ge bond, Ir1-Ge2 = 2.4930(9) A˚. Interestingly, (18) (a) Bau, R.; Drabnis, M. H. Inorg. Chim. Acta 1997, 259, 27–50. (b) Teller, R. G.; Bau, R. Struct. Bonding 1981, 41, 1–82. (19) Adams, R. D.; Captain, B.; Hollandsworth, C. B.; Johansson, M.; Smith, J. L., Jr. Organometallics 2006, 25, 3848–3855.
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in the crystal, a molecule of H2O was found cocrystallized with the complex. This water molecule was located proximate to the OH group in the Ph2GeOHGePh2 group. Its oxygen atom O(2) lies only 2.65(1) A˚ from the bridging oxygen atom O(1) and is consistent with a strong hydrogen-bonding interaction.20 The dashed line shown in Figure 4 between O(2) and H(2) is drawn to represent this hydrogen-bonding interaction, O(2) 3 3 3 H(2) = 1.93(9) A˚. The oxygen atom O(1) in the Ph2GeOHGePh2 ligand is formally positively charged. If viewed overall as uncharged, then the Ph2GeOHGePh2 ligand serves as a three-electron donor to the two iridium atoms. Thus, in the presence of an Ir-Ir single bond, each iridium atom obtains an 18-electron configuration. A systematic synthesis to 6 is not yet available. It seems likely that 6 is a byproduct formed by a reaction with adventitious trace quantities of H2O that may have been present in the reaction solvents. In an effort to find an alternative route to 5, the reaction of 4 with H2GePh2 was performed. Indeed, some 5 (8% yield) and 6 (9% yield) were formed, but surprisingly a new compound, H2Ir2(CO)4(μ-GePh2)(GePh2H)2, 7, was obtained in 12% yield. Compound 7 was also characterized crystallographically. As with 5, the complex lies on a crystallographic center of symmetry and the molecule is rigorously centrosymmetrical in the solid state. An ORTEP diagram of the molecular structure of 7 is shown in Figure 6. While there are many similarities between the structures of 5 and 7, there are also some important differences. Both compounds contain two iridium atoms bridged by two GePh2 ligands, and each iridium atom contains one hydride ligand, two linear terminal carbonyl ligands, and a terminal germanium ligand, but in 7 that terminal germanium ligand is a GePh2H ligand instead of a GePh3 ligand. The Ir-Ir bond distance in 7 is slightly longer than that in 5, Ir1-Ir1* = 2.9556(5) A˚. The Ir-Ge distance to the GePh2H ligand, Ir1-Ge1 = 2.5129(8) A˚, is similar to that to the GePh3 ligand in 5. Interestingly, unlike the structure of 5, the Ir-H bond in 7 lies perpendicular to the Ir2Ge2 plane, Ir1-H1 = 1.71(6) A˚. The hydride ligand exhibits a similar high-field resonance shift, δ = -9.24 (s, 2H), in the 1H NMR spectrum. The resonance of the germanium-bonded hydrogen atom of the GePh2H ligand lies at δ = 5.78. The CO ligands on each iridium atom that were trans-positioned in 5 are cis-positioned in 7; one lies in the Ir2Ge2 plane and the other is perpendicular to the Ir2Ge2 plane and trans to the hydride ligand. As a result of the increase in steric crowding in the Ir2Ge2 plane, the terminal GePh2H ligand shifts to a position that is nearly trans to one of the Ir-Ge bonds to the bridging GePh2 ligand, Ge1-Ir1-Ge2* = 170.93(3)o. This change is possible because the GePh2H ligand is less bulky than the GePh3 ligand found in 5. Interestingly, the Ir-Ge bond distances to the bridging GePh2 ligand in 7 are also significantly different, Ir1-Ge2 = 2.4478(7) A˚, Ir1-Ge2* = 2.5634(7) A˚, with the bond trans to the GePh2H ligand being the longer one. We think this is not an effect related to the hydride ligand, but is instead due to the change of position of the terminal GePh2H ligand in the Ir2Ge2 plane; that is, one Ir-Ge bond is trans to the GePh 2H ligand and the other is trans to a CO ligand. Similar asymmetrically bridged GePh2 ligands were observed in the structure of the platinum compound Pt2(CO)2(GePh3)2(μ-GePh2)2, 11, which contains no hydride ligands at all. 7 As in 5, (20) Gilli, P.; Bertolasi, V.; Ferretti, V.; Gilli, G. J. Am. Chem. Soc. 1994, 116, 909–915.
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Figure 7. Selected Fenske-Hall molecular orbital diagrams for 5 showing the Ir-Ir and Ir-Ge orbital interactions and their associated calculated energies in eV. Figure 6. ORTEP diagram of the molecular structure of H2Ir2(CO)4(μ-GePh2)(GePh2H)2, 7, showing 30% thermal ellipsoid probability. Selected bond distances (A˚) and angles (deg) are as follows: Ir1-Ir1* = 2.9556(5), Ir1-Ge2 = 2.4478(7), Ir1Ge1 = 2.5129(8), Ir1-Ge2* = 2.5634(7), Ir1-H1 = 1.71(6), Ge1-H2 = 1.55(7); Ir1-Ge2-Ir1 = 72.24(2), Ge2-Ir1Ge1 = 79.69(2), Ge2-Ir1-Ge2* = 107.76(2), Ge1-Ir1-Ge2* = 170.93(3).
each of the iridium atoms in 7 contains an 18-electron configuration.
In order to understand the bonding in 5 and 7, FenskeHall molecular orbital calculations were performed.12 To simplify the calculations, the phenyl groups on the GePh3 and GePh2 ligands were replaced by hydrogen atoms to give GeH3 and GeH2 ligands. The molecular symmetry of 5 is approximately C2h, and that of 7 is Ci. Molecular orbital diagrams of the lowest unoccupied molecular orbital (LUMO) and five selected occupied molecular orbitals of 5 are shown in Figure 7. The LUMO in 5 is a σ-antibonding orbital between the two metal atoms. The highest occupied molecular orbital (HOMO) at -9.79 eV is a combination of Ir-Ir bonding and Ir-Ge bonding. The HOMO-1 shows bonding between the iridium atom and the hydride ligands and the Ir-Ge interactions to the bridging GePh2 ligand trans to the hydride ligands. The Ir-Ge interactions to the terminal GePh3 ligand are represented by the HOMO-7. The HOMO-9 shows substantial direct Ir-Ir bonding, and the HOMO-10 shows delocalized Ir-Ge bonding to the two bridging GePh2 ligands. Molecular orbital diagrams of the LUMO and five selected occupied molecular orbitals of 7 are shown in Figure 8. The LUMO and HOMO in 7 are quite similar to the LUMO and HOMO in 5. The HOMO at -10.42 eV is a combination of Ir-Ir bonding and Ir-Ge bonding. The HOMO-1 in 7 lies in the plane of the iridium atoms and the bridging GePh2 ligands and includes interactions to the terminal GeHPh2 ligands instead of the hydride ligands as in 5 since the hydrides are out of the Ir2Ge2 plane in 7. Substantial direct Ir-Ir interactions are seen in the HOMO-8. The bonding to the hydride ligands in 7 is shown by the HOMO-11, which
Figure 8. Selected Fenske-Hall molecular orbital diagrams for 7 showing the Ir-Ir and Ir-Ge orbital interactions and their associated calculated energies in eV.
shows that the structure having the hydride ligands in positions perpendicular to the Ir2Ge4 plane is greatly stabilized over the structure exhibited 5, where the hydride ligands lie in the Ir2Ge4 plane. Accordingly, we think the structure exhibited by 5 is adopted largely for steric reasons; that is, the bulky GePh3 ligands in 5 force the CO ligands out of their preferred position in the Ir2Ge4 plane and the hydride ligands then occupy the in-plane sites in order to minimize the unfavorable steric interactions. The delocalized bonding between the Ir atoms and the bridging GePh2 ligands is shown by HOMO-12. HOMO-12 is similar to HOMO-10 in 5.
Summary A summary of the reactions reported here is shown in Scheme 1. Several new iridium-germanium compounds and one iridium-tin compound have been obtained from reactions of the chloro-bridged dimer, [Ir(COD)Cl]2, with HGePh3 and HSnPh3. Treatment of HGePh3 with BuLi is known to generate the anion [GePh3]-.21 This approach has been used here to split the chloro-bridged dimer, [Ir(COD)Cl]2, and displace the chloride ligand to synthesize the mononuclear iridium complex 1. By a similar treatment using HSnPh3 and BuLi with [Ir(COD)Cl]2, it has been possible to prepare compound 2, the tin homologue of 1. Treatment of 1 with HGePh3 yielded the (21) Castel, A.; Riviere, P.; Saint-Roch, B.; Stage, J.; Malrieu, J. P. J. Organomet. Chem. 1983, 247, 149–160.
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Scheme 1
bis-GePh3 compound 3, but it was subsequently shown that compound 3 could be obtained in a better yield in one step by the reaction of [Ir(COD)Cl]2 with HGePh3 under CO without the addition of BuLi. When heated, compound 3 was transformed into the diiridium complex 4 simply by heating to 110 °C. Two other products, 5 and 6, were also formed but in very low yields. Compound 5 contains two hydride ligands, and its yield was increased substantially when 3 was heated to 110 °C under an atmosphere of hydrogen. The yield of 4 was increased slightly when 3 was heated to 110 °C under an atmosphere of CO. We recently obtained the rhodium homologue of 4 from the reaction of Rh(CO)4GePh3 with HGePh3.8 In an attempt to make 5 independently from the reaction of 4 with H2GePh2, the new compound 7 was obtained. Compound 7 is similar to 5 but contains GeHPh2 ligands instead of the GePh3 ligands.
The hydride ligands in 7 have changed their coordination position relative to those in 5, most likely due to steric differences between the GeHPh2 and GePh3 ligands. We have not yet been able to prepare any of the tin homologues of compounds 3-7. It is hoped that these new IrGe complexes might serve as precursors to new catalysts for hydrogenation or hydrocarbon-based reforming processes.1-4
Acknowledgment. This research was supported by the National Science Foundation under Grant No. CHE0743190. We thank the USC NanoCenter for partial support of this work. Supporting Information Available: CIF tables for the structural analyses of compounds 1-7. This material is available free of charge via the Internet at http://pubs.acs.org.
