Sol−Gel Processed Diamine(diphosphine)ruthenium(II) Complexes for the Catalytic Hydrogenation of...

Sol-Gel Processed Diamine(diphosphine)ruthenium(II) Complexesfor the Catalytic Hydrogenation of r,â-Unsaturated Ketones1,2

Da-Yong Wu,† Ekkehard Lindner,*,† Hermann A. Mayer,† Zheng-Jin Jiang,‡

Venkata Krishnan,§ and Helmut Bertagnolli§

Institut fur Anorganische Chemie and Institut fu¨r Organische Chemie, UniVersitat Tubingen, Auf derMorgenstelle 18, 72076 Tu¨bingen, Germany, and Institut fu¨r Physikalische Chemie, UniVersitat Stuttgart,

Pfaffenwaldring 55, 70569 Stuttgart, Germany

ReceiVed January 24, 2005. ReVised Manuscript ReceiVed June 2, 2005

Diphenyldiphosphinopropane4T0, provided with a T0-silyl functionalized (CH2)6-spacer in the symmetric2-position of the C3 bridge, was obtained via an improved synthetic route in high yields, starting from8-chloro-7-chloromethyl-1-octene (1) (Scheme 1). Reaction of4T0 with trans-RuCl2(NBD)Py2 in CH2Cl2resulted in the formation of the corresponding (diphos)ruthenium(II) complex5T0 (Scheme 2), which,by treatment with 1,2-diaminopropane, was transformed to the T0-silyl functionalized diamine-(diphosphine)ruthenium(II) complex6T0. In the presence of four different amounts of the co-condensationagent MeSi(OMe)3, 6T0 was subjected to a sol-gel process (Scheme 3). The resulting inorganic/organichybrid materialsX1-X4 [6T0/MeSi(OMe)3 ) 1:10/15/20/50] were characterized by31P and29Si solid-state NMR and EXAFS spectroscopy, as well as by EDX and BET measurements. It was confirmed thatthe integrity of the organometallic centers inX1-X4 is maintained compared to the monomeric counterpart6T0. The materialsX1-X4 proved to be catalytically active in the direct hydrogenation of the modelsubstratetrans-4-phenyl-3-butene-2-one. With a conversion rate of 100% and a selectivity to the alcoholA (Scheme 4) of approximately 91%, the interphase catalystX1 showed the best performance. It couldbe recovered eight times without detectable leaching and remarkable deactivation. The catalytic activitiesof X1 and monomeric6T0 were compared with each other.

Introduction

The hydrogenation of differently substituted carbonylcompounds to the respective alcohols is among the mostimportant and applied processes in organic chemistry.3-5

Recently, Noyori et al. discovered a system of ruthenium(II)complexes containing phosphine or diphospine as well as1,2-diamine ligands which, in the presence of a base and2-propanol, proved to be excellent catalysts for the hydro-genation of ketones under mild conditions.6 Subsequently,by the same group, chiral ruthenium(II) complexes wereintroduced for the asymmetric hydrogenation of functional-ized ketones.7,8 The mechanism of this hydrogenation hasbeen thoroughly studied by several authors.7b,c,9-12

To alleviate the separation of the catalyst from the reac-tion mixture for recovery and reuse, it is indispensable toanchor Noyori’s catalysts to a polymeric matrix. How-ever, so far, only a few investigations to address this pointhave been published.13-17 Noyori et al. reported on thelinkage of BINAP(dichloro)-1,2-diphenylethylenediamine-

* To whom correspondence should be addressed. E-mail:[email protected]. Tel: 0049-7071-29-72039. Fax:0049-7071-29-5194.

† Institut fur Anorganische Chemie, Universita¨t Tubingen.‡ Institut fur Organische Chemie, Universita¨t Tubingen.§ Universitat Stuttgart.

(1) Dedicated to Professor William C. Kaska on the occasion of his 70thbirthday.

(2) Supported Organometallic Complexes Part 40. Part 39: see ref 21f(Warad, I.; Eichele, K.; Mayer, H. A.; Lindner, E.Inorg. Chim. Acta2004, 357, 1847.).

(3) Ramachandran, P. V.; Brown, H. C. Reduction in Organic Synthesis:Recent Advances and Practical Applications.ACS Symp. Ser. 1996,641.

(4) Aramini, A.; Brinchi, L.; Germani, R.; Savelli, G.Eur. J. Org. Chem.2000, 1793.

(5) Handique, J. G.; Purkayashtha, A.; Baruah, J. B.J. Organomet. Chem.2001, 620, 90.

(6) Ohkuma, T.; Ooka, H.; Ikariya, T.; Noyori, R.J. Am. Chem. Soc.1995, 117, 10417.

(7) (a) Noyori, R.; Ohkuma, T.Pure Appl. Chem. 1999, 71, 1493. (b)Noyori, R.; Koizumi, M.; Ishii, D.; Ohkuma, T.Pure Appl. Chem.2001, 73, 227. (c) Noyori, R.; Ohkuma, T.Angew. Chem., Int. Ed.2001, 40, 40. (d) Noyori, R.Angew. Chem., Int. Ed. 2002, 41, 2008.

(8) (a) Ohkuma, T.; Ooka, H.; Hashiguchi, S.; Ikariya, T.; Noyori, R.J.Am. Chem. Soc.1995, 117, 2675. (b) Doucet, H.; Ohkuma, T.; Murata,K.; Yokozawa, T.; Kozawa, M.; Katayama, E.; England, A. F. Ikariya,T.; Noyori, R.Angew. Chem., Int. Ed. 1998, 37, 1703. (c) Ohkuma,T.; Koizumi, M.; Doucet, H.; Pham, T.; Kozawa, M.; Murata, K.;Katayama, E.; Yokozawa, T.; Ikariya, T.; Noyori, R.J. Am. Chem.Soc.1998, 120, 13529. (d) Yamakawa, M.; Ito, H.; Noyori, R.J. Am.Chem. Soc.2000, 122, 1466. (e) Ohkuma, T.; Ishii, D.; Takeno, H.;Noyori, R. J. Am. Chem. Soc.2000, 122, 6510. (f) Ohkuma, T.;Koizumi, M.; Yoshida, M.; Noyori, R.Org. Lett.2000, 2, 1749. (g)Ohkuma, T.; Takeno, H.; Honda, Y.; Noyori, R.AdV. Synth. Catal.2001, 343, 369. (h) Ohkuma, T.; Koizumi, M.; Mun˜iz, K.; Hilt, G.;Kabuto, C.; Noyori, R.J. Am. Chem.Soc. 2002, 124, 6508. (i)Ohkuma, T.; Hattori, T.; Ooka, H.; Inoue, T.; Noyori, R.Org. Lett.2004, 6, 2681.

(9) Hartmann, R.; Chen, P.Angew. Chem., Int. Ed. 2001, 40, 3581.(10) (a) Noyori, R.; Yamakawa, M.; Hashiguchi, S.J. Org. Chem.2001,

66, 7931. (b) Sandoval, C. A.; Ohkuma, T.; Mun˜iz, K.; Noyori, R.J.Am. Chem. Soc.2003, 125, 13490.

(11) Yamanaka, M.; Mikami, K.Organometallics2002, 21, 5847.(12) (a) Abdur-Rashid, K.; Faatz, M.; Lough, A. J.; Morris, R. H.J. Am.

Chem. Soc. 2001, 123, 7473. (b) Abdur-Rashid, K.; Clapham, S. E.;Hadzovic, A.; Harvey, J. N.; Lough, A. J.; Morris, R. H.J. Am Chem.Soc.2002, 124, 15104.

(13) Polborn, K.; Severin, K.Chem. Commun. 1999, 2481.(14) Li, X.; Chen, W.; Hems, W.; King, F.; Xiao, J.Org. Lett. 2003, 5,

4559.

3951Chem. Mater.2005,17, 3951-3959

10.1021/cm0501618 CCC: $30.25 © 2005 American Chemical SocietyPublished on Web 07/01/2005

ruthenium(II) [BINAP ) 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl] precatalysts to a polystyrene resin for theasymmetric hydrogenation of simple ketones.18

For the combination of the advantages of homogeneousand heterogeneous catalysis, several concepts have beenestablished.19 With the aim to develop high-performanceheterogenized catalysts, the idea of chemistry in interphaseshas been recently introduced.19,20 Major drawbacks ofconventional supported catalysts can be overcome with thisprinciple. For the introduction of suitable interphase catalysts,our group has designed and synthesized highly active achiraland chiral 1,2- and 1,3-diamine(ether-phosphine)-21,22 and-(diphenyldiphosphinopropane)ruthenium(II) complexes23 andconducted preliminary tests in the selective hydrogenationof trans-4-phenyl-3-butene-2-one in homogeneous phase.Another investigation was devoted to the heterogenizationof diamine(ether-phosphine)ruthenium(II) complexes.24 Un-fortunately, hemilabile ether-phosphine ligands give rise toleaching problems. Therefore, in this work we present animproved approach in which no leaching could be observed.A T0-silyl functionalized 1,2-diaminopropane(diphenyl-diphosphinopropane)ruthenium(II) complex is introduced, inwhich the chelating diphosphine is attached to a (CH2)6-spacer carrying a-Si(OMe)3 function. In the presence ofdifferent amounts of the co-condensation agent MeSi(OMe)3

this complex was subjected to a subsequent sol-gel processand the resulting materials were used as interphase catalystsfor the hydrogenation oftrans-4-phenyl-3-butene-2-one.

Experimental Section

Instruments and Characterization. Solution nuclear magneticresonance spectra (NMR) were recorded on a Bruker DRX 250spectrometer at 296 K. Frequencies were as follows.1H NMR:250.13 MHz.13C{1H} NMR: 62.90 MHz.31P{1H} NMR: 101.25MHz (referenced to 85% H3PO4). 29Si{1H} NMR (DEPT45 pulsesequence): 49.69 MHz. Chemical shifts in1H, 13C{1H}, and29Si{1H} NMR spectra are given relative to tetramethylsilane.

CP/MAS (cross polarization/magic angle spinning) and HPDEC(high-power decoupling) solid-state NMR spectra were recordedon a Bruker ASX 300 spectrometer (field strength 7.05 T). CP/MAS measurements for31P were obtained at a spinning rate of 10kHz with 4-mm ZrO2 rotors. 29Si HPDEC measurements wereperformed at 4 kHz with 7-mm ZrO2 rotors, and a recycle delay of30 s. Frequencies and standards were as follows:31P, 121.49 MHz[85% H3PO4, NH4H2PO4 (δ ) 0.8) as the second standard];29Si,59.59 MHz [Q8M8 (δ ) 12.03)]. All samples were packed underexclusion of molecular oxygen.

Elemental analyses were carried out on a Carlo-Erba analyzer,model 1106.

EXAFS measurements of complex6T0 and the supported inter-phase catalystX1 were performed at the Ru K-edge at 22117 eVon the beamline X1.1 at the Hamburger Synchrotronstrahlungslabor(HASYLAB) at DESY, Hamburg, Germany and at the XASbeamline at the Angstroemquelle Karlsruhe (ANKA) in Karlsruhe,Germany, respectively. The measurements were performed with aSi(311) double-crystal monochromator under ambient conditionsand the data were collected in transmission mode using ionchambers filled with argon. The energy was calibrated with aruthenium metal foil of 20µm thickness. All data were analyzedwith a program package specially developed for the investi-gation of amorphous solids.25 The programs AUTOBK26 andEXCURV9827 were applied for background removal and dataevaluation, respectively. Data analysis ink-space was performedusing the curved wave theory with XALPHA potentials and phaseshifts and the resulting EXAFS function was weighted withk3. Themean free paths of the scattered electrons were calculated fromthe imaginary part of the potential (VPI set to-4.00), the amplitudereduction factor AFAC was fixed at 0.8, and the Fermi energyEF

was introduced to give a best fit to the data.Surface areas were determined by analyzing the N2 adsorption

isotherm according to the BET method using Micromeritics Gemini.SEM and EDX measurements were performed on a Philips XL

30 instrument equipped with a DX-4 energy-dispersive X-raydetection system by EDAX. This consists of a liquid nitrogen cooledlithium-drifted silicon detector with an active area of 10 mm2 andthe eDXi 2.11 software package. The detector resolution was 149eV at Mn KR (5.984 keV) and the sample-detector distance was50 mm at a takeoff angle of 35° in the present system. The samplepowder was placed on a commercial specimen stub covered withan adhesive tab and subsequently provided with a sputtered 20-nmgold layer to ensure conductivity. The primary beam energy was20 keV during all investigations. A probe current of 192 pA wasapplied for recording electron micrographs, whereas X-ray emissionspectra were acquired under spot illumination applying a probecurrent of 569 pA for 400 live seconds. Under these conditions,rates of 2000-3000 counts per second at dead times of ap-proximately 33% are achieved with the present compounds.Measurements were repeated several times at various specimenpositions to ensure reproducibility. Quantification of X-ray spectrawas carried out employing the ZAF correction procedure28 aftersubtraction of the Bremsstrahlung background.

Syntheses.All manipulations and reactions were performedunder argon using a vacuum line and Schlenk techniques. Allsolvents were dried, distilled, and stored under argon. Diethyl

(15) (a) Hu, A.; Ngo, H. L.; Lin, W.J. Am. Chem. Soc. 2003, 125, 11490.(b) Hu, A.; Ngo, H. L.; Lin, W.Angew. Chem., Int. Ed. 2004, 43,1043.

(16) Liu, P. N.; Gu, P. M.; Wang, F.; Tu, Y. Q.Org. Lett. 2004, 6, 169.(17) Reginek, M.; Warad, I.; Mayer, H. A.; Lindner, E. Poster,14th

International Symposium on Homogeneous Catalysis, Munich, Ger-many, 2004.

(18) Ohkuma, T.; Takeno, H.; Honda, Y.; Noyori, R.AdV. Synth. Catal.2001, 343, 369.

(19) Lu, Z.; Lindner, E.; Mayer, H. A.Chem. ReV. 2002, 102, 3543 andreferences therein.

(20) Lindner, E.; Schneller, T.; Auer, F.; Mayer, H. A.Angew. Chem., Int.Ed. 1999, 38, 2154.

(21) (a) Nachtigal, C.; Al-Gharabli, S.; Eichele, K.; Lindner, E.; Mayer,H. A. Organometallics2002, 21, 105. (b) Lindner, E.; Al-Gharabli,S.; Mayer, H. A.Inorg. Chim. Acta2002, 334, 113. (c) Lindner, E.;Warad, I.; Eichele, K.; Mayer, H. A.Inorg. Chim. Acta2003, 350,49. (d) Lu, Z.; Eichele, K.; Lindner, E.; Mayer, H. A.Inorg. Chem.Commun.2003, 6, 365. (e) Lu, Z.; Eichele, K.; Warad, I.; Mayer, H.A.; Lindner, E.; Jiang, Z.; Schurig, V.Z. Anorg. Allg. Chem. 2003,629, 1308. (f) Warad, I.; Eichele, K.; Mayer, H. A.; Lindner, E.Inorg.Chim. Acta2004, 357, 1847.

(22) Lindner, E.; Ghanem, A.; Warad, I.; Eichele, K.; Mayer, H. A.;Schurig, V.Tetrahedron: Asymmetry2003, 14, 1045.

(23) Lindner, E.; Mayer, H. A.; Warad, I.; Eichele, K.J. Organomet. Chem.2003, 665, 176.

(24) Lindner, E.; Al-Gharabli, S.; Warad, I.; Mayer, H. A.; Steinbrecher,S.; Plies, E.; Seiler, M.; Bertagnolli, H.Z. Anorg. Allg. Chem. 2003,629, 161.

(25) Ertel, T. S.; Bertagnolli, H.; Hu¨ckmann, S.; Kolb, U.; Peter, D.Appl.Spectrosc.1992, 46, 690.

(26) Newville, M.; Livins, P.; Yakoby, Y.; Rehr, J. J.; Stern, E. A.Phys.ReV. B 1993, 47, 14126.

(27) Gurman, S. J.; Binstead, N.; Ross, I.J. Phys. C1986, 19, 1845.(28) (a) Scott, V. D.; Love, G.X-ray Spectrom. 1992, 21, 27. (b) Wernisch,

J.X-ray Spectrom. 1985, 14, 109. (c) Poehn, C.; Wernisch, J.; Hanke,W. X-ray Spectrom. 1985, 14, 120.

3952 Chem. Mater., Vol. 17, No. 15, 2005 Wu et al.

malonate and 6-bromo-1-hexene were used as received from Fluka.1,2-Diaminopropane was purchased from Fluka and stored underargon. Other chemicals were used as received from Aldrich.

[8-Chloro-7-(chloromethyl)octyl]trimethoxysilane (3T0). Hexa-chloroplatinic acid (20 mg, 0.039 mmol) was added to a solutionof 6.8 g (34.87 mmol) of 8-chloro-7-chloromethyl-1-octene (1,obtained from diethyl malonate and 6-bromo-1-hexene accordingto literature methods29,30) in 50 mL of THF. Ultrasonic treatmentmade the catalyst well-dispersed. After adding trichlorosilane (9.5g, 70.11 mmol), the reaction mixture was stirred for 3 d at 50°C.The solvent and excess trichlorosilane were removed in vacuo. Theresidue was treated with HC(OCH3)3 (14.75 g, 140 mmol). Thereaction was completed within 15 h at room temperature. Afterevaporation of excess HC(OCH3)3 and distillation under reducedpressure,3T0 was obtained as a colorless liquid (yield 89.5%); bp112-120°C (0.5 mbar).13C{1H} NMR data are in agreement withthose reported in the literature.29 Anal. Calcd for C12H26O3Cl2Si:C, 45.45; H, 8.26; Cl, 22.36. Found: C, 45.35; H, 7.92; Cl, 21.69.MS (EI) m/z 317.1 (M+).

{2-[(Diphenylphosphino)methyl]-8-(trimethoxysilyl)octyl}-diphenylphosphine (4T0). 3T0 (6.34 g, 20.0 mmol) was dissolvedin 25 mL of THF and the solution was added dropwise to Ph2PLi(7.44 g, 40 mmol, dissolved in 50 mL of THF) under vigorousstirring at 0°C. After an overnight reaction, a white solid (LiCl)precipitated, which was removed by filtration (P3). A short neutralsilica column (ca. 8 cm) was used for the purification of4T0. Priorto filtration, the silica was treated with 100 mL of chloro(trimethyl)-silane at 50°C for 24 h, washed with 200 mL of THF, and driedin vacuo for 7 d. As a solvent for the chromatographic purification,n-pentane was used. After this process the solvent was removedand4T0 was obtained as a waxlike product (yield 84%).13C{1H},31P{1H}, and29Si{1H} NMR spectra are in good agreement withthose reported in the literature.29 Anal. Calcd for C36H46O3P2Si:C, 70.16; H, 7.52. Found: C, 70.05; H, 7.46. MS (EI)m/z 616.3(M+).

trans-Dichloro{2-[(diphenylphosphino)methyl]-8-(trimethoxy-silyl)octyl}(diphenylphosphine)(dipyridine)ruthenium(II) (5T 0).Under stirring, a solution of4T0 (3.08 g, 5.0 mmol) in THF (50mL) was added dropwise totrans-RuCl2(NBD)Py2

31 (2.20 g, 5.2mmol) dissolved in CH2Cl2 (100 mL). The reaction mixture waskept for 24 h at room temperature. After evaporating the solvents,the product was washed with a mixture of ethyl acetate and diethylether (20 mL, 1:5) to remove excesstrans-RuCl2(NBD)Py2. Then,the solid product was washed again with 10 mL of diethyl etherand dried in vacuo. Complex5T0 was obtained as a yellow-greencompound (yield 88%).1H NMR (CDCl3) δ 0.5-2.3 [m, 17H,(CH2)6CH(CH2)2], 3.46 [s, 9H, (OMe)3], 7.0-7.5 [m, 20H (Ar)+4H (Py)], 7.70 [t,3JHH ) 6.8 Hz, 2H (Py)], 8.52 [d,3JHH ) 5.5 Hz,4H (Py)]. 31P{1H} NMR (CDCl3) δ 40.47. Anal. Calcd forC46H56O3N2P2Cl2SiRu: C, 58.35; H, 5.92; N, 2.96; Cl, 7.51.Found: C, 58.19; H, 5.85; N, 2.99; Cl, 7.62. MS (FAB)m/z 946.1(M+).

trans-Dichloro{2-[(diphenylphosphino)methyl]-8-(trimethoxy-silyl)octyl}(diphenylphosphine)(1,2-diaminopropane)ruthenium(II)(6T0). A solution of 5T0 (2.84 g, 3.0 mmol) in dichloromethane(60 mL) was treated with 1,2-diaminopropane (0.29 g, 3.9 mmol)for 30 min at room temperature. Subsequently, dichloromethane,pyridine, and excess 1,2-diaminopropane were removed in vacuo.After the product was washed with 20 mL ofn-hexane and

dichloromethane, respectively, it was dried in vacuo. Complex6T0

was obtained as a bright yellow powder (yield 95.8%).1H NMR(CDCl3) δ 0.54 (br. m, 2H, Si-CH2), 1.02 (d,3JHH ) 5.6 Hz, 3H,CH3), 1.05-3.0 [br. m, 21H, NH2, NCH2, (CH2)5CH(CH2)2], 3.22,(m, 1H, NCH), 3.48 [s, 9H, (OCH3)3], 7.0-7.5 (m, 20H, C6H5).13C{1H}NMR (DMF-d7) δ 135.0-128.9 (m, C-phenyl), 52.46 (C9),50.53 (C11), 49.10 (C10), 36.02 (C3), 35.46 (C1), 32.80 (C2), 33.1,32.0, 25.9, 23.0 (C4-C7), 19.69 (C12), 10.40 (C8).31P{1H} NMR(CDCl3) δ 43.9 (A part of an AB pattern,2JPP ) 52.1 Hz), 44.9 (Bpart of an AB pattern,2JPP ) 52.1 Hz).29Si{1H} NMR (THF-d8)δ -43.24. Anal. Calcd for C39H56O3N2P2Cl2SiRu: C, 54.28; H,6.50; N, 3.25; Cl, 8.24. Found: C, 53.91; H, 6.25; N, 3.52; Cl,8.73. MS (ESI, measured in THF)m/z 935.2 [M + H + THF]+.

General Procedure of the Sol-Gel Process.The calculatedamounts of THF, methanol, and water (pH) 10.5-11, adjustedby adding 1,2-diaminopropane) were mixed and degassed withultrasonics for 15 min. Then,6T0 and the co-condensation agentMeSi(OMe)3 were added to the mixture of solvents. The sol-gelprocesses required 48 h at 30°C and magnetic stirring. The solidproducts formed gradually from the solution. Subsequently, thesolvents were removed under reduced pressure and a Soxhletextractor was used to wash the obtained supported materials with150 mL of dichloromethane. The materials were dried in vacuofor 3 d. The yields were almost quantitative in all cases.

X1. A 0.460-g (0.513 mmol) portion of6T0 and 0.726 g (5.13mmol) of MeSi(OCH3)3 were sol-gel processed in THF (4.5 mL),MeOH (4.5 mL), and water (2.25 mL).31P CP/MAS NMRδ 10-60. 29Si HPDEC NMRδ -58.0 (T2, 7%),32a -66.6 (T3, 93%).32a

Anal. Calcd for (C46H77.8O16.9N2P2Cl2RuSi11)n (corrected stoi-chiometry32b): C, 37.55; H, 5.29; N, 1.90. Found: C, 37.91; H,5.34; N, 1.80.SBET < 10 m2g-1.

X2. A 0.270-g (0.314 mmol) portion of6T0 and 0.64 g (4.70mmol) of MeSi(OCH3)3 were sol-gel processed in THF (4 mL),MeOH (4 mL), and water (2 mL).31P CP/MAS NMRδ 10-60.29Si HPDEC NMRδ -58.0 (T2, 8%),32a-66.3 (T3, 92%).32aAnal.Calcd for (C51H93.3O24.7N2P2Cl2RuSi16)n (corrected stoi-chiometry32b): C, 33.81; H, 5.15; N, 1.55. Found: C, 34.12; H,5.25; N, 1.64.SBET < 10 m2g-1.





General Procedure of the Catalysis.The hydrogenation oftrans-4-phenyl-3-butene-2-one was chosen as a model reaction totest the catalytic activity of the interphase catalysts and6T0. Forevery run,trans-4-phenyl-3-butene-2-one (2.92 g, 20.0 mmol), KOH(11.2 mg, 0.2 mmol), and 0.02 mmol of the respective interphasecatalyst, or the monomeric complex6T0 (30, 36, 44, and 84 mg ofX1-X4, respectively, and 17 mg of6T0), and 2-propanol (50 mL)

(29) Lindner, E.; Enderle, A.; Baumann, A.J. Organomet. Chem. 1998,558, 235.

(30) Juang, T.; Leu, Y.; Hsu, C.Mol. Cryst. Liq. Cryst. 1993, 237, 223.(31) Akotsi, O. M.; Metera, K.; Reid, R. D.; Mcdonald, R.; Bergens, S. H.

Chirality 2000, 12, 514.

(32) (a) The ratios between T3 and T2 groups ofX1-X4 were calculatedby deconvolution according to the obtained29Si HPDEC spectra,respectively. (b) The corrected stoichiometry was obtained by addingthe additional number of OH units to the idealized stoichiometry ofthe catalyst according to the obtained29Si HPDEC NMR spectrum.

Sol-Gel Diamine(Diphosphine)ruthenium(II) Complexes Chem. Mater., Vol. 17, No. 15, 20053953

were placed into a glass reactor. A degassing procedure22 wasthoroughly carried out to ensure that the catalysis was conductedunder exclusion of aerial oxygen. Prior to pressurizing the reactorwith hydrogen, the reaction mixture was treated with ultrasonicsfor 30 min. After that, the hydrogenation started under the followingconditions: 35°C, hydrogen pressure of 3 bar, magnetic stirring.The analyses of the hydrogenation experiments were performedon a GC 6000 Vega Series 2 (Carlo Erba Instrument) with a FIDdetector and a 10 m× 25 µm fused silica capillary columnimmobilized with permethylâ-cyclodextrin, carrier gas H2 (100kPa).

Recycling of the Interphase Catalyst X1. The interphasecatalystX1 was separated from the reaction mixture by filtration(pore size 0.2µm), washed with about 30 mL of dichloromethaneand dried in vacuo. After this procedureX1 was ready for the nextrun. In each following run the amounts oftrans-4-phenyl-3-butene-2-one, 2-propanol, and KOH were the same as in the first run.

Results and Discussion

Improved Synthesis of the T0-Silyl FunctionalizedLigand 4T0. Since its first publication a couple of yearsago,29 the diphosphine ligand4T0 has attracted muchattention. It is provided with a T0-silyl functionalized spacerof six methylene units in the symmetric position of the C3bridge. Thus an optimal flexibility of the heterogenizedcatalyst is achieved. However, some problems have arisenin the reproducibility of the synthesis of this ligand.Therefore, in this work, a revised route for the access to4T0

is presented.

It was reported that the hydrosilylation of 8-chloro-7-chloromethyl-1-octene (1) with trimethoxysilane in thepresence of hexachloroplatinic(IV) acid affords [8-chloro-7-(chloromethyl)octyl]trimethoxysilane (3T0) in a yield of57%.29 However, this particular step is difficult to verify. Inthe course of a repeated investigation, it turned out that it ismuch better to employ trichlorosilane for the hydrosilylationreaction, which results in the formation of [8-chloro-7-(chloromethyl)octyl]trichlorosilane (2). Subsequently, com-pound2 was transformed to3T0 by exchanging the chlorinefunctions for methoxy groups with trimethyl orthoformate(Scheme 1). Thus, the yield of3T0 could be improved up toapproximately 90%. The introduction of both PPh2 moietiesto give4T0 succeeded according to a literature method.29 Itis important to chromatographically purify the T0-silylfunctionalized diphosphine ligand4T0 using a pretreatedcolumn (see Experimental Section). The colorless, waxlikeproduct 4T0, which is sensitive to air and moisture, wasobtained after removing the solvent. It is soluble in polarorganic solvents, like THF or DMF.1H, 13C{1H }, 31P{1H },and 29Si{1H } NMR spectra of4T0 are in full agreementwith literature data.29

Synthesis of the Precursor Complex 5T0. For thestepwise introduction of the T0-silyl functionalized diphos-phine ligand4T0 and 1,2-diaminopropane into a dichloro-ruthenium(II) unit to generate the mixed ligand complex6T0, a substitution-labile starting compound liketrans-RuCl2(NBD)Py2 (NBD ) norbornadiene, Py) pyridine) isa necessary prerequisite. According to Scheme 2, first NBDwas replaced for4T0 in dichloromethane at room tempera-

ture. This reaction accounts for high yields if a slight excessof trans-RuCl2(NBD)Py2 is applied. After drying,5T0 wasobtained as a yellow-amber solid with good solubility in polarorganic media. Compared to the1H NMR spectrum of4T0,that of 5T0 (in CDCl3) displays peaks atδ 7.70 (t, 3JHH )6.8 Hz, 2H, Py) and 8.52 (d,3JHH ) 5.5 Hz, 4H, Py), whichare characteristic for the pyridine ligand. In the31P{1H} NMRspectrum (in CDCl3) the resonance atδ 40.47 is assigned tothe coordinated diphosphine.31

5T0 is a valuable starting complex, because it can bereacted with different 1,2- and 1,3-diamines to give T0-silylfunctionalized diamine(diphosphine)ruthenium(II) catalystprecursors for the hydrogenation of ketones.

Scheme 1

Scheme 2


Synthesis of the T0-Silyl Functionalized Diamine(di-phosphine)ruthenium(II) Complex 6T0. To incorporatediamine(diphosphine)ruthenium(II) complexes into a flexiblesiloxane network with a potentially high mobility of theruthenium centers and a low leaching of the active centers,6T0 was designed and prepared by treating a solution of5T0

in dichloromethane with excess 1,2-diaminopropane (Scheme2). In that case, pyridine was quantitatively substituted forthe diamine without attacking the Ru-P bonds of the(diphos)ruthenium moiety. A bright-yellow compound, whichis sensitive to moisture and air, was isolated in almostquantitative yield. It readily dissolves in polar organicsolvents such as THF or DMF, whereas it shows only poorsolubility in chlorinated hydrocarbons.

The 1H NMR spectrum of 6T0 (in CDCl3) revealsresonances atδ 3.22, (m, 1H, NCH) and 1.02 (d,3JHH ) 5.6Hz, 3H, CH3) showing the presence of the diamine ligand.Expectedly, the31P{1H} NMR spectrum of6T0 (in CDCl3)is characterized by an AB pattern atδ 43.9 and 44.9 (2JPP )52.1 Hz), due to the different chemical environments of thetwo phosphorus donor atoms. A singlet atδ -43.24 in the29Si{1H} NMR spectrum of6T0 (THF-d8) is attributed tothe silicon atom in the T0-silyl function. All NMR data of6T0 are comparable to a recently published complex withoutthe (MeO)3Si(CH2)6 chain in the symmetric 2-position of theC3 bridge.23

Sol-Gel Processing of 6T0. To combine the monomericruthenium(II) complex6T0 with a polysiloxane matrixas a carrier, it was subjected to a sol-gel process in thepresence of different amounts of the co-condensation agentMeSi(OMe)3 (Scheme 3). Among various candidates20,33 ofco-condensation agents, methyl(trimethoxy)silane has beenselected. It is able to incorporate the T0-silyl function-alized complex6T0 into a highly cross-linked siloxanenetwork, considerably reducing the cleavage of the reactiveorganometallic centers. Concomitantly, a mobility of theactive centers comparable to that in bulk liquids is achieved.34

For the optimization of the mobility of the expectedinterphase catalystsX1-X4 different ratios of 6T0 andMeSi(OMe)3 (1:10, 1:15, 1:20, and 1:50) were employed(Scheme 3).

Four sol-gel processes were carried out in a mixture ofTHF, methanol, and water (2:2:1). Thus a good solubilityof 6T0 is provided. To initiate the sol-gel process 1,2-diaminopropane served as a catalyst and the pH value wasadjusted to 10.5-11. Under these conditions, the materialsX1-X4 were obtained as particles (vide infra). Accordingto structural investigations ofX1-X4, the complex6T0

maintained its integrity during the entire sol-gel process.Solid-State NMR Investigations of X1-X4. The 29Si

HPDEC NMR spectra ofX1-X4 each display one mainresonance atδ -66 and a very small shoulder atδ -58,which are assigned to T3 and T2 substructures, respectively(for the relative integrals, see Experimental Section). Thusalmost all of the Si-O functions are incorporated into a Si-O-Si network. From the integration ratios of the T2 and T3

substructures, the degree of condensation is estimated to 98%(X1), 97% (X2), 97% (X3), and 97% (X4), respectively.35

Such a high cross-linkage leads to stable materials. Arepresentative29Si HPDEC NMR spectrum ofX1 is shownin Figure 1.

In the31P CP/MAS NMR spectra ofX1-X4 broad signalsin the range between 10 and 60 ppm indicate that the metalcomplex fragments have been preserved. This broad chemicalshift range has to be compared to the rather small chemicalshift difference of the two inequivalent phosphine groups ofthe monomer6T0 in the solution31P{1H} NMR spectrum(∆δ ) 1 ppm). In general going from solution to sol-gelprocessed materials such asX1-X4 leads to increased linewidths of the peaks and the loss of the fine structure due toenhanced dispersion of the chemical shift but not to largedifferences in chemical shifts as observed forX1-X4. Ourprevious results on other ruthenium diphosphine diaminecomplexes have demonstrated that they may isomerize ongoing from solution to the solid state.21a-e,23 According tothat, the complex centers inX1-X4 may either form an all-cis-RuP2N2Cl2 or a cis-cis-trans-RuP2N2Cl2 structure. Fur-thermore mixtures of different solid phases are also commonphenomena and lead to different peaks in the NMR spectraof powders. Recently, we have shown that a rutheniumdiphosphine diamine complex of the type used here displaysa singlet in the solution31P{1H} NMR spectrum (δ 38.8),whereas the solid state31P CP/MAS NMR spectrum is rather

(33) (a) Lindner, E.; Schreiber, R.; Kemmler, M.; Schneller, T.; Mayer,H. A. Chem. Mater. 1995, 7, 951. (b) Lindner, E.; Ja¨ger, A.; Schneller,T.; Mayer, H. A.Chem. Mater. 1997, 9, 81. (c) Lindner, E.; Schneller,T.; Mayer, H. A.; Bertagnolli, H.; Ertel, T. S.; Ho¨rner, W. Chem.Mater. 1997, 9, 1524.

(34) Holder, E.; Oelkrug, D.; Egelhaaf, H. J.; Mayer, H. A.; Lindner, E.J.Fluoresc.2002, 12, 383.

(35) The degree of condensation was calculated (in percentage) by theformula T ) 100(T1 + 2T2 + 3T3)/3(T1 + T2 + T3).

Scheme 3

Figure 1. 29Si HPDEC solid-state NMR spectrum ofX1.


complicated, covering a range of chemical shifts from 27.3to 40.1 ppm.36 In summary the broad range of chemical shiftsin the 31P CP/MAS spectra ofX1-X4 is fully compatiblewith the ruthenium diamine diphosphine complex of6T0.However, different structures have to be considered.

EDX, SEM, and BET Measurements of X1-X4. Theelemental composition of the interphase catalystsX1-X4was determined by EDX (energy dispersive X-ray analysis).37

A quantification of the EDX spectra was carried out usingthe ZAF correction procedure.28 However, since X-rays arestrongly attenuated by the detector entrance window, EDXis not very sensitive toward the detection and quantificationof light elements embedded into a matrix of higher Zmaterial. Uncertainties in fundamental parameters and spec-trometer calibration in the soft X-ray regime are an importantsource of error in the quantification of light elements, forwhich a relative error of up to 10% has to be taken intoaccount. Phosphorus, silicon, chlorine, and ruthenium el-emental analyses ofX1-X4 obtained by EDX are sum-marized in Table 1 and compared to those data which arecalculated from the corrected stoichiometry.32b According tothe EDX results, the experimentally determined P/Ru ratiosof X1-X4 are approximately 2:1, indicating that theruthenium complex fragment is preserved in the matrix andhas survived the sol-gel process.

Scanning electron micrographs ofX1-X4 show non-uniform particles with a dimension between 1 and 100µm.Such a particle size was intended to be obtained for ease ofisolating the particles from a reaction suspension by filtration.

Owing to the high portion of organic components in thesestationary phases, surface area measurements according tothe BET method reveal low values (<10 m2 g-1), which arein agreement with materials of this type.33c,38,39

EXAFS Measurements of the Monomeric Complex 6T0

and the Stationary Phase X1.Due to the amorphous natureof 6T0 andX1-X4, the structures of these materials cannotbe investigated by an X-ray structural analysis. A suitablemethod, however, is EXAFS (extended X-ray absorption finestructure), which is able to determine the local structurearound the ruthenium center. EXAFS spectroscopy is apowerful technique for probing the neighborhood environ-

ment of a selected atom regardless of the physical state ofthe sample and provides information on the coordinationnumber, the nature of the scattering atoms surrounding theabsorbing atom, the interatomic distance between the absorb-ing atom and the backscattering atoms, and the Debye-Waller factor, which accounts for the disorders due to thestatic displacements and thermal vibrations.40

To determine the local structure, the stationary phaseX1was selected as an example and the results were comparedwith those obtained for the monomeric complex6T0.

The experimentally determined and calculated EXAFSfunctions ink-space and the corresponding Fourier transformsin real space are shown in Figures 2 and 3 for6T0 andX1,respectively. The structural parameters are summarized inTable 2.

In the fitting procedure the coordination numbers werefixed to the known values for the ligands around theruthenium atom. The other parameters, which include theinteratomic distances, Debye-Waller factors, and Fermienergy values, were determined by iterations. Thek3-weighted EXAFS functions were described best by threedifferent shells. The first shell in each case consisting of twonitrogen backscatterers arising from the diamine ligand wasfound at distances of about 2.17 Å (6T0) and 2.14 Å (X1);the second shell having two phosphorus backscatterersstemming from the diphosphine ligand was fitted at distancesof about 2.27 Å (6T0) and 2.24 Å (X1); the third shellcomprising two chlorine backscatterers in each case wasdetermined at distances of approximately 2.41 Å (6T0) and2.38 Å (X1). The EXAFS results are in satisfactory agree-ment with the crystal structure data of the unmodifiedcounterpart.23 Furthermore, the structural parameters obtainedfor X1 are in good accordance with those of6T0 (see Table2) and certify that6T0 retained its integrity after the sol-gel process. Only marginal differences were observedconcerning the ruthenium-ligand bond distances, which arecommon in the case of interphase materials.24

Hydrogenation of trans-4-Phenyl-3-butene-2-one withthe Interphase Catalysts X1-X4 and the MonomericCongener 6T0. The successful introduction of6T0 into asupporting polysiloxane network to form the interphasecatalystsX1-X4 is an important extension of Noyori’scatalytic system for the hydrogenation of functionalizedketones.7 They can be easily recycled without loss of activity.As a substrate for the catalytic hydrogenationtrans-4-phenyl-3-butene-2-one has been selected, because it is a nice modelsystem to study the selectivity of three possible productsA,B, andC (see Scheme 4). It has been successfully employedin many studies.21c,f,22,23 KOH and 2-propanol served ascocatalyst and solvent, respectively. All experiments werecarried out under mild conditions (H2 pressure 3 bar,temperature 35°C) and the molar ratio between the respec-tive interphase catalyst, KOH, and the substrate has beenadjusted to 1:10:1000. It is important to exclude even tracesof aerial oxygen.22

(36) Eichele, K.; Nachtigal, C.; Jung, S.; Mayer, H. A.; Lindner, E.;Strobele, M.Magn. Reson. Chem.2004, 42, 807.

(37) Reimer, E.Scanning Electron Microscopy; Springer: New York, 1998.(38) Lindner, E.; Brugger, S.; Steinbrecher, S.; Plies, E.; Seilber, M.;

Bertagnolli, H.; Wegner, P.; Mayer, H. A.Inorg. Chim. Acta2002,327, 54.

(39) (a) Lindner, E.; Salesch, T.; Hoehn, F.; Mayer, H. A.Z. Anorg. Allg.Chem. 1999, 625, 2133. (b) Lindner, E.; Brugger, S.; Steinbrecher,S.; Plies, E.; Mayer, H. A.J. Mater. Chem. 2001, 11, 1393. (c) Lindner,E.; Jager, A.; Auer, F.; Wielandt, W.; Wegner, P.J. Mol. Catal. A1998, 129, 91.

(40) Teo, B. K.EXAFS: Basic Principles and Data Analysis; Springer:Berlin, 1986. (b) Koningsberger, D. C., Prins, R., Eds.;X-rayAbsorption: Principles, Applications, Techniques of EXAFS, SEXAFSand XANES; Wiley: New York, 1988.

Table 1. Elemental Analyses (Composition %) of X1-X4 by EDX

reference dataa EDXb

P Si Cl Ru P Si Cl Ru P/Ru

X1 4.2 20.9 4.8 6.9 3.9 18.6 4.4 6.6 2.0X2 3.4 24.7 3.9 5.6 3.1 24.8 3.5 5.3 1.9X3 2.9 27.3 3.3 4.7 2.6 27.0 3.6 4.3 2.0X4 1.5 34.1 1.7 2.4 1.4 35.7 1.6 2.4 1.9

a Derived from the corrected stoichiometry32b of the educts, excludinghydrogen and nitrogen.b Quantified by the ZAF correction procedure.


Without doubt catalystX1 showed the best performancecompared toX2-X4. A conversion of 100% and a selectivityto the unsaturated alcoholA (Scheme 4) of 91.2% was foundwithin 24 h (Table 3).X2 andX3 exhibited nearly the sameselectivity, however, the conversion rates decreased to 63.1%

and 45.8%, respectively. In the case ofX4, the conversiondropped to less than 10% in 48 h. It turned out that aprolonged reaction time increases the selectivity toC at theexpense ofA and B. Obviously, productC is mainlyproduced fromA by further hydrogenation. A similarobservation was recently made when a diamine(ether-phosphine)ruthenium(II) complex was used as an interphasecatalyst.24 Expectedly the homogeneous counterpart ofX1without a (CH2)6Si(OMe)3 group in the symmetric 2-positionof the C3 bridge revealed a much higher activity andselectivity to productA.23

Due to the decreasing concentration of the reactive centerswithin the polymeric matrix on going fromX1 to X4, theactivity of these interphase catalysts is markedly reduced.On the other side, the employment of a co-condensation agent

Figure 2. Experimental (solid line) and simulated (dotted line) EXAFS functions and their corresponding Fourier transform plots of complex6T0 measuredat the Ru K-edge.

Figure 3. Experimental (solid line) and simulated (dotted line) EXAFS functions and their corresponding Fourier transform plots of compoundX1 measuredat the Ru K-edge.

Table 2. EXAFS Determined Structural Parameters of 6T0 and X1

compound A - Bsa Nb rc [Å] σd [Å] EFe [eV] k-range [Å-1] R-factor

6T0 Ru-N 2 2.17( 0.02 0.074( 0.007 7.155 3.01-15.00 23.29Ru-P 2 2.27( 0.02 0.050( 0.006Ru-Cl 2 2.41( 0.03 0.059( 0.007

X1 Ru-N 2 2.14( 0.02 0.050( 0.005 8.746 3.02-12.02 26.38Ru-P 2 2.24( 0.02 0.059( 0.006Ru-Cl 2 2.38( 0.03 0.089( 0.012

a Absorber (A) - backscatterers (Bs).b Coordination numberN. c Interatomic distancer. d Debye-Waller factorσ with its calculated deviation.e FermienergyEF.

Scheme 4

Table 3. Hydrogenation of trans-4-Phenyl-3-butene-2-one Catalyzedwith Catalysts X1-X4 (First Run) and Monomeric 6T0

selectivity

catalystsconversion

rate (%) A (%) B (%) C (%)

X1a 100 91.2 8.8 0X2a 63.1 90.8 9.2 0X3a 45.8 92.0 8.0 0X4b <10 41.0 22.5 36.56T0c 100 93.1 6.9 0

a Reaction time 24 h.b Reaction time 48 h.c Reaction time 3 h.


is indispensable to improve the stability of the polysiloxanenetwork and to reduce the leaching effect. However,if the sol-gel processing of6T0 is carried out with a loweramount of the co-condensation agent MeSi(OMe)3 (lessthan 1:10) the resulting material is sticky and unstablewith respect to hydrolysis. Hence, a ratio of 1:10 [6T0/MeSi(OMe)3] offers an optimal condition referring to activityand stability.

A further study on the hydrogenation withX1 showed theconversion ratio as a function of the reaction time (Figure4). After 1 h reaction time, the TOF value was calculated to155.

As a control experiment, the hydrogenation was alsoconducted under the same conditions with the monomericcomplex6T0, and the results are included in Table 3. Within3 h, a conversion of 100% with a selectivity to productA of93.1% was achieved. After 1 h reaction time, the TOF valuewas calculated to 685, which is expectedly higher than therespective TOFs for catalystsX1-X4.

Recovery of the Interphase Catalyst X1 and LeachingTest.An essential advantage of heterogenized homogeneouscatalysts is their easy separation from the reaction mixturefor repeated reuse without loss of activity. However,frequently leaching and deactivation problems of supportedcatalysts are responsible for severe drawbacks.41 In severalcases interphase catalysts offered a possibility to overcomethese problems.19,20,42In this work a successful recovery ofthe interphase catalystX1 has been achieved. After each run,X1 was separated by filtration, washed with dichloromethane,and dried under argon. The same amount of KOH andsubstrate was added and the hydrogenation was repeated. InTable 4, the results of subsequent 10 runs are summarized.Within the course of eight runs, both the catalytic activityand the selectivity to productA (Scheme 4) remained high.This observation strongly suggests that no leaching of theactive centers and deactivation has taken place. Due to the

excellent stability of the entire polymeric matrix and thebidentate character of the phosphine ligand an eliminationof the active ruthenium center during the catalysis isprevented or at least considerably impeded. To verify thisobservation and hypothesis, respectively, a specific leachingtest was carried out. It was conducted in a way that, afterthe first run, catalystX1 was separated by filtration fromthe reaction mixture. Subsequently, another dose of thesubstratetrans-4-phenyl-3-butene-2-one was added to thefiltrate in the reactor. The mixture was subjected to ahydrogenation procedure under the same conditions. Ac-cording to GC analysis, after 24 h no detectable additionalhydrogenation products were found, indicating that noleaching has taken place. A gradual decline of the conversionwas noticed in the last two runs (runs 9 and 10, see Table4). Probably a decomposition of the reactive centers with aconcomitant oxidation of the phosphine ligand occurredduring the recycling procedure.

Conclusion

For the first time polysiloxane-supported ruthenium(II)interphase catalysts have been proven to be a successfulapproach to endow Noyori’s catalytic hydrogenation system7

with the ability to be recycled while maintaining theiractivity. As a prerequisite for this study, we succeeded inan improved synthesis of the chelating diphenylphosphino-propane ligand, which is provided with a flexible C6-spacerand a T0-silyl function. The adopted synthetic route offers ageneral way for the access to similar ligands with differentspacer lengths and organophosphines. The incorporation ofthis functionalized ligand into the ruthenium complex asapplied here converts it into a suitable precursor for sol-gel processing.20,43 Methyl(trimethoxy)silane served as anappropriate co-condensation agent. Together with the T0-silyl functionalized diamine(diphosphine)ruthenium(II) com-plex, the sol-gel process affords a highly cross-linkedpolysiloxane network, reducing cleavage of the mobileorganometallic centers. Four different amounts of the men-tioned co-condensation agent yielded the interphase catalystsX1-X4. In the hydrogenation oftrans-4-phenyl-3-butene-2-one, catalystX1 turned out to be the best choice with

(41) Choplin, A.; Quignard, F.Coord. Chem. ReV. 1998, 180, 1679.(42) Lindner, E.; Kemmler, M.; Schneller, T.; Mayer, H. A.Inorg. Chem.

1995, 34, 5489.

(43) (a) Baiker, A.; Grunwaldt, J. D.; Muller, C. A.; Schmid, L.Chimia1998, 52, 517. (b) Huesing, N.; Schubert, U.Angew. Chem., Int. Ed.1998, 37, 23. (c) Moreau, J. J. E.; Man, M. W. C.Coord. Chem. ReV.1998, 180, 1073.

Figure 4. Conversion oftrans-4-phenyl-3-butene-2-one dependence ontime.

Table 4. Repeated Use of Catalyst X1 in the Hydrogenation oftrans-4-Phenyl-3-butene-2-onea

runb time [h] conversion [%] A [%] B [%] C [%]

1 24 100 91 9 02 22 100 92 8 03 22 99 91 9 04 24 100 90 10 05 22 97 91 9 06 24 99 90 10 07 22 94 91 9 08 22 92 91 9 09 24 83 91 9 0

10 24 71 90 10 0

a Reactions were conducted at a hydrogen pressure of 3 bar, 35°C.b Number of times the catalyst was used.


respect to conversion and selectivity referring to the hydro-genation of the carbonyl group. By way of contrast, catalystsX2-X4 revealed lower activities, indicating that the con-centration of the reactive centers within the polymeric matrixplays an important role. After 1 h the activity of monomeric6T0 is four times higher.

Within eight runs the recycling of catalystX1 proceededwithout leaching and deactivation problems. This behavioris attributed to the optimal cross linkage of the hybridpolymer and the bidentate character of the phosphine ligand.

Acknowledgment. The support of this research by theDeutsche Forschungsgemeinschaft (Graduiertenkolleg “Chem-istry in Interphases”, Grant 441/02 and 441/03, Bonn-BadGodesberg) and by the Fonds der Chemischen Industrie,Frankfurt/Main, is gratefully acknowledged. We thank DorotheaAdam, Institute of Applied Physics, University of Tu¨bingen,for EDX and SEM measurements, and Michael Marzini andMichaela Reginek, Institute of Inorganic Chemistry, Universityof Tubingen, for BET measurements and valuable discussions.

CM0501618


Sol−Gel Processed Diamine(diphosphine)ruthenium(II) Complexes for the Catalytic Hydrogenation of...

Documents

Transcript of Sol−Gel Processed Diamine(diphosphine)ruthenium(II) Complexes for the Catalytic Hydrogenation of...