Efficient Synthesis of Ruthenium(II) η5-Dienyl Compounds Starting

Efficient Synthesis of Ruthenium(II) η5-Dienyl Compounds Starting from Di-μ-chlorodichloro- bis[(1−3η:6−8η)-2,7-dimethyloctadienediyl]diruthen...
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Organometallics 2000, 19, 5471-5476

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Efficient Synthesis of Ruthenium(II) η5-Dienyl Compounds Starting from Di-µ-chlorodichlorobis[(1-3η:6-8η)-2,7-dimethyloctadienediyl]diruthenium(IV). Versatile Precursors for Enantioselective Hydrogenation Catalysts Andre´ Bauer, Ulli Englert, Stefan Geyser, Frank Podewils, and Albrecht Salzer* Institut fu¨ r Anorganische Chemie der RWTH Aachen, D 52056 Aachen, Germany Received August 14, 2000

The dimeric complex di-µ-chlorodichloro-bis[(1-3η:6-8η)-2,7-dimethyloctadienediyl]diruthenium(IV) in the presence of base reacts with cyclic and acyclic dienes to the corresponding bis(η5-dienyl)ruthenium(II) compounds. Crystalline yellow compounds have been isolated in high yields for dienyl ) cyclopentadienyl, pentamethylpentadienyl, cycloheptadienyl, indenyl, dimethylpentadienyl, and trimethylpentadienyl. The analogous reaction of cyclohexa1,3-diene gives the ruthenium(0) compound (η6-benzene)(η4-cyclohexa-1,3-diene)ruthenium. The “open” bis(dienyl)ruthenium complexes can be converted into half-sandwich complexes through protonation and subsequent ligand exchange. These compounds can be used as precursors for efficient enantioselective hydrogenation catalysts. Introduction Organometallic ruthenium complexes are becoming increasingly important in homogeneous catalysis such as metathesis, the Murai reaction, hydrogenation, and hydrogen transfer.1 The preparation of the necessary ruthenium catalysts most often starts from RuCl3‚nH2O, [Ru(H2O)6]2+, RuCl2(PPh3)3, [(cyclooctadiene)RuCl2]n, or [(cymene)RuCl2]n.2 For the synthesis of diolefin and dienyl complexes, two general methods have evolved: the so-called “FischerMu¨ ller synthesis” where RuCl3‚nH2O is treated with an isopropyl Grignard reagent and irradiated in the presence of a diolefin,3 and the "Vitulli method" where RuCl3‚nH2O is treated with zinc in the presence of diolefines.4 Both methods suffer from unpredictable yields and are difficult to reproduce. This may be due to the uncertain nature of commercial RuCl3‚nH2O as well as the poorly understood mechanism of such conversions (vide infra). In continuation of our studies on open and half-open ruthenocenes,5 we therefore sought a rational high-yield synthesis for this class of compounds, as we ourselves (1) (a) Murahashi, S.-I.; Naota, T.; Takaya, H. Chem. Rev. 1998, 98, 2599. (b) Beller, M.; Bolm, C. Transition Metals for Organic Synthesis; VCH: Weinheim, 1998. (c) Schwab, P.; Ziller, J. W.; Grubbs, R. H. J. Am. Chem. Soc. 1996, 118, 100. Murai, S.; Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonoda, M.; Chatani, N. Pure Appl. Chem. 1994, 66, 1527. (d) Noyori, R. Acta Chem. Scand. 1996, 113, 8518. (e) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97. (2) (a) Ko¨lle, U. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; John Wiley: Chichester, 1994; Vol. 7, p 3533. (b) Bruce, M. I.; Bennett, M. A.; Matheson, T. W. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982, 1994. (c) Bu¨rgi, H.-B.; Ludi, A.; Salzer, A.; SteblerRo¨thlisberger, M. Organometallics 1986, 5, 298-302. (3) Mu¨ller, J.; Kreiter, C. G.; B. Mertschenk, B.; Schmitt, S. Chem. Ber. 1975, 108, 273-282. (4) (a) Partici, P.; Vitulli, G.; Paci, M.; Porri, L. J. Chem. Soc., Dalton Trans. 1980, 1961-1964. (b) Dahlenburg, L.; Frosin, K.-M. Inorg. Chim. Acta 1990, 167, 83-89.

Scheme 1

were unable to prepare them following traditional methods.6 Results and Discussion Cox and Roulet have described an alternate method for the preparation of bis(2,4-dimethylpentadienyl)ruthenium derivatives starting from di-µ-chlorodichlorobis[(1-3η:6-8η)-2,7-dimethyloctadienediyl]diruthenium(IV) (1). Their method involves silver tetrafluoroborate and produces the cation [(C7H11)2RuH]+.7 Following this procedure we tried to prepare this compound but isolated to our surprise the [(C7H11)Ru(toluene)]+ cation (2) in good yields. It turned out that the source of toluene most likely was the ethanol used, which contained small amounts of toluene as a denaturizing agent. On repeating the reaction with purified ethanol in the presence of added benzene or toluene we were able to prepare [(C7H11)Ru(benzene)]+ (3) and [(C7H11)Ru(toluene)]+ in very high yields (Scheme 1). (5) (a) Bosch, H. W.; Hund, H.-U.; Nietlispach, D. Organometallics 1992, 11, 2087. (b) Bertling, U.; Englert, U.; Salzer, A. Angew. Chem. 1994, 106, 1026; Angew. Chem., Int. Ed. Engl. 1994, 33, 1003. (c) Englert, U.; Podewils, F.; Schiffers, I.; Salzer, A. Angew. Chem. 1998, 110, 2196; Angew. Chem., Int. Ed. Engl. 1998, 37, 2134. (6) Ernst, R. D.; Stahl, L. Organometallics 1983, 2, 1229. (7) Cox, D. N.; Roulet, R. J. Chem. Soc., Chem Commun. 1988, 951.

10.1021/om0007015 CCC: $19.00 © 2000 American Chemical Society Publication on Web 11/08/2000

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Organometallics, Vol. 19, No. 25, 2000

Table 1. Yield of 4 with Different Alkali Carbonate Bases solid base

yield (%)

K2CO3 Na2CO3 Li2CO3

48 72 95

Bauer et al. Scheme 3

Scheme 2

This reaction is similar to the reaction conditions of Ludi where [Ru(H2O)6]2+ in the presence of dienes and arenes gives high yields of the arene cation.2c Using high- purity ethanol and AgBF4 leads as described by Cox and Roulet to the protonated open ruthenocene. As we however sought a procedure to prepare neutral bis(pentadienyl)ruthenium complexes, we modified the Cox/Roulet method extensively. We first optimized the preparation on the dimeric starting material 1 by changing the solvent to a 1:3 mixture of 2-methoxyethanol and isoprene in the procedure described by Cox and Roulet.8 This improved the yield to 95%. In a second step, we treated 1 with 1 equiv of acetonitrile to form the monomeric species8 and to make the compound more soluble. Instead of using AgBF4 for dehalogenation, we used different bases to neutralize the 2 equiv of HCl that must be formed during the reaction. There is a striking dependence of the yield of this reaction on the solid base used, for which we currently have no explanation (Table 1). In this way, open ruthenocene (C7H11)2Ru (4) could be prepared in almost quantitative yield, avoiding the use of expensive AgBF4 and the protonation of the product. This method also allows the reduction of the amount of ligand to a 2-fold excess per ruthenium, while the Vitulli method always requires a large excess (>20-fold) of the diolefinic ligand (Scheme 2). We have extensively varied the type of base used but found that only nonsoluble, nonnucleophilic bases such as the carbonates give satisfactory results. Other bases such as sodium amide, pyridine, or sodium methanolate either destroy the bis(allyl) starting material or break up the dimeric structure of 1 and form stable adducts, as observed by Cox and Roulet.8 Even acetonitrile can only be used in equimolar amounts, as otherwise yields of 4 are drastically reduced. The increase in yields going from potassium to sodium to lithium may possibly be due to the increasing solubility of the alkali halides in ethanol in this order. The method described here also indicates that the role of zinc in the Vitulli method most probably is that of an HCl quencher and not of a reducing agent, in contrast to the assumption of Vitulli.4a In our method, the fate of the various agents can easily be explained. The octadienediyl ligand is eliminated by reductive coupling leading to 1,6-dimethyl-1,5-cyclooctadiene, which was detected spectroscopically, while the two molar equivalents of HCl are absorbed by the base. It is not (8) Cox, D. N.; R. Roulet, R. Inorg. Chem. 1990, 29, 1360-1365.

surprising that in the Roulet method the open ruthenocene immediately is protonated by HBF4 formed during the reaction, as no base is present. In further experiments we have found that bis(dienyl) complexes not sensitive to the presence of strong acids such as HCl and HBr can be directly prepared from RuCl3‚nH2O. Refluxing of RuCl3‚nH2O in the presence of cyclopentadiene (CpH) in 2-propanol but without zinc dust also produces ruthenocene in 61% yield. The success of this method is probably due to the fact that Cp2Ru is less sensitive to strong acids and is not easily protonated. In this case, the reduction of Ru(III) (if this is assumed to be the predominant oxidation state of “RuCl3‚nH2O”) is most likely performed by 2-propanol, which is oxidized to acetone. When Li2CO3 is used, the yield is increased to 98% and therefore higher than in the Vitulli method in the presence of zinc dust. The presence of solid bases is essential for the synthesis of other dienyl complexes of ruthenium. We were able to prepare a whole series of ruthenium(II) and ruthenium(0) complexes 4-11 in good to excellent yields (Scheme 3). The reaction conditions were optimized for (C7H11)2Ru; modified reaction conditions may give better yield for the other dienyl complexes. These complexes thus prepared served as highly useful starting materials for a variety of ruthenium(II) complexes. It was possible to protonate bis(cycloheptadienyl)ruthenium (C7H9)2Ru (6) similar to (C7H11)2Ru in 80% yield. At room temperature, nearly all protons are equivalent on the NMR time scale. These scrambling processes are similar to those previously described for similar protonated olefin complexes (Scheme 4).9 On cooling (-100 °C), we observed that some of the rearrangements are significantly slowed and the limiting spectrum observed at that temperature is that of a bis(9) Buchmann, B.; Piantini, U.; von Philipsborn, W.; Salzer, A. Helv. Chim. Acta 1987, 70, 1487.

Synthesis of Ruthenium(II) η5-Dienyl Compounds

Organometallics, Vol. 19, No. 25, 2000 5473

Scheme 4

Scheme 5

Figure 1. Molecular structure and crystallographic numbering scheme for compound 13 (PLATON representation). Ellipsoids are scaled to enclose 30% probability. Hydrogen atoms are drawn with arbitrary radii. Table 2. Selected Bond Lengths (Å)a and Angles (deg)a for Compound 13 Ru-I Ru-C(1) Ru-C(2) Ru-C(3) Ru-C(4) Ru-C(11) Ru-C(12) Ru-C(13) Ru-C(14) Ru-C(15) C(1)-C(2)

2.7446(8) 2.213(4) 2.211(3) 2.198(4) 2.188(4) 2.245(4) 2.167(4) 2.179(4) 2.170(4) 2.246(4) 1.401(5)

C(2)-C(3) C(3)-C(4) C(11)-C(12) C(12)-C(13) C(13)-C(14) C(14)-C(15) C(1)-C(2)-C(3) C(2)-C(3)-C(4) C(11)-C(12)-C(13) C(12)-C(13)-C(14) C(13)-C(14)-C(15)

1.434(5) 1.408(6) 1.38.9(5) 1.408(6) 1.413(6) 1.408(6) 118.0(4) 118.2(4) 123.2(4) 124.3(4) 125.5(4)

a Estimated standard deviations in the least-squares significant figure are given in parentheses.

(heptadienyl)ruthenium hydrido cation in which the agostic hydride bond rapidly interchanges between the four equivalent positions of the terminal carbons of the dienyl moieties.5a,10 This protonated species is highly susceptible to ligand exchange similar to the protonated open ruthenocenes10,11 We treated [(C7H9)2RuH]BF4 (12) with KI as a halide source in the presence of dimethylbutadiene and obtained the neutral half-sandwich complex (C7H9)Ru(C6H10)I (13) (Scheme 5). This compound was characterized by an X-ray structure analysis (Figure 1, Table 2). The analogous pentadienyl ruthenium dimethylbutadiene complex (15) previously described by Cox and Roulet11 reacts with TlCp to give the half-open ruthenocene (C5H5)Ru(C7H11) (16) in almost quantitative yields (Scheme 6). Starting from [(C7H9)2RuH]BF4 (12) and [(C7H11)2RuH]BF4 (14), we were able to prepare the cationic BINAP complexes [(C7H11)Ru(BINAP)(acetonitrile)]BF4 (17) and [(C7H9)Ru(BINAP)(acetonitrile)]BF4 (18) (Scheme 7). These BINAP complexes react under hydrogen atmosphere in acetone to an identical solvated hydrido species [Ru(BINAP)H(solv)x]+ with facile loss of the

second dienyl ligand. This species apparently is identical to that described by Bergens,12 which was shown to be a highly efficient catalyst for the enantioselective hydrogenation of R,β-unsaturated esters. We were able to hydrogenate various unsaturated ester derivatives in

(10) Newbound, T. D.; Stahl, L.; Ziegler, M. L.; Ernst, R. D. Organometallics 1990, 9, 2962. (11) (a) Cox, D. N.; Lumini, T.; Roulet, R.; Schenk, K. J. Organomet. Chem. 1992, 434, 363. (b) Cox, D. N.; Lumini, T.; Roulet, R. J. Organomet. Chem. 1992, 438, 195.

(12) (a) Bergens, S. H.; Wiles, J. A. Organometallics 1998, 17, 2228. (b) Wiles, J. A.; Lee, C. E.; McDonald, R.; Bergens, S. H. Organometallics, 1996, 15, 3782. (c) Wiles, J. A.; Bergens, S. H.; Young, V. G. J. Am. Chem. Soc. 1997, 119, 2940. (d) Daley, C. J. A.; Wiles, J. A.; Bergens, S. H. Can. J. Chem. 1998, 76, 1447.

Scheme 6

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Organometallics, Vol. 19, No. 25, 2000 Scheme 7

Bauer et al.

and closed dienyl complexes of ruthenium, making in particular “open” and “half-open” ruthenocene available for the first time in almost quantitative yields. Open ruthenocenes were used by us among other reactions for the unprecedented synthesis of the first bis(metallabenzene)ruthenium sandwich complexes.5c After protonation of open ruthenocenes, these are readily and quantitatively converted into half-sandwich complexes, which in turn are an efficient source for enantioselective hydrogenation catalysts of ruthenium(II). Experimental Section

Scheme 8

good agreement with results of Bergens with very high enantioselectivities (Scheme 8).12 A similar hydrogenation catalyst with DUPHOS and JOSIPHOS ligands obtained by other routes has also very recently found industrial application in the catalytic hydrogenation of jasmonates.13 Our method of obtaining these hydrogenation catalysts seems to be superior to the published or patented methods,12,13 as all synthetic conversions described in this paper starting from RuCl3‚nH2O and isoprene are nearly quantitative. The catalyst can be prepared directly in situ from the protonated “open” ruthenocene 14 without prior isolation of any intermediates. Conclusions We have demonstrated that the easily accessible dimeric di-µ-chlorodichloro-bis[(1-3η:1-3η)-2,7-dimethyloctadienediyl]diruthenium(IV) compound is an almost universal reagent for the rational synthesis of open (13) Dobbs, D. A.; Vanhessche, K. P. M.; Brazi, E.; Rautenstrauch, V.; Lenoir, J.-Y.; Geneˆt, J.-P.; Wiles, J. A.; Bergens, S. H. Angew. Chem. 2000, 112, 2080-2083; Angew. Chem., Int. Ed. Engl. 2000, 39, 1992.

All reactions were carried out under nitrogen using standard Schlenck techniques. Solvents were dried and deoxygenated by standard methods. NMR spectra were recorded on a Varian Mercury 200 (200 MHz, 1H; 50 MHz, 13C; 81 MHz, 31P) and a Varian Unity 500 (500 MHz, 1H; 125 MHz, 13C; 202 MHz, 31P) at ambient temperature. Chemical shifts (δ) are given in ppm relative to SiMe4. Mass spectra were obtained with a Finnigan MAT 95 spectrometer. Elemental analyses were obtained on a Carlo Erba element analyzer, model 1106. Isoprene, 1,3cyclohexadiene, 1,3-cyclooctadiene, indene, ruthenium chloride, HBF4.Et2O (54% in diethyl ether), KI, tetraethylammonium chloride, (S)-BINAP, and (R)-p-tol-BINAP were purchased from Fluka, Merck, Johnson Matthey, or Strem and used as received. Monomeric C5H6 was obtained from commercial dicyclopentadiene (Fluka) by dropping into hot Decaline and distillation through a vigreux column and was stored under nitrogen at -80 °C. The compounds 2,4-dimethylpentadiene, 2,3,4-trimethylpentadiene, pentamethylcyclopentadiene, cycloheptadiene, and TlCp were prepared by standard methods. X-ray Structure Determination of 13. Geometry and intensity data were collected with Mo KR radiation at 203 K on an Enraf-Nonius CAD4 diffractometer equipped with a graphite monochromator (λ ) 0.7107 Å). Crystal data: monoclinic space group P21/n (14), a ) 8.206(3) Å, b ) 15.291(7) Å, c ) 10.643(2) Å, β ) 104.23(2)°, V ) 1294.6(8) Å3, Z ) 4, dc ) 2.069 g cm-3, µ ) 35.18 cm-1, F(000) ) 776. Intensity data (3910) were in the range 2.0 < θ < 27.0° on a yellow rod of approximate dimensions 0.4 × 0.2 × 0.2 mm3. An empirical absorption correction based on azimuthal scans14 was applied before averaging over symmetry equivalent data. The structure was solved by direct methods15 and refined16 on F with anisotropic displacement parameters for all non-hydrogen and isotropic displacement parameters for H atoms. Independent observations (2589) with I > 1.0 σ(I) for 193 variables resulted in R ) 0.027, Rw ) 0.032 (GOF ) 1.060). Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication No. CCDC-149752. Copies of the data can be obtained free of charge on application to The Director, CCDC 12 Union Road, Cambridge CB2 1EZ, U.K. (FAX, int. +1223/336-033; E-mail, [email protected]). Dichloro-bis-µ-chloro-bis[(1-3η:6-8η)-2,7-dimethyloctadienediyl]diruthenium(II) (1). A solution of ruthenium chloride in a mixture of isoprene (400 mL) and 2-methoxyethanol (160 mL) was refluxed for 10 days. The purple crystalline product was collected in a sintered glass funnel, washed with diethyl ether, and dried in vacuo; yield 95%. 1H NMR (250 MHz, CDCl ): 5.72, 5.37, 5.22, (s, 2H, H-1, 3 H-8), 4.65 (m, 2H, H-3, H-6), 4.49 (m, 4H, H-1, H-3, H-6, H-8), 2.7-2.4 (m, 8H, H-4, H-5), 2.37 (s, 6H, H-9, H-10), 2.28 (s, 6H, (14) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr. 1968, A24, 351. (15) Sheldrick, G. M. SHELX97, Program for Crystal Structure Determination; University of Go¨ttingen, 1997. (16) ENRAF-Nonius. SDP Version 5.0, 1989.

Synthesis of Ruthenium(II) η5-Dienyl Compounds H-9, H-10).13C NMR (125 MHz, CDCl3): 124.33 (C-2, C-7), 119.32 (C-2, C-7), 96.12 (C-3, C-6), 94.57 (C-3, C-6), 84.58 (C1, C-8), 80.96 (C-1, C-8), 33.97 (C-4, C-5), 32.36 (C-4, C-5), 19.81 (C-9, C-10), 19.01 (C-9, C-10) for the Ci-isomer of 1. 1H NMR (250 MHz, CDCl3): 6.09, 5.07, 4.87, (s, 2H, H-1, H-8), 4.73 (m, 4H, H-1, H-3, H-6, H-8), 4.45 (m, 2H, H-3, H-6), 2.7-2.4 (m, 8H, H-4, H-5), 2.47 (s, 6H, H-9, H-10), 2.24 (s, 6H, H-9, H-10). 13 C NMR (125 MHz, CDCl3): 124.10 (C-2, C-7), 120.16 (C-2, C-7), 96.50 (C-3, C-6), 94.57 (C-3, C-6), 86.75 (C-1, C-8), 78.83 (C-1, C-8), 33.91 (C-4, C-5), 32.92 (C-4, C-5), 19.75 (C-9, C-10), 19.25 (C-9, C-10) for the C2-isomer of 1. Anal. Calcd (Found) for C20H32Cl4Ru2: C, 38.97 (39.00), H, 5.23 (5.19). MS (EI) m/z: 616 (M+). These NMR data are basically identical to those reported in the literature.8 (η6-Toluene)(η5-2,4-dimethylpentadienyl)ruthenium Tetrafluoroborate (2). To a solution of silver tetrafluoroborate (0.77 g, 4.0 mmol) in 20 mL of ethanol, 2,4-dimethylpenta-1,3-diene (0.62 g, 6.5 mmol) and 2 mL toluene were added. This solution was added dropwise and under vigorous stirring to 1 (0.61 g, 2.0 mmol) dissolved in 15 mL of methylene chloride. Silver chloride was separated by centrifugation and washed with 5 mL of methylene chloride. The combined solutions were concentrated, and the orange product was precipitated by addition of diethyl ether; yield 67%. 1H NMR (500 MHz, CD2Cl2): 6.18 (td, 2H, J ) 6.0/1.0 Hz, toluene), 6.14 (tt, 1H, J ) 5.8/0.9 Hz, toluene), 6.02 (d, 2H, J ) 5.8 Hz, toluene), 3.53 (d, 2H, 3.4 Hz, CH2,endo), 2.31 (s, 3H, CH3), 2.10 (s, 6H, 2 CH3), 1.03 (d, 2H, 3.05, CH2,endo). 13C NMR (75 MHz, CD2Cl2): 108.3 (CCH3, toluene), 105.8 (2 CCH3), 97.6 (1 CH), 92.0 (2 CH, toluene), 91.4 (CH, toluene), 53.4 (2 CH2), 26.3 (2 CH3), 20.0 (CH3). Anal. Calcd (Found) for C14H19RuBF4: C, 44.82 (44.99); H, 5.10 (4.92). (η6-Benzene)(η5-2,4-dimethylpentadienyl)ruthenium Tetrafluoroborate (3). The orange crystalline compound was isolated as described for 2 substituting toluene for benzene; yield 75%. 1H NMR (250 MHz, CD2Cl2): 6.36 (s, 6H, benzene), 3.53 (d, 2H, J ) 4 Hz, CH2,exo), 2.16 (s, 6H, CH3), 1.15 (d, 2H, J ) 4 Hz, CH2,endo).13C NMR (75 MHz, CD2Cl2): 106.3 (2 CCH3), 97.9 (1 CH), 92.7 (6 CH), 51.6 (2 CH2), 25.7 (2 CH3). Anal. Calcd (Found) for C13H17RuBF4: C, 43.24 (43.29); H, 4.74 (4.67). Bis(η5-2,4-dimethylpentadienyl)ruthenium (4). A solution of 1 (0.31 g, 0.5 mmol) and Li2CO3 (0.15 g, 2.0 mmol) in a mixture of 10 mL of ethanol, 26 µL (0.5 mmol) of acetonitrile, and 2,4-dimethylpenta-1,3-diene (0.38 g, 4.0 mmol) was refluxed for 4 h. After evaporation of the solvents, the brown crude product was purified by sublimation and 4 was obtained as yellow crystals. On a larger scale, it is more convenient to extract the dry brown crude product with diethyl ether and to filter the solution over a pad of alumina prior to sublimation; yield 95%. 1H NMR (250 MHz, C6D6): 4.63 (s, 1H), 2.71 (s, 2H, J ) 2 Hz), 1.73 (s, 6H), 0.86 (s, 2H, J ) 2 Hz). 13C NMR (62.9 MHz, C6D6): 100.3 (C-2), 97.8 (C-3), 46.8 (C-1), 26.3 (C4). These NMR data are basically identical to those reported in the literature.6 Anal. Calcd (Found) for C14H22Ru: C, 57.71 (57.99); H, 7.61 (7.82). Bis(η5-2,3,4-trimethylpentadienyl)ruthenium (5). The yellow crystalline compound was isolated as described for 4 substituting 2,4-dimethyl-1,3-pentadiene for 2,3,4-trimethyl1,3-pentadiene; yield 62%. 1H NMR (250 MHz, C6D6): 2.73 (s, 4H, H-1exo), 1.53 (s, 12H, H-4), 1.46 (s, 6H, H-5), 0.86 (s, 4H, H-1endo). 13C NMR (62.9 MHz, C6D6): 105.9 (C-3), 96.26 (C-2), 49.0 (C-1), 25.2 (C-4), 16.4 (C-5). Anal. Calcd (Found) for C16H26Ru: C, 60.16 (60.09); H, 8.20 (8.11). Bis(η5-cyloheptadienyl)ruthenium (6). The yellow crystalline compound was isolated as described for 4 substituting 2,4-dimethyl-1,3-pentadiene for 1,3-cycloheptadiene; yield 80%. 1H NMR (250 MHz, C D ): 5.01 (t, 2H, H-1), 4.37 (dd, 4H, H-2), 6 6 3.88 (m, 4H, H-3), 2.15, 1.66 (m, 8H, H-4). 13C NMR (62.9 MHz, C6D6): 94.56 (C-1); 88.21 (C-2); 64.88 (C-3); 34.95 (C-4). Anal. Calcd (Found) for C14H18Ru: C, 58.52 (57.99); H, 6.31 (6.21).

Organometallics, Vol. 19, No. 25, 2000 5475 (η6-Benzene)(η4-cyclohexadiene)ruthenium (7). A solution of 1 (0.24 g, 0.4 mmol) and Li2CO3 (0.29 g, 4.0 mmol) in a mixture of 10 mL of ethanol, 26 µL (0.5 mmol) of acetonitrile, and freshly distilled cyclohexadiene (0.24 g, 3.1 mmol) was refluxed for 4 h. After evaporation of the solvents, the yellowbrown crude product was extracted with diethyl ether, filtered over a pad of alumina, and cooled to -80 °C. 7 was obtained as yellow crystals; yield 69%. 1H NMR (250 MHz, C6D6): 4.92 (s, 6H, C6H6), 4.86 (dd, 2H, CH)CHCH2,H-2), 3.20 (m, 2H, CHdCHCH2 H-3), 1.70 (m, 4H, CHdCHCH2 H-4). Anal. Calcd (Found) for C12H14Ru: C, 55.58 (55.11); H, 5.44 (5.19). Bis(η5-indenyl)ruthenium (8). The orange compound was prepared as described for 7 substituting cyclohexadiene for indene; yield 46%. 1H NMR (200 MHz, C6D6): δ ) 6.52-6.69 (m, 8H, H-1,2), 4.80 (d, 3J ) 2.4 Hz, 4H, H-3), 4.46(t, 3J ) 2.4 Hz, 2H, H-4). MS (EI) m/z: 332 (M+, 100%), 217 (M+ - indene, 20%). Anal. Calcd (Found) for C18H14Ru: C, 65.25 (65.02); H, 4.26 (4.19). Bis(η5-pentamethylcyclopentadienyl)ruthenium (9). The off-white crystalline compound was isolated as described for 7 substituting cyclohexadiene for pentamethylcyclopentadiene; yield 47%. 1H NMR (200 MHz, C6D6): 1.64 (s, Me) ppm. 13C NMR (50 MHz, C D ): 82.9 (CCH ), 10.5 (CCH ) ppm. MS 6 6 3 3 (EI) m/z: 372 (M+, 100%). Anal. Calcd (Found) for C20H30Ru: C, 64.66 (65.01); H, 8.14 (8.19). Bis(η5-methylcyclopentadienyl)ruthenium (10). The off-white crystalline compound was isolated as described for 7 substituting cyclohexadiene for methylcyclopentadiene; yield 50%. 1H NMR (200 MHz, C6D6): 4.39 (m, Cp), 1.81 (s, Me). 13C NMR (50 MHz, C D ): 86.5, 72.7, 70.3 (Cp), 14.7 (Me). MS 6 6 (EI) m/z: 259 (M+, 100%), 245 (M+ - CH3, 20%), 181 (M+ CpMe, 14%), 102 (M+ - 2CpMe, 4%). Anal. Calcd (Found) for C12H14Ru: C, 55.56 (56.11); H, 5.44 (5.31). Bis(η5-cyclopentadienyl)ruthenium (11). The off-white crystalline compound was isolated as described for 7 substituting cyclohexadiene for cyclopentadiene; yield 98%. 1H NMR (200 MHz, C6D6): 4.46 (s, Cp). 13C NMR (50 MHz, C6D6): 70.4 (Cp). MS (EI) m/z: 232 (M+, 100%), 169 (M+ - Cp, 20%). Anal. Calcd (Found) for C10H10Ru: C, 51.94 (50.99); H, 4.36 (4.41). Bis(η5-cycloheptadienyl)hydridoruthenium Tetrafluoroborate (12). A solution of 6 (0.16 g, 0.56 mmol) in 40 mL of diethyl ether was cooled to -78 °C, and HBF4‚Et2O (0.1 mL, 0.61 mmol) was added with stirring. A yellow precipitate was immediately formed. The reaction mixture was slowly warmed to room temperature, and after removal of the magnetic stirring bar the yellow precipitate settled out of the solution. The supernatant liquid was removed, and the solid was washed with diethyl ether and dried in vacuo; yield 99%. 1H NMR (500 MHz, 296.2 K, CD2Cl2): 4.1 (br s), 1.5 (br s) ppm. 1H NMR (500 MHz, 183.2 K, CD Cl ): 5.9 (CH), 5.1 (CH), 4.4 2 2 (CH), 2.1 (CH2,exo), 1.4 (CH2,endo), -6.0 (RuH) ppm. (η4-2,3-Dimethylbutadiene)(η5-cycloheptadienyl)ruthenium Iodide (13). To a solution of the hydrido complex 12 (0.205 g, 0.55 mmol) in 20 mL of acetone, potassium iodide (0.095 g, 0.57 mmol) and dimethylbutadiene (0.898 g, 10.9 mmol) dissolved in acetone were added dropwise at -78 °C. The reaction mixture was stirred and slowly warmed to room temperature over a period of 16 h. The product was isolated as a yellow solid after cooling to -30 °C for 24 h; yield 90%. 1H NMR (500 MHz, CD Cl ): 4.58-4.53 (m, 3H, CH), 4.32 (dd, 2 2 J ) 6.1 Hz/8.6 Hz, 2H, CH), 2.71 (d, J ) 1.8 Hz, 2H, CHexo,diene), 2.60 (m, 2H, CHexo), 1.82 (s, 6H, CH3,diene), 1.75 (m, 2H, CHendo) 1.4 (d, J ) 1.8 Hz, CHendo,diene), 13C NMR (125 MHz, CD2Cl2): 102.1 (C), 96.28 (CH), 95.6 (CH), 80.5 (CH), 52.2 (CH2), 33.2 (CH2), 17.7 (CH3_). MS (EI): 403 (M+), 322 (M+ - dimethylbutadiene), 277 (M+ - I), 195 (M+ - I - dimethylbutadiene). Anal. Calcd (Found) for C13H19RuI: C, 38.72 (39.02); H, 4.75 (4.79). Bis(η5-2,4-dimethylpentadienyl)hydridoruthenium Tetrafluoroborate (14). This compound was obtained by a synthesis previously described by Ernst and co-workers.10 A

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well-stirred solution of 4 (0.97 g, 3.3 mmol) in 50 mL of diethyl ether was cooled to -75 °C, and over a period of 15 min a 54% solution of HBF4 in ether (0.45 mL) was added dropwise. The product precipitated as a yellow solid and was collected in a sintered glass funnel, washed with diethyl ether, and dried in vacuo; yield 99%. 1H NMR (250 MHz, CD2Cl2): 5.61 (s, 1H,CH), 2.09 (s, 6H, CH3), 1.3 (b, 5H, Ru-H/CH2). 13C NMR (62.9 MHz, CD2Cl2): 100.05 (CCH3), 98.65 (CH), 47.19 (CH2), 25.33 (CH3). (η4-2,3-Dimethylbutadiene)(η5-2,4-dimethylpentadienyl)iodoruthenium (15). This compound was obtained by a synthesis previously described by Cox and Roulet. A solution of 14 (1.3 g, 3.3 mmol) in 30 mL of acetone was added dropwise to a solution of 2,3-dimethylbutadiene (5.7 g, 69.0 mmol) and potassium iodide (0.6 g, 3.6 mmol) at -78 °C. The mixture was stirred for 16 h and allowed to warm to room temperature. The product precipitated and was collected in a sintered glass funnel and dried in vacuo, yield 93%. 1H NMR (250 MHz, CD2Cl2): 4.85 (s, 1H, H-3), 3.80 (d, J ) 0.9 Hz, 2H, H-1exo), 2.65 (d, J ) 2.5 Hz, 2H, H-1′exo), 1.89 (s, 6H, H-3′), 1.83 (s, 6H, H-4), 1.72 (d, J ) 2.5 Hz, 2H, H-1′exo), 1.67 (d, J ) 0.9 Hz, 2H, H-1exo). 13C NMR (62.9 MHz, CD Cl ): 106.05 (C-2), 100.37 (C-2′), 93.30 2 2 (C-3), 60.57 (C-1′), 52.64 (C-1), 22.93 (C-4), 20.03 (C-3′). (η5-Cyclopentadienyl)(η5-2,4-dimethylpentadienyl)ruthenium (16). To a suspension of 15 (1.25 g, 3.1 mmol) in 50 mL of toluene TlCp (0.91 g, 3.4 mmol) was added, and the suspension was refluxed for 16 h. The solvent was removed, and the brown residue was extracted three times with 30 mL of hexane. The solution was concentrated, and the yellow crude product was purified by sublimation in vacuo (80 °C); yield 99%. 1H NMR (250 MHz, C6D6): 5.31 (s, 1H, H-3), 4.46 (s, 5H, H-5), 2.93 (s, 2H, H-1exo), 1.83 (s, 6H, H-4), 0.17 (s, 2H, H-1endo). 13C NMR (62,9 MHz, C D ): 92.64 (C-3), 92.19 (C-2), 78.11 (C6 6 5), 40.75 (C-1), 28.02 (C-4). [Ru(acetonitrile)((R)-BINAP)(η5-2,4-dimethylpentadienyl)][BF4] (17). A solution of the hydrido complex 14 (0.129 mg, 0.34 mmol) and (R)-BINAP (0.220 g, 0.35 mmol) in 10 mL of methylene chloride and 20 mL of acetonitrile was stirred for 16 h at room temperature. The solution was concentrated, and the product was precipitated by addition of diethyl ether; yield 82%. 1H NMR (500 MHz, CD2Cl2): 8.20-5.90 (m, 32H, aromatic), 5.21 (s, 1H, CH), 3.17, 2.57 (bs, 1H each, CHexo) 2.11 (s, 3H, NCCH3), 1.60 (s, 3H, CH3), 1.06 (d, J ) 3 Hz, 3H, CH3), -0.34, -0.80 (bs, 1H each, CHendo).13C NMR (125 MHz, CD2Cl2): 116.9 (NCCH3), 106.0, 93.7 (C-2,2′), 94.0 (d, J ) 24.7 Hz, C-1), 75.2 (d, J ) 20.3, C-3/3′), 59.9 (s, C-3, 3′) 33.3, 25.5 (C-4, 4′), 2.0 (NCCH3). 31P NMR (202 MHz, CD2Cl2): 46.5 (J ) 34.6 Hz), 37.5 (J ) 34.6 Hz). Anal. Calcd (Found) for C13H19RuI: C, 67.38 (68.02); H, 4.69 (4.72). [Ru(MeCN)((R-BINAP)(η5-cycloheptadienyl)][BF4] (18). A solution of the hydrido complex 12 (0.129 mg, 0.34 mmol)

Bauer et al. and ®-BINAP (0.220 g, 0.35 mmol) in 10 mL of methylene chloride and 20 mL of acetonitrile was stirred for 16 h at room temperature. The solution was concentrated, and the product was precipitated by addition of diethyl ether; yield 82%. 1H NMR (500 MHz, CD2Cl2): 8.20-5.90 (m, 32H, aromatic), 5.12, 4.91, 4.49, 4.45, 3.50 (m, 1H, CH), 2.97 (s, 3H, NCCH3) 1.34, 1.01, 0.66, 0.38 (m, 1H, CH2).13C NMR (125 MHz, CD2Cl2): 116.9 (NCCH3), 106.0, 93.7 (CH), 94.0 (d, J ) 24.7 Hz, CH), 75.2 (d, J ) 20.3, CH), 59.9 (s, C-H) 33.3, 25.5 (CH2), 2.0 (NCCH3). 31P NMR (202 MHz, CD2Cl2): 46.5 (J ) 34.6 Hz), 37.5 (J ) 34.6 Hz). Anal. Calcd (Found) for C13H19RuI: C, 67.38 (68.02); H, 4.69 (4.72). Catalytic Hydrogenations. A glass pressure reactor (Bu¨chi) was charged with 1.0 mmol of the substrate [(Z)-methylR acetamidocinnamate, tiglic acid, dimethyl itaconate] dissolved in 20 mL of acetone and with a solution of the catalyst (1 mol %) in 5 mL of acetone under an atmosphere of nitrogen gas. The catalyst is formed by stirring a solution of the open ruthenocene 4 with (S)-BINAP or (R)-p-tol-BINAP, respectively, in 5 mL of acetone for 16 h at room temperature. In the case of tiglic acid, methanol was used as solvent instead of acetone. The reaction vessel was flushed with dihydrogen gas (three cycles). The reactor was pressurized to 5 bar, heated to 40 °C, and allowed to react for 3 h while stirring. After complete conversion, confirmed by GC (CP-Sil-8, 10.9 psi H2, T ) 100 °C, 5 min, then 20 K/min up to 250 °C), the catalyst was separated by filtration over a thin pad of alox. The resulting solution was analyzed by GC without further purification. Enantiomeric excesses were determined by GC (Chirasil-Val-L, 14.9 psi H2, T ) 50 °C, 5 min, then 10 K/min up to 100 °C), and the absolute configuration was assigned by comparison to commercial samples of the optically pure products.

Acknowledgment. The authors gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft DFG within the Collaborative Research Center (SFB) 380: “Asymmetric Syntheses with Chemical and Biological Means” and by the “Fonds der Deutschen Chemischen Industrie”. We also thank C. Vermeeren from the Group of Prof. Gais, RWTH Aachen, for performing the GC analyses. Supporting Information Available: Tables with crystal data, atomic coordinates, anisotropic displacement parameters, and listings of interatomic distances and angles. This material is available free of charge via the Internet at http://pubs.acs.org. OM0007015