Preparation of Thiolate-Bridged Dinuclear Ruthenium Complexes

Preparation of Thiolate-Bridged Dinuclear Ruthenium Complexes Bearing a Phosphine Ligand and Application to Propargylic Reduction of Propargylic Alcoh...
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Organometallics 2010, 29, 5994–6001 DOI: 10.1021/om100852x

Preparation of Thiolate-Bridged Dinuclear Ruthenium Complexes Bearing a Phosphine Ligand and Application to Propargylic Reduction of Propargylic Alcohols with 2-Propanol Masahiro Yuki, Yoshihiro Miyake, and Yoshiaki Nishibayashi* Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan Received September 2, 2010

Novel thiolate-bridged dinuclear ruthenium complexes bearing a phosphine ligand, [Cp*Ru{PhP(C6H4-o-S)2}RuCp*](OTf)2, [CpRu{PhP(C6H4-o-S)2}RuCp*(OH2)](OTf)2, and [Cp*Fe{PhP(C6H4o-S)2}RuCp*](OTf)2, are prepared and characterized by X-ray analysis. These dinuclear complexes work as effective catalysts toward propargylic reduction of propargylic alcohols with 2-propanol via allenylidene complexes as key intermediates to give the corresponding alkynes in good to high yields.

Introduction

Chart 1

Since the first report on the ruthenium-catalyzed propargylic substitution reactions of propargylic alcohols with nucleophiles to give the corresponding propargylic-substituted products in good to high yields with a complete selectivity,1 we have found novel transformations of propargylic alcohols catalyzed only by thiolate-bridged diruthenium complexes *To whom correspondence should be addressed. E-mail: ynishiba@ sogo.t.u-tokyo.ac.jp. (1) For recent selected examples, see: (a) Nishibayashi, Y.; Milton, M. D.; Inada, Y.; Yoshikawa, M.; Wakiji, I.; Hidai, M.; Uemura, S. Chem.;Eur. J. 2005, 11, 1433. (b) Inada, Y.; Yoshikawa, M.; Milton, M. D.; Nishibayashi, Y.; Uemura, S. Eur. J. Org. Chem. 2006, 881. (c) Yamauchi, Y.; Onodera, G.; Sakata, K.; Yuki, M.; Miyake, Y.; Uemura, S.; Nishibayashi, Y. J. Am. Chem. Soc. 2007, 129, 5175. (d) Daini, M.; Yoshikawa, M.; Inada, Y.; Uemura, S.; Sakata, K.; Kanao, K.; Miyake, Y.; Nishibayashi, Y. Organometallics 2008, 27, 2046. (e) Yamauchi, Y.; Yuki, M.; Tanabe, Y.; Miyake, Y.; Inada, Y.; Uemura, S.; Nishibayashi, Y. J. Am. Chem. Soc. 2008, 130, 2908. (f) Yada, Y.; Miyake, Y.; Nishibayashi, Y. Organometallics 2008, 27, 3614. (g) Yamauchi, Y.; Miyake, Y.; Nishibayashi, Y. Organometallics 2009, 28, 48. (h) Fukamizu, K.; Miyake, Y.; Nishibayashi, Y. Angew. Chem., Int. Ed. 2009, 48, 2534. (i) Miyake, Y.; Uemura, S.; Nishibayashi, Y. ChemCatChem 2009, 1, 342, and references therein. (2) (a) Dev, S.; Imagawa, K.; Mizobe, Y.; Cheng, G.; Wakatsuki, Y.; Yamazaki, H.; Hidai, M. Organometallics 1989, 8, 1232. (b) Q€u, J.-P.; Masui, D.; Ishii, Y.; Hidai, M. Chem. Lett. 1998, 1003. (c) Hidai, M.; Mizobe, Y. Can. J. Chem. 2005, 83, 358, and references therein. (3) (a) Nishibayashi, Y.; Imajima, H.; Onodera, G.; Hidai, M.; Uemura, S. Organometallics 2004, 23, 26. (b) Nishibayashi, Y.; Imajima, H.; Onodera, G.; Inada, Y.; Hidai, M.; Uemura, S. Organometallics 2004, 23, 5100. (c) Miyake, Y.; Endo, S.; Nomaguchi, Y.; Yuki, M.; Nishibayashi, Y. Organometallics 2008, 27, 4017. (d) Miyake, Y.; Endo, S.; Yuki, M.; Tanabe, Y.; Nishibayashi, Y. Organometallics 2008, 27, 6039. (4) (a) Nishibayashi, Y.; Onodera, G.; Inada, Y.; Hidai, M.; Uemura, S. Organometallics 2003, 22, 873. (b) Inada, Y.; Nishibayashi, Y.; Uemura, S. Angew. Chem., Int. Ed. 2005, 44, 7715. (c) Matsuzawa, H.; Miyake, Y.; Nishibayashi, Y. Angew. Chem., Int. Ed. 2007, 46, 6488. (d) Matsuzawa, H.; Kanao, K.; Miyake, Y.; Nishibayashi, Y. Org. Lett. 2007, 9, 5561. (e) Kanao, K.; Matsuzawa, H.; Miyake, Y.; Nishibayashi, Y. Synthesis 2008, 3869. (f) Fukamizu, K.; Miyake, Y.; Nishibayashi, Y. J. Am. Chem. Soc. 2008, 130, 10498. (g) Kanao, K.; Miyake, Y.; Nishibayashi, Y. Organometallics 2009, 28, 2920. (h) Kanao, K.; Miyake, Y.; Nishibayashi, Y. Organometallics 2010, 29, 2126. (i) Kanao, K.; Tanabe, Y.; Miyake, Y.; Nishibayashi, Y. Organometallics 2010, 29, 2381. (j) Ikeda, M.; Miyake, Y.; Nishibayashi, Y. Angew. Chem., Int. Ed. 2010, 49, 7289. pubs.acs.org/Organometallics

Published on Web 10/22/2010

[Cp*RuCl(μ-SR)]2 (1; R = Me, Et, nPr, iPr).2,3 More recently, we have developed enantioselective versions of these catalytic reactions by using optically active thiolate-bridged diruthenium complexes [Cp*RuCl( μ-SR*)]2 (SR*=(R)-SCH(Et)C6H2Ph3 and (R)-SCH(Et)C6H3Ph2) as catalysts.4 The result of the density functional theory calculation on the model reaction also supports the proposed reaction pathway of the rutheniumcatalyzed propargylic substitution reactions of propargylic alcohols with nucleophiles, where ruthenium-allenylidene complexes work as key intermediates and where the possible charge transfer between two ruthenium atoms (synergistic effect) is one of the key factors to promote the catalytic reactions.5 As an extension of our study, we have envisaged the change from chloride ligand in 1 to a phosphine ligand because the catalytic activity of diruthenium complexes was affected to a considerable degree by halide ligands coordinated to the ruthenium atoms in 1.6 Toward this end, we have designed a stepwise incorporation of two different transition metals to prepare the corresponding thiolate-bridged dinuclear complexes bearing a phosphine ligand (Chart 1). Herein, we describe the results of the preparation of thiolate-bridged dinuclear ruthenium complexes bearing a phosphine ligand and their (5) The result of the density functional theory calculation on the model reaction also supports the proposed reaction pathway of the rutheniumcatalyzed propargylic substitution reactions of propargylic alcohols with nucleophiles, where ruthenium-allenylidene complexes work as key intermediates; see: (a) Ammal, C. S.; Yoshikai, N.; Inada, Y.; Nishibayashi, Y.; Nakamura, E. J. Am. Chem. Soc. 2005, 127, 9428. (b) Sakata, K.; Miyake, Y.; Nishibayashi, Y. Chem. Asian J. 2009, 4, 81. (6) Tanabe, Y.; Kanao, K.; Miyake, Y.; Nishibayashi, Y. Organometallics 2009, 28, 1138. r 2010 American Chemical Society

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Scheme 1

Figure 1. ORTEP view of [Cp*Ru{PhP(C6H4-o-S)2}] (2a) with 50% ellipsoids. Selected interatomic distances (A˚) and angles (deg): Ru-P 2.2650(8), Ru-S1 2.3061(9), Ru-S2 2.3055(9), S1Ru-S2 104.60(4).

catalytic activities toward the propargylic reduction7,8 of propargylic alcohols with 2-propanol in detail.

Results and Discussion Treatment of [Cp*RuCl(μ-Cl)]2 with 2 equiv of [PhP(C6H4-o-SLi)2], which was generated in situ from the reaction of [PhP(C6H4-o-SH)2]9 with 2 equiv of nBuLi in THF at 0 °C for 15 min, in THF at room temperature for 18 h afforded [Cp*Ru{PhP(C6H4-o-S)2}] (2a) in 77% isolated yield (Scheme 1). The complex 2a is paramagnetic. The molecular structure of 2a was confirmed by X-ray crystallography. An ORTEP drawing of 2a is shown in Figure 1. Complex 2a adopts a three-legged piano stool geometry with an S-Ru-S (7) Nishibayashi, Y.; Shinoda, A.; Miyake, Y.; Matsuzawa, H.; Sato, M. Angew. Chem., Int. Ed. 2006, 45, 4835. (8) Georgy, M.; Boucard, V.; Debleds, O.; Zotto, C. D.; Campagne, J.-M. Tetrahedron 2009, 65, 1758. (9) Block, E.; Ofori-Okai, G.; Zubieta, J. J. Am. Chem. Soc. 1989, 111, 2327.

angle of 104.60(4)°. The ruthenium complex bearing a cyclopentadienyl ligand was prepared from the reaction of [CpRu(NCMe)3]PF6 with [PhP(C6H4-o-SLi)2] at room temperature for 18 h to give [CpRu{PhP(C6H4-o-S)2}] (2b) in 68% isolated yield after air oxidation (Scheme 1). Interestingly, treatment of [Cp*FeCl(tmeda)] (tmeda = N,N,N0 N0 -tetramethylethylenediamine) with [PhP(C6H4-o-SLi)2] in THF at room temperature for 18 h afforded [Cp*Fe{PhP(C6H4-o-S)2}] (2c) in 74% isolated yield after air oxidation (Scheme 1). The molecular structures of 2b and 2c were similar to that of 2a. ORTEP drawings of 2b and 2c are shown in Figures S1 and S2. The reaction of [Cp*RuCl( μ-Cl)]2 with 2 equiv of 2a in CH2Cl2 at room temperature for 20 h afforded dicationic diruthenium complex [Cp*Ru{PhP(C6H4-o-S)2}RuCp*](OTf)2 (4a; OTf = OSO2CF3) in 83% isolated yield after treatment of crude monocationic diruthenium complex [Cp*Ru{PhP(C6H4-o-S)2}RuCp*Cl]Cl10 (3a) with 2 equiv of AgOTf in dichloromethane at room temperature for 1 h (Scheme 2). The 1H NMR spectrum of 4a shows two Cp* signals as a doublet signal at 1.70 ppm (JHP = 2 Hz) and a singlet signal at 1.48 ppm in a 1:1 ratio. The molecular structure of 4a was confirmed by X-ray crystallography. An ORTEP drawing of 4a is shown in Figure 2. The distance between the two ruthenium atoms of 4a (2.6170(6) A˚) indicates the presence of a direct bonding interaction between them similar to those of the thiolate-bridged diruthenium complexes.2,3 The reaction of [Cp*RuCl( μ-Cl)]2 with 2 equiv of 2b under the same reaction conditions afforded dicationic diruthenium complex [CpRu{PhP(C6H4-o-S)2}RuCp*(OH2)](OTf )2 (4b) in 82% isolated yield after treatment with 2 equiv of AgOTf (Scheme 2). The 1H NMR spectrum of 4b shows a Cp signal and Cp* signals at 5.57 and 1.79 ppm, respectively, in a 5:15 ratio. The molecular structure of 4b was confirmed by X-ray crystallography. An ORTEP drawing of 4b is shown in Figure 3, where one H2O molecule, probably derived from adventitious (10) Unfortunately, we have not yet isolated 3a as an analytically pure form from the reaction mixture, but the molecular structure of 3a was characterized by X-ray crystallography (Figure S3). A related diruthenium complex [Cp*Ru{S(CH2CH2S)2}RuCp*Cl]PF6 was previously prepared from the reaction of [Cp*RuCl(μ-Cl)]2 with [Cp*Ru{S(CH2CH2S)2}] according to the same methodology. Goh, L. Y.; Teo, M. E.; Khoo, S. B.; Leong, W. K.; Vittal, J. J. J. Organomet. Chem. 2002, 664, 161.

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Figure 2. ORTEP view of the cationic part in [Cp*Ru{PhP(C6H4o-S)2}RuCp*](OTf)2 (4a). Selected interatomic distances (A˚) and angles (deg): Ru1-Ru2 2.6170(6), Ru1-P 2.3005(16), Ru1-S 2.2890(11), Ru2-S 2.3140(11), S-Ru1-S* 111.03(5), S-Ru2-S* 109.25(5). Asterisks denote atoms related by symmetry operation þx, -y, þz.

water in solvents, was coordinated to the Cp*Ru moiety in 4b. The distance between the two ruthenium atoms of 4b (2.7784(9) A˚) indicates the presence of a direct bonding interaction between them. In a similar procedure, dicationic iron-ruthenium dinuclear complex [Cp*Fe{PhP(C6H4-o-S)2}RuCp*](OTf)2 (4c) was obtained in 77% isolated yield from the reaction of [Cp*RuCl(μ-Cl)]2 with 2 equiv of 2c and further treatment with 2 equiv of AgOTf (Scheme 2). The 1H NMR spectrum of 4c shows two Cp* signals as a doublet at 1.60 ppm (JHP = 2 Hz) and a singlet at 1.45 ppm in a 1:1 ratio, corresponding

Figure 3. ORTEP view of the cationic part in [CpRu{PhP(C6H4o-S)2}RuCp*(OH2)](OTf)2 (4b). Selected interatomic distances (A˚) and angles (deg): Ru1-Ru2 2.7784(9), Ru1-P 2.258(2), Ru1-S1 2.296(2), Ru1-S2 2.289(2), Ru2-S1 2.306(2), Ru2-S2 2.324(2), Ru2-O1 2.181(5), S1-Ru1-S2 103.29(8), S1-Ru2-S2 101.92(8).

to the Cp*Fe and Cp*Ru moieties, respectively. The molecular structure of 4c was confirmed by X-ray crystallography. An ORTEP drawing of 4c is shown in Figure 4. The ironruthenium distance (2.5639(10) A˚) indicates the presence of a bonding interaction between the two metal centers. Next, we examined the catalytic activity of the dinuclear complexes 4 toward reactions of propargylic alcohols with 2-propanol. Typical results are shown in Table 1. Heating of 1-phenyl-2-propyn-1-ol (5a) with 4 equiv of 2-propanol in the presence of 5 mol % of 4a in 1,2-dichloroethane at 60 °C for 2 h gave 3-phenyl-1-propyne (6a) in 90% GLC yield (Table 1, run 1). This catalytic reduction proceeded even at

Scheme 2

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Figure 4. ORTEP view of the cationic part in [Cp*Fe{PhP(C6H4o-S)2}RuCp*](OTf)2 (4c). Selected interatomic distances (A˚) and angles (deg): Fe-Ru 2.5639(10), Fe-P 2.231(2), Fe-S 2.2046(12), Ru-S 2.2898(12), S-Fe-S* 113.00(7), S-Ru-S* 106.81(6). Asterisks denote atoms related by symmetry operation þx, þy, 1/2-z.

room temperature, although a prolonged reaction time such as 70 h was necessary to complete the reaction (Table 1, run 2). When the reaction was carried out in THF and toluene, in place of 1,2-dichloroethane, 6a was obtained in high yields, but a longer reaction time such as 20 h was required for completion (Table 1, runs 3 and 4). In contrast, the catalytic reduction of propargylic alcohols did not proceed smoothly when other polar solvents such as acetone, acetonitrile, and ethanol were used (Table 1, runs 5-7). Use of 2 equiv of 2-propanol in 1,2-dichloroethane at 60 °C gave 6a in a similar high yield (Table 1, run 8). But, 6a was produced in a substantially lower yield when only 1.2 equiv of 2-propanol was used as a reducing reagent (Table 1, run 9). Use of 2 mol % of 4a as a catalyst was not enough to obtain 6a in high yield (Table 1, run 10). When benzyl alcohol was used in place of 2-propanol as a reductant, 6a was obtained in 74% yield together with benzyl propargylic ether in 10% yield (Table 1, run 11). Interestingly, the reaction of 5a in the absence of 2-propanol under the same reaction conditions gave only 6a in 12% yield together with the corresponding ether and ketones in 46% and 11% yields, respectively (Table 1, runs 12). These results indicate that 2-propanol works as a more effective reducing agent than benzyl alcohol toward the propargylic reduction of propargylic alcohols.

Dinuclear complexes 4b and 4c have a similar catalytic activity toward the propargylic reduction. 6a was obtained in 75% and 80% yields, respectively, under the same reaction conditions (Table 1, runs 13 and 14). In sharp contrast to the unique catalytic activity of 4 toward the propargylic reduction, other thiolate-bridged durthenium complexes such as 1a (R = Me), 3a, 7a (R = Me), [Cp*Ru( μ-SMe)RuCp*(OH2)](OTf)2 (8a; R=Me), chloride-bridged diruthenium complex

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[Cp*RuCl( μ-Cl)]2, and other transition metal complexes such as FeCl3 3 6H2O11 and MeReO512 did not work at all as catalysts.13 These results indicate that only the dinuclear complexes 4 work as effective catalysts toward the propargylic reduction of propargylic alcohols with 2-propanol. Next, the propargylic reduction of other propargylic alcohols with 2-propanol was carried out in the presence of 5 mol % of 4a as a catalyst. Typical results are shown in Table 2. Introduction of a methyl, chloro, or phenyl group to the benzene ring of propargylic alcohol did not affect much the yields of the corresponding alkynes (Table 2, runs 2-7). A similar reactivity was observed when 1-naphthyl-2-propyn-1-ols were used as substrates (Table 2, runs 8 and 9). Unfortunately, no propargylic reduction occurred at all in reactions of 1-cyclohexyl-2-propyn-1-ol and 1,1-diphenyl-1-propyn-1-ol with 2-propanol (Table 2, runs 10 and 11). These results indicate that only the use of 1-aryl-2-propyn-1-ols as substrates promotes the propargylic reduction catalyzed by 4a as a catalyst. Separately, we confirmed that thiolate-bridged dinuclear complexes 4 as catalysts promote the propargylic reduction of only propargylic alcohols bearing a terminal alkyne moiety with 2-propanol as a reducing reagent. In fact, the corresponding propargylic reduced products were not obtained from reactions of propargylic alcohol bearing an internal alkyne moiety as a substrate with 2-propanol. This is complementary to our previous findings that only monocationic thiolatebridged diruthenium complexes 7 worked as effective catalysts to promote the propargylic reduction of propargylic alcohols bearing an internal alkyne moiety with triethylsilane.7 To get more information on the reaction pathway, we investigated the following catalytic reactions. When 5d was treated with 2-propanol-d8 in the presence of a catalytic amount of 4a, deuterated 6d-d2 was produced with high deuterium incorporation at the propargylic position (94%) (Scheme 3). This result indicates that 2-propanol works as a reducing agent for the propargylic reduction at the propargylic position. The relatively low deuterium incorporation at the C-1 position (49%) of 6d-d2 is considered to be due to the exchange of the proton of the hydroxyl group in 2-propanol-d8 with that of 5d or produced water from 5d. The propargylic reduction did not proceed smoothly when propargylic ether was used in place of propargylic alcohol as a substrate in the presence of 5 mol % of 4a in 1,2-dichloroethane at 60 °C for 20 h (Scheme 4). In fact, the corresponding alkyne 6a was obtained only in 27% yield, and the unreacted propargylic ether was recovered in 21% recovery from the reaction mixture. This result indicates that this propargylic reduction of propargylic alcohols with 2-propanol did not proceed via propargylic ether as a reactive intermediate. On the basis of experimental results described in this paper, we propose a reaction pathway for the propargylic reduction of propargylic alcohols bearing a terminal alkyne moiety with 2-propanol as shown in Scheme 5. The initial step is the formation of the allenylidene complex14 (B) by the (11) Huang, W.; Zhang, Z.; Xiang, X.; Liu, R.; Zhou, X. J. Org. Chem. 2009, 74, 3299. (12) Zhu, Z.; Espenson, J. H. J. Org. Chem. 1996, 61, 324. (13) Wang, J.; L’Hermite, N.; Giraud, A.; Provot, O.; Peyrat, J.-F.; Alami, M.; Brion, J.-D. Tetrahedron 2006, 62, 11994. (14) For recent reviews of transition metal-allenylidene complexes, see: (a) Bruneau, C.; Dixneuf, P. H. Angew. Chem., Int. Ed. 2006, 45, 2176. (b) Metal Vinylidenes and Allenylidenes in Catalysis: From Reactivity to Applications in Synthesis; Bruneau, C., Dixneuf, P. H., Eds.; WileyVCH: Weinheim, 2008. (c) Cadierno, V.; Gimeno, J. Chem. Rev. 2009, 109, 3512.

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Table 1. Ruthenium-Catalyzed Propargylic Reduction of Propargylic Alcohol (5a) with 2-Propanola

run

catalyst (mol %)

2-propanol (equiv)

solvent

temp (°C)

time (h)

yieldb (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14

4a (5) 4a (5) 4a (5) 4a (5) 4a (5) 4a (5) 4a (5) 4a (5) 4a (5) 4a (2) 4a (5) 4a (5) 4b (5) 4c (5)

4 4 4 4 4 4 4 2 1.2 2 2d -f 2 2

ClCH2CH2Cl ClCH2CH2Cl THF toluene acetone MeCN EtOH ClCH2CH2Cl ClCH2CH2Cl ClCH2CH2Cl ClCH2CH2Cl ClCH2CH2Cl ClCH2CH2Cl ClCH2CH2Cl

60 rt 60 60 60 60 60 60 60 60 60 60 60 60

2 70 20 20 20 20 20 2 2 6 1 2 2 2

90 97 95 93 2 0 8 90 (76)c 68 57 74e 12g 75 80

a All reactions of 5a (0.20 mmol) with 2-propanol were carried out in the presence of catalyst in ClCH2CH2Cl (1.0 mL). b GLC yield of 6a. c Isolated yield of 6a. d Benzyl alcohol was used in place of 2-propanol. e Benzyl propargylic ether was formed in 10% yield. f The reaction was carried out in the absence of 2-propanol. g Bis(l-phenyl-2-propyl) ether and 1-phenyl-2-propyn-1-one were formed in 46% and 11% yields, respectively.

Table 2. Ruthenium-Catalyzed Propargylic Reduction of Propargylic Alcohols (5) with 2-Propanola

Scheme 3

Scheme 4 run

5, R1, R2

time (h)

yield b (%)

1 2 3 4 5 6 7 8 9 10 11

5a, Ph, H 5b, p-MeC6H4, H 5c, p-ClC6H4, H 5d, p-PhC6H4, H 5e, o-MeC6H4, H 5f, 2,4-Cl2C6H3, H 5g, 2,6-Me2C6H3, Hc 5h, 2-naphthyl, H 5i, 1-naphthyl, H 5j, cyclohexyl, H 5k, Ph, Ph

2 2 2 2 2 6 2 2 4 2 6

6a, 76 6b, 87 6c, 85 6d, 80 6e, 82 6f, 59 6g, 66 6h, 83 6i, 56 6j, 0d 6k, 0e

a All reactions of 5 (0.20 mmol) with 2-propanol (0.40 mmol) were carried out in the presence of 4a (0.01 mmol) in ClCH2CH2Cl (1.0 mL) at 60 °C. b Isolated yield of 6. c 10 mol % of 4a was used as a catalyst. d 1-Ethynylcyclohex-l-ene was formed in 90% yield. e β-Phenylcinnamaldehyde was formed in 88% yield.

reaction of propargylic alcohol 5 with 4a via the vinylidene complex (A).15 The attack of the oxygen atom of 2-propanol on the R-carbon atom of B resulted in the formation of the alkoxycarbene complex14 (D) via the transition state with 2-propanol (C). Then, the intramolecular hydrogen transfer at the 2-position of 2-propanoxide into the γ-carbon atom of D leads to the vinylidene complex (E) together with the formation of acetone. Finally, the reduced product 6 is formed from E by ligand exchange with another propargylic alcohol 5. The exact reason that only the thiolate-bridged dinuclear complexes bearing a phosphine ligand 4a promote the propargylic reduction of propargylic alcohols with 2-propanol (15) The stoichiometric reaction of 4a with 5a gave only a complex mixture, although the IR spectrum of the reaction mixture showed an absorbance at 1960 cm-1.

has not yet been determined, but we believe that this catalytic reaction proceeds via ruthenium-allenylidene complexes as key reactive intermediates. At present, we consider that the dicationic 4a may increase the electrophilic property at the R-carbon of the allenylidene ligand. Thus, the presence of the phosphine ligand may promote the attack of the oxygen atom in 2-propanol on the electrophilic R-carbon in the allenylidene ligand. This result is in sharp contrast to our previous findings that thiolate-bridged diruthenium complexes 1 and 7 work as effective catalysts toward the propargylic substitution reactions of propargylic alcohols with 2-propanol as a nucleophile to give the corresponding propargylic ethers in good to high yields with complete selectivity (Scheme 6). In summary, we have newly prepared thiolate-bridged dinuclear ruthenium complexes 4 bearing a phosphine ligand ([Cp*Ru{PhP(C6H4-o-S)2}RuCp*](OTf )2, [CpRu{PhP(C6H4o-S)2}RuCp*(OH2)](OTf )2, and [Cp*Fe{PhP(C6H4-o-S)2}RuCp*](OTf )2) and characterized them by X-ray analysis. These dinuclear ruthenium complexes 4 have been revealed to work as effective catalysts toward the propargylic reduction of propargylic alcohols with 2-propanol via allenylidene complexes as key intermediates to give the corresponding alkynes in good to high yields. The result described in this article provides a new concept of design of the preparation of dinuclear complexes having a unique catalytic activity. Further work is

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Scheme 6

currently in progress to broaden its synthetic applicability to thiolate-bridged dinuclear ruthenium complexes bearing other ligands and to develop unique catalytic properties of these dinuclear complexes.

Experimental Section General Methods. All manipulations were carried out using standard Schlenk-line techniques. Solvents were dried over appropriate agents under an atmosphere of dinitrogen. Compounds PhP(C6H4-o-SH)2,9 [Cp*RuCl( μ-Cl)]2,16 and [Cp*FeCl(tmeda)]17 were prepared by the literature methods. Other reagents were used as purchased from commercial sources including AgOTf. NMR spectra were recorded on JEOL JNM-EX270 spectrometers, and chemical shifts are quoted in ppm. 31P chemical shifts were reported relative to an external standard of 85% H3PO4. GLC analyses were carried out on a Shimadzu GC-MS QP-2010/ PARVUM2 instrument using a 30 m 0.25 mm Rtx-5MS fused (16) (a) Tilley, T. D.; Grubbs, R. H.; Bercaw, J. E. Organometallics 1984, 3, 274. (b) Oshima, N.; Suzuki, H.; Moro-oka, Y. Chem. Lett. 1984, 1161. (17) Jonas, K.; Klusmann, P.; Goddard, R. Z. Naturforsch., B: Chem. Sci. 1995, 50, 394.

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silica capillary column. Elemental analyses were performed on an Exeter Analytical CE-440 elemental analyzer or at the Microanalytical Center of The University of Tokyo. Preparation of [Cp*Ru{PhP(C6H4-o-S)2}] (2a). To a solution of [PhP(C6H4-o-SH)2] (653 mg, 2.00 mmol) in THF (20 mL) was added nBuLi (1.57 M in hexane, 2.60 mL, 4.08 mmol) at 0 °C. After 15 min, the resulting yellow solution was added to a suspension of [Cp*RuCl(μ-Cl)]2 (609 mg, 0.991 mmol) in THF (10 mL) at room temperature. The mixture was stirred at room temperature for 18 h. The purple solution was concentrated to dryness, leaving a purple solid. Recrystallization from CH2Cl2-hexane gave purple needles of 2a 3 0.5CH2Cl2 (916 mg, 1.52 mmol, 77%). Anal. Calcd for C28H28PRuS2: C, 59.98; H, 5.03. Found: C, 60.24; H, 4.84. Preparation of [CpRu{PhP(C6H4-o-S)2}] (2b). To a solution of [PhP(C6H4-o-SH)2] (163 mg, 0.498 mmol) in THF (15 mL) was added nBuLi (1.65 M in hexane, 0.60 mL, 0.990 mmol) at 0 °C. After 30 min, the yellow solution was added to a solution of [CpRu(NCMe)3]PF6 (219 mg, 0.504 mmol) in THF (10 mL) at room temperature. The resulting red-brown solution was stirred at room temperature overnight (18 h). The solution was airoxidized over 3 h, giving an orange-brown solution, which was concentrated under reduced pressure. The product was purified by passing through a silica gel pad with CH2Cl2 as eluent. Recrystallization from THF-hexane afforded black rectangles of 2b 3 0.5C6H14 (182 mg, 0.341 mmol, 68%). Anal. Calcd for C23H18PRuS2: C, 56.31; H, 3.70. Found: C, 56.13; H, 3.89. Preparation of [Cp*Fe{PhP(C6H4-o-S)2}] (2c). To a solution of [PhP(C6H4-o-SH)2] (326 mg, 1.00 mmol) in 20 mL of THF was added nBuLi (1.57 M in hexane, 1.28 mL, 2.01 mmol) at 0 °C. After 15 min, the yellow solution was transferred to a flask containing a solution of [Cp*FeCl(tmeda)] (343 mg, 1.00 mmol) in THF (10 mL), and the mixture was stirred at room temperature for 18 h. The resulting dark green solution was exposed to air with vigorous stirring for 1 h. The solution turned purple immediately. The product was purified by passing through a silica gel pad with CH2Cl2 as eluent. Recrystallization from CH2Cl2hexane afforded purple needles of 2c (382 mg, 0.741 mmol, 74%). Anal. Calcd for C28H28FePS2: C, 65.24; H, 5.48. Found: C, 65.13; H, 5.43. Preparation of [Cp*Ru{PhP(C6H4-o-S)2}RuCp*Cl]Cl (3a). A mixture of 2a (113 mg, 0.201 mmol) and [Cp*RuCl( μ-Cl)]2 (61.5 mg, 0.100 mmol) in CH2Cl2 (10 mL) was stirred at room temperature for 20 h. The solution was concentrated to dryness. The brown residue was washed with THF. Recrystallization from CH2Cl2-hexane afforded amber prisms of 3a 3 CH2Cl2 (167 mg, 0.175 mmol, 88%). 1H NMR (CD2Cl2): δ 7.67-7.58 (m, 3H), 7.50-7.39 (m, 4H), 7.35-7.26 (m, 4H), 7.13-7.03 (m, 2H), 1.68 (s, 15H), 1.62 (d, J = 2 Hz, 15H). 31P{1H} NMR (CD2Cl2): δ 99.2 (s). Preparation of [Cp*Ru{PhP(C6H4-o-S)2}RuCp*](OTf)2 (4a). A mixture of 2a (114 mg, 0.203 mmol) and [Cp*RuCl( μ-Cl)]2 (60.4 mg, 0.0983 mmol) in CH2Cl2 (10 mL) was stirred at room temperature for 20 h. To the solution was added AgOTf (113 mg, 0.438 mmol). The mixture was stirred at room temperature for 1 h. Filtration and concentration of the reaction mixture, followed by recrystallization first from EtOH-ether, then from CH2Cl2-hexane, gave a crystalline solid of 4a 3 0.5CH2Cl2 (186 mg, 0.164 mmol, 83%). 1H NMR (CD2Cl2): δ 8.45 (dd, J=8 and 2 Hz, 2H), 7.92-7.83 (m, 2H), 7.69-7.45 (m, 7H), 6.84-6.75 (m, 2H), 1.70 (d, J = 2 Hz, 15H), 1.48 (s, 15H). 31P{1H} NMR (CD2Cl2): δ 94.8 (s). Anal. Calcd for C40.5H44ClF6O6PRu2S4 (4a 3 0.5CH2Cl2): C, 42.76; H, 3.90. Found: C, 42.89; H, 3.74. Preparation of [CpRu{PhP(C6H4-o-S)2}RuCp*(OH2)](OTf)2 (4b). A mixture of 2b (50.0 mg, 0.102 mmol) and [Cp*RuCl( μ-Cl)]2 (30.0 mg, 0.0488 mmol) in CH2Cl2 (5 mL) was stirred at room temperature for 20 h. To the solution was added AgOTf (55.6 mg, 0.216 mmol). The mixture was stirred at room temperature for 1 h. Filtration and concentration of the reaction mixture, followed by recrystallization from CH2Cl2-hexane,

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Table 3. Summary of Crystallographic Data 2a 3 0.5C6H14

4a 3 0.5CH2Cl2

4b 3 CH2Cl2

C42.5H50F6FeO7PRuS4 1102.95 0.50  0.15  0.03 dark green plate trigonal P63/m (No. 176) 26.4554(11) 26.4554(11) 11.6852(5) 90 90 120 7082.6(5) 6 1.552 0.909 65 488 5652 (0.138) 528 0.053 0.140 1.12 0.03(4) þ1.90 to -1.67

)

)

formula C31H35PRuS2 C40.5H44F6O6PRu2S4 C36H36Cl2F6O7PRu2S4 fw 603.75 1102.95 1126.90 cryst size/mm 0.50  0.40  0.35 0.50  0.15  0.03 0.25  0.25  0.05 color, habit purple needle green plate green plate cryst syst monoclinic monoclinic monoclinic C2/m (No. 12) Pn (No. 7) space group P21/c (No. 14) a/A˚ 8.1044(3) 18.0789(7) 11.6815(9) b/A˚ 20.0487(5) 12.7091(6) 12.2521(12) c/A˚ 17.4171(5) 20.9807(7) 15.3294(15) R/deg 90 90 90 β/deg 99.3060(10) 109.7230(10) 104.493(5) γ/deg 90 90 90 2792.73(15) 4537.9(3) 2124.2(3) V/A˚3 Z 4 4 2 -3 1.436 1.665 1.762 dc/g cm 0.787 1.013 1.144 μ(Mo KR)/mm-1 no. of data collected (2θ < 55°) 22 189 22 117 19 363 5101 (0.026) 5375 (0.041) 9030 (0.071) no. of unique data (Rint) no. of params refined 321 267 315 0.038 0.054 0.061 R1a (F2 > 2σ) 0.104 0.170 0.158 wR2b (all data) c 1.09 1.08 1.04 goodness of fit indicator Flack param þ1.35 to -0.67 þ1.68 to -1.46 þ0.62 to -0.60 residual electron density/e A˚-3 P P P P P a R1 = Fo| - |Fc / |Fo|. b wR2 = [ w(Fo2 - Fc2)2/ w(Fo)2]1/2. c [ w(Fo2 - Fc2)2/(Nobs - Nparam)]1/2.

4c 3 0.75EtOH 3 0.25Et2O

gave a green crystalline solid of 4b 3 0.5CH2Cl2 (87.4 mg, 0.0805 mmol, 82%). 1H NMR (CD2Cl2): δ 7.94 (dd, J = 8 and 2 Hz, 2H), 7.68-7.45 (m, 9H), 7.23 (dd, J = 13 and 7 Hz, 2H), 5.37 (s, 5H), 1.77 (s, 15H). 31P{1H} NMR (CD2Cl2): δ 103.1 (s). Anal. Calcd for C35.5H36ClF6O7PRu2S4 (4b 3 0.5CH2Cl2): C, 39.28; H, 3.34. Found: C, 39.20; H, 3.27. Preparation of [Cp*Fe{PhP(C6H4-o-S)2}RuCp*](OTf )2 (4c). A mixture of 2c (111 mg, 0.216 mmol) and [Cp*RuCl( μ-Cl)]2 (61.0 mg, 0.0993 mmol) in CH2Cl2 (10 mL) was stirred at room temperature for 20 h. To the solution was added AgOTf (110 mg, 0.428 mmol). The mixture was stirred at room temperature for 1 h. Filtration and concentration of the reaction mixture, followed by recrystallization first from EtOH-ether, then from CH2Cl2-hexane, gave a green crystalline solid of 4c 3 0.5CH2Cl2 (167 mg, 0.153 mmol, 77%). 1H NMR (CD2Cl2): δ 8.47 (dd, J= 8 and 2 Hz, 2H), 7.92-7.82 (m, 2H), 7.67-7.40 (m, 7H), 6.806.69 (m, 2H), 1.60 (s, 15H), 1.45 (s, 15H). 31P{1H} NMR (CD2Cl2): δ 110.9 (s). Anal. Calcd for C40.5H44ClF6FeO6PRuS4 (4c 3 0.5CH2Cl2): C, 44.53, H, 4.06. Found: C, 44.55; H, 3.88. Catalytic Propargylic Reduction of Propargylic Alcohols with 2-Propanol. A typical procedure for the reaction of 5a with 2-propanol catalyzed by 4a is described below. To a solution of 5a (27.3 mg, 0.207 mmol) and 2-propanol (30.6 μL, 0.400 mmol) in dichloroethane (1.0 mL) was added 4a (11.4 mg, 0.010 mmol). The solution was heated at 60 °C for 2 h. After cooling, the solution was diluted with pentane (10 mL). The solution was passed through a short silica gel column (2 cm  5 cm) with pentane (20 mL) as eluent. Concentration of the eluent gave 6a18 (18.4 mg, 0.158 mmol, 76%) as a colorless oil. 3-Aryl-1-propynes (6b,19 6c,18 6d,20 6e,21 and 6g20) were known compounds. Spectroscopic data for other compounds 6 are as follows. 3-(2,4-Dichlorophenyl)-1-propyne (6f): colorless oil. 1H NMR (CDCl3): δ 7.56 (d, J = 8 Hz, 1H), 7.38 (d, J = 2 Hz, 1H), 7.25 (dd, J=8 and 2 Hz, 1H), 3.64 (d, J=3 Hz, 2H), 2.26 (t, J=3 Hz, 1H). 13C{1H} NMR (CDCl3): δ 134.0, 133.3, 132.4, 130.3, 129.0, (18) Libman, N. M.; Dmitrieva, T. L.; Kuznetsov, S. G.; Andreev, A. A. J. Org. Chem. USSR 1979, 15, 112. (19) Pincock, J. A.; Somawardhana, C. Can. J. Chem. 1978, 56, 1164. (20) Taherirastgar, F.; Brandsma, L. Synth. Commun. 1997, 27, 4035. (21) Heimgartner, H.; Zsindely, J.; Hansen, H.-J.; Schmid, H. Helv. Chim. Acta 1972, 55, 1113.

127.2, 80.0, 71.8, 22.6. HRMS(EI): calcd for C9H6Cl2 [M] 183.9847, found 183.9846. 3-(2-Naphthyl)-1-propyne (6h): white solid, mp 53.6-54.4 °C. 1 H NMR (CDCl3): δ 7.86-7.78 (m, 4H), 7.52-7.43 (m, 3H), 3.78 (d, J = 3 Hz, 2H), 2.27 (t, J = 3 Hz, 1H). 13C{1H} NMR (CDCl3): δ 133.5, 132.4, 128.2, 127.62, 127.60, 126.3, 126.2, 126.1, 125.6, 81.9, 70.7, 25.0. Anal. Calcd for C13H10: C, 93.94; H, 6.06. Found: C, 93.81; H, 6.18. 3-(1-Naphthyl)-1-propyne (6i): colorless oil. 1H NMR (CDCl3): δ 8.05 (d, J=8 Hz, 1H), 7.92-7.86 (m, 1H), 7.79 (d, J=8 Hz, 1H), 7.65 (dd, J = 7 and 1 Hz), 7.61-7.42 (m, 3H), 4.03 (d, J = 3 Hz, 2H), 2.28 (t, J=3 Hz, 1H). 13C{1H} NMR (CDCl3): δ 133.7, 131.9, 131.3, 128.7, 127.7, 126.2, 125.8, 125.7, 125.6, 123.2, 81.6, 71.3, 22.7. HRMS(EI): calcd for C13H10 [M] 166.0783, found 166.0784. X-ray Crystallography. Crystallographic data are given in Table 3. The paraffin-coated crystals were placed on a nylon loop and mounted on a Rigaku RAXIS RAPID imagining plate system. Data were collected at -100 °C under a cold nitrogen stream using graphite-monochromated Mo KR radiation (λ = 0.71069 A˚). Data were corrected for Lorenz, polarization, and absorption effects. Structures were solved by direct methods (SIR97)22 and refined on F2 by full-matrix least-squares techniques. Anisotropic thermal parameters were introduced for all non-hydrogen atoms. Hydrogen atoms were treated as riding atoms. In the crystal of 4a 3 0.5CH2Cl2, one Cp* ligand and one triflate anion were disordered. The Cp* ligand was treated as two rigid groups with site occupancy factors of 50% each, and the positional parameters of the triflate anion were fixed at the final stage of refinement to reach better convergence. In the crystal of 4c 3 0.75EtOH 3 0.25Et2O, solvent molecules and one of two triflate anions were heavily disordered and could not be modeled appropriately. The electron density associated with these fragments was removed by SQUEEZE.23 All calculations were carried out using WinGX/SHELXL software suites.24,25 (22) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. C.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115. (23) Spek, A. L. PLATON99, A Multipurpose Crystallographic Tool; Utrecht University: Utrecht, The Netherlands, 1999. (24) Sheldrick, G. M. SHELX-97; University of G€ottingen: G€ottingen, Germany, 1998. (25) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.

Article The thermal ellipsoid plots were drawn with ORTEP3.26 Crystallographic data are given in a CIF file.

Acknowledgment. This work was supported by a Grant-in-Aid for Scientific Research for Young Scientists (S) (No. 19675002) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. (26) Farrugia, L. J. ORTEP3 for Windows. J. Appl. Crystallogr. 1997, 30, 565.

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Supporting Information Available: Crystallographic data for 2, 3, and 4 are available in CIF format. This material is available free of charge via the Internet at http://pubs. acs.org.

Note Added after ASAP Publication. This paper was published on the Web on Oct 22, 2010, with an error in Table 1, footnote g and in the tenth paragraph of the Experimental Section. The corrected version was reposted on Oct 27, 2010.