RUTHENIUM-PHOSPHINE COMPLEXES

Abstract: A ruthenium-phosphine complex is represented by the formula: [RuH₁(R-BINAP) m ]X n , (I) wherein R-BINAP is a tertiary phosphine represented by formula (II): R is hydrogen or metal; X is ClO₄, BF₄ or PF₆; and when l is 0, then m is 1 and n′ is 2, and when l is 1, then m is 2 and n′ is 1. Synthesis methods are (a) Ru₂ Cl₄(R-BINAP)₂(N(C₂H₅)₂) reacted with a salt MX where M is Na, K, Li, Mg or Ag in mixed water and methylene chloride in presence of a quaternary ammonium or phosphonium salt as transfer agent, (b) Ru(R-BINAP) (OAc)₂ reacted with an acid HX with stirring in mixed methylene chloride and methanol; and (c) RuHCl(R-BINAP)₂ reacted with MX in mixed water and methylene chloride in presence of a quaternary ammonium or phosphonium salt, to give complex where l=1, m=2 and n′=1. The complex is used as catalyst in synthesis, especially asymmetric hydrogenation of allyl alcohols, and is effective at pressure even at room temperature, e.g. for making citronellol from geraniol, in high selectivity.

Description: The present invention relates to a ruthenium-phosphine complex that can be used as a catalyst not only in various organic syntheses but also is asymmetric syntheses such as asymmetric hydrogenation and asymmetric isomerization. A number of organic synthetic reactions using metal complexes as a catalyst have been devised and utilized for many purposes. In particular, many reports have been made on asymmetric catalysts that are used in asymmetric syntheses typified by asymmetric isomerization and asymmetric hydrogenation. Among them, metal complexes composed of metallic rhodium and an optically active tertiary phosphine are well known as a catalyst for asymmetric hydrogenation, and a rhodium-phosphine complex using 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (hereinafter abbreviated as BINAP) as a ligand is reported in J. Am. Chem. Soc. , 102 , pp. 7932-7934 (1980). Further, it is reported in Inoue et al., Chemistry Letters , pp. 1007-1008 (1985) that asymmetric hydrogenation of geraniol or nerol was performed by using various rhodium-phosphine catalysts to obtain citronellol in an optical yield of 66%. On the other hand, known ruthenium complexes, though not so widely studied as compared with rhodium complexes, include those having BINAP or 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl (hereinafter abbreviated as T-BINAP) as a ligand, i.e., Ru₂Cl₄(BINAP)₂(NEt₃) (wherein Et represents an ethyl group, which abbreviation is used hereinafter) and Ru₂Cl₄(T-BINAP)₂(NEt₃), as reported in Ikariya et al, J. Chem. Soc., Chem. Commun., pp. 922 (1985). However, the known ruthenium complexes are not satisfactory in stability as well as yield of optically active product. Although metallic rhodium provides excellent complex catalysts, it is expensive due to limitation in place and quantity of production. When used as a catalyst component, it forms a large proportion in the cost of the catalyst, ultimately resulting in an increase in cost of the final commercial products. While metallic ruthenium is cheaper than rhodium and appears promising as a catalyst component for industrial application, there still are problems as regards its activity to cope with precision reactions and its range of application. Our EP 0235450 summarises the improved BINAP-ruthenium complexes of our EP 0156607, 0170470 and 0174057. There is still a need for a further such catalyst which is inexpensive, has high activity and durability, and catalyzes asymmetric reactions to attain high optical yields, i.e., to produce reaction products having high optical purity. As a result of extensive investigations in order to meet the above-described industrial demand, the inventors have discovered a novel ruthenium complex having high catalytic activity, which is usable either for general syntheses when the ligand thereof is optically inactive or for asymmetric syntheses when the ligand thereof is optically active. The present invention relates to a ruthenium-phosphine complex represented by formula (I): [RuH ℓ (R-BINAP) m ]X n′ (I) wherein R-BINAP is a tertiary phosphine represented by formula (II): R is a hydrogen atom or a methyl group; X is ClO₄, BF₄ or PF₆; and when ℓ is 0, then m is 1 and n′ is 2, and when ℓ is 1, then m is 2 and n′ is 1. A ruthenium-phosphine complex of formula (I) wherein ℓ is 0, m is 1, and n′ is 2 is produced by reacting, as a starting compound, Ru₂Cl₄(R-BINAP)₂(NEt₃) (this compound can be prepared by the method disclosed in European Patent No. 174,057A) with a salt represented by formula (III): MX (III) wherein M is a metal selected from Na, K, Li, Mg and Ag; and X is ClO₄, BF₄ or PF₆, in a solvent composed of water and methylene chloride in the presence of, as a phase transfer catalyst, a quaternary ammonium salt or a quaternary phosphonium salt represented by formula (IV): R¹R²R³R⁴QZ (IV) wherein R¹, R², R³, and R⁴ are each an alkyl group having from 1 to 16 carbon atoms, a phenyl group or a benzyl group; Q is nitrogen or phosphorus; and Z is a halogen. The reaction between Ru₂Cl₄(R-BINAP)₂(NEt₃) and the salt of formula (III) is carried out by adding these two compounds and the phase transfer catalyst of formula (IV) in a mixed solvent of water and methylene chloride and stirring the mixture. The salt of formula (III) is used in an amount of from 2 to 10 moles and preferably 5 moles per mole of the ruthenium, and the phase transfer catalyst of formula (IV) is used in an amount of from 1/100 to 1.10 mole per mole of the ruthenium, respectively. It suffices to continue the stirring for a period of time of from 6 to 18 hours and typically 12 hours at a temperature of from 5 to 30°C, and an optimum condition is determined depending on the types of the starting complex and the salt of formula (III) used. It is generally advantageous to mix water and methylene chloride in substantially equal amounts. The salt of formula (III) and the phase transfer catalyst of formula (IV) are added to the reaction system after being dissolved in water. Examples of the salt formula (III) include perchlorates, borofluorides and hexafluorophosphates of Na, K, Li, Mg or Ag, and they introduce a corresponding anionic group into the ruthenium complex. Compounds useful as the phase transfer catalyst of formula (IV) are found in appropriate publications, such as W. P. Weber and G. W. Gokel, Phase Transfer Catalysis in Organic Synthesis , Springer-Verlag, pp. 6 (1977), including quaternary ammonium salts such as tetramethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium iodide, octyltrimethylammonium bromide, lauryltrimethylammonium bromide, lauryltriphenylammonium bromide, cetyltrimethylammonium chloride, methyltrioctylammonium chlolride, and benzyltriethylammonium bromide; and quaternary phosphonium salts such as tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium iodide, lauryltriethylphosphonium bromide, lauryltributylphosphonium bromide, trioctylethylphosphonium bromide, butyltriphenylphosphonium chloride, and benzyltributylphosphonium bromide. After completion of the reaction, the reaction mixture is allowed to stand, and the methylene chloride solution separated from the aqueous layer is washed and stripped of the methylene chloride by evaporation under vacuum so as to obtain the end product. Alternatively, the end product can be synthesized using a complex Ru(R-BINAP)(OAc)₂ (wherein Ac is an acetyl group, hereinafter the same) as a starting material, which the present inventors have previously disclosed in Japanese Patent Application No. 108888/1986 (corresponding to U.S. Appln. Serial No. 38,570 and EPA 87303216.3). According to this alternative method, Ru(R-BINAP)(OAc)₂ is reacted with an acid represented by the formula (V): HX (V) wherein X is ClO₄, BF₄, or PF₆, under stirring in a mixed solvent of methylene chloride and methanol. The acid of formula (V) is used in an amount of from 2 to 6 moles and preferably 4 moles per mole of the ruthenium. It suffices to continue the stirring for a period of time of from 6 to 18 hours and typically 12 hours at a temperature of from 5 to 30°C, and an optimum condition is determined depending on the types of the starting complex and the acid of formula (V) used. It is generally advantageous to mix methylene chloride and methanol in substantially equal amounts. A compound of formula (I) wherein ℓ is 1, m is 2, and n ′ is 1, in which a two-equivalent amount of the R-BINAP is coordinated to the ruthenium metal can be produced by reaction of, as a starting material, RuHCl(R-BINAP)₂ (a process of the preparation thereof is disclosed in European Patent No. 174,057A) with the salt of formula (III) in a mixed solvent of water and methylene chloride in the presence of the phase transfer catalyst of formula (IV). The salt of formula (III) is used in an amount of from 2 to 10 moles and preferably 5 moles per mole of the ruthenium, and the phase transfer catalyst of formula (IV) is used in an amount of from 1/100 to 1/10 mole per mole of the ruthenium. It suffices to continue the stirring for a period of time of from 6 to 18 hours and typically 12 hours at a temperature of from 5 to 30°C, and an optimum condition is determined depending on the types of the starting complex and the salt of formula (III). It is generally advantageous to mix water and methylene chloride in substantially equal amounts. The salt of formula (III) and the phase transfer catalysyt of formula (IV) are added to the reaction system after being dissolved in water. If an optically active R-BINAP is used as a starting material in each of the methods described above, a ruthenium-phosphine complex of formula (I) having corresponding optically active properties can be produced. The thus prepared ruthenium-phosphine complex of formula (I) of the present invention exhibits excellent performance when used as a catalyst to be used, for example, in asymmetric hydrogenation. For example, in asymmetric hydrogenation of allyl alcohols such as geraniol and nerol, the ruthenium-phosphine complex of formula (I) of the invention shows a very high catalytic activity even at room temperature. To take geraniol as an example of the substrate, the reaction proceeds rapidly with the complex being present at a molar concentration of from 1/10,000 to 1/50,000 per mole of geraniol to yield citronellol as a hydrogenation product at a selectivity reaching almost 100%. The resulting citronellol has an optical purity of from 96 to 98%. Therefore, the ruthenium-phosphine complex of the present invention can be used as an industrial catalyst that ensures very good results. The present invention is hereunder described in greater detail by way of Referential Examples, Examples, and Use Examples which, however, should not be taken as limiting. REFERENTIAL EXAMPLE 1 Preparation of Ru₂Cl₄[(-)-T-BINAP]₂NEt₃ : One gram (3.56 mmoles) of [RuCl₂(COD)] n (the term "COD" is an abbreviation for cycloocta-1,5-diene), 2.9 g (4.27 mmoles) of (-)-T-BINAP, and 1.5 g of triethylamine were added to 50 ml of toluene in a nitrogen atmosphere. The mixture was heated with stirring under toluene refluxing. Six hours later, the reaction mixture was cooled, and the resulting crystal was recovered by filtration. The separated crystal was dissolved in toluene, and recrystallization was effected by gradual addition of diethyl ether. As a result, a purified crystal was obtained in an amount of 2.24 g. This complex had the following data for its elemental analysis except for Ru: (NEt₃ appearing hereinafter represents triethylamine.) REFERENTIAL EXAMPLE 2 Preparation of RuHCl[(-)-T-BINAP] ₂: One gram (3.56 mmoles) of [RuCl₂(COD)] n , 5.43 g (8 mmoles) of (-)-T-BINAP, 1.6 g of triethylamine were added to 100 ml of ethanol in a reactor. The contents of the reactor were heated under reflux for 6 hours with stirring in a nitrogen atmosphere. After completion of the reaction, the ethanol was distilled off, and the residue was dissolved in 40 ml of dichloromethane, with the insoluble matter being filtered off. The filtrate was recrystallized by gradual addition of diethyl ether. Upon vacuum dr ying, a purified crystal was obtained in an amount of 3.4 g. REFERENTIAL EXAMPLE 3 Preparation of Ru[(-)-BINAP](O₂CCH) ₂: A 250-ml Schlenk-tube was charged with 1.43 g (0.9 mmole) of the Ru₂Cl₄[(-)-BINAP]₂(NEt₃) that was prepared by the process as disclosed in European Patent No. 174,057A and 3.06 g (37 mmoles) of sodium acetate. After the atmosphere in the tube had been thoroughly displaced with nitrogen, 100 ml of t-butanol was added thereon, and the mixture was heated under reflux for 12 hours. After completion of the reaction, the t-butanol was distilled off at 20 mmHg, and the resulting dry solid was extracted twice with 10-ml portions of diethyl ether. After distilling off the diethyl ether, the resulting dry solid was further extracted twice with 10-ml portions of ethanol. The extract was concentrated to dryness to obtain 1.5 g of crude Ru[(-)-BINAP](O₂CCH₃)₂. Recrystallization from ethyl acetate gave a yellowish brown solid in an amount of 0.79 g (yield: 52%). Melting point: 180 to 181°C (with decomposition) Elemental analysis for C₄₈H₃₈O₃P₂Ru: EXAMPLE 1 Preparation of [Ru((-)-T-BINAP)](BF₄)₂ ([2,2′-Bis)di-p-tolylphosphino)-1,1′-binaphthyl]ruthenium-ditet afluoroborate) A 250-ml Schlenk-tube was charged with 0.54 g (0.3 mmole) of the Ru₂Cl₄[(-)-T-BINAP]₂NEt₃ as prepared in Referential Example 1. After the atmosphere in the tube had been thoroughly displaced with nitrogen, 60 ml of methylene chloride was added thereto, followed by addition of 0.66 g (6.0 mmoles) of sodium tetrafluoroborate in 60 ml of water and 16 mg (0.06 mmole) of triethylbenzylammonium bromide in 3 ml of water. Reaction was performed by stirring the contents for 12 hours at room temperature. After completion of the reaction, the reaction mixture was allowed to stand, and the methylene chloride solution separated from the aqueous layer was washed with 50 ml of water. After liquid separation, the methylene chloride was distilled off under vacuum, and the residue was vacuum-dried to obtain a dark brown solid of [Ru((-)-T-BINAP)](BF₄)₂ in an amount of 0.55 g (yield: 95.8%). Elemental analysis for C₄₈H₄₀B₂F₈P₂Ru: Instrumental analysis of ³¹p nuclear magnetic resonance spectrum (hereinafter abbreviated as ³¹p NMR) was conducted with a Model JNM-GX400 (161 MHz) of JEOL Ltd., with chemical shifts being determined with 85% phosphoric acid used as an external standard. The results are shown below. EXAMPLE 2 Preparation of [RuH((-)-T-BINAP)₂[BF₄ )[Hydride Bis[2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl]ruthenium-tet afluoroborate) : A Schlenk-tube was charged with 1.15 g (0.77 mmole) of the RuHCl[(-)-T-BINAP]₂ as prepared in Referential Example 2. After the atmosphere in the tube had been thoroughly displaced with nitrogen, 75 ml of methylene chloride was added thereto, followed by addition of 0.85 g (7.7 mmoles) of sodium tetrafluoroborate in 75 ml of water and 21 mg (0.08 mmoles) of triethylbenzylammonium bromide in 4 ml of water. Reaction was performed by stirring the contents for 12 hours at room temperature. After completion of the reaction, the reaction mixture was allowed to stand, and the methylene chloride solution separated from the aqueous layer was washed with 50 ml of water. After liquid separation, the methylene chloride was distilled off under vacuum, and the residue was vacuum-dried to obtain a dark brown solid of [RuH((-)-T-BINAP)₂]BF₄ in an amount of 1.16 g (yield: 97.0%). Elemental analysis for C₉₆H₈₁BF₄P₄Ru: EXAMPLE 3 Preparation of [Ru((-)-BINAP)](BF₄)₂ ([2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl]ruthenium-ditetrafluoroborate): A Shlenk-tube was charged with 0.51 g (0.61 mmole) of Ru[(-)-BINAP](O₂CCH₃)₂ as prepared in Referential Example 3. After the atmosphere in the tube had been thoroughly displaced with nitrogen, 7 ml of methylene chloride, 7 ml of methanol, and 0.52 ml (2.48 mmoles) of an aqueous solution Of 42% borofluoric acid were added thereto, and the mixture was stirred for 12 hours at room temperature. Thereafter, the reaction mixture was concentrated under vacuum to obtain a yellowish brown solid of [Ru((-)-BINAP)](BF₄)₂ in an amount of 0.53 g (yield: 97.2%). Elemental analysis for C₄₄H₃₂B₂F₈P₂Ru: EXAMPLES 4 TO 9 The results of Examples 4 to 9 are summarized in Table 1. Except for the types of the starting ruthenium-phosphine complex and the salt of formula (III), the compounds of Examples 4 to 6 were synthesized in accordance with Example 1, and those of Examples 7 to 9 in accordance with Example 2, respectively. USE EXAMPLE 1 A 200-ml autoclave was charged with 62 g (0.4 mole) of geraniol and 75 ml of oxygen-free methanol, and 7.8 mg (0.008 mmole) of the [Ru((-)-T-BINAP)](ClO₄)₂ as prepared in Example 5 was added under a nitrogen stream to effect hydrogenation at 20°C for 15 hours at a hydrogen pressure of 30 kg/cm². After the solvent had been distilled off, the residue was subjected to distillation to obtain 61.8 g of a fraction having a boiling point of 108°C/100 mmHg. This fraction was found to contain 99.9% citronellol by gas chromatography with a silica capillary ("OV-101" of Gasukuro Kogyo Inc.) of 0.25 mm and 25 m L with the temperature increased from 100 to 250°C at a rate of 3°C/min. The specific rotation ([α] D ²⁵) of the citronellol was +5.19° (c=19.8, chloroform). The citronellol was converted to citronellic acid by Jones' oxidation, which was then reacted with R-(+)-1-(1-naphthyl)ethylamine to synthesize its amide form. The amide was subjected to analysis of diastereomers by high-performance liquid chromatography on a Chemopack (a column of Chemco Co., Ltd.) packed with Nucleosil 100-3 (a carrier of Chemco Co., Ltd.; 4.6 mm x 300 mm L ) that was eluted with a hexane/diethyl ether (7:3 by volume) mixture at a flow rate of 1 ml/min. UV detection was conducted at 254 nm. The analysis showed that the starting alcohol was a mixture of 97.5% of (R)-(+)-citronellol and 2.5% of (S)-(-)-citronellol, indicating that the optical yield of the reaction was 95% ee. USE EXAMPLES 2 TO 9 Using ruthenium-phosphine complexes prepared in accordance with the present invention, asymmetric hydrogenation of geraniol was conducted by repeating the procedures of Use Example 1. The results are shown in Table 2. As is apparent from the foregoing description and experimental results, the present invention provides a novel ruthenium-phosphine complex that exhibits a superior performance when used as a catalyst for a variety of organic syntheses including asymmetric hydrogenation. This complex achieves industrially satisfactory results in terms of selective hydrogenation of olefins and catalytic activity for attaining it. In addition, the complex of the present invention can be manufactured at a lower cost than the conventional rhodium catalysts, to thereby contribute to a reduction in the price of the product manufactured by using the complex as a catalyst.

Claims: A ruthenium-phosphine complex represented by form ula (I): [RuH ℓ (R-BINAP) m ]X n′ (I) wherein R-BINAP is a tertiary phosphine represented by formula (II): R is a hydrogen atom or a methyl group; X is ClO₄, BF₄, or PF₆; and when ℓ is 0, then m is 1 and n′ is 2, and when ℓ is 1, then m is 2 and n′ is 1. A method of preparing a complex as claimed in Claim 1, which comprises reacting a compound of the formula Ru₂Cl₄(R-BINAP)₂(N(C₂H₅)₂) with a salt of formula MX where M is sodium, potassium, lithium, magnesium or silver and X is as defined in Claim 1, in a solvent mixture of water and methylene chloride in the presence as a phase transfer agent of a quaternary ammonium salt or a quaternary phosphonium salt. A method of preparing a complex as claimed in Claim 1, which comprises reacting a compound of the formula Ru(R-BINAP) (OAc)₂ wherein Ac is an acetyl group, with an acid of formula HX where X is as defined in Claim 1, under stirring in a solvent mixture of methylene chloride and methanol. A method of preparing a complex as claimed in Claim 1, wherein l is 1, m is 2 and n is 1, which comprises reacting a compound of the formula RuHCl(R-BINAP)₂ with a salt of formula MX as defined in Claim 2, in a solvent mixture of water and methylene chloride in the presence as a phase transport agent of a quaternary ammonium or phosphonium salt. A method of asymmetric hydrogenation wherein a complex as claimed in Claim 1 is used as a catalyst. A method as claimed in Claim 5, wherein an allyl alcohol is subject to said hydrogenation.

Inventors: AKUTAGAWA, SUSUMU, KUMOBAYASHI, HIDENORI, NOYORI, RYOJI, OHTA, TETSUO, SAYO, NOBORU, TAKAYA, HIDEMASA
Applicants: TAKASAGO PERFUMERY CO., LTD.
Application year: 1987
Main classification: C07F15
IPC codes: C07B61, B01J31, C07C29, C07F15, C07C51