RUTHENIUM-PHOSPHINE COMPLEXES

Abstract: A ruthenium-phosphine complex having a 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl or its derivative as a ligand and carboxyl groups bonded to the ruthenium atom is of the formula: where X is H an amino, acetylamino or sulfo group; R is a H or Cl-4 alkyl; R₁ and R₂ each is a Cl-9 alkyl, halogenated Cl-4 alkyl, phenyl, phenyl substituted with Cl-4 alkyl, Cl-4 α-aminoalkyl, or a C7-10 α-aminophenylalkyl group, or R₁ and R₂ together form a Cl-4 alkylene group; and n is 1 or 2. 17 specific complexes are disclosed. Synthesis is by treatment of a complex wherein the portion outside the bracket is Ru₂Cl₄ . N(C₂H₅)₃ with a carboxylic acid salt.

Description: This invention relates to a ruthenium-phosphine complex useful as a catalyst for various organic syntheses, and particularly for asymmetric hydrogenation. Various transition metal complexes have hitherto been employed as catalysts for organic syntheses, and intensive studies have been conducted on syntheses using noble metal complexes as catalysts taking advantages of their stability and easiness in handling though they are expensive. In particular, studies have been directed to asymmetric catalysts to be used in asymmetric syntheses, such as asymmetric isomerization, asymmetric hydrogenation, and the like. Of the reported asymmetric catalysts, metal complexes formed between an olefinic rhodium complex and an optically active tertiary phosphine are especially well known. Such complexes typically include a rhodium-phosphine complex using 2,2′-bis(diphenylphosphino)-l,l′-binaphthyl (hereinafter abbreviated as BINAP) as a ligand as disclosed in Japanese Patent Application (OPI) No. 6l937/80 (the term "OPI" as used herein means "unexamined published application"). One example of application is described in Inoue et al., Chemistry Letters , pp. l007-l008 (l985), in which they obtained citronellol by asymmetric hydrogenation of geraniol or nerol using various rhodium-phosphine catalysts in an optical yield of 66%. On the other hand, known ruthenium complexes, through there are not so many reports 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., p. 922 (1985). However, the known ruthenium complexes are not satisfactory in stability nor in asymmetric yield. Although metallic rhodium provides excellent complex catalysts, it is expensive, due to limitations 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 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 are still problems as regards its activity to cope with precision reactions and its range of application. Therefore, it has been much desired to develop a catalyst which is inexpensive, has high activity and durability, and catalyzes asymmetric reactions to again high optical yields, i.e., to produce reaction products having high optical purity. As a result of extensive investigations with the purpose of meeting 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 in which carboxyl groups are bonded to a ruthenium atom, which is represented by the formula (I): wherein X represents a hydrogen atom, an amino group, an acetylamino group, or a sulfo group; R represents a hydrogen atom or a lower alkyl group having from l to 4 carbon atoms; R₁ and R₂ each represents an alkyl group having from 1 to 9 carbon atoms; a halogenated lower alkyl group having from 1 to 4 carbon atoms; examples of the halogen include fluorine, chlorine and bromine), a phenyl group, a phenyl group substituted with a lower alkyl group having from l to 4 carbon atoms, an α-aminoalkyl group having from 1 to 4 carb on atoms, or an α-aminophenylalkyl group from 7 to 10 carbon atoms or R₁ and R₂ are taken together to form an alkylene group having from 1 to 4 carbon atoms; and n represents 1 or 2. For the sake of brevity, the BINAP derivative moiety in formula (I) as represented by formula will be hereinafter represented by "L". The novel ruthenium-phosphine complex of formula (I) according to the present invention can be prepared from Ru₂Cl₄(L)₂(NEt₃) as a starting compound. The starting compound, Ru₂Cl₄(L)₂(NEt₃), can be obtained by the process disclosed in our Japanese Patent Application (OPI) No. 63690/86 (corresponding to European Specification No. 174,057A). Of the starting materials L used herein, those having a sulfo group or an amino group as X can be prepared easily by sulfonation, or nitration followed by reduction, of BINAP, etc., respectively, in a known manner. L in which X is an acetylamino group can be obtained by acetylation of those wherein X is an amino group. In the preparation of the ruthenium-phosphine complex of the invention, Ru₂Cl₄(L)₂(NEt₃) and a carboxylic acid salt are reacted in an alcohol as solvent, such as methanol, ethanol or t-butanol, at a temperature of from about 20 to about ll0°C for a period of from 3 to l5 hours. After the solvent is removed by distillation, the desired complex is extracted with a solvent such as diethyl ether, ethanol, etc., and the extract is evaporated to dryness to obtain a crude complex. The resulting crude complex as produced may be used directly as a catalyst for asymmetric hydrogenation or the like reaction, or it may be purified by recrystallization from ethyl acetate, and the like. Ruthenium-phosphine complexes having any carboxyl group introduced can be obtained by varying the kind of carboxylic acid salt used. Specific examples of the carboxylic acid salts which can be used are sodium acetate, sodium propionate, potassium acetate, silver acetate, sodium butyrate, sodium isobutyrate, sodium monochloroacetate, sodium dichloroacetate, sodium trichloroacetate, sodium nonylate, sodium benzoate, sodium p-methylbenzoate, sodium glutarate, sodium octylate, sodium adipate, sodium phthalate, glycine sodium salt, alanine sodium salt, phenylalanine sodium salt, valine sodium salt, leucine sodium salt, isoleucine sodium salt, etc. Complexes of formula (I) having a trifluoroacetate group are obtained by reacting a diacetate complex of formula (I), Ru(L)(O₂CCH₃)₂, as prepared by the above-described process, with trifluoroacetic acid in methylene chloride as a solvent at about 25°C for about l2 hours. Complexes of formula (I) wherein a 2-equivalent L is coordinated to a ruthenium atom are obtained by reacting RuHCl(L)₂ (obtainable by the process disclosed in Japanese Patent Application (OPI) No. 63690/86) with a carboxylic acid salt in a solvent such as methylene chloride. When an optically active L is used, ruthenium-phosphine complexes having corresponding optically active carboxyl groups bonded thereto can be obtained. The thus obtained ruthenium-phosphine complex of formula (I) according to the present invention has excellent performance properties as a catalyst for asymmetric hydrogenation or the like reaction. For example, when the complex is applied to asymmetric hydrogenation of allyl alcohols such as geraniol and nerol, it exhibits very high catalytic activity even at room temperature. In some detail, the reaction of geraniol rapidly proceeds in the presence of the complex at a molar concentration of from l/5000 to l/50000 based on the geraniol as a substrate to yield a hydrogenation product, i.e., citronellol, at a selectivity reaching almost l00%. The resulting citronellol has an optical purity of from 96 to 98%. To the contrary, the aforesaid known ruthenium complexes des cribed in Japanese Patent Application (OPI) No. 63690/86 are less sufficient in stability, selectivity to citronellol, and solubility in a substrate than the complexes of the invention. In particular, the selectivity to citronellol achieved by the conventional ruthenium complexes is so low that the reaction is accompanied by formation of, as a by-product, dihydrocitronellol having 2 mols of hydrogen added to geraniol or nerol depending on the reaction conditions. The present invention will now be illustrated in greater detail by way of Examples and Use Examples, wherein percentagers are by weight unless otherwise indicated. EXAMPLE l Preparation of Ru((-)-BINAP)(O₂CCH₃)₂ ([2,2′-Bis(diphenylphosphino)-l,l′-binaphthyl]ruthenium-diacetate) In a 250 ml-volume Schlenk-tube were placed l.43 g (0.9 mmol) of an Ru₂Cl₄((-)-BINAP)₂(NEt₃) complex which was prepared by the process of Japanese Patent Application (OPI) No. 63690/86 and 3.06 g (37 mmol) of sodium acetate. After the atmosphere was thoroughly displaced with nitrogen, l00 ml of t-butanol was added thereto, followed by heat-refluxing for l2 hours. After completion of the reaction, the t-butanol was removed by distillation under a reduced pressure of 20 mmHg, and the residual solid was extracted twice with l0 ml portions of diethyl ether. The diethyl ether was distilled off to dryness, and the resulting solid was further extracted twice with l0 ml portions of ethanol. The extract was concentrated to dryness to obtain l.5 g of crude Ru((-)-BINAP)(O₂CCH₃)₂. Recrystallization from ethyl acetate gave 0.79 g (yield: 54%) of a yellowish brown solid having a melting point of l80 to l8l°C (with decomposition). Elemental Analysis for C₄₈H₃₈O₄P₂Ru: The results of instrumental analyses are as follows. The ¹H nuclear magnetic resonance spectrum (¹H NMR) was determined with a model of JNM-GX400 (400 MHz) manufactured by JEOL Ltd., and the chemical shift was determined using tetramethylsilane as an internal standard. The ³¹P nuclear magnetic resonance spectrum (³¹P NMR) was determined with a model of JNM-GX400 (l6l MHz) manufactured by JEOL Ltd., and the chemical shift was determined using 85% phosphoric acid as an external standard. ³¹P NMR (CDCℓ₃) δ ppm: 65.00 (s) ¹H NMR (CDCℓ₃) δ ppm: l.75 (s, 6H, OCH₃) 6.5-7.8 (m, 32H, naphthyl ring and phenyl proton) EXAMPLE 2 Preparation of Ru((-)-BINAP) (O₂CCF₃)₂ ([2,2′-Bis(diphenylphosphino)-l,l′-binaphthyl]ruthenium-ditrifl oroacetate) 0.46 g (0.5l mmol) of Ru((-)-BINAP) (O₂CCH₃)₂ as prepared in Example l was precisely weighed out and placed in a Schlenk-tube with its atmosphere having been replaced with nitrogen. The content was dissolved in 5 ml of oxygen-free methylene chloride to form a uniform solution. To the solution was added 0.09 ml (l.l5 mmol) of trifluoroacetic acid having been purified by distillation, followed by stirring at room temperature for l2 hours. After completion of the reaction, the reaction mixture was concentrated to dryness to obtain 0.6 g of a crude complex. The resulting complex was dissolved in l ml of toluene, and 5 ml of hexane was added thereto in small portions. The mixture was allowed to stand at room temperature overnight, and the precipitated solid was collected by filtration and dried under reduced pressure (0.2 mmHg) for l0 hours to obtain 0.339 g (yield: 70%) of a purified complex. The resulting complex was identified to be Ru((-)-BINAP) (O₂CCF₃)₂ from the results of elemental analysis and instrumental analyses. Elemental Analysis for C₄₈H₃₂F₆O₄P₂Ru: ³¹P NMR (CDCℓ₃) δ ppm: 63.0l6 ¹H NMR (CDCℓ₃) δ ppm: 6.l-8.2 (m, 32H) EXAMPLE 3 Preparation of Ru((-)-T-BINAP)₂(O₂CCH₃)₂ (Bis[2,2′-bis(di-p-tolylphosphino)-l,l′-binaphthyl]ruthenium-diacetate) 0.45 g (0.3 mmol) of RuHCl((-)-T-BINAP)₂ synthesized by the process of Japanese Patent Application (OPI) No. 63690/86 and 0.ll g (0.66 mmol) of silver acetate were precisely weighed out and placed in a Schlenk-tube, and 5 ml of oxygen-free methylene chloride was added thereto, followed by stirring at room temperature for l2 hours. After completion of the reaction, the reaction mixture was filtered through Celite under a nitrogen stream. The filtrate was concentrated to dryness to obtain 0.57 g of a crude complex. The resulting complex was dissolved in l ml of toluene, and 5 ml of hexane was slowly added thereto. The precipitated solid was collected by filtration under a nitrogen stream and dried under reduced pressure (0.5 mmHg) at room temperature to obtain 0.246 g (yield: 52%) of a purified complex. This complex was identified to be Ru((-)-T-BINAP)₂(O₂CCH₃)₂ by the results of elemental analysis and instrumental analyses. Elemental Analysis for C₁₀₀H₈₆O₄P₄Ru: ³¹P NMR (CDCℓ₃) δ ppm: 63.79 ¹H NMR (CDCℓ₃) δ ppm: l.94 (s, 2H, OCH₃) 2.34, 2.38 (s, l2H, CH₃ for each) 6.2-7.8 (m, 56H) EXAMPLES 4 TO l7 Complexes were prepared in the same manner as in Examples l, 2, or 3 except for replacing the respective L and carboxylic acid salt with those shown in Table l. The preparation was in accordance with Example l for Examples 4 to 7, 9 to l3, l5, l6, and l7; Example 2 for Example 8; and Examples 3 for Example l4, respectively. In Table l, the following abbreviations are used. t-Bu: t-Butyl group i-Pr: Isopropyl group Ph: Phenyl group BINAP: 2,2′-Bis(diphenylphosphino)-l,l′-binaphthyl T-BINAP; 2,2′-Bis(di-p-tolylphosphino)-l,l′-binaphthyl t-BuBINAP: 2,2′-Bis(di-p-t-butylphenylphosphino)-l,l′-binaphtyl sulfon ted BINAP: 2,2′-Bis(diphenylphosphino)-5,5′-bis-(sodium sulfonate)-l,l′-naphthyl amino BINAP: 2,2′-Bis(diphenylphosphino)-5,5′-bis-(amino)-l,l′-binaphthy acetylamino BINAP: 2,2′-Bis(diphenylphosphino)-5,5′-bis-(acetylamino)-l,l′-bin phthyl USE EXAMPLE l A 200 ml-volume autoclave was charged with 62 g (0.4 mol) of geraniol and 75 ml of oxygen-free methanol, and ll2 mg (0.l3 mmol) of Ru((-)-BINAP) (O₂CCH₃)₂ as prepared in Example l was added thereto under a nitrogen stream to effect hydrogenation of 20°C for 27 hours under a hydrogen pressure of 30 kg/cm². After the solvent was distilled off, the residue was subjected to distillation to obtain 6l.5 g of a fraction having a boiling point of l08°C/l0 mmHg. The resulting fraction was found to contain 98.9% of citronellol by gas chromatography (silica capillary column "OV-l0l" manufactured by Gasukuro Kogyo Inc; diameter: 0.25 mm; length: 25 m). The gas chromatography was carried out by increasing the temperature from l00 to 250°C at a rate of 3°C/min. Optical Rotation, [α] D ²⁵ +4.96° (c=3l, chloroform). The resulting citronellol was led to citronellic acid by Jones' oxidation, which was then converted to its amide using R-(+)-(l-naphthyl)ethylamine. The amide was subjected to analysis of diastereomers by high performance liquid chromatography (column: Nucleosil l00-3 produced by Chemco Co., Ltd.; diameter: 4.6 mm; length: 300 mm; eluent: hexane/diethyl ether = 7:3 by volume; flow rate: l ml/min; detection wavelength: UV 254 nm). As a result, it was found that the starting alcohol was a mixture comprising 97.45% of (R)-(+)-citronellol and 2.55% of (S)-(-)-citronellol. Therefore, the optical yield of this reaction was 94.9%ee. USE EXAMPLES 2 TO l7 In the same manner as in Use Example l, geraniol was subjected to asymmetric hydrogenation by using each of the ruthenium-phosphine complexes of the invention as shown in Table 2. The results obtained are also shown in Table 2. In Table 2, the abbreviations used have the same meanings as described above. As described above, the present invention provides a novel ruthenium-phosphine complex in which carboxylic groups are bonded to metallic ruthenium. The ruthenium-phosphine complex according to this invention exhibits superior performances as a catalyst for various organic syntheses, and particularly for asymmetric hydrogenation, to accomplish satisfactory results in selective hydrogenation of olefins and catalytic activity from the industrial viewpoint. In addition, the complex of the invention can be prepared at a lower cost as compared with the conventional rhodium catalysts, thus making a great contribution to reduction of price of products.

Claims: 1. A ruthenium-phosphine complex represented by the general formula: wherein X represents a hydrogen atom, an amino group, an acetylamino group, or a sulfo group; R represents a hydrogen atom or a Cl-4 alkyl group R₁ and R₂ each represents a Cl-9 alkyl group, a halogenated Cl-4 alkyl group, a phenyl group, a phenyl group substituted with a Cl-4 alkyl group, a Cl-4 α-aminoalkyl group, or a C7-10 α-aminophenylalkyl group, or R₁ and R₂ together form a Cl-4 alkylene group; and n represents 1 or 2. 2. [2,2′-Bis(diphenylphosphino)-1,1′-binaphthyl]ruthenium-diacetate. 3. [2,2′-Bis(diphenylphosphino)-1,1′-binaphthyl]ruthenium-ditrifluoroacetate. 4. Bis[2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl] ruthenium-diacetate. 5. Bis[2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl]ruthenium-ditrifluoroacetate.

Inventors: AKUTAGAWA, SUSUMU, KUMOBAYASHI, HIDENORI, NOYORI, RYOJI, OHTA, TETSUO, SAYO, NOBORU, TAKAYA, HIDEMASA, TAKETOMI, TAKANAO, TAKEZAWA, TOSHIYUKI, YAMADA, NOBUO
Applicants: TAKASAGO PERFUMERY CO., LTD.
Application year: 1987
Main classification: C07F15
IPC codes: C07C29, C07C33, B01J31, C07C51, C07B61, C07F15