Improved process for the preparation of halogenated bis(olefin)rhodium(i) dimer or halogenated bis(olefin)iridium(i) dimer

Abstract

The present invention provides a process for preparing a complex of the formula [MHal(R 1 R 2 C=CR 3 R 4 )2]2, wherein M = Rh or Ir; Hal = Cl, Br or I; and R 1 R 2 C=CR 3 R 4 = a gaseous mono-olefin having 2 to 4 carbon atoms, comprising the steps of: (1) preparing an aqueous alcohol solution of MHal3 hydrate salt, (2) reacting the dissolved MHal3 hydrate salt with the gaseous mono-olefin R 1 R 2 C=CR 3 R 4 , thereby forming precipitated [MHal(R 1 R 2 C=CR 3 R 4 )2]2, (3) optionally, cooling the reaction mixture obtained at the end of step (2) to a temperature in the range of > 0 °C to 10 °C and keeping it at this temperature, and (4) collecting and drying the precipitated [MHal(R 1 R 2 C=CR 3 R 4 )2]2, wherein the temperature of the reaction mixture during step (2) is kept in the range of 15 °C to 30 °C.

Description

[0001] This invention relates to an improved method for preparing halodi(olefin)rhodium(I) dimers or halodi(olefin)iridium(I) dimers.

[0002] Chlorobis(ethylene)rhodium(I) dimer or di-μ-chlorotetra(ethylene)dirhodium(I) is the most well-known representative of halobis(olefin)rhodium(I) dimers and halobis(olefin)iridium(I) dimers. Chlorobis(ethylene)rhodium(I) dimer has the following formula:

[0003]

[0004] Chlorobis(ethylene)rhodium(I) dimers are commonly used as homogeneous catalysts in organic synthesis in the presence of specific ligands. Notable specific reactions include hydrogenation of carbon-carbon double bonds, addition of organometallic reagents to activated alkenes, 1,2-addition of organometallic reagents, catalysis of addition / cyclization cascades, and decarbonylation coupling of alkenes with aromatic sulfonyl chlorides and aromatic acyl chlorides.

[0005] The dichlorobis(ethylene)rhodium(I) dimer was first reported by R. Cramer in 1962 (see R. Cramer in Inorganic Chemistry, Vol. 1, No. 3, August 1962, pages 722-723). The dichlorobis(ethylene)rhodium(I) dimer can be prepared by treating an aqueous methanolic solution of hydrated rhodium trichloride with ethylene according to the following equation: 2 RhCl3(H2O)3 + 6 C2H4 → Rh2Cl2(C2H4)4 + 2 CH3CHO + 4 HCl + 4 H2O. The prior art synthesis process is disclosed in detail in *Inorganic Syntheses*, Volume XV, McGraw-Hill, Inc., 1974, pages 14-16. Yields are reported as 60%-65% (first batch) or 75% (combined yield of first and second batches). The first batch is obtained by harvesting and drying the precipitate, and the second batch can be obtained by further treating the filtrate with ethylene after neutralizing it with NaOH.

[0006] The object of this invention is to develop a synthesis process that allows for high yields of dichloro(olefin)rhodium(I) dimers or dichloro(olefin)iridium(I) dimers, without requiring a second batch as in prior art synthesis processes. Another object of this invention is to provide a synthesis process suitable for industrial scale-up with high space-time yields.

[0007] Surprisingly and unexpectedly, this objective can be achieved through the preparation of [MHal(R)] 1 R 2 C = CR 3 R 4 The method of complexing )2]2 is used to solve this problem; where M = Rh (rhodium) or Ir (iridium); Hal = Cl (chlorine), Br (bromine) or I (iodine); and R 1 R 2 C = CR 3 R 4 = A gaseous monoolefin having 2 to 4 carbon atoms, the method comprising the following steps:

[0008] (1) Preparation of an alcoholic aqueous solution of MHal3 hydrate salt

[0009] (2) To react the dissolved MHal3 hydrate salt with the gaseous monoolefin R 1 R 2 C = CR 3 R 4 The reaction forms a precipitate of [MHal(R)]. 1 R 2 C = CR 3 R 4 )2]2,

[0010] (3) Optionally, the reaction mixture obtained after step (2) is cooled to a temperature in the range of >0°C to 10°C and maintained at that temperature, and

[0011] (4) Collect and dry the precipitate [MHal(R)] 1 R 2 C = CR 3 R 4 )2]2,

[0012] The characteristic feature is that the temperature of the reaction mixture during step (2) is maintained in the range of 15°C to 30°C.

[0013] In a preferred embodiment, the noble metal M is Rh, and Hal is Cl. In other words, in such preferred embodiments, the method of the present invention is used to prepare [RhCl(R...] 1 R 2 C = CR 3 R 4Methods for the complexation of )2]2.

[0014] In a preferred embodiment, the noble metal M is Rh, Hal is Cl, and R 1 R 2 C = CR 3 R 4 It is ethylene (C2H4). In other words, in this most preferred embodiment, the method of the present invention is a method for preparing [RhCl(C2H4)2]2.

[0015] In step (1) of the method of the present invention, an alcoholic aqueous solution of MHal3 hydrate salt is prepared, wherein M = Rh or Ir; and Hal = Cl, Br or I. Preferably, M represents Rh, and Hal represents Cl.

[0016] This can be advantageous when the purity of the noble metal M or MHal3 hydrate salt is at the standard reagent grade.

[0017] Advantageously, the MHal3 hydrate salt is dissolved in a minimal amount of water, for example, at a concentration in the range of 2 to 4 mol of noble metal M per liter of aqueous solution, preferably in the range of 2.5 to 3.5 mol of noble metal M per liter of aqueous solution, and further diluted with an aqueous miscible alcohol. The aqueous miscible alcohol may be selected from methanol, ethanol, isopropanol, or any mixture thereof. Dilution with methanol alone is preferred. It is also preferable to introduce a small volume of the MHal3 hydrate salt aqueous solution into a larger volume of alcohol solvent.

[0018] The typical concentration of the alcohol-water solution prepared in step (1) is in the range of 0.2 mol to 0.4 mol of noble metal M per liter of alcohol-water solution, preferably in the range of 0.25 mol to 0.35 mol of noble metal M per liter of alcohol-water solution.

[0019] In step (2) of the method of the present invention, the dissolved MHal3 hydrate salt reacts with a gaseous monoolefin R having 2 to 4 carbon atoms. 1 R 2 C = CR 3 R 4 The reaction forms a precipitate of [MHal(R)]. 1 R 2 C = CR 3 R 4 )2]2.

[0020] As is evident from the above, the reaction takes place in an aqueous alcohol matrix.

[0021] Mono-olefins R with 2 to 4 carbon atoms 1 R 2 C = CR 3 R 4It is a gas under standard conditions. Examples include any isomers of ethylene, propylene, and butene, with ethylene being the preferred monoolefin.

[0022] The monoolefin gas reacts simply by contacting with dissolved MHal3 hydrate salt, i.e., by using the monoolefin gas as the reaction atmosphere, or preferably by actively bubbling it into and through the alcohol-water solution. The monoolefin gas flow rate can be, for example, in the range of 2 L / h / L reactor volume to 3 L / h / L reactor volume, preferably in the range of 2.5 L / h / L reactor volume to 2.75 L / h / L reactor volume. Operation under pressure is not required; that is, step (2) can be performed under normal pressure without the use of an autoclave or similar equipment.

[0023] During step (2), a gaseous monoolefin is supplied in stoichiometric excess. Throughout step (2), a molar ratio of, for example, 1 mol of noble metal M to >3 mol to 10 mol of monoolefin, typically >7 mol to 10 mol of monoolefin, can be used.

[0024] It is advantageous to stir the reaction mixture during step (2).

[0025] Step (2) is advantageous when it has a duration in the range of 12 to 24 hours, preferably in the range of 15 to 18 hours. Longer reaction times do not necessarily result in significantly higher yields of [MHal(R)]. 1 R 2 C = CR 3 R 4 )2]2, which precipitates during step (2).

[0026] It is important to maintain the temperature of the reaction mixture during step (2) within the range of 15°C to 30°C, preferably within the range of 20°C to 25°C. Temperatures exceeding or falling below this range have an adverse effect on the yield. Maintaining the temperature within this range can be achieved by adequately cooling the reaction mixture using conventional internal and / or external cooling devices. Without such cooling, the temperature of the reaction mixture can be raised to, for example, 35°C to 40°C.

[0027] After step (2) is completed, an optional step (3) may be performed, in which the obtained reaction mixture is cooled to a temperature range of >0°C to 10°C and maintained at that temperature; that is, after cooling the reaction mixture to >0°C to 10°C, the temperature is maintained for a period of time, for example, 2 to 3 hours.

[0028] The cold reaction mixture at >0°C to 10°C can be stirred during such optional step (3), and the feed of monoolefin gas can be stopped or preferably maintained.

[0029] After step (2) is completed, or, depending on the circumstances, after optional step (3), the precipitate [MHal(R)] is collected and dried. 1 R 2 C = CR 3 R 4 Step (4) of )2]2.

[0030] Precipitated [MHal(R)] 1 R 2 C = CR 3 R 4 [2]2 can be collected by any conventional solid-liquid separation process, for example, by filtering the suspension obtained after step (2) or optional step (3) using a Nutsche filtration device or similar apparatus. The product can be washed with a minimal amount of alcohol solvent before drying, or it can be dried directly. Preferably, drying can be carried out in a vacuum at a temperature in the range of 20°C to 25°C.

[0031] [MHal(R) prepared according to the method of the present invention 1 R 2 C = CR 3 R 4 The yield of [MHal(R)]2 (first-batch yield) is in the range of, for example, 82% to 87%, and is therefore significantly higher than the yield of existing methods, and this does not even produce a second batch. 1 R 2 C = CR 3 R 4 The purity and quality of )2]2 are similar to those prepared according to existing technical processes.

[0032] The method of this invention can be operated on an industrial scale with high space-time yield. For example, 10.5 kg of [RhCl(C2H4)2]2 can be produced from a 200-liter reaction. For comparative purposes, if [RhCl(C2H4)2]2 is directly scaled down from a prior art process, only about 4.8 kg of [RhCl(C2H4)2]2 is produced.

[0033] Example 1 (according to the present invention) :

[0034] 1500 ml of H₂O was added to a 4 L beaker equipped with a stir bar and a watch glass. The solvent was heated to 70 °C, and 1200 g of Rh(III) chloride hydrate was added in portions over 3 hours. After the Rh(III) chloride hydrate was completely added, the solution was heated for another hour. The Rh(III) chloride solution was then cooled and filtered through a 1 μm glass membrane at <40 °C to remove any insoluble matter, and the membrane was washed with a minimal amount of water (50 ml).

[0035] 12.0 L of methanol was added to a separate 22 L reactor equipped with a mechanical stirrer, aeration tube, an inlet pipe attached to a mineral oil bubbler, and a thermocouple sheath. Under moderate stirring, a Rh(III) chloride solution was added to the 22 L reactor, and the filter flask was washed with an additional 1200 ml of methanol. Ethylene gas was bubbled into the reactor at sufficient pressure, resulting in vigorous bubbling observed in the mineral oil bubbler. Ethylene bubbling continued for 15 h. The reactor was placed in a water bath to maintain a temperature <25 °C. During the reaction, the ethylene bubbling rate needed to be adjusted periodically due to ethylene absorption and the formation of [RhCl(C2H4)2]2. A total of 1020 g of ethylene was bubbled through. After 12 h, the reaction mixture was cooled to <10 °C. At 15 h, ethylene bubbling was stopped, and the product was harvested by vacuum filtration onto a filter plate. The product was washed with a minimum amount of methanol (150 ml) and dried on a filter plate for 15-20 min. The [RhCl(C2H4)2]2 was then transferred to a drying tray and dried to constant weight in a vacuum furnace at ambient temperature. The yield was 809.8 g (85% yield). The [RhCl(C2H4)2]2 was then screened and placed in a suitable (amber glass) container under an inert argon atmosphere. The product containers were stored in a refrigerated environment at <5°C.

[0036] Comparative Example 2 :

[0037] Example 1 was repeated, except that no cooling method was used, i.e., the reactor was not placed in a water bath to maintain a temperature <25°C. The yield was 638.3 g (67% yield).

Claims

1. A method for preparing [MHal(R)] 1 R 2 C=CR 3 R 4 The method for a complex of )2]2, wherein M = Rh; Hal = Cl or Br; and R 1 R 2 C=CR 3 R 4 =A gaseous monoolefin having 2 to 4 carbon atoms, the method comprising the following steps: (1) Preparation of an alcoholic aqueous solution of MHal3 hydrate salt, (2) The dissolved MHal3 hydrate salt reacts with the gaseous monoolefin R 1 R 2 C=CR 3 R 4 The reaction forms a precipitate of [MHal(R)]. 1 R 2 C=CR 3 R 4 )2]2, wherein step (2) is performed under normal pressure without using an autoclave, (3) Cool the reaction mixture obtained after step (2) to a temperature in the range of >0°C to 10°C and maintain it at said temperature, while maintaining the feed of monoolefin gas, and (4) Collect and dry the precipitate [MHal(R)] 1 R 2 C=CR 3 R 4 )2]2, The temperature of the reaction mixture during step (2) is maintained in the range of 15°C to 30°C.

2. The method according to claim 1, wherein the noble metal M is Rh and Hal is Cl.

3. The method according to claim 1, wherein R 1 R 2 C=CR 3 R 4 It is ethylene (C2H4).

4. The method according to claim 2, wherein R 1 R 2 C=CR 3 R 4 It is ethylene (C2H4).

5. The method according to claim 1, wherein during step (1), the MHal3 hydrate salt is dissolved in water at a concentration in the range of 2 mol to 4 mol of noble metal M per liter of aqueous solution, and further diluted with a water-miscible alcohol at a concentration in the range of 0.2 mol to 0.4 mol of noble metal M per liter of aqueous alcohol solution.

6. The method according to claim 2, wherein during step (1), the MHal3 hydrate salt is dissolved in water at a concentration in the range of 2 mol to 4 mol of noble metal M per liter of aqueous solution, and further diluted with a water-miscible alcohol at a concentration in the range of 0.2 mol to 0.4 mol of noble metal M per liter of aqueous alcohol solution.

7. The method according to claim 3, wherein during step (1), the MHal3 hydrate salt is dissolved in water at a concentration in the range of 2 mol to 4 mol of noble metal M per liter of aqueous solution, and is further diluted with a water-miscible alcohol at a concentration in the range of 0.2 mol to 0.4 mol of noble metal M per liter of aqueous alcohol solution.

8. The method according to claim 4, wherein during step (1), the MHal3 hydrate salt is dissolved in water at a concentration in the range of 2 mol to 4 mol of noble metal M per liter of aqueous solution, and is further diluted with a water-miscible alcohol at a concentration in the range of 0.2 mol to 0.4 mol of noble metal M per liter of aqueous alcohol solution.

9. The method according to any one of claims 5 to 8, wherein the water-miscible alcohol is selected from methanol, ethanol, isopropanol, or any mixture thereof.

10. The method according to any one of claims 5 to 8, wherein the water-miscible alcohol is methanol.

11. The method according to any one of claims 1 to 8, wherein the monoolefin gas is used as a reaction atmosphere or is actively bubbled into and through the aqueous alcohol solution.

12. The method of claim 9, wherein the monoolefin gas is used as a reaction atmosphere or is actively bubbled into and through the aqueous alcohol solution.

13. The method of claim 10, wherein the monoolefin gas is used as a reaction atmosphere or is actively bubbled into and through the aqueous alcohol solution.

14. The method of claim 11, wherein the monoolefin gas flow rate is in the range of 2 L / h / L reactor volume to 3 L / h / L reactor volume.

15. The method of claim 12, wherein the monoolefin gas flow rate is in the range of 2 L / h / L reactor volume to 3 L / h / L reactor volume.

16. The method of claim 13, wherein the monoolefin gas flow rate is in the range of 2 L / h / L reactor volume to 3 L / h / L reactor volume.

17. The method according to any one of claims 1 to 8, 12 to 16, wherein the monoolefin is supplied in a stoichiometric excess during step (2).

18. The method of claim 11, wherein the monoolefin is supplied in a stoichiometric excess during step (2).

19. The method according to any one of claims 1 to 8, 12 to 16, 18, wherein step (2) has a duration in the range of 12 hours to 24 hours.

20. The method of claim 17, wherein step (2) has a duration in the range of 12 hours to 24 hours.

21. The method according to any one of claims 1 to 8, 12 to 16, 18, 20, wherein the temperature of the reaction mixture during step (2) is maintained in the range of 20°C to 25°C.

22. The method of claim 19, wherein the temperature of the reaction mixture during step (2) is maintained in the range of 20°C to 25°C.

23. The method according to any one of claims 1 to 8, 12 to 16, 18, 20, 22, wherein step (3) is performed, and wherein the cooling reaction mixture at >0°C to 10°C is maintained at such temperature for 2 to 3 hours.

24. The method of claim 21, wherein step (3) is performed, and wherein the cooling reaction mixture at >0°C to 10°C is maintained at such temperature for 2 to 3 hours.

25. The method according to any one of claims 1 to 8, 12 to 16, 18, 20, 22, 24, wherein the temperature of the reaction mixture during step (2) is maintained by adequately cooling the reaction mixture with conventional internal and / or external cooling devices.

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