Process for the preparation of a nickel/phosphorous ligand catalyst

This invention relates to a process for the preparation of a catalyst which is a complex of nickel and a bidentate phosphorous compound.

It is well known in the art that complexes of nickel with phosphorus-containing ligands are useful as catalysts in hydrocyanation reactions. Such nickel complexes using monodentate phosphites are known to catalyze hydrocyanation of butadiene to produce a mixture of pentenenitriles. These catalysts are also useful in the subsequent hydrocyanation of pentenenitriles to produce adiponitrile, an important intermediate in the production of nylon. It is further known that bidentate phoshite and phosphinite ligands can be used to form nickel-based catalysts to perform such hydrocyanation reactions.

U.S. Pat. No. 3,903,120 discloses a process for preparing zerovalent nickel complexes by reacting elemental nickel with a monodentate phosphorous ligand of the formula PZ 3 where Z is an alkyl or alkoxy group, preferably an aryloxy group. The process uses finely divided elemental nickel and is preferably carried out in the presence of a nitrile solvent. The reaction is taught to be carried out in the presence of excess ligand.

U.S. Pat. No. 3,846,461 discloses a process for preparing zerovalent nickel complexes of triorganophosphites by reacting triorganophosphite compounds with nickel chloride in the presence of a finely divided reducing metal which is more electropositive than nickel, and in the presence of a promoter selected from the group consisting of NH 3 , NH 4 X, Zn(NH 3 ) 2 X 2 , and mixtures of NH 4 X and ZnX 2 , where X is a halide. Reducing metals include Na, Li, Mg, Ca, Ba, Sr, Ti, V, Fe, Co, Cu, Zn, Cd, Al, Ga, In, Sn, Pb, and Th, with Zn being preferred.

U.S. Pat. No. 5,523,453 discloses a method of preparing nickel hydrocyanation catalysts containing bidentate phosphorous ligands. Zero-valent nickel compounds that contain ligands that can be displaced by the bidentate phosphorous ligand are a preferred source of nickel. Two such compounds are Ni(COD) 2 , where COD is 1,5-cyclooctadiene, and (oTTP) 2 Ni(C 2 H 4 ), where oTTP is P(O-ortho-C 6 H 4 CH 3 ) 3 . Alternatively, divalent nickel compounds may be combined with reducing agents to produce a suitable nickel source. In the latter method of preparing catalyst, as the temperature of the catalyst preparation increases, the catalyst formation rate increases, but the amount of degradation product also increases.

U.S. Pat. No. 6,069,267 describes a method for preparing a crude bidentate phosphorus-containing ligand suitable for use in the catalyst preparation. The resulting product is, however, not pure ligand, but rather a crude ligand mixture that contains byproducts of the reaction which may affect the rate of formation of the nickel-containing catalyst. That process does not provide for isolation and purification of the bidentate ligand. The present inventors observed that, compared to the use of purified ligand, such crude ligand mixtures do inhibit catalyst preparation reactions wherein divalent nickel compounds are contacted with reducing agents to produce the nickel catalyst.

Accordingly, in order to avoid costly purification of the ligand, there is a need in the art for a process for nickel catalyst preparation that counteracts the inhibiting effects of the impurities contained in the crude ligand.

The present invention is a process for preparing a nickel/ligand catalyst, said process comprising:

(a) contacting one molar equivalent of PCl 3 with about two molar equivalents of R 1 OH, wherein R 1 is a substituted or unsubstituted aryl group, and at least two molar equivalents of an organic base at a temperature between about −25 deg C. and about 35 deg C., to produce a first reaction product comprising a di(aryloxy) phosphorous chloride of the formula (R 1 O) 2 PCl and a salt formed from the organic base, said salt being substantially insoluble in the first reaction product; (b) contacting the first reaction product at a temperature between about −25 deg C. and about 35 deg C. with about one half molar equivalent of HO—Z—OH, wherein Z is a substituted or unsubstituted aryl group different from R 1 , to produce a second reaction product comprising a solids content, provided that if less than three molar equivalents of organic base are used in step (a), then sufficient organic base is used in step (b) to bring the total amount of organic base used in steps (a) and (b) combined to at least three molar equivalents of organic base relative to the PCl 3 ; (c) separating the solids content from the second reaction product by filtration or extraction with water to produce a crude ligand mixture, said solids content comprising a salt formed from the organic base used in step (a) and optionally in step (b); (d) contacting the crude ligand mixture with at least one member selected from the group consisting of (i) a weakly acidic organic resin, (ii) a weakly basic organic resin, (iii) a high-surface-area organic resin, (iv) activated carbon, (v) aluminosilicate zeolite, (vi) a two phase solvent system for liquid-liquid extraction and (vii) a Lewis acid; (e) recovering from the product of step (d) a solution containing a ligand of the formula

(R 1 O) 2 POZOP(OR 1 ) 2 ; and

(f) contacting the solution of step (e) with nickel chloride in the presence of a nitrile solvent and a reducing metal which is more electropositive than nickel to produce the nickel/ligand catalyst.

It has been discovered that in a process for preparing a nickel/ligand catalyst comprising reaction of nickel chloride in the presence of a crude bidentate phosphite ligand with a reducing metal more electropositive than nickel, that various treatments of crude ligand may overcome deleterious rate inhibiting effects of byproduct impurities which are present in the crude ligand.

U.S. Pat. No. 6,069,267 describes a method for preparing bidentate phosphite ligands suitable for the instant process. The resulting product is, however, not pure ligand, but rather a crude ligand mixture that contains byproducts of the reaction. When this crude ligand mixture is reacted with nickel chloride in the presence of a reducing metal that is more electropositive than nickel, the reaction is slow compared to that when purified ligand is utilized. Without wishing to be bound to any particular theory, the present inventors believe that the slow reaction rate may be attributable to one or more byproducts in the crude ligand mixture.

It has been discovered that if a crude ligand mixture produced by the method of U.S. Pat. No. 6,069,267 is treated in accordance with the present invention, the rate of catalyst formation is increased. Suitable treatment methods include contacting the crude ligand mixture with the one or more of the following:

(1) a weakly acidic organic resin including organic polymers with carboxylic acid functional groups, such as Amberlyst CG-50 (Rohm & Haas), (2) a weakly basic organic resin including organic polymers with alkylamine functional groups, such as Amberlyst® 21 (Rohm & Haas), (3) a high-surface-area neutral organic resin including polystyrene adsorbent, such as Amberlite® XAD-4, and polyacrylate adsorbent, such as Amberlite® XAD-7 (Rohm & Haas), (4) activated carbon, (5) an aluminosilicate zeolite, commonly referred to in the art as molecular sieves, such as 3A or 13X molecular sieves, (6) a two phase solvent system for liquid-liquid extraction where one phase is a non-polar aliphatic hydrocarbon such as hexane or cyclohexane and the other phase is a polar organic species such as adiponitrile, methylglutaronitrile, ethylsuccinonitrile, acetonitrile, ethyleneglycol or propyleneglycol, and (7) a Lewis acid.

A solvent may be employed during the treatment to improve flowability and contact between the crude ligand and the treating agent. Suitable solvents include aliphatic hydrocarbons and nitrites. 3-Pentenenitrile is a preferred solvent.

The material used for treatment is then separated from the crude ligand mixture to recover a treated ligand mixture that is then reacted with nickel chloride in the presence of a nitrile solvent and a reducing metal, to form a nickel/ligand catalyst at a higher reaction rate than that obtained by using a untreated crude ligand mixture. The reducing metal, hereafter referred to as MET, can be any metal which is more electropositive than nickel. Such metals include Na, Li, K, Mg, Ca, Ba, Sr, Ti, V, Fe, Co, Cu, Zn, Cd, Al, Ga, In, Sn, Pb, and Th. Most preferred are Fe and Zn.

The source of nickel for this invention is preferably nickel (II) chloride, NiCl 2 . Either hydrated or anhydrous forms of NiCl 2 may be used. Anhydrous NiCl 2 is preferred in order to minimize the hydrolytic degradation of the ligand. The expression “anhydrous” means that the nickel chloride contains less than 2% by weight water. Nickel chloride containing 1% or less water is preferred. Processes for producing anhydrous nickel chloride have been described in co-pending application Ser. No. 09/994,102. The expression “hydrated NiCl 2 ” means NiCl 2 containing 2% or more water by weight. Examples of hydrated NiCl 2 include the dihydrate, the hexahydrate and aqueous solutions of NiCl 2 . Preferred sources for producing anhydrous NiCl 2 are the hexahydrate product and an aqueous solution. NiCl 2 as an aqueous solution is particularly preferred. The aqueous solution is available commercially as an approximately 29 weight percent NiCl 2 aqueous solution.

The catalyst formation reaction is carried out in the presence of a nitrile solvent, preferably 3-pentenenitrile or 2-methyl-butenenitrile. The concentration of ligand may range from about 1% to 90% by weight. For practical reasons the preferred range of ligand concentration is 5% to 50%. The amount of reducing metal (MET) will generally fall in the range of 0.1% to 5% of the reaction mass. The molar ratio of NiCl 2 to MET ranges from 0.1:1 to 100:1. The preferred ratio of NiCl 2 :MET ranges from 2:1 to 50:1. The reaction temperature may range from 0° C. to 120° C. The preferred temperature range is dependent on the NiCl 2 form. Hydrated forms of NiCl 2 react rapidly at lower temperatures than anhydrous NiCl 2 . For NiCl 2 .2H 2 O, the preferred temperature range is 0° C. to 60° C., and the most preferred range is 25° C. to 50° C. For anhydrous NiCl 2 , the preferred temperature range is 30° C. to 110° C., and the most preferred range is 50° C. to 100° C. The reaction may be run within a wide pressure range. For practical reasons, the preferred pressure ranges from about 5 psia to 50 psia (34 to 340 kPa). The reaction may be run in batch or continuous mode.

Suitable ligands for the present invention are bidentate phosphorous-containing ligands selected from the group consisting of bidentate phosphites and bidentate phosphinites. Preferred ligands are bidentate phosphite ligands.

The preferred bidentate phosphite ligands are of the following structural formulae:

(R 1 O) 2 P(OZO)P(OR 1 ) 2 ,  I

wherein R 1 is phenyl, unsubstituted or substituted with one or more C 1 to C 12 alkyl or C 1 to C 12 alkoxy groups; or naphthyl, unsubstituted or substituted with one or more C 1 to C 12 alkyl or C 1 to C 12 alkoxy groups; and Z is independently selected from the group consisting of structural formulae II, III, IV, V, and VI:

wherein R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , and R 9 are independently selected from the group consisting of H, C 1 to C 12 alkyl, and C 1 to C 12 alkoxy; X is O, S, or CH(R 10 ); R 10 is H or C 1 to C 12 alkyl;

wherein R 11 and R 12 are independently selected from the group consisting of H, C 1 to C 12 alkyl, and C 1 to C 12 alkoxy; and CO 2 R 13 , R 13 is C 1 to C 12 alkyl or C 6 to C 10 aryl, unsubstituted or substituted, with C 1 to C 4 alkyl; Y is O, S, or CH(R 14 ); R 14 is H or C 1 to C 12 alkyl;

wherein R 15 is selected from the group consisting of H, C 1 to C 12 alkyl, and C 1 to C 12 alkoxy and CO 2 R 16 ; R 16 is C 1 to C 12 alkyl or C 6 to C 10 aryl, unsubstituted or substituted with C 1 to C 4 alkyl.

In the structural formulae I through VIII, the C 1 to C 12 alkyl, and C 1 to C 12 alkoxy groups may be straight chains or branched.

Examples of bidentate phosphite ligands that are useful in the present process include those having the formulae VII to XXIV, shown below wherein for each formula, R 17 is selected from the group consisting of methyl, ethyl or isopropyl, and R 18 and R 19 are independently selected from H or methyl:

Additional suitable bidentate phosphites are of the type disclosed in U.S. Pat. Nos. 5,512,695; 5,512,696; 5,663,369; 5,688,986; 5,723,641; 5,847,101; 5,959,135; 6,120,700; 6,171,996; 6,171,997 and 6,399,534; the disclosures of which are incorporated herein by reference. Suitable bidentate phosphinites are of the type disclosed in U.S. Pat. Nos. 5,523,453 and 5,693,843, the disclosures of which are incorporated herein by reference.

The reaction may be carried out in a manner such that unreacted NiCl 2 and MET may be separated from the reaction product by filtration or centrifugation. The collected excess nickel chloride can then be recycled back to a catalyst preparation reactor.

The invention is illustrated by the following non-limiting examples. In the following examples, the reducing metal is the limiting reagent in each reaction, and therefore the extent of reaction (conversion) is expressed as the percentage of the reducing metal reacted. The extent of reaction (conversion) is determined by analyzing for the amount of active nickel produced by the catalyst synthesis reaction. The analysis is carried out by treating a solids-free aliquot of the reaction solution with dimethyl acetylenedicarboxylate (DMAD), which forms a stable nickel complex, (Ligand)Ni(DMAD), and analyzing quantitatively for this complex by High Pressure Liquid Chromatography (HPLC).

The Comparative Example illustrates typical reaction behavior when the crude ligand mixture is not treated according to this invention.

Examples 2, 3, and 5 illustrate that treating the crude ligand with various resins results in higher rates of reaction compared with reaction using no treatment of the ligand (Comparative Example). Example 6 illustrates the effect of treating the crude ligand with activated carbon. Examples 4 and 7 illustrate the positive effect of treatment with alumino silicate zeolites (molecular sieves). Examples 1, 8, and 10 illustrate the benefits of utilizing liquid-liquid extraction to treat the crude ligand mixture. Example 9 illustrates the benefits of treating the crude ligand mixture with small amount of a Lewis acid prior to the catalyst preparation.

For the Comparative Example and Examples 1 through 10, a “crude ligand VII” was prepared by

a) treating a toluene solution of PCl 3 with two molar equivalents of thymol and three molar equivalents of triethylamine while maintaining a reaction temperature of about −5° C., to produce a first reaction product comprising di(2-isopropyl-5-methylphenoxy)phosphorus chloride, triethylammonium chloride (which is substantially insoluble in the mixture), unreacted triethylamine and toluene, b) adding one half molar equivalent of binaphthol (relative to PCl 3 ) to the reaction mixture while maintaining the reaction temperature at about −5° C., c) treating the product of step (b) with water to extract the triethylammonium hydrochloride and separating the resulting aqueous lower phase from the organic product solution, and subsequently distilling a portion of the toluene from the organic product solution to produce a mixture comprising about 33 wt % ligand VII (werein R 17 is isopropyl, R 18 is H, and R 19 is methyl) in toluene, said mixture hereinafter referred to as “crude ligand VII”.

“Ligand VII Stock Solution” was prepared by:

(1) dissolving 830 grams of “crude ligand VII” in 1000 grams of 3-pentenenitrile in an air-free 3 liter round bottom flask fitted with an over head stirrer, a heating mantel, a distillation head, a dip tube to draw off material out of the flask and an addition funnel, (2) heating the solution from step (1) under vacuum to 45 to 60 deg C. to distill off the toluene and then allowing the solution to cool to ambient temperature.

Analysis showed this “Ligand VII Stock Solution” to have about 24 wt % ligand in it.

Comparative Example

“Ligand VII Stock Solution” (12.067 grams) was put into a dried 20 cc vial. Into this vial was also placed 0.493 grams of anhydrous NiCl 2 and 0.096 grams of finely divided zinc metal. A small magnetic stirring bar was added to the vial. The vial was capped and placed into a heated aluminum block that had been pre-heated to 100 deg C. A stop watch was started when the vial was placed into the heated block. The contents of the vial were agitated using a rotating magnetic bar coupled to the magnetic bar inside the vial. At 1.5 hours a sample was taken of the solution. Analysis of this sample showed 425 ppm of Ni as catalyst in solution.