Catalyst for reductive amination

Abstract

The present disclosure provides for a catalyst for reductive amination. The catalyst can be formed from the steps that include mixing a cobalt coordination compound with 2-(2-aminoethoxy)ethanol (AEE) and potassium bis(trimethylsilyl)amide (KHMDS) to form a metal solution; mixing the metal solution with a heterogeneous solid support to form a supported precatalyst, wherein the heterogeneous solid support includes a ruthenium species; and chemically reducing the supported precatalyst at a predetermined pressure of hydrogen and at a predetermined temperature over a predetermined time to produce the catalyst for reductive amination.

Description

[0001]CATALYST FOR REDUCTIVE AMINATION Technical Field The present disclosure relates generally to catalysts and more particularly to catalysts for reductive amination. Background The selective catalysis of reductive amination over transamination reactions is a significant area of interest in the field of organic synthesis, especially in the production of amines for pharmaceuticals, fine chemicals, and other applications. Developing techniques to synthesize such catalysts is difficult at best, but research continues in an effort to improve catalytic performance and selectivity for reductive amination over transamination reactions. To this end, there are examples of catalysts that perform reductive amination that use either nickel or cobalt as the major metal. These single metal catalysts, however, do not produce the desired products in high selectivity. There are also examples of catalysts that incorporate two metals in an effort to achieve the desired higher selectivity. The process used with these two metal catalysts, however, typically require elevated pressures to force the equilibrium towards the desired product. A catalyst with higher selectivity would result in either lower waste or less expensive operations to produce the same material. As such, there continues to be a need in the art to produce catalysts that selectively catalyze reductive amination over transamination reactions. Summary Embodiments of the present disclosure provide for a catalyst that has improved selectivity for reductive amination reactions. The catalyst of the present disclosure includes metal nanoparticles supported on a heterogeneous support material that are catalytically active for reductive amination chemistry. For the various embodiments, the metal nanoparticles are formed from two different metals, discussed herein, and are supported on an oxide surface of the heterogeneous support material. Specifically, the method of forming the catalyst uses 2-(2- aminoethoxy)ethanol (AEE) to form an AEE precursor with cobalt (Co) and ruthenium (Ru) compounds prior to reduction to Co / Ru nanoparticles on a solid support. For the various embodiments, the catalyst can be used, among other things, to perform reductive amination chemistry. For the various embodiments, the catalyst of the present disclosure can be used for reductive amination. The catalyst can take the form of metal nanoparticles supported on a heterogeneous support material that is catalytically active for reductive amination chemistry. The catalyst of the present disclosure is formed by mixing a cobalt coordination compound with AEE and potassium bis(trimethylsilyl)amide to form a metal solution; mixing the metal solution with a heterogeneous solid support to form a supported precatalyst, where the heterogeneous solid support includes a ruthenium species; and chemically reducing the supported precatalyst at a predetermined pressure of hydrogen and at a predetermined temperature over a predetermined time to produce the catalyst for reductive amination. The metal nanoparticles supported on the heterogeneous support material is catalytically active for reductive amination, as discussed herein. The following provides further details on the catalyst of the present disclosure. For the various embodiments, the cobalt coordination compound can be selected from the groupconsisting of CoCl2, Co(NO3)2, CoSO4, Co2(CO)8, Co[N(SiMe3)2]2, Co-AEE2andcombinations thereof. For the various embodiments, the heterogeneous solid support can be selected from the group consisting of γ-Al2O3, α-Al2O3, SiO2, TiO2, ZrO2, ZnO and combinations thereof. For the various embodiments, the heterogeneous solid support can include 1 to 4 weight percent of the ruthenium species based on a total weight of the heterogeneous solid support. For these embodiments, the ruthenium species can be formed from, for example, RuOHx, RuCl3and combinations thereof, where x is 3 or 4. For the various embodiments, the supported precatalyst has a cobalt to ruthenium molar ratio of about 95:5. In an additional embodiment, the ruthenium based heterogeneous catalyst can have a cobalt to ruthenium molar ratio of in a range of 10:1 to 99:1. For the various embodiments, the predetermined pressure of hydrogen is at a pressure of 0 to 20684 kPa. In additional embodiments, the predetermined pressure of hydrogen is at a pressure of 0 to 6895 kPa. In one embodiment, the predetermined pressure of hydrogen is, preferably, 1724 kPa. For the various embodiments, the predetermined temperature is in a range of 100 to 200oC. Preferably, the predetermined temperature is 180oC. For the various embodiments, the predetermined time can be in a range of 1 to 48 hours. Preferably, the predetermined time can be, preferably, 24 hours. Brief Description of Drawings FIG. 1 provides the structure of the Co(AEE)2mixture using extended x-ray absorption fine structure (EXAFS) according to the present embodiment. FIG. 2 provides an EXAFS of the CoRu@γ-Al2O3catalyst taken after 1 hour of reaction under hydrogen at 180oC. FIG. 3 provides an EXAFS of the CoRu@γ-Al2O3catalyst taken after the reaction is complete at 15 hours. Detailed Description Embodiments of the present disclosure provide a catalyst that has improved selectivity for reductive amination reactions. The catalyst of the present disclosure includes metal nanoparticles supported on a heterogeneous support material that are catalytically active for reductive amination chemistry. For the various embodiments, the metal nanoparticles can be formed from two different metals, discussed herein, and are supported on an oxide surface of the heterogeneous support material. Specifically, the method of forming the catalyst uses 2-(2- aminoethoxy)ethanol (AEE) to form an AEE precursor with cobalt (Co) and ruthenium (Ru) compounds prior to reduction to Co / Ru nanoparticles on a solid support. For the various embodiments, the catalyst can be used, among other things, to perform reductive amination chemistry. For the various embodiments, the catalyst of the present disclosure can be used for reductive amination. As discussed herein , the catalyst for reductive amination can take the form of metal nanoparticles supported on a heterogeneous support material that is catalytically active for reductive amination chemistry. The catalyst for reductive amination is formed by mixing a cobalt coordination compound with AEE and potassium bis(trimethylsilyl)amide (KHMDS) to form a metal solution. For the various embodiments, mixing the cobalt coordination compound with AEE and KHMDS to form the metal solution can occur at a predetermined temperature in the range of 10 to 80oC and at a predetermined pressure of 101 to 20,684 kPa. Preferably, the predetermined temperature can be in the range of 20 to 50oC and at a predetermined pressure of 101 to 3,477 kPa. Preferably, the predetermined temperature is 23oC (room temperature) and the predetermined pressure is 101 kPa (standard atmospheric pressure). For the various embodiments, the cobalt coordination compound can be selected from the group consisting of CoCl2, Co(NO3)2, CoSO4, Co2(CO)8, Co[N(SiMe3)2]2, Co-AEE2and combinations thereof. An example of forming Co-AEE2is provided in the Examples section herein. Preferably, the cobalt coordination compound is CoCl2. For the various embodiments, the metal solution can include 1 molar equivalents of the cobalt coordination compound, which is dissolved in 10 to 100 molar equivalents of AEE to form a mixture. To this mixture, KHMDS is added at a 1 to 10 molar equivalent to the cobalt coordination compound to form the metal solution, which is stirred at the predetermined temperature and predetermined pressure noted above for a predetermined time of 1 to 48 hours. Preferably, the cobalt coordination compound is mixed with 50 to 100 molar equivalents of AEE and 2 to 3 molar equivalents of KHMDS, more preferably 2 molar equivalents of KHMDS, to form the metal solution, which is stirred at the predetermined temperature and predetermined pressure noted above for a predetermined time of 1 to 48 hours. Preferably, the resulting metal solution is stirred at the predetermined temperature and predetermined pressure for 24 hours. Filtration can be used to remove any precipitants (e.g., KCl) formed in the metal solution. For the various embodiments, forming the catalyst further includes mixing the metal solution with a heterogeneous solid support that includes a ruthenium species to form a supported precatalyst. For the various embodiments, the heterogeneous solid support can be selected from the group consisting of γ-Al2O3, α-Al2O3, SiO2, TiO2, ZrO2, ZnO and combinations thereof. Preferably, the heterogeneous solid support is γ-Al2O3. For the various embodiments, the heterogeneous solid support further include the ruthenium species. For example, the heterogeneous solid support can further include 1 to 4 weight percent of a ruthenium species based on a total weight of the heterogeneous solid support (dry basis). For the various embodiments, the ruthenium species can be formed from, for example, RuOHx, RuCl3and combinations thereof, where x is 3 or 4. The RuOHx can be prepared as described in “Supported Ruthenium Catalyst for the Heterogeneous Oxidation of Alcohols with Molecular Oxygen” Yamaguchi & Mizuno; Angewandte Chemie International Edition; 2002, 41, 4538-4542, which is incorporated herein by reference in its entirety. Briefly, the RuOHx is prepared by mixing a high surface area γ- Al2O3 catalyst support in an aqueous solution of RuCl3at room temperature. The solid is filtered and washed with water then dried under vacuum. The solid is then resuspended in water and made basic by addition of aqueous NaOH to a pH of 13.2. The solid is again recovered by filtration and washing with water and dried under vacuum. For the various embodiments, the supported precatalyst can have a cobalt to ruthenium molar ratio of about 95:5. In an additional embodiment, the supported precatalyst can have a cobalt to ruthenium molar ratio of in a range of 10:1 to 99:1. For the various embodiments, the amount of metal solution mixed with the heterogeneous solid support to form the supported precatalyst can be determined from a ratio of Co metal mass in solution to the heterogeneous solid support mass plus the Co mass. Preferably, the ratio is provided such that the wt.% of Co in solution is 12.4 wt.% relative to the heterogeneous solid support weight plus the Co weight. For the various embodiments, however, the range can be 1 to 30 wt.%. Put in other terms, the ratio of heterogeneous solid support mass : dissolved Co mass is in a range of 99:1 to 2.33:1, where a ratio of 7.06 : 1 is preferred. Mixing of the metal solution and the heterogeneous solid support to form the supported precatalyst can be done, preferably, under an inert atmosphere at a temperature and pressure as noted above. For the various embodiments, the inert atmosphere can be a nitrogen atmosphere or others as are known in the art, such as argon and helium among others. For the various embodiments, the metal solution and the heterogeneous solid support can be mixed at the predetermined temperature and pressure noted above for a time of 1 to 24 hours to form the supported precatalyst. Preferably, the metal solution and the heterogeneous solid support are mixed at the predetermined temperature and pressure noted above for a time of 1 to 4 hours to form the supported precatalyst. For the various embodiments, the supported precatalyst is then chemically reduced at a predetermined pressure of hydrogen (H2) and at a predetermined temperature over a Co-AEE2to produce the catalyst for reductive amination. For the various embodiments, chemically reducing the supported precatalyst can occur under mixing conditions. For the various embodiments, the predetermined pressure of hydrogen is at a pressure of 0 to 20684 kPa of H2gas. In additional embodiments, the predetermined pressure of hydrogen is at a pressure of 0 to 6895 kPa of H2gas. In one embodiment, the predetermined pressure of hydrogen is, preferably, 1724 kPa of H2gas. For the various embodiments, the predetermined temperature for chemically reducing the supported precatalyst can be in the range of 100 to 200oC. Preferably, the predetermined temperature for chemically reducing the supported precatalyst can be in the range of 160 to 200oC. Preferably, the predetermined temperature for chemically reducing the supported precatalyst is 180oC. For the various embodiments, the predetermined time is in a range of 1 to 48 hours. Preferably, the predetermined time is in a range of 1 to 24 hours. The resulting catalyst for reductive amination formed according to the method herein has metal nanoparticles supported on the heterogeneous support material that are catalytically active for reductive amination, as discussed herein. Given the above discussion and by way of example, the method of the present disclosure can therefore involve taking a metal precursor such as, for example, CoCl2and mixing it with AEE and KHMDS to produce a metal solution containing the metal moiety (e.g., Co) in AEE. The metal solution is then mixed with a heterogeneous solid support such as, for example, γ- Al2O3. For the various embodiments, the heterogeneous solid support can include a metal moiety (e.g., RuOHx on γ-Al2O3). The catalyst can then be activated by reduction through heating in the presence of hydrogen gas (H2) at a predetermined pressure and temperature (e.g., 1724 kPa H2and 180oC). This method can be performed, if desired, in situ (e.g., in one container). The reaction produces metal nanoparticles supported on the heterogeneous support material that, after being filtered and washed, are catalytically active for reductive amination. Examples All components purchased from commercial vendors and used as received unless otherwise noted. All percentages are weight percentages (wt.%) based on the total weight of the mixture used to form the following Examples and Comparative Examples, unless otherwise noted. Example Reactions Anhydrous CoCl2(97% purity) was purchased from Alfa Aesar and stored in a glove box under an inert N2atmosphere. Aluminum oxide (γ-Al2O3, >99% purity, 150-200 mesh) was purchased from Alfa Aesar, ground using a mortar and pestle to break down any large pieces, then dried in an oven at 200 °C and stored under a N2atmosphere in a glove box. 2-(2- aminoethoxy)ethanol (AEE, 98% purity) was purchased from Acros Organics, distilled over CaH2under vacuum, degassed, and stored under an inert N2atmosphere. Potassium bis(trimethylsilyl)amide) (KHMDS, 95% purity) was purchased from Sigma Aldrich and stored under an inert N2atmosphere in a glove box. RuOHx@γ-Al2O3was prepared according to “Rational Design of Selective Metal Catalysts for Alcohol Amination with Ammonia”, Wang T., et al. Nat. Catal. 2, 773-779 (2019), which is incorporated herein by reference. Reductive aminations were performed using an H.E.L. DigiCAT high-pressure system equipped with 16 mL stainless steel (SS316) reactor vessels. Co(AEE)2In a nitrogen atmosphere glove box anhydrous CoCl2(1.695 g, 13.05 mmol) was added to a 100 mL oven-dried Schlenk flask equipped with a Teflon cap and stir-bar. While vigorously stirring, AEE (80 mL, 798.9 mmol) was added to dissolve CoCl2which immediately turned from blue to purple upon dissolution in AEE. This solution was stirred for 20 minutes at room temperature. KHMDS (5.205g, 26.09 mmol) was then added slowly in portions over 10 minutes, resulting in a dark purple solution and a white suspension (KCl). After complete addition of KHMDS the solution was stirred at room temperature (23oC) for 24 hours. The solution was then filtered over a 150 mL medium porosity frit to remove KCl to produce the Co(AEE)2mixture. The Co(AEE)2mixture was used as is without further purification (est. 0.16 M [Co] in AEE). HRMS (m / z +H): calc. 286.0833; found 268.0895.CoRu@γ-Al2O3In a nitrogen atmosphere glove box, 200mg of RuOHx@γ-Al2O3was weighed into a 16 mL stainless steel vessel. A solution of Co(AEE)2(3.0 mL, 0.16 M) was slowly added via syringe over RuOHx@γ-Al2O3while stirring. After complete addition the reactor was sealed inside the glovebox and the heterogeneous mixture was stirred at room temperature for 1 hour. The reactor vessel was then removed from the glovebox, placed in an aluminum heating block with a stir rate of 700 rpm and connected to the H.E.L DigiCAT high-pressure system. To ensure the removal of all residual oxygen, the reactor was charged with 1724 kPa H2, then vented and this process was repeated three times. After the final cycle, the reactor was held under a static pressure of 1724 kPa H2and heated to 180 °C with a stir rate of 700 rpm. After 16 hours, the reactor was cooled to room temperature and vented. To remove residual H2and NH3(produced during the reaction), the headspace was replaced with 689 kPa argon and vented three times. The reactor was then transferred back into the glove box and CoRu@γ-Al2O3was recovered by filtering over a 15 mL medium porosity frit. The supported catalyst was washed with portions of tetrahydrofuran (THF, 3 x 10 mL), dried under vacuum to yield 260 mg black powder, and stored under an inert atmosphere inside the glovebox. The filtrate was analyzed by GC-FID using tetraglyme as an internal standard, providing 99% conversion of AEE and 42% GC yield of morpholine. The structure of the Co(AEE)2mixture taken after filtration, but before reduction under the H2atmosphere, was analyzed using extended x-ray absorption fine structure (EXAFS) to confirm the structure illustrated in Fig. 1, in which the Co atom is coordinated by nitrogen (100) and oxygen (102) atoms connected by two carbon (104) atoms similar to the structure of AEE. EXAFS K-edge measurements were taken on the Taiwan Photon Source. Referring now to Figs. 2 and 3, there is illustrated a set of EXAFS performed on the CoRu@γ-Al2O3catalyst formed as described above. Fig. 2 is an EXAFS of the CoRu@γ- Al2O3catalyst taken after 1 hour of reaction under hydrogen at 180oC and Fig. 3 is an EXAFS of the CoRu@γ-Al2O3catalyst taken after the reaction is complete at 15 hours. Fits to the K-edge measurements allow for estimated bond distances and coordination numbers (CN) as summarized in Tables 1 and 2, below. The data in Table 1 supports the position that the Co exists as nanoparticles with Ru existing on the surface of the nanoparticles in segregated regions. The CN for the Co-Co bonds is consistent with nanoparticles as being < 2 nm. Equal CN for Ru-Co and Ru-Ru bonds indicate there is phase segregation between Ru and Co. The partial oxidation of Ru, as evidenced by Ru-O bonds that increase during the reaction, also support that Ru is located on the surface of the nanoparticles. Table 1 Co Fitting 1 h 15 h Ru Fitting The resulting particles are catalytically active as demonstrated in co-pending application 63 / 631,794, which is incorporated herein by reference in its entirety.

Claims

What is Claimed is:

1. A catalyst for reductive amination, the catalyst formed from the steps comprising: mixing a cobalt coordination compound with 2-(2-aminoethoxy)ethanol (AEE) and potassium bis(trimethylsilyl)amide (KHMDS) to form a metal solution; mixing the metal solution with a heterogeneous solid support to form a supported precatalyst, wherein the heterogeneous solid support includes a ruthenium species; and chemically reducing the supported precatalyst at a predetermined pressure of hydrogen and at a predetermined temperature over a predetermined time to produce the catalyst for reductive amination.

2. The method of claim 1, wherein the cobalt coordination compound is selected from the group consisting of CoCl2, Co(NO3)2, CoSO4, Co2(CO)8, Co[N(SiMe3)2]2, Co-AEE2and combinations thereof.

3. The method of claim 1, wherein the heterogeneous solid support is selected from the group consisting of γ-Al2O3, α-Al2O3, SiO2, TiO2, ZrO2, ZnO and combinations thereof.

4. The catalyst of any one of claims 1-3, wherein the heterogeneous solid support includes 1 to 4 weight percent of the ruthenium species based on a total weight of the heterogeneous solid support.

5. The catalyst of any one of claims 1-4, wherein the ruthenium species is formed from RuOHx, RuCl3and combinations thereof, wherein x is 3 or 4.

6. The catalyst of any one of claims 1-5, wherein the predetermined pressure of hydrogen is a pressure of 0 to 20684 kPa.

7. The catalyst of any one of claims 1-6, wherein the predetermined temperature is in a range of 100 to 200oC.

8. The catalyst of any one of claims 1-7, wherein the predetermined time is in a range of 1 to 48 hours.

9. The catalyst of any one of claims 1-8, wherein the supported precatalyst has a cobalt to ruthenium molar ratio of about 95:5.

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