MICROPOROUS CATALYSTS FOR DIRECT SYNTHESIS OF BRANCHED ENALS WITH HIGH SELECTIVITY

Abstract

Disclosed herein are new metallated MOF catalysts, preferably, Rh-PCM-101 or Rh-AsCM-102, as well of methods using such catalysts in hydroformylation reactions and in tandem hydroformylation/enolization reactions. In a specific embodiment, a metallated phosphine MOF catalyst according to the disclosure, preferably Rh-PCM-101, is used in a single-step hydroformylation process to transform propene into 2-ethyl-2-hexenal.

Claims

1. A catalyst comprised of: a. a metal-organic framework; and b. a 4d or 5d transition metal species contained in one or more active sites, wherein the catalyst is a microporous solid state ligand.

2. The catalyst of claim 1 wherein the metal-organic framework is a phosphine-based metal organic framework.

3. The catalyst of claim 2 wherein the metal-organic framework is PCM-101, PCM-102, or PCM-201.

4. The catalyst of claim 1 wherein the metal-organic framework is an arsine-based metal organic framework.

5. The catalyst of claim 4 wherein the arsine-based metal organic framework is AsCM-102, AsCM-201, or AsCM-303.

6. The catalyst of claim 1 wherein the 4d or 5d transition metal species is one of Ru.sup.II, Rh.sup.I, Ir.sup.I, Os, Pd.sup.II, and Pt.sup.II bearing common ligands.

7. The catalyst of claim 1 wherein the metal-organic framework is PCM-101 and the 4d or 5d transition metal species is a Rh.sup.I bearing common ligand.

8. The catalyst of claim 1 wherein the metal-organic framework is PCM-101 and the 4d or 5d transition metal species is a Ir.sup.I bearing common ligand.

9. The catalyst of claim 1 wherein the metal-organic framework is PCM-101 and the 4d or 5d transition metal species is a Pt.sup.II bearing common ligand.

10. The catalyst of claim 1 wherein the metal-organic framework is AsCM-102 and the 4d or 5d transition metal species is a Rh.sup.I bearing common ligand.

11. A catalysis method comprising: a. submerging a metallated MOF catalyst in a liquid solvent inside a reactor; b. adding an olefin to the reactor; c. maintaining a CO:H.sub.2 partial pressure ratio in the reactor within a range of 1:1 and 3:1; d. maintaining the temperature of the reactor between 55 C. and 85 C. for a reaction time; e. maintaining the overall pressure in the reactor between 40 and 55 bar during the reaction time; wherein the reaction time is between eleven and twenty-four hours.

12. The method of claim 11 further comprising (f) removing the metallated MOF catalyst; (g) adding one or more of aqueous sodium hydroxide, an organic base, or a Bronsted acid to the reactor; and (h) recovering an enal product.

13. The method of claim 11 wherein the metallated MOF catalyst is one of Rh-PCM-101, Ir-PCM-101, Pt-PCM-101, Rh-PCM-102, Ir-PCM-102, Pt-PCM-102, Rh-PCM-201, Ir-PCM-201, Pt-PCM-201, Rh-AsCM-102, Rh-AsCM-201, Rh-AsCM-303, Ir-AsCM-102, Ir-AsCM-201, Ir-AsCM-303, Pt-AsCM-102, Pt-AsCM-201, or Pt-AsCM-303.

14. The method of claim 11 wherein the olefin is one of: styrene, cyclobutene, cyclopropene, cyclohexene, cyclooctene, propene, butene, pentene, hexene, heptene and octene.

15. The method of claim 12 wherein the metallated MOF catalyst is Rh-PCM-101, the olefin is propene, and the recovered enal product is 2-ethyl-2-hexenal.

16. The method of claim 12 wherein the metallated MOF catalyst is Rh-AsCM-102, the olefin is propene, and the recovered enal product is 2-ethyl-2-hexenal.

17. The method of claim 12 wherein the CO:H.sub.2 partial pressure ratio is 1:1.

18. The method of claim 12 wherein removing the metallated MOF catalyst comprises filtering out the metallated MOF catalyst.

19. The method of claim 12 wherein the reactor is a moving bed reactor and removing the metallated MOF catalyst comprises using a moving bed assembly to remove the metallated MOF catalyst from one or more reactants before steps (g) and (h) are performed.

20. The method of claim 12 wherein removing the metallated MOF catalyst comprises partitioning the metallated MOF catalyst away from one or more reactants before steps (g) and (h) are performed.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0022] FIG. 1 shows space-filling models of the periodic structure of PCM-101 (with Ni.sub.3OH nodes) (101) in the conversion reaction using [RhCl(CO).sub.2].sub.2 to form the metallated phosphine MOF catalyst Rh-PCM-101 (102) and depicts the structure of the catalytic sites in the resulting Rh-PCM-101 (103) as well as the impact on those catalytic sites when under 40 bar pressure with only CO gas (104) or H.sub.2 gas (105).

[0023] FIG. 2(a) shows space-filling models of the periodic structure of PCM-101 in the conversion reaction using IrCl(C.sub.2H.sub.4).sub.2 to form the metallated phosphine MOF catalyst Ir-PCM-101. FIG. 2(b) shows space-filling models of the periodic structure of PCM-101 in the conversion reaction using Pt(CH.sub.3).sub.2Cl.sub.2 to form the metallated phosphine MOF catalyst Pt-PCM-101.

[0024] FIG. 3 shows FT-IR spectra of Rh-PCM-101. Specifically, FIG. 3 shows the FT-IR spectra for CO only (301), Rh-PCM-101 post-catalysis (302), and Rh-PCM-101 (303).

[0025] FIG. 4 shows PXRD (powder x-ray diffraction) results of H.sub.2 only (401), CO only (402), Rh-PCM-101 post-catalysis (403), and Rh-PCM-101 (404).

[0026] FIG. 5 shows GC-MS (gas chromatography mass spectrometry) product distribution results for the catalysis reactions of 1-hexene at CO:H.sub.2 of 3:1 with Rh-PCM-101 as the catalyst (black bar), n-heptanal at CO:H2 of 3:1 with Rh-PCM-101 as the catalyst (hatched bars), and n-heptanal at CO:H.sub.2 of 3:1 with no Rh-PCM-101 catalyst (white bars).

[0027] FIG. 6 shows the conversion of olefins to enals and branched alcohols via either the prior art multi-step process or direct tandem catalysis using one of the metallated MOF catalysts described herein.

[0028] FIG. 7 shows the structure of AsCM-303 with catalytic sites of metal ligands.

[0029] FIG. 8 shows the FT-IR spectra of Rh-PCM-101 charged with CO (901), Rh-PCM-101 post-catalysis (902), and Rh-PCM-101 (903).

[0030] FIG. 9 shows PXRD results for Rh-PCM-101 post-catalysis (1001), Rh-CO-PCM-101 (1002), and PCM-101 (1003).

[0031] FIG. 10 shows an HMF reaction of 1-hexene (1101), which may yield various products depending on the conditions including n-heptanal (1102), 2-methyl-hexanal (1103), and 2-ethyl-pentanal (1104).

[0032] FIG. 11 shows a graph with conversion percentage and TOF (turnover frequency) plotted against time for an HMF reaction of 1-Hexene using Rh-AsCM-102-Co as the catalyst at a partial pressure ratio of 1:1 for CO:H.sub.2, 40 bar pressure, and 70 C.

[0033] FIG. 12 shows (a) an HFM reaction of 1-hexene (1301) using Rh-AsCM-102 as the catalyst to yield n-heptanal (1302) as the major product with 2-methyl-hexanal (1303) and 2-ethyl pentanal (1304) as minor products, (b) followed by enolization of the heptanal to yield (Z)-2-pentylidenenonanal (1305).

DETAILED DESCRIPTION OF THE INVENTION

[0034] Unless defined otherwise, all scientific or technical terms used herein shall have the same meaning as is commonly understood by one of skill in the art. Unless specific definitions are provided, the nomenclature used in connection with, and the procedures and techniques of chemistry, including inorganic, organic, and physical chemistry described herein are those well-known and commonly used in the art. Standard techniques may be used for chemical synthesis and chemical analysis consistent with the additional disclosures provided herein.

Definitions

[0035] As used in the specification and the claims, the singular forms a, an, and the include the plural unless the context clearly dictates otherwise.

[0036] Unless otherwise explicitly noted, where the disclosures uses the phrase within a range, it is meant to include the values given for the beginning and end of such range.

[0037] In the specification and the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings: [0038] 2-EH is an acronym for the chemical compound 2-ethylhexanol.

[0039] Aldehyde refers to an organic compound containing a functional group with the structure RCHO. Common aldehydes include methanal (formaldehyde) and ethanal (acetylaldehyde).

[0040] AsCM is an acronym for arsine coordination materials. Specific arsine-based MOFs known in the art may be referred to by AsCM combined with a specific number, e.g. AsCM-102.

[0041] Catalyst has its plain and ordinary meaning; however, this disclosure uses the phrase metallated MOF catalyst to refer to the heterogeneous catalyst that consists of a MOF backbone (i.e., a solid micropore metal-organic framework structure) with one or more metal ligand catalysts each contained in a catalytic site. Similarly, metallated phosphine MOF catalyst refers to the heterogeneous catalyst that consists of a phospine-based MOF backbone, such as, but not limited to, PCM-101, PCM-102, or PCM-201, with one or more metal ligand catalysts each contained in a catalytic site. Likewise, metallated arsine-based MOF catalyst refers to the heterogeneous catalyst that consists of an arsine-based MOF backbone, such as, but not limited to, AsCM-102, AsCM-201, and AsCM-303, with one or more metal ligand catalysts each contained in a catalytic site.

[0042] COD is an acronym for cyclooctadiene.

[0043] DCM is an acronym for dichloromethane.

[0044] DMF is an acronym for dimethylformamide.

[0045] HFM is an acronym referring to hydroformylation.

[0046] MOF is an acronym referring to metal-organic framework.

[0047] Olefins refers to compounds made of carbon and hydrogen that contain at least one double bond between a pair of carbon atoms. Olefins includes alkenes and arenes.

[0048] PCM is an acronym for phosphine coordination materials. Specific phosphine-based MOFs known in the art may be referred to by PCM combined with a specific number, e.g. PCM-101.

[0049] Pnictogen refers to a chemical element or compound that is part of group 15 of the periodic table, such as nitrogen, phosphorus, arsenic, antimony, or bismuth.

[0050] SSL is an acronym referring to solid state ligand.

[0051] Syngas refers to synthesis gas, which is a mixture of carbon monoxide (CO) and hydrogen (H.sub.2).

Overview

[0052] The present disclosure describes new catalyst materials, including those prepared by post-synthetic modification of a phosphine-based MOF such as PCM-101, PCM-102, or PCM-201, or prepared using an arsine-based MOF, such as AsCM-102, AsCM-201, or AsCM-303, by installation of secondary low-valent metal species, specifically, 4d and 5d transition metals. These new catalyst materials are unique examples of MOF-supported catalysts that contain catalytic sites not accessible to conventional molecular chemistry. Secondary low-valent metal species useful for such catalysts include complexes based on Ru.sup.II, Rh.sup.I, Ir.sup.I, Pd.sup.II, and Pt.sup.II, bearing common ligands including halides, CO, and/or alkyls.

[0053] The present disclosure also describes use of these new catalyst materials as hydroformylation catalysts, which are able to achieve different product outcomes than their molecular counterparts. For example, Rh-based PCM-101 or AsCM-102 catalysts according to the invention can achieve direct production of 2-ethyl-2-hexenal from propene in a single step (as opposed to three steps in the prior art process) with near 100% selectivity as a direct function of control over CO:H.sub.2 gas partial pressures. Ideally in this direct tandem HFM/aldol condensation method, the CO:H.sub.2 ratio is 1:1, the overall pressure is maintained in a range of 40-55 bar, preferably 40 bar, the reaction temperature is in a range between 55 C. and 85 C., preferably 70 C., the metallated MOF catalyst is removed from the reaction, and one or more of aqueous sodium hydroxide, an organic base, such as t-BuOK, or a Bronsted acid, such as ZSM-5, is then added at a concentration within the range from 0.001M to 1M, and most preferably, at a concentration of 0.01M in order to promote aldol condensation to the 2-ethyl-2-hexenal product.

[0054] Benefits of the catalysts described herein include: (i) catalyst enabled direct access to value-added products that exist within the current product chain but do not require isolation at each intermediate stage; (ii) unlike conventional homogeneous catalysts used in this filed, the catalysts described herein are heterogeneous microporous solid state ligands so catalyst recovery is greatly simplified; (iii) the same process works for lighter and heavier n-alkenes (for example, 1-hexene+CO+H.sub.2 to yield directly the corresponding C-14 enals); and (iv) the MOF pores are hydrophobic in the catalysts of the invention, so the catalysts resist the presence of water, which is a potential poison to molecular catalysts.

Post-Synthetic Metallation of MOFs to Form New Catalysts

[0055] Post-synthetic metallation of MOFs as solid-state ligands generates crystalline, heterogeneous catalyst materials with crystallographically-defined, single-site (i.e., homogeneous) active sites in unique microenvironments. This can be thought of as a scaffold-like structure to protect catalytic sites. Low-valent metal site-occupancy, also known as loading, in MOFs as solid state ligands (SSLs) can be controlled by post-synthetic metalation using specified molar amounts of low-valent 4d and 5d transition metal species. Examples of low-valent 4d and 5d transition metal species that may be used in post-synthetic metalation of MOFs include: [RhCl(CO).sub.2]2, [IrCl(C.sub.2H.sub.4).sub.2].sub.2, Pt(CH.sub.3).sub.2Cl.sub.2, Pt(COD)(CH.sub.3).sub.2, and PdCl.sub.2(COD).

[0056] Phosphine MOFs useful as backbones for the catalysts described herein include PCM-101, PCM-102, and PCM-201, which have been previously characterized. See, e.g., Humphrey et al., A Metal-Organic Framework with Cooperative Phosphines That Permit Post-Synthetic Installation of Open Metal Sites, Angewandte Chemie, 2018, 57, 30, pp. 9295-9299 (characterizing PCM-101); Humphrey et al., Low-Valent Metal Ions as MOF Pillars: A New Route Toward Stable and Multifunctional MOFs, J. Am. Chem. Soc., 2021, 143, 34, pp. 13710-13720 (characterizing PCM-102), each of which is herein incorporated by reference. Other MOFs useful as backbones for the catalysts described herein include arsine-based MOFs, including AsCM-102, AsCM-201, and AsCM-303 (Zns(ClO.sub.4)(TPZA).sub.4). Metallated arsine-based MOF catalysts can have a higher activity than metallated phosphine MOF catalysts using the same metal. However, use of metallated phosphine MOF catalysts may be more industrial acceptable due to a perceived risk of arsenic toxicity if it were to leach from the metallated arsine-based catalysts. However, the scaffold structure imparted in the metallated arsine-based catalysts described herein appears to prevent leaching and greatly reduce any risk of toxicity.

[0057] In a reaction to form the metallated MOF catalyst, consideration is given to the number of coordination sites available in the MOF such that the molar amount of the transition metal species added does not result in a loading ratio above 1. While it is not necessary for every potential coordination site to include a transition metal species to act as a catalyst-meaning loading ratios above zero and below 1 are acceptablea loading ratio above 1 indicates more transition metal species than coordination sites, and the excess metal may negatively impact the efficiency of catalysis. Stated another way, 100% coordination site occupancy is not required in the metallated MOF catalysts disclosed herein. The coordination site occupancy in the metallated MOF catalyst may be in a range from 1-100%, 10-100%, 20-100%, 30-100%, 40-100%, 50-100%, 60-100%, 70-100%, 80-100, or most preferably, 90-100%.

[0058] Examples of post-synthetic metalation of MOFs to form catalysts include incorporation of low-valent 4d and 5d transition metal species in trans-P2 binding pockets of the solid state ligand PCM-101 to form Rh-PCM-101, Ir-PCM-101, and Pt-PCM-101. FIG. 1 shows space-filling models of the periodic structure of PCM-101 (with Ni.sub.3OH nodes) (101) in the conversion reaction using [RhCl(CO).sub.2].sub.2 to form the metallated phosphine MOF catalyst Rh-PCM-101 (102) and depicts the structure of the catalytic sites in the resulting Rh-PCM-101 (103) as well as the impact on those catalytic sites when under 40 bar pressure with only CO gas (104) or H.sub.2 gas (105). To prepare Rh-PCM-101 (102) as shown in FIG. 1, [RhCl(CO.sub.2).sub.2].sub.2 was added to PCM-101 with DMF as a solvent in a reaction at 75 C. that was allowed to continue for eighteen hours. The resulting metallated phosphine MOF catalyst Rh-PCM-101 is comprised of the PCM-101 backbone, which protects [RhCl].sup.+ dimers inside the catalytic site(s) as shown. The structure of the catalytic sites during an HFM reaction may be slightly altered by controlling the partial pressures of CO gas (104) and H.sub.2 gas (105) to facilitate recovery of specific products and change the reaction rate. The partial pressure ratio of CO:H.sub.2 gas has been shown to change the selectivity of reaction products in an HFM reaction resulting in the ability to control whether linear or branched products are the major products.

[0059] FIG. 2(a) shows space-filling models of the periodic structure of PCM-101 in the conversion reaction using IrCl(C.sub.2H.sub.4).sub.2 to form the metallated phosphine MOF catalyst Ir-PCM-101. That reaction was performed in the presence of DMF at 75 C. and allowed to continue for eighteen hours. FIG. 2(b) shows space-filling models of the periodic structure of PCM-101 in the conversion reaction using Pt(CH.sub.3).sub.2Cl.sub.2 to form the metallated phosphine MOF catalyst Pt-PCM-101. That reaction was also performed in the presence of DMF at 75 C. and allowed to continue for eighteen hours.

[0060] Low-valent 4d and 5d transition metals useful in post-synthetic metalation of MOFs to generate catalysts according to the disclosure herein include: ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). Preferred low-valent metal species useful for the metallated MOF catalysts disclosed herein include complexes based on Ru.sup.II, Rh.sup.I, Ir.sup.I, Pd.sup.II, and Pt.sup.II, bearing common ligands including halides, CO, and/or alkyls. Examples of low-valent 4d and 5d transition metal species that may be used in post-synthetic metalation of MOFs include: [RhCl(CO).sub.2].sub.2, IrCl(C.sub.2H.sub.4).sub.2, Pt(CH.sub.3).sub.2Cl.sub.2, Pt(COD)(CH.sub.3).sub.2, and PdCl.sub.2(COD).

[0061] Metallated MOF catalysts according to the disclosure herein may be characterized by FT-IR spectra, as well as PXRD. FIG. 3 shows FT-IR spectra of Rh-PCM-101. Specifically, FIG. 3 shows the FT-IR spectra for CO only (301), Rh-PCM-101 post-catalysis (302), and Rh-PCM-101 (303). FIG. 4 shows PXRD (powder x-ray diffraction) results of H.sub.2 only (401), CO only (402), Rh-PCM-101 post-catalysis (403), and Rh-PCM-101 (404). As demonstrated in FIG. 3 and FIG. 4, the structure of the active sites in Rh-PCM-101 are stable even after being used as a catalyst.

Hydroformylation Reactions Using Metallated MOF Catalysts

[0062] Hydroformylation reactions using metallated MOF catalysts of the present invention may be performed by submerging the metallated MOF catalyst solid directly in an olefin (alkenes, arenes) in a Parr pressure reactor or other reactor that enables control of the overall pressure and the partial pressures of CO gas and H.sub.2 gas. The solid state of the metallated MOF catalysts enables the ability to partition the catalyst in a reactor such that separation of the catalyst from the reaction product is easy and efficient. For example, the metallated MOF catalyst could be removed by centrifugation, filtration, a moving bed assembly, or partitioning within the reactor. This easy separation reduces the number of steps necessary to convert olefins to aldehydes or enals.

[0063] Metallated MOF catalysts, particularly metallated phosphine MOF catalysts, according to the invention maintain structural integrity following catalysis, which allows for characterization of the catalytic site and surrounding environment, including any potential changes to the MOF structure via SC/PXRD (Single Crystal/Powder X-ray Diffraction), FT-IR (Fourier Transform Infrared Spectroscopy), Raman spectroscopy, XPS (X-ray Photoelectron Spectroscopy) and other known characterization techniques. Metallated MOFs demonstrate steric controlled selectivity of linear/branched aldehyde products and increased aldol condensation products at lower total pressure or for CO-rich syngas mixtures when used in hydroformylation reactions.

[0064] Examples of olefins that can be used in accordance with the disclosure herein include arenes and alkenes such as: styrene, cyclobutene, cyclopropene, cyclohexene, cyclooctene, propene, butene, pentene, hexene, heptene and octene. Other examples of olefins that can be used in accordance with the disclosure herein include alpha-olefins, dienes, or polyenes.

[0065] HFM reactions using metallated MOF catalysts may be performed at temperatures ranging from 70 C. to 110 C., preferably within a range of 70 C. to 80 C. The pressure maintained for the HFM reactions may preferably range from 40 to 55 bar, most preferably 40 bar.

[0066] For example, Table 1 below provides a comparison of Rh-PCM-101 hydroformylation results with substrates including styrene, 1-hexene, and cyclohexene where the partial pressure CO:H.sub.2 ratio is 1:1 and the catalyst loading percentage was determined by ICP-OES (Inductively Coupled Optical-Emission Spectroscopy).

TABLE-US-00001 TABLE 1 Comparison of Rh-PCM-101 HFM results with a range of substrates where the partial pressure ratio of CO:H.sub.2 is 1:1. Catalyst Loading Temper- Pres- Isomeric Percent- Time ature sure Yield n/ Product Substrate age (%) (h) ( C.) (bar) (%) iso (%) Styrene 0.20 20 80 55 90 0.4 N/A 1-hexene 0.21 18 80 50 55 4.0 <1.0 Cyclo- 0.17 18 80 50 85 N/A N/A hexene

[0067] FIG. 5 shows GC-MS (gas chromatography mass spectrometry) product distribution results for the catalysis reactions of 1-hexene at CO:H.sub.2 of 3:1 with Rh-PCM-101 as the catalyst (black bar), n-heptanal at CO:H.sub.2 of 3:1 with Rh-PCM-101 as the catalyst (hatched bars), and n-heptanal at CO:H2 of 3:1 with no Rh-PCM-101 catalyst (white bars). As demonstrated in FIG. 5, use of Rh-PCM-101 as the catalyst in an HFM reaction with 1-hexene as the feedstock and a partial pressure ratio of CO:H.sub.2 of 3:1 results exclusively in aldol condensation products. Alternatively, use of Rh-PCM-101 as the catalyst in an HFM reaction with n-heptanal as the feedstock and a partial pressure ratio of CO:H.sub.2 of 3:1 results in aldol condensation products, ketonization products, and acidic HFM products. When Rh-PCM-101 is not present in the HFM reaction, no aldol condensation products are recovered.

[0068] FIG. 6 shows the conversion of olefins to enals and branched alcohols via either the prior art multi-step process or direct tandem catalysis using one of the metallated MOF catalysts described herein. Direct tandem catalysis involves including an acid or base in the same reactor as the olefin feedstock to promote the tandem reaction of HFM followed by aldol condensation. When Rh-PCM-101 is used as a catalyst in a direct tandem HFM/aldol condensation reaction using 1-hexene as the feedstock, the recovered products depend on the partial pressure ratio of CO:H.sub.2 as shown in TABLE 2 below. Specifically, a partial pressure ratio of 1:1 yields Cn+1 n-carboxylic acid products at a yield of 89% and C.sub.2n+2 enals at a yield percentage of 11%. When the partial pressure ratio is increased to 3:1, C.sub.2n+2 enals are recovered at a yield percentage of 97%. In this fashion, the same metallated MOF catalyst may be used in different HFM/aldol condensation reactions to recover different types of product by altering the pCO:pH.sub.2 ratio.

TABLE-US-00002 TABLE 2 Comparison of the effect of the partial pressure ratio of CO:H2 on products recovered from an HFM reaction C.sub.2n+2 enals (a,b-unsaturated C.sub.n+1 n-carboxylic aldehydes) acid Olefin pCO:pH.sub.2 Yield % Yield % 1-hexene 1:1 11 89 1-hexene 3:1 97 3

Arsine-Based MOF Catalysts

[0069] In addition to phosphine-based MOFs, arsine-based MOFs, such as AsCM-102, AsCM-201, or AsCM-303, may be useful as the backbone in metallated MOF catalysts. FIG. 7 shows the structure of AsCM-303 with catalytic sites of metal ligands. 4d and 5d transition metal species are used as the catalyst in a metallated arsine-based MOF catalyst. Preferably, low-valent metal species useful for such catalysts include complexes based on Ru.sup.II, Rh.sup.I, Ir.sup.I, Pd.sup.II, and Pt.sup.II, bearing common ligands including halides, CO, and/or alkyls. For example, the following are 4d or 5d transition metal species useful to form the arsine-based MOF catalysts disclosed herein: [RhCl(CO).sub.2].sub.2, IrCl(C.sub.2H.sub.4).sub.2, Pt(CH.sub.3).sub.2Cl.sub.2, Pt(COD)(CH.sub.3).sub.2, and PdCl.sub.2(COD).

EXAMPLES

[0070] The following examples demonstrate the formation of metallated MOF catalysts, as well as their use in HFM and direct tandem HFM/aldol condensation reactions, including at variable reaction conditions to identify the optimal solvent, temperature, and pressures for specific reaction products. Although the examples provided herein are on a smaller scale than might be required for industrial applications, one of ordinary skill in the art would be able to scale up the conditions indicated to perform reactions on a larger scale.

Example 1. Rh-PCM-101 Catalyst Formation

[0071] To form PCM-101, the MOF-forming linker tris-p-carboxylato(triphenyl)phosphine (tctpH.sub.3) was combined with one equivalent of 4,4-bipyridine (bipy) and three equivalents of Ni(BF.sub.4).sub.2.Math.xH.sub.2O in a glass jar. Under an inert N.sub.2 atmosphere, a degassed 5:2:1 mixture of DMF:MeOH:H.sub.2O was added, and the reaction vessel was sealed. The jar was sonicated for 5 minutes to dissolve all solids and then heated at 75 C. for 3 days in a conventional oven. The green crystals of PCM-101(Ni) were then washed with fresh degassed DMF and filtered under vacuum to yield PCM-101, which was stored in air. Additionally, AsCM-101 has been synthesized via the same synthetic procedure, with tris-p-carboxylato(triphenyl)arsine being used in place of the phosphine MOF-forming linker.

[0072] To form Rh-PCM-101, under an inert atmosphere, dry crystals of PCM-101 were treated with stoichiometric equivalents of the co-linker 4,4-bipyridine (bipy) and [RhCl(CO).sub.2].sub.2 in a ratio of 1:1:1 (PCM-101:bipy:[RhCl(CO).sub.2]2) in degassed DMF and heated for 18 hours at 75 C. The flask was swirled periodically throughout the reaction, however not stirred to preserve catalyst crystallinity. Following the reaction, the crystals were cooled to room temperature and washed with degassed DMF and dried under a flow of nitrogen, before being stored under a dry, inert atmosphere. To prepare for catalysis, the solvent in the MOF crystals was removed under vacuum at 80 C. for 18 hours, and subsequently resolvated with the desired chosen catalysis solvent regime.

[0073] Although the above example describes how to make Rh-PCM-101, to generate other metallated MOF catalysts based on PCM-101, a different 4d or 5d transition metal species could be substituted for [RhCl(CO).sub.2].sub.2 so long as the loading ratio is 1 or below, and preferably, that the stoichiometric equivalent ratio of the MOF backbone, co-linker, and transition metal species is maintained at approximately 1:1:1 with all other conditions kept the same. Examples of those 4d or 5d transition metal species include: IrCl(C.sub.2H.sub.4).sub.2, Pt(CH.sub.3).sub.2Cl.sub.2, Pt(COD)(CH.sub.3).sub.2, and PdCl.sub.2(COD). In addition, PCM-102 or PCM-201 could be substituted for PCM-101 under the same conditions as described above to generate other metallated MOF catalysts based on those MOF backbones.

[0074] PCM-201 materials may be formed via coordination of the phosphine MOF-linker (tctpH.sub.3) to a transition metal dimer species prior to MOF synthesis. One example of this is the synthesis of a diosmium material, Os.sub.2-PCM-201. For the synthesis of this material, [Os.sub.2(CO).sub.6(.sub.2-O.sub.2CH).sub.2] was combined with the phosphine MOF-forming compound, tctpH.sub.3, and heated to reflux in degassed tetrahydrofuran to yield the new MOF-forming diosmium complex, [Os.sub.2(CO).sub.4(.sub.2-O.sub.2CH).sub.2(tctpH.sub.3).sub.2]. To form the PCM-201 material, the osmium-phosphine complex was combined with three equivalents of Co(BF.sub.4).sub.2.Math.xH.sub.2O in a glass jar, a degassed mixture of 5:2:1 DMF:MeOH:H.sub.2O was then added and the reaction vessel was sealed under an inert atmosphere. The vessel was then sonicated for 5 minutes to dissolve all solids, and heated for 2 days at 75 C. in a conventional oven. The formed pink crystals were then washed with degassed DMF and filtered under vacuum to yield the Os.sub.2-PCM-201 material which was stored in air. Under the same procedure, the Os.sub.2-AsCM-201 material can be formed with the arsine compound, tctaH.sub.3, being used in place of the phosphine compound, tctpH.sub.3, to form the MOF-forming arsine-osmium complex, [Os.sub.2(CO).sub.6(.sub.2-O.sub.2CH).sub.2(tctaH.sub.3).sub.2].

Example 2. Solvent Analysis of Rh-PCM-101

[0075] 3 mg of Rh-PCM-101 was submerged in 50 microliters of 1-octene in a Parr pressure reactor with syngas (CO:H.sub.2 partial pressures at a ratio of 1:1). The temperature was set to 70 C. and the pressure in the reactor set to 40 bar. The same conditions were used for three different reactions, each using 5 ml of a solvent. Toulene, hexane, and DCM were tested. Each reaction was allowed to continue for 15 hours, and the resulting reaction products were characterized as linear, branched-1 or branched-2 products. Table 3 below demonstrates that DCM was the solvent that promoted the best total conversion rate. Also included in Table 3 is the turnover number (TON) and the ratio of linear to branched products (n/iso). The n/iso ratio is particularly important. Typical molecular catalyst-based HFM reactions are much higher than shown in this and the other examples. Metallated MOF catalysts according to the present disclosure demonstrate low n/iso ratios most likely because of the different environment of the catalysts, which are inside micropores that restrict the orientation of the catalyst reaction. This enables a relatively low ratio of linear to branched products.

TABLE-US-00003 TABLE 3 Comparison of the effect of solvent on Rh-PCM-101 catalysis in an HFM reaction Branched- Branched- Total Solvent Linear 1 2 Conversion TON n/iso Toulene 50.4% 42.6% 8.0% 65.1% 150 1.0 Hexane 50.8% 36.6% 12.6% 73.8% 169 1.0 DCM 57.2% 33.3% 9.6% 84.6% 202 1.3

Example 3. Temperature Analysis of Rh-PCM-101

[0076] In each of two reactions, 3 mg of Rh-PCM-101 was submerged in 100 microliters of 1-octene in a Parr pressure reactor with 5 milliliters of toluene, CO:H.sub.2 partial pressures at a ratio of 1:1, and overall pressure set to 40 bar. The temperature was set in one reaction to 70 C. and in a second reaction to 110 C. Each reaction was allowed to continue for 17 hours, and the resulting reaction products were characterized as linear, branched-1 or branched-2 products. Table 4 below demonstrates that the lower temperature resulted in a slightly higher percentage of linear products and lower percentage of branched-1 products, all other variables being held equal. Temperature appeared to have no effect on the percentage of branched-2 products under these conditions. Also included in Table 4 is the turnover number (TON) and the ratio of linear to branched products (n/iso).

TABLE-US-00004 TABLE 4 Comparison of the effect of temperature on Rh-PCM-101 catalysis in an HFM reaction Temper- Branched- Branched- Total ature Linear 1 2 Conversion TON n/iso 70 C. 52.05% 36.71% 11.24% 33.40% 67 1.09 110 C. 46.04% 42.66% 11.30% 27.55% 41 0.90

Example 4. Catalyst Stability and Reusability Analysis of Rh-PCM-101

[0077] 3 mg of Rh-PCM-101 was submerged in 100 microliters of 1-octene in a Parr pressure reactor with 5 milliliters of toluene, CO:H.sub.2 partial pressures at a ratio of 1:1, temperature set to 70 C., and overall pressure set to 40 bar. To evaluate catalyst stability and reusability, the resulting reaction products were characterized after 1, 2, and 3 cycles of catalysis, with each cycle lasting 15 hours. Table 5 below demonstrates that a only small amount of total conversion percentage of Rh-PCM-101 is lost after the first cycle, and it remains relatively stable over multiple cycles of catalysis.

TABLE-US-00005 TABLE 5 Comparison of the effect of repeated cycles on Rh-PCM-101 catalysis in an HFM reaction Branched- Branched- Total Catalyst Linear 1 2 Conversion TON n/iso Cycle-1 52.05% 36.71% 11.24% 33.40% 67 1.09 Cycle-2 46.08% 40.86% 13.06% 29.70% 50 0.85 Cycle-3 39.80% 39.80% 13.02% 28.90% 53 0.89

[0078] Further analysis was done to look at the structure of Rh-PCM-101 before and after catalysis. FIG. 8 shows the FT-IR spectra of Rh-PCM-101 charged with CO (801), Rh-PCM-101 post-catalysis (802), and Rh-PCM-101 (803). This FT-IR spectra of Rh-PCM-101 before and after an HFM reaction shows new Rh-CO environments formed, that may also be formed by charging the Rh-PCM-101 with CO gas.

[0079] FIG. 9 shows PXRD results for Rh-PCM-101 post-catalysis (901), Rh-CO-PCM-101 (902), and PCM-101 (903). These results demonstrate the stability of the PCM-101 backbone structure both after metalation with Rh and charging with CO gas and after catalysis.

Example 5. Rh-AsCM-102 Catalyst Formation

[0080] To form AsCM-102, the MOF-forming linker tris-p-carboxylato(triphenyl)arsine (tctaH.sub.3) was combined with one equivalent of 4,4-bipyridine (bipy), three equivalents of Co(BF.sub.4).sub.2.Math.xH.sub.2O, and twenty equivalents of benzoic acid into a glass jar. Under an inert N.sub.2 atmosphere, a degassed 5:2:1 mixture of DMF:MeOH:H.sub.2O was added, and the reaction vessel was sealed. The jar was sonicated for 5 minutes to dissolve all solids and then heated at 75 C. for 2 days in a conventional oven. The pink crystals of AsCM-102(Co) were then washed with fresh degassed DMF and filtered under vacuum to yield the AsCM-102 which was stored in air. Alternatively, PCM-102 has been synthesized via the same synthetic procedure, with tris-p-carboxylato(triphenyl)phosphine used in place of the arsine MOF-forming linker.

[0081] To form Rh-AsCM-102, under an inert atmosphere, AsCM-102 was treated with a half equivalent of [RhCl(CO).sub.2].sub.2 in a degassed 1:1 DMF:DCM mixture and heated for 18 hours at 75 C. In other words, the stoichiometric equivalent ratio of [RhCl(CO).sub.2].sub.2 to AsCM-102 was 1:2. The flask was swirled periodically throughout the reaction, however it was not stirred to preserve catalyst crystallinity. Following the reaction, the crystals were cooled to room temperature and washed with degassed DMF, dried under a flow of nitrogen, before being stored under a dry, inert atmosphere. To prepare for catalysis, the solvent in the MOF crystals was removed under vacuum at 80 C. for 18 hours, and subsequently resolvated with the desired chosen catalysis solvent regime.

[0082] Although the above example describes how to make Rh-AsCM-102, to generate other metallated MOF catalysts based on AsCM-102, a different 4d or 5d transition metal species could be substituted for [RhCl(CO).sub.2].sub.2 so long as the loading ratio is 1 or below, and preferably, that the stoichiometric equivalent ratio of the transition metal species to MOF backbone is maintained at approximately 1:2 with all other conditions kept the same. Examples of those 4d or 5d transition metal species include: IrCl(C.sub.2H.sub.4).sub.2, Pt(CH.sub.3).sub.2Cl.sub.2, Pt(COD)(CH.sub.3).sub.2, and PdCl.sub.2(COD). In addition, AsCM-101 or AsCM-303 could be substituted for AsCM-102 under the same conditions as described above to generate other metallated MOF catalysts based on those MOF backbones.

Example 6. Solvent Analysis of Rh-AsCM-102

[0083] FIG. 10 shows an HMF reaction of 1-hexene (1001), which may yield various products depending on the conditions including n-heptanal (1002, linear), 2-methyl-hexanal (1003, branched-1), and 2-ethyl-pentanal (1004, branched-2). To evaluate the optimal solvent for this reaction, 20 microliters of 1-hexene were reacted in a Parr pressure reactor with 5 mg of Rh-AsCM-102-Co, 5 ml of solvent, a partial pressure ratio for CO:H2 of 1:1 and total pressure of 40 bar for seventeen hours at 70 C. Solvents tested included toluene, hexane, and THF. Characterization of the resulting reaction products indicated that hexane was optimal for the total conversion rate. Table 6 provides characterization of the reaction products for each solvent tested, as well as the TON, TOF/h (turnover frequency per hour), and n/iso.

TABLE-US-00006 TABLE 6 Comparison of the effect of solvent on Rh- AsCM-102 catalysis in an HFM reaction Branched- Branched- Total Solvent Linear 1 2 Conversion TON n/iso Toulene 41.29% 49.25% 9.46% 29.9% 121.04 0.70 Hexane 41.40% 54.74% 3.86% 95.16% 385.25 0.71 THF 39.69% 49.59% 10.72% 60.46% 244.75 0.66

Example 7. Temperature Analysis of Rh-AsCM-102

[0084] In each of three reactions, 5 mg of Rh-AsCM-102-Co was submerged in 20 microliters of 1-hexene in a Parr pressure reactor with 5 milliliters of hexane, CO:H.sub.2 partial pressures at a ratio of 1:1, and overall pressure set to 40 bar. The temperature was set in one reaction to 50 C., in a second reaction to 70 C., and in a third reaction to 100 C. Each reaction was allowed to continue for 17 hours, and the resulting reaction products were characterized as linear, branched-1 or branched-2 products. Table 7 below demonstrates that the 70 C. resulted in a higher percentage total conversation percentage. Also included in Table 7 is the TOF, turnover number (TON)/h, and the ratio of linear to branched products (n/iso).

TABLE-US-00007 TABLE 7 Comparison of the effect of temperature on Rh-AsCM-102 catalysis in an HFM reaction Total Temper- Branch- Branch- Conver- ature Linear ed-1 ed-2 sion TOF TON n/iso 50 C. 41.44% 53.17% 5.38% 79.41% 321.47 21.43 0.71 70 C. 41.40% 54.74% 3.86% 95.16% 385.25 25.68 0.71 100 C. 50.10% 50.10% 3.53% 90.45% 366.18 24.41 0.86

Example 8. Time Analysis of Rh-AsCM-102 Catalysis

[0085] The impact of reaction time on Rh-AsCM-102 was also investigated. Six independent HFM reactions were run where the only changed variable was the time of the reaction cycle. Reactions proceeded for 1 hour, 3 hours, 5 hours, 10 hours, 17 hours, and 24 hours. Each reaction otherwise had the following conditions: 20 microliters 1-hexene, 5 milligrams Rh-AsCM-102, partial pressure ratio CO:H.sub.2 of 1:1, overall pressure of 40 bar, 5 ml of hexane as the solvent and 70 C. Table 8 presents the results of this experiment and demonstrates that the total conversion percentage jumped significantly from 10 hours to 17 hours and by 24 hours, the turnover frequency had been significantly reduced.

TABLE-US-00008 TABLE 8 Comparison of the effect of reaction time on Rh-AsCM-102 catalysis in an HFM reaction Total Branched- Branched- Conver- TOF Time Linear 1 2 sion TON (h.sup.1) n/iso 1 h 43.1 50.6 6.3 26.6% 107.6 107.6 0.76 3 h 43.3 51.6 5.2 38.4% 155.4 23.9 0.77 5 h 43.5 51.6 4.9 41.5% 168.0 6.3 0.77 10 h 41.6 54.0 4.4 52.4% 212.0 8.8 0.71 17 h 41.4 54.7 3.9 95.2% 385.3 24.8 0.71 24 h 41.2 48.5 3.8 95.6% 386.9 1.6 0.70

[0086] FIG. 11 shows a graph with conversion percentage and TOF (turnover frequency) plotted against time for the HMF reactions of 1-Hexene using Rh-AsCM-102 as the catalyst at a partial pressure ratio of 1:1 for CO:H.sub.2, 40 bar pressure, and 70 C.

Example 9. Catalyst Stability and Reusability Analysis of Rh-AsCM-102

[0087] 5 mg of Rh-AsCM-102-Co was submerged in 20 microliters of 1-hexene in a Parr pressure reactor with 5 milliliters of hexane, CO:H.sub.2 partial pressures at a ratio of 1:1, temperature set to 70 C., and overall pressure set to 40 bar. To evaluate catalyst stability and reusability, the resulting reaction products were characterized after 1, 2, 3, 4, and 5 cycles of catalysis, with each cycle lasting 17 hours. Table 9 below demonstrates that the highest total conversion rate for Rh-AsCm-102 is seen after the first cycle, but it remains an effective catalyst through multiple cycles.

TABLE-US-00009 TABLE 9 Comparison of the effect of repeated cycles on Rh-AsCM-102 catalysis in an HFM reaction Branched- Branched- Total n/ Catalyst Linear 1 2 Conversion TON iso Cycle-1 41.40% 54.74% 3.86% 95.16% 385.25 0.71 Cycle-2 41.66% 54.15% 4.19% 92.04% 372.63 0.71 Cycle-3 44.44% 52.22% 3.34% 85.79% 347.30 0.80 Cycle-4 43.71% 51.36% 4.93% 78.46% 317.64 0.78 Cycle-5 45.27% 49.46% 5.28% 62.60% 253.44 0.83

[0088] PXRD analysis of Rh-AsCM-102 comparing AsCM-102, Rh-AsCM-102, and Rh-AsCM-102 after three cycles of catalysis indicated that the structure of AsCM-102 remains relatively stable when metallated with Rh and after multiple rounds of catalysis.

Example 10. Analysis of Metallated MOF Catalysts in an HFM Reaction

[0089] Multiple metallated MOF catalysts were analyzed in HFM reactions using 1-hexene as the feedstock. Specifically, Rh-AsCM-102, Rh-PCM-102, and a combination containing a material where phosphine and arsine sites are mixed in a 1:1 ratio within a single crystal, Rh-PCM-102:Rh-AsCM-102, were evaluated. In each reaction, 20 microliters of 1-hexene and 5 mg of the catalyst being tested were used in an HFM reaction in a Parr pressure reactor. For each reaction, temperature was set to 70 C., the partial pressure ratio of CO:H.sub.2 was 1:1, and the total overall pressure was maintained at 40 bar. Table 10 presents the results of those reactions and demonstrates that Rh-AsCM-102 performed the best in terms of total conversion percentage under these conditions.

TABLE-US-00010 TABLE 10 Comparison of the effect of the catalyst on HFM reactions Total Branch- Branch- Conver- n/ Catalyst Linear ed-1 ed-2 sion TON iso Rh-AsCM-102 41.40% 54.74% 3.86% 95.16% 385.25 0.71 Rh-PCM-102 41.44% 53.17% 5.38% 79.41% 321.47 0.71 Rh-PCM- 45.70% 49.34% 4.96% 80.16% 324.51 0.84 102:Rh- AsCM-102 (1:1)

Example 11. Hydroformylation of Hexene Using Rh-AsCM-102, Followed by Enolization of Heptanal

[0090] FIG. 12 shows (a) an HFM reaction of 1-hexene (1201) using Rh-AsCM-102 as the catalyst to yield n-heptanal (1202) as the major product with 2-methyl-hexanal (1203) and 2-ethyl pentanal (1204) as minor products, (b) followed by enolization of the heptanal to yield (Z)-2-pentylidenenonanal (1205). Each HFM reaction used 20 microliters 1-hexene, 5 mg Rh-AsCM-102, partial pressure ratio CO:H2 of 1:1, overall pressure of 40 bar, 5 ml hexane as the solvent and continued for 17 hours at 70 C. The Rh-AsCM-102 was then removed from the reactor, and one of the following added at a concentration of 0.01M to the direct liquid products of the HFM reaction: aqueous sodium hydroxide, t-BuOK, or ZSM-5. The aqueous NaOH is an inorganic base, the t-BuOK acts as an organic base, and ZSM-5 is a Bronsted acid. Each enolization reaction was allowed to proceed for 17 hours at 70 C. with a partial pressure ratio CO:H.sub.2 of 1:1 and overall pressure of 40 bar. Each reaction (whether using aqueous sodium hydroxide, t-BuOK, or ZSM-5) demonstrated the quantitative conversion of the linear product from the HFM reaction into an enal, specifically, the enolization of the heptanal to yield (Z)-2-pentylidenenonanal.