Salen aluminum complex and its use as a catalyst

Abstract

The present invention relates to optionally substituted salen aluminum complexes having a 3-pyridinium bridging group. Furthermore, a catalyst system is described comprising this optionally supported complex and a bromide or iodide salt as a co-catalyst. This catalyst system is used in a method for preparing cyclic carbonates by reacting an epoxide compound with carbon dioxide under moderate pressure.

Description

[Technical Field]

[0001] This invention relates to optionally substituted salen aluminum complexes, and to the use of these complexes as part of a catalyst for reactions involving epoxide compounds and carbon dioxide. [Background technology]

[0002] Substituted salen aluminum complexes are known components of catalytic systems for converting epoxide compounds with carbon dioxide. Such reactions may be targeted at the production of cyclic carbonate compounds or copolymerization processes for preparing aliphatic polycarbonates or aliphatic polyesters.

[0003] WO2010 / 106324 describes a method for preparing cyclic carbonate compounds from carbon dioxide and epoxide compounds using a catalytic system containing oxodimers of substituted salen-aluminum complexes. The two nitrogen atoms of the salen structure are linked via a bridging group. The disclosed bridging groups are phenylene, C5-heterocyclic, and ethylene. In the presence of tetrabutylammonium bromide (TBAB) acting as a co-catalyst, these dimeric aluminum (salen) complexes are highly active homogeneous catalysts for the reaction to produce cyclic carbonates from epoxides and carbon dioxide. The reaction can be carried out at room temperature and atmospheric pressure, with short reaction times and using commercially viable amounts of catalyst.

[0004] WO2009109765 describes a dimeric aluminum (salen) complex similar to that described in WO2010 / 106324, immobilized on a solid support via an anchor group consisting of a quaternary ammonium ion combined with a bromide ion. The anchor group acts as the co-catalyst mentioned earlier. This heterogeneous catalyst was also found to be highly active compared to the reaction of epoxides with carbon dioxide to produce cyclic carbonates at moderate temperatures and atmospheric pressures.

[0005] EP3728213B1 describes a method for preparing cyclic carbonate compounds from carbon dioxide and epoxide compounds in a suspension of heterogeneous catalysts. The heterogeneous catalyst is an oxodimer supported with a substituted salenaluminum ligand, as described, for example, in WO2009109765. Benzyl bromide is present in the solution to maintain catalytic activity.

[0006] The advantage of the catalyst described in WO2009109765 and EP3728213B1 is that the catalytic process for preparing cyclic carbonate compounds from carbon dioxide and epoxide compounds can be carried out at moderate temperatures and pressures. The problem is that the supported salen aluminum ligand is difficult to prepare and requires at least nine synthesis steps. Some of these steps have low yields, resulting in an overall yield of less than 10%, and large amounts of solvent are used in the synthesis process.

[0007] ANTONELLO DECORTES et al.: "Ambient Fixation of Carbon Dioxide using a Zn(II) salphen Catalyst," CHEMCATCHEM, JOHN WILEY & SONS, INC; HOBOKEN, USA, part 3, nr. 5, March 2, 2011 (2011-03-02), pp. 831-834, XP072430479, ISSN: 1867-3880, DOI: 10.1002 / CCTC.201100031 describes Zn(II) sulfen used as part of a catalyst in a method for preparing cyclic carbonate compounds from epoxy hexane and carbon dioxide in an inert reaction solvent, i.e., dichloromethane (DCM), under a CO2 pressure of 1 MPa. The catalytic activity of complexes with different metals is compared. The bridging group linking the nitrogen atoms in these complexes, the "en" bridging group, is a phenylene group. This publication compares the catalytic activity of zinc complexes with other bridging groups under a CO2 pressure of 1 MPa. Complexes with methylalkylated pyridinium bridging groups showed no catalytic activity whatsoever.

[0008] MARTIN C. et al.: "Easily accessible bifunctional Zn(salpyr) catalysts for the formation of organic carbonates," CATALYSIS SCIENCE & TECHNOLOGY, part 4, nr. 6, January 23, 2014 (2014-01-23), pp. 1615-1621, XP093114624, ISSN:2044-4753, DOI:10.1039 / C3CY01043K describes bifunctional Zn(salpyr) complexes having methylalkylated pyridinium bridged groups. The complexes are used as part of a catalytic system for preparing cyclic carbonate compounds from epoxyhexane and carbon dioxide under a CO2 pressure of 1 MPa. Experiments were performed in pure epoxyhexane. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2010 / 106324 [Patent Document 2] International Publication No. 2009 / 109765 [Patent Document 3] European Patent No. 3728213 [Non-patent literature]

[0010] [Non-Patent Document 1] ANTONELLO DECORTES et al.: "Ambient Fixation of Carbon Dioxide using a Zn(II) salphen Catalyst", CHEMCATCHEM, JOHN WILEY & SONS,INC [Non-Patent Document 2] HOBOKEN, USA, part 3, nr.5, March 2, 2011 (2011-03-02), pp. 831-834, XP072430479, ISSN: 1867-3880, DOI: 10.1002 / CCTC.201100031 [Non-Patent Document 3] MARTIN C et al.: “Easily accessible bifunctional Zn(salpyr) catalysts for the formation of organic carbonates”, CATALYSIS SCIENCE & TECHNOLOGY, part 4, nr.6, January 23, 2014 (2014-01-23), pp. 1615-1621, XP093114624, ISSN:2044-4753, DOI:10.1039 / C3CY01043K [Overview of the project] [Problems that the invention aims to solve]

[0011] The object of the present invention is to provide a complex that can be used as part of a catalyst when preparing cyclic carbonates from epoxides and carbon dioxide at low pressure. [Means for solving the problem]

[0012] This is the following optionally substituted salen aluminum complex having the following general formula (1),

[0013] [ka] This is achieved by (wherein B is a halogen, alkoxy or alkyl group, the phenyl group of the salen aluminum complex is optionally substituted, R is a hydrocarbon group, and X is a halogen anion).

[0014] The applicants have found that this novel complex is catalytically active at the desired low pressure. Further, the salen aluminum complex can be prepared in a simpler manner with fewer synthetic steps and substantially higher yields than the oxo dimers of the substituted salen aluminum ligands of the prior art. The aluminum complex having a pyridine bridge can be alkylated with different alkyl bromides and has been found to enable functionalization and immobilization of the complex. The quaternary nitrogen ion of the pyridinium bridging group acts as a cocatalyst for the catalyst system. The optionally substituted complex having a pyridine bridging group is a novel intermediate product in the preparation of the corresponding optionally substituted complex having a pyridinium bridging group. The optionally substituted complex having a pyridine bridging group can also be used as part of a homogeneous or heterogeneous catalyst for the reaction of an epoxide and carbon dioxide to produce a cyclic carbonate.

[0015] The present invention further relates to the following method for preparing an optionally substituted salen aluminum complex having a pyridinium bridging group.

[0016] A method for preparing an optionally substituted salen aluminum complex having a pyridinium bridging group from a corresponding optionally substituted salen nickel complex or salen zinc complex having a pyridine bridging group comprises the following steps: (a) demetallizing the corresponding optionally substituted salen nickel complex or salen zinc complex to obtain a demetallized salen ligand, and (b) contacting the demetallized salen ligand of step (a) with an aluminum compound to obtain an optionally substituted salen aluminum intermediate complex having a 3-pyridine bridge, and (c) subjecting the optionally substituted salen aluminum intermediate complex having a 3-pyridine bridge to alkylation to obtain the corresponding optionally substituted salen aluminum complex having a 3-pyridinium bridge are carried out.

[0017] Further advantages will be discussed when describing the present invention in more detail.

[0018] The pyridine crosslinking group is a 3-pyridine group crosslinking group.

[0019] The alkoxy group B in formula (1) may be a methoxy, ethoxy, and / or isopropoxy group. The alkyl group B may have 1 to 5 carbon atoms, such as methyl or ethyl. B may also be a chloride, bromide, or iodide. When synthesizing the complex, the choice of B may depend on the availability of the starting aluminum compound. For this reason, B is preferably a chloride.

[0020] The anion X in formula (1) is preferably a halogen anion, preferably an iodide anion or a bromide anion, and more preferably a bromide anion. When used as part of a catalytic system, a complex based on iodide, or preferably bromide, is preferred. The optional halogen anion X is called the catalytic system halogen.

[0021] The phenyl group in formula (1) is preferably substituted at its 3-position. The phenyl group in formula (1) may be substituted with a halogen, optionally substituted C1-20 alkyl, optionally substituted C5-20 aryl, optionally substituted C3-20 heterocyclyl, ether, ammonium, and nitro group. Preferably, it is substituted at its 3-position, and optionally at its 5-position as well. An example is described in EP2146977. Preferably, the phenyl group is substituted at its 3-position, and optionally at its 5-position, with a butyl group, more preferably with a tert-butyl group.

[0022] The group R in formula (1) can be any group, such as an optionally substituted C1-20 alkyl group, an optionally substituted C5-20 aryl group, or an optionally substituted C3-20 heterocyclyl group. Examples of possible groups are benzyl groups and C3-C10 alkyl groups, such as propyl, butyl, pentyl, hexyl, heptyl, octyl, and nonyl.

[0023] Preferably, R in formula (1) is an anchor group for immobilizing the salen-aluminum complex on a support to obtain a supported catalyst. Therefore, R can be an anchor group that covalently fixes an optionally substituted salen-aluminum ligand to a heterogeneous support. A suitable anchor group is a group that can bond the ligand to the heterogeneous support and is determined by the type of heterogeneous support. When the support has a silanol group (Si-OH), such as a silica support, or an aluminol group (Al-OH), such as an alumina support, the anchor group is preferably an alkyl(trialkoxy)silane or alkyltrichlorosilane that can form a covalent bond with the silanol group. Examples of suitable alkyl(trialkoxy)silane or alkyltrichlorosilane groups are propyl(trimethoxy)silane, propyl(triethoxy)silane, propyltrichlorosilane, propyl(alkyl)dichlorosilane, and propyl(dialkyl)chlorosilane. Other possible anchor groups include styryl(trialkyl)silane, propylbis(methylallyl)silane, propyltris(methylallyl)silane, propyl phosphate, propyl(dialkyl)phosphonate, and alkyl-1,1-bisphenol acid.

[0024] The heterogeneous support may be relatively large particles that can be present in the reactor as a packed bed. The supported catalyst may also be used as a suspension in the reaction mixture. The heterogeneous support then exists as a powder having dimensions small enough to generate a highly active catalyst surface per unit weight of the heterogeneous support, and large enough to be easily separated from the cyclic carbonate inside or outside the reactor. Preferably, at least 90% by weight of the heterogeneous support powder particles have a particle size of more than 10 μm and less than 2000 μm. The particle size is measured by Malvern® Mastersizer® 2000.

[0025] The present invention particularly applies to the following specific complexes: [Al(3,4-Py-sulfen(N-propyl(trimethoxy)silane))(Cl)]Br, [Al(3,4-Py-sulfen(N-propyl(triethoxy)silane))(Cl)]Br, [Al(3,4-Py-sulfen(N-propyl(triethoxy)silane))(OEt)]Br, [Al(3,4-Py-sulfen(N-propyl(triethoxy)silane))(Cl)]I, [Al(3,4-Py-sulfen(N-propyl(diethoxyphosphonate)(Cl)]Br, [Al(3,4-Py-sulfen(N-propyl(phosphate)(Cl)]Br, [Al(3,4-Py-sulfen(N-butyl(diethylphosphonate)(OEt)]Br and [Al(3,4-Py-sulfen(N-pentyl(phosphate)(Cl)]Br This also applies, where the above complex has optionally substituents at the 3-position of the phenyl group in the sulfen structure, preferably at the 3-position, and optionally at the 5-position as well. In the above description, Et is ethyl.

[0026] Figure 1 shows an example of a demetallated salen ligand that yields the complex according to the present invention after metallization.

[0027] The present invention also covers supported aluminum complexes, including the complex and heterogeneous carrier according to the present invention. The carrier is preferably silica, alumina, or silica-alumina. The complex can be immobilized to phenyl groups via substituents, such as a diethylaminomethyl group as described in EP2257559. Preferably, the complex is immobilized to the surface of the carrier by a group R in formula (1) that functions as an anchor group.

[0028] The starting, optionally substituted salen nickel or salen zinc complexes having pyridine bridging groups can be obtained by well-known synthetic routes, such as those described in Catal. Sci. Technol., April 2014, p. 1615, and ChemCatChem, March 2011, pp. 831-834.

[0029] In step (a), the corresponding optionally substituted salen nickel or salen zinc complex is demetallated to obtain a demetallated salen ligand. Demetallation can be carried out by known demetallation processes, such as those described in Organometallics 2002, 21, 14, pp. 2950-2957. Demetallation is preferably carried out by an anhydrous demetallation process in acetonitrile or toluene, preferably in the presence of imidazole in toluene. This step is carried out in high yield.

[0030] In step (b), the demetallated salen ligand from step (a) comes into contact with an aluminum compound. This aluminum compound contains a precursor of group B, which is used to exhibit a preferred complex in this specification. When B is a chloride, the aluminum compound is preferably diethylaluminum chloride (Al(Et)2Cl). When B is an alkoxy group such as ethoxy, the aluminum compound is preferably triethoxide aluminum. When B is an alkyl group, the aluminum compound is preferably a trialkylaluminum compound, preferably such as trimethylaluminum or triethylaluminum, where the alkyl group has 1 to 5 carbon atoms.

[0031] To facilitate reagent contact when the process is carried out on a large scale, preferably in step (b), the aluminum compound is slowly added to the demetallated salen ligand as a dissolved or dispersed slurry in a suitable solvent. It has been found that if the aluminum compound is not added slowly, the reaction mass solidifies, making effective mixing of the reagents impossible. The demetallated salen ligand is preferably dissolved or dispersed as a slurry in a suitable solvent such as toluene or THF (tetrahydrofuran). The slow addition is preferably carried out for more than 1 hour, preferably more than 1.5 hours. Preferably, the addition is continued for 3 hours or less. The temperature is preferably 20 to 90°C, more preferably 50 to 80°C. To reduce the solubility of the resulting optionally substituted salen-aluminum complex, preferably a C5 to C10 hydrocarbon alkane solvent, preferably heptane, is added. The solidified complex can be separated from the solvent by filtration.

[0032] The optionally substituted salen-aluminum complex having the corresponding pyridinium crosslinking group, as shown in formula (1), is prepared in step (c). In step (c), the optionally substituted salen-aluminum complex having the pyridine crosslinking group obtained in step (b) is subjected to an alkylation reaction to obtain the optionally substituted salen-aluminum complex having the corresponding pyridinium crosslinking group. Alkylation is preferably carried out by contacting the optionally substituted salen-aluminum complex having the pyridine crosslinking group with a halogen-R compound in a suitable solvent. The halogen may be a system halogen or a different halogen. Preferably, halogen-R is a bromide compound, Br-R (wherein R is as described above). Suitable solvents are tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or a mixture of dimethyl sulfoxide (DMSO) and acetonitrile. It was found to be advantageous to start alkylation from an optionally substituted salen-aluminum complex rather than starting alkylation from an optionally substituted salen-zinc complex having a pyridine crosslinking group. It was found that zinc complexes cannot be subjected to alkylation with a bromide compound, Br-R. Starting from an aluminum complex, such alkylation with Br-R is possible, and thus the preparation of the complex of the present invention (X is a bromide ion) becomes possible. When preparing complexes having a pyridinium crosslinking group, complexes having a pyridine crosslinking group can be considered novel and original intermediate compounds.

[0033] Therefore, the present invention relates to optionally substituted aluminum salen intermediate complexes:

[0034] [ka] (wherein B is a halogen, alkoxy, or alkyl group, and the phenyl group of the salen aluminum complex is optionally substituted as described above) is also included.

[0035] The present invention also covers a method for preparing the above-mentioned optionally substituted salen aluminum intermediate complexes, starting from the corresponding optionally substituted salen nickel or salen zinc complex having a pyridine crosslinking group, and the steps are as follows: (a) The step of demetallizing the optionally substituted corresponding salen nickel complex or salen zinc complex to obtain a demetallized salen ligand, and (b) The demetallated salen ligand from step (b) is brought into contact with an aluminum compound to obtain an optionally substituted salen-aluminum intermediate complex. Steps (a) and (b) are preferably carried out as described above.

[0036] The present invention also covers a method for preparing an optionally substituted salen-aluminum intermediate complex according to the present invention from an optionally substituted salen-aluminum intermediate complex according to the present invention, wherein the optionally substituted salen-aluminum intermediate complex is subjected to the alkylation described above to obtain an optionally substituted salen-aluminum intermediate complex.

[0037] The present invention also covers catalytic systems comprising the complex or supported aluminum complex and co-catalyst according to the present invention. This co-catalyst can be any compound that provides a bromide anion or iodide anion as the halogen in the catalytic system. This compound can be organic or inorganic. Optionally substituted salen complexes can be advantageously used as catalytic systems. Because the complex has a pyridinium halogen salt, the complex can be used as a catalyst without the addition of a halogen salt. Typical halogen salts added as co-catalysts to such catalytic systems are bromide salts or iodide salts. The bromide salt may be a quaternary ammonium bromide salt or phosphonium bromide salt, such as tetrabutylammonium bromide (TBAB), and the iodide salt may be a quaternary ammonium iodide salt or phosphonium iodide salt. When the complex of the present invention is used, the catalytic process can be carried out without such added halogen salts, or in the presence of small amounts of added halogen salts.

[0038] In copolymerization processes for preparing aliphatic polycarbonates starting from epoxide compounds and carbon dioxide, catalytic systems may be used as a catalyst or as part of a catalyst. Another reaction in which catalytic systems may be used is in methods for preparing polyesters by ring-opening polymerization of lactone compounds or ring-opening polymerization of maleic anhydride, as described, for example, in WO2012 / 065711.

[0039] Preferably, the catalyst system is used as a catalyst or as part of a catalyst in a method for preparing a cyclic carbonate by reacting an epoxide compound with carbon dioxide.

[0040] Accordingly, the present invention also covers a method for preparing cyclic carbonates by reacting an epoxide compound with carbon dioxide in the presence of a catalytic system. The catalytic system preferably comprises, after the complex of the present invention, another halogen salt, such as a bromide salt or iodide salt as previously mentioned.

[0041] The molar ratio (moles / moles) of the optionally substituted salen aluminum ligand having a pyridinium bridge expressed as Al / Br to the bromide salt is preferably 0.1 to 20, more preferably 1 to 8, and most preferably 2 to 5.

[0042] The starting epoxide compound preferably has 2 to 8 carbon atoms. Suitable epoxide compounds are ethylene oxide, propylene oxide, butylene oxide, pentene oxide, glycidol, styrene oxide, epichlorohydrin, or fluoroethylene oxide.

[0043] Carbon dioxide is suitably contacted with the epoxide compound in a liquid, which also includes a catalyst system. The liquid may be an inert solvent. Possible inert solvents are toluene, the cyclic carbonate compound, and / or preferably the cyclic carbonate product itself. The supported catalyst may also be used as a suspension in the reaction mixture. Carbon dioxide is suitably contacted with the epoxide compound in the aforementioned inert solvent, preferably in a suspension of the liquid cyclic carbonate and heterogeneous catalyst. Temperature and pressure conditions are selected so that the cyclic carbonate is in its liquid state. Temperature and pressure conditions are further selected so that carbon dioxide and epoxide readily dissolve in the liquid cyclic carbonate reaction medium. The temperature may be 0 to 200°C and the pressure 0 to 5.0 MPa (absolute), and the temperature is below the boiling point of the cyclic carbonate product under the selected pressure. At the upper end of these temperature and pressure ranges, a complex reaction vessel is required. For the desired carbonate product, favorable results in terms of selectivity and yield can be achieved at low temperatures and pressures; therefore, the temperature is preferably 20 to 150°C, more preferably 40 to 120°C, and the absolute pressure is preferably 0.1 to 0.5 MPa, more preferably 0.1 to 0.3 MPa. The partial pressure of carbon dioxide is below this pressure. [Brief explanation of the drawing]

[0044] [Figure 1] An example of a demetallated salen ligand that yields the complex according to the present invention after metallization is shown. [Modes for carrying out the invention]

[0045] [Example 1] In this embodiment, [Zn(3,4-Py-sulfen)] is prepared according to the following scheme.

[0046] [ka]

[0047] 100 mL of methanol in a round-bottom flask was mixed with 3,4-diaminepyridine (1.44 g, 13.2 mmol), 3-tert-butylsalicylaldehyde (4.8 mL, 28.0 mmol), zinc acetate dihydrate (3.08 g, 13.8 mmol), and triethylamine (5.0 mL, 35.9 mmol). The mixture was heated with stirring and refluxed for 24 hours to obtain a bright red solid. The solid was filtered and washed with methanol (3 × 20 mL). The yield of [Zn(3,4-Py-sulfen)] was 6.24 grams (95.6%).

[0048] The product is 1 Characterized by H-NMR: 1 ¹H NMR (300 MHz, DMSO-d6) δ 9.20 (s, 1H), 9.15 (s, 2H), 8.48 (d, J = 5.5 Hz, 1H), 7.88 (d, J = 5.5 Hz, 1H), 7.29 (m, 4H), 6.48 (td, J = 7.5, 3.2 Hz, 2H), 1.48 (s, 18H). The NMR data indicates that the desired product was formed.

[0049] [Example 2] This example illustrates step (a) of a method for preparing the complex according to the present invention. The [Zn(3,4-Py-sulfen)] obtained in Example 1 is demetallated by the following scheme.

[0050] [ka]

[0051] [Zn(3,4-Py-sulfen)] (6.24 g, 12.65 mmol) from Example 1 was placed in a flask and dissolved in 60 mL of toluene. Imidazole (3.48 g, 50.6 mmol) was added to this solution and the mixture was heated at 60°C for 2 hours. The solid was filtered and washed with toluene. Alternative solvents to toluene are methanol and MTBE. The solid was again dissolved in methanol (60 mL) and heated at 60°C for 2 hours. The solid was filtered and dried to obtain 4.27 g of orange powder. Yield 78.6%.

[0052] The product is 1 Characterized by H-NMR: 1 ¹H NMR (300 MHz, DMSO-d6) δ 13.80 (s, 1H), 13.73 (s, 1H), 9.07 (d, J = 8.7 Hz, 2H), 8.71 (s, 1H), 8.58 (d, J = 5.3 Hz, 1H), 7.62 - 7.48 (m, 3H), 7.42 (td, J = 8.0, 1.7 Hz, 2H), 6.95 (td, J = 7.7, 3.3 Hz, 2H), 1.38 (s, 18H). The NMR data indicates that the desired product was formed.

[0053] [Example 3] This example illustrates step (b) of a method for preparing an intermediate complex according to the present invention. A substituted salen aluminium complex having pyridine crosslinks is prepared from the demetallated ligand obtained in Example 2 by the following scheme.

[0054] [ka]

[0055] In a flame-dried Schlenk oven, the 3,4-Py-sulfen ligand obtained in Example 2 (2.6 g, 6.0 mmol) was dissolved in 24 mL of toluene and heated to 60°C. Al(Et)2Cl (1.8 M in toluene, 6.4 mL, 11.6 mmol) was added, and the reaction mixture was stirred for 17 hours. The reaction mixture was cooled to room temperature, the product was filtered, and washed with toluene (10 mL) and pentane (2 × 10 mL) to obtain a yellow solid (1.19 g, 40%).

[0056] The product is 1 Characterized by H-NMR: 1 ¹H NMR (300 MHz, DMSO-d6) δ 9.50 (s, 1H), 9.44 (d, J = 5.0 Hz, 2H), 8.65 (d, J = 5.6 Hz, 1H), 8.13 (d, J = 5.7 Hz, 1H), 7.57 (td, J = 11.8, 10.6, 4.8 Hz, 4H), 6.90 - 6.75 (m, 2H), 1.56 (d, J = 1.8 Hz, 19H). The NMR data indicates that the desired product was formed.

[0057] [Example 3a] Example 3 was repeated, except that Al(OEt)3 was used as the B (where B is an ethoxy group)-containing aluminum compound and 2,3-Py-sulfen was used, to obtain a 2,3-Py-sulfen complex.

[0058] In a flame-dried Schlenk container, 0.2 g of 2,3-Py-sulfen ligand was dissolved in 9 ml of dry toluene and heated under reflux. 0.151 g of aluminum triethoxide was added, followed by 2 ml of toluene, and the reaction mixture was stirred for 17 hours. The reaction mixture was cooled to room temperature, the product was filtered, and washed three times with 5 ml of toluene. The solid was dried under vacuum. Yield: 43%.

[0059] The product 1Characterization was performed by ¹H-NMR: ¹H NMR (300 MHz, chloroform-d) δ 9.80 (s, 1H), 8.94 (s, 1H), 8.51 - 8.37 (d, J=4.1 Hz, 1H), 8.04 (d, J = 8.1 Hz, 1H), 7.61 (t, J = 8.6 Hz, 2H), 7.47 (d, J = 7.4, 1H), 7.38 - 7.25 (m, 2H), 6.85 (q, J = 8.1 Hz, 2H), 3.41 (q, J = 6.9 Hz, 2H), 1.64 (s, 18H), 0.76 (t, J = 6.9 Hz, 3H). The NMR data indicates that the desired product was formed.

[0060] [Example 3b] The procedure in Example 3 was repeated on a larger scale. 3,4-Py-sulfen ligand (327.32 g, 0.76 mol) was packed into a dry 5 L reactor under a nitrogen stream, followed by the addition of 1 L of toluene and 0.5 L of heptane. The reaction mixture was stirred with an overhead stirrer and heated to 60°C. Once the 3,4-Py-sulfen ligand was dissolved, Al(Et)2Cl (1.0 M in hexane, 800 mL, 0.8 mol) was added over 2 hours. The reaction temperature was maintained at 60°C during the addition. After the addition, the reaction mixture was stirred further at 60°C for 18 hours, and then cooled to 25°C. Next, heptane (600 mL) was added, and the reaction mixture was stirred further for 30 minutes, after which it was discharged from the reactor. The precipitate was filtered, washed with heptane (3 × 500 mL), and dried to obtain 346 g (92% yield).

[0061] In this large-scale experiment, it was found that it is important to slowly add Al(Et)2Cl for more than one hour, preferably 1.5 to 3 hours, to avoid excessive exothermic reactions and uncontrollable gas generation. Furthermore, the addition of heptane was beneficial in improving product precipitation. Alternatives to heptane include alkanes, cycloalkanes, and ethers such as MTBE.

[0062] [Example 4] This embodiment shows step (c) of a method for preparing a complex according to the present invention.

[0063] [ka]

[0064] 400 mg of [Al(3,4-Py-sulfen(Cl)] complex (0.93 mmol), obtained by a process similar to that described in Examples 1-3, was suspended in 5 mL of toluene, and 1 mL of dry DMF and 800 μL of octyl bromide (4.6 mmol) were added. The solution was heated to 80°C under a protective N2 atmosphere until the complex was completely dissolved, and the solution changed from an orange to a red slurry. After the reaction overnight, the conversion rate was 37%, and an additional 2 mL of octyl bromide was added to the reaction mixture, and heating was continued until the starting materials were completely converted. The complex was separated as a DMF complex with the overall formula [Al(3,4-Py-sulfen(N-Oct))](Cl)Br(DMF)2. Yield 480 mg, 63% yield.

[0065] The product is 1 Characterization was performed by ¹H-NMR: ¹H NMR (300 MHz, DMSO-d6) δ 9.92 (s, 1H), 9.63 (s, 1H), 9.56 (s, 1H), 9.09 (d, J = 6.9 Hz, 1H), 8.69 (d, J = 7.0 Hz, 1H), 7.96 (s, 3H), 7.71 - 7.51 (m, 4H), 6.89 (t, J = 7.6 Hz, 2H), 4.61 (t, J = 7.3 Hz, 2H), 2.08 (br. 2H), 1.33 (br., 12H), 0.97 - 0.81 (m, 3H). The NMR data indicates that the desired product was formed.

[0066] Examples 1-4 demonstrate the synthesis of salen aluminum complexes in only four steps and with high overall yield.

[0067] [Example 5] Example 4 was repeated except that benzyl bromide was used instead of octyl bromide, and a complex having the overall formula of the benzyl-containing catalyst [Al(3,4-Py-sulfen(N-benzyl))(Cl)]Br was obtained. The product was 1 characterized by 1H-NMR: 1 1H NMR (300 MHz, DMSO-d6) δ 10.18 (s, 1H), 9.60 (s, 2H), 9.16 (d, J = 6.9 Hz, 1H), 8.69 (d, J = 7.0 Hz, 1H), 7.72 (s, 1H), 7.85 - 7.35 (m, 9H), 6.89 (td, J = 7.7, 3.2 Hz, 2H), 5.84 (s, 2H), 1.55 (d, J = 4.6 Hz, 18H). The NMR data indicate that the desired product was formed.

[0068] [Example 5a] Add [Al(3,4-Py-sulfen(Cl)] complex (7.36 g, 15 mmol)) and dry DMF (16.8 mL) to a flame-dried Schlenk. The reaction mixture is heated to 80 °C until all solids dissolve, then 3-bromopropyltrimethoxysilane (11.3 mL, 60 mmol) is added. The reaction mixture is stirred at 80 °C for 3 days and then cooled. The resulting precipitate is filtered, washed with Et2O (3 × 20 mL) and dried to give 8.54 g of an orange solid (57% yield). The product was 1 characterized by 1H-NMR: 1H NMR (300 MHz, DMSO-d6) δ 10.04 (s, 1H), 9.68 (s, 1H), 9.64 (s, 1H), 9.09 (d, J = 6.9 Hz, 1H), 8.74 (d, J = 7.0 Hz, 1H), 7.82 - 7.46 (m, 4H), 6.89 (t, J = 7.6 Hz, 2H), 4.58 (t, J = 7.5 Hz, 2H), 3.47 (s, 9H), 2.13 (p, J = 7.9 Hz, 2H), 0.77 - 0.53 (m, 2H).

[0069] [Example 6] In this example, the catalytic activity of the complex obtained in Example 4 is tested in the following reaction of styrene oxide and carbon dioxide to prepare 4-phenyl-1,3-dioxolan-2-one in the presence of added tetrabutylammonium bromide.

[0070] [ka]

[0071] 57.98 mg of [Al(3,4-Py-sulfen(N-Oct))(Cl)]Br and 22.59 mg of tetrabutylammonium bromide (TBAB) were placed in a Schlenk reaction flask, heated to 100°C, and then vacuumed. CO2 gas was added to the flask, and then propylene carbonate (3.5 mL) and styrene oxide (1.0 mL) were added. The flask was purged of CO2, and stirring was started. The CO2 partial pressure and total pressure at the start of the experiment were 0.106 MPa. After a certain interval, samples were taken for analysis. Base material filling amount = 2.0M Catalyst packing amount = 0.8 mol% Tetrabutylammonium bromide filling amount = 0.8 mol%

[0072] The conversion rate of styrene oxide and the formation of styrene carbonate (4-phenyl-1,3-dioxolan-2-one) are shown in Table 1.

[0073] [Example 7] In this example, the catalytic activity of the complex obtained in Example 4 is tested in the reaction of styrene oxide with carbon dioxide to prepare 4-phenyl-1,3-dioxolan-2-one in the absence of added tetrabutylammonium bromide. Example 6 was repeated except that tetrabutylammonium bromide was not added. The conversion rate of styrene oxide and the formation of styrene carbonate (4-phenyl-1,3-dioxolan-2-one) are shown in Table 1.

[0074] [Example 8] The complex prepared in Example 5: Repeat Example 7 using the benzyl-containing catalyst [Al(3,4-Py-sulfen(N-benzyl))(Cl)]Br. The conversion rate of styrene oxide and the formation of styrene carbonate (4-phenyl-1,3-dioxolan-2-one) are shown in Table 1.

[0075] [Example 9] The complex prepared in Example 5: Repeat Example 7 using the benzyl-containing catalyst [Al(3,4-Py-sulfen(N-benzyl))(Cl)]Br. The conversion rate of styrene oxide and the formation of styrene carbonate (4-phenyl-1,3-dioxolan-2-one) are shown in Table 1.

[0076] [Comparative Experiment A] The procedure in Example 6 was repeated using the same complex as the one used in Example 6, except that the crosslinking group was a conventional phenylene crosslinking group. The conversion rate of styrene oxide and the formation of styrene carbonate (4-phenyl-1,3-dioxolan-2-one) are shown in Table 1.

[0077] [Comparative Experiment B] The procedure for Example 7 was repeated using the same complex as the one used in Example 7, except that the crosslinking group was a conventional phenylene crosslinking group. The conversion rate of styrene oxide and the formation of styrene carbonate (4-phenyl-1,3-dioxolan-2-one) are shown in Table 1.

[0078] [Table 1]

[0079] Examples 6-9 demonstrate that the catalyst system according to the present invention can be advantageously used as a catalyst or as part of a catalyst in a method for preparing cyclic carbonates by reacting epoxide compounds with carbon dioxide. The results in Table 1 show that the conversion rate is high when the reaction is carried out in the presence of added tetrabutylammonium bromide. The results also show that the complex having a pyridinium bridge group exhibits catalytic activity even in the absence of added tetrabutylammonium bromide. The bromide anion associated with the pyridinium nitrogen is thought to act as a co-catalyst. The results also show that the complex having a pyridinium bridge is significantly more active than the conventional complex having a phenyl bridge group, with or without TBAB.

[0080] [Example 10] 0.020 mmol of catalyst and 4.0 mmol of maleic anhydride (MA) were placed in a flame-dried Schlenk flask equipped with a stirring bar. A suitable solvent (1.0 mL of toluene) was added, followed by 4.0 mmol of styrene epoxide (SO). The vial was sealed with a Teflon®-lined cap and placed on an aluminum heat block preheated to the desired temperature (65°C to 80°C). After the reaction mixture became viscous, the vial was removed from the heat block. 1 Small aliquots were taken for 1H NMR spectroscopy analysis to determine the monomer conversion rate. The viscous reaction mixture was then dissolved in the minimum amount of dichloromethane and precipitated in excess hexane. The solid was separated and dried under reduced pressure. 1 The formation of unsaturated polyester was confirmed by ¹H NMR. ¹H NMR (300 MHz, DMSO-d6) δ values: 6.46 (m, 2H), 5.12 (m, 1H), 4.21 (m, 2H), 1.23 (d, J = 6.6 Hz, 3H).

[0081] The examples were repeated at different temperatures and with different catalyst loads. The results are shown in Table 2, where conversion rate (%) is the monomer conversion rate, MW is the molecular weight of the polyester, and Mn / Mw is the molar mass distribution / polydispersity of the polyester.

[0082] [Table 2]

[0083] [Comparative Experiment C] The alkylation of the following zinc complexes was attempted using octyl bromide.

[0084] [ka]

[0085] Experiments C1 to C10 were conducted regarding the alkylation of [Zn(3,4-Py-sulfen)] using octyl bromide, and different solvent mixtures were tested as shown in Table 3. It was found that alkylation of [Zn(3,4-Py-sulfen)] using octyl bromide did not show any reactivity or decomposition of [Zn(3,4-Py-sulfen)]. Therefore, alkylation of [Zn(3,4-Py-sulfen)] using octyl bromide in a method similar to that used for [Al(3,4-Py-sulfen)(Cl)] in Example 4 was not possible.

[0086] [Table 3]

[0087] [Example 11] In this embodiment, step (c) of the method for preparing the complex according to the present invention is shown to be starting with [Al(3,4-Py-sulfen)(Cl)] and using methyl iodide as the halogen-R compound as shown below.

[0088] [ka]

[0089] A red solution was obtained by reacting [Al(3,4-Py-sulfen)(Cl)] complex (200 mg, 0.41 mmol, 1.0 equivalent) in DMF (4 mL). Methyl iodide (1 mL, 3.08 mmol, 7.5 equivalents) was added to this solution, and the reaction mixture was heated to 40°C for 20 hours. After this reaction time, isopropyl acetate (40 mL) was added to the reaction mixture to obtain a red precipitate, which was separated. The solid was washed with isopropyl acetate (3 × 5 mL) and dried in a vacuum furnace (40°C, 5 mbar, 16 hours). The product was separated as a red powder (231.5 mg, 89%). 1 The formation of the product is confirmed by 1H-NMR. 1 H NMR (300 MHz, DMSO-d6) δ 9.80 (d, J = 1.4 Hz, 1H), 9.60 (s, 1H), 9.48 (s, 1H), 8.99 (dd, J = 7.0, 1.3 Hz, 1H), 8.66 (d, J = 7.1 Hz, 1H), 7.65-7.54 (m, 2H), 6.89 (t, J = 7.6 Hz, 1H), 4.38 (s, 2H), 1.55 (d, J = 3.9 Hz, 18H).

[0090] [Example 12] The [Al(3,4-Py-sulfen(N-Me))(Cl)] complex prepared in Example 11 was tested under low CO2 partial pressure. Other reaction conditions are as described in the previously mentioned paper, ANTONELLO DECORTES et al.: "Ambient Fixation of Carbon Dioxide using a Zn(II) salphen Catalyst", CHEMCATCHEM, JOHN WILEY & SONS, INC; HOBOKEN, USA, part 3, nr. 5, March 2, 2011 (2011-03-02), pp. 831-834, XP072430479, ISSN:1867-3880, DOI:10.1002 / CCTC.201100031. Experiment D in Table 4 is derived from Table 2 of this paper.

[0091] [Table 4]

Claims

1. The following optionally substituted aluminum salen complex has the following general formula: 【Chemistry 1】 (In the formula, B is a halogen, alkoxy, or alkyl group, the phenyl group of the salen aluminum complex is optionally substituted, R is a hydrocarbon group, and X is a halogen anion.)

2. The optionally substituted salen aluminum complex according to claim 1, wherein X is an iodide anion or a bromide anion.

3. The optionally substituted salen-aluminum complex according to claim 1 or 2, wherein R is an anchor group for fixing the salen-aluminum complex to a heterogeneous support.

4. The optionally substituted salen aluminum complex according to claim 3, wherein the anchor group is an alkyl (trialkoxy) silane.

5. The aluminum complex according to claim 4, wherein the aluminum complex is [Al(3,4-Py-sulfen(N-propyl(trimethoxy)silane))(Cl)]Br in which the phenyl group of the sulfen structure is optionally substituted at the 3-position.

6. A supported complex wherein the aluminum complex according to any one of claims 1 to 5 is immobilized on the surface of silica, alumina, and / or silica-alumina particles by anchor groups R.

7. A catalyst system comprising the complex described in any one of claims 1 to 5 or the supported aluminum complex described in claim 6 and a bromide salt or iodide salt as a co-catalyst.

8. The catalyst system according to claim 7, wherein the bromide salt is a quaternary ammonium bromide salt or a phosphonium bromide salt, and the iodide salt is a quaternary ammonium iodide salt or a phosphonium iodide salt.

9. Optionally substituted aluminum salen intermediate complexes: 【Chemistry 2】 (In the formula, B is a halogen, alkoxy, or alkyl group, and the phenyl group of the salen aluminum complex is optionally substituted.)

10. A method for preparing the optionally substituted salen aluminum intermediate complex described in claim 9 from the corresponding optionally substituted salen nickel complex or salen zinc complex having a pyridine crosslinking group, comprising the following steps: (a) The step of demetallizing the corresponding optionally substituted salen nickel complex or salen zinc complex to obtain a demetallized salen ligand, and (b) The demetallated salen ligand from step (a) is brought into contact with an aluminum compound to obtain an optionally substituted salen-aluminum intermediate complex. A method for carrying out this.

11. In step (b), the demetallated salen ligand in step (a) is diethylaluminum chloride (Al(Et)) as an aluminum compound. ２ The method according to claim 10, wherein the contact is made with Cl.

12. The method according to claim 10 or 11, wherein in step (a), the corresponding substituted salen nickel ligand or salen zinc ligand is demetallated in an anhydrous demetallation process in the presence of imidazole in acetonitrile or imidazole in toluene.

13. The method according to any one of claims 10 to 12, wherein in step (c), an optionally substituted salenaluminum intermediate complex having a 3-pyridine bridge is subjected to alkylation to obtain a corresponding optionally substituted salenaluminum complex having a 3-pyridinium bridge group.

14. A method for preparing an optionally substituted salenaluminum intermediate complex according to any one of claims 1 to 5 from an optionally substituted salenaluminum intermediate complex according to claim 9, comprising subjecting the optionally substituted salenaluminum intermediate complex to alkylation to obtain an optionally substituted salenaluminum intermediate complex according to any one of claims 1 to 5.

15. Use as a catalyst or as part of a catalyst in the catalyst system according to claim 7 or 8, in a method for preparing a cyclic carbonate by reacting an epoxide compound with carbon dioxide.

16. A method for preparing a cyclic carbonate by reacting an epoxide compound with carbon dioxide at a pressure of 0.1 to 0.3 MPa in the presence of the catalyst system described in claim 7 or 8.

17. The method according to claim 16, wherein X is a bromide ion and the catalyst system includes a bromide salt co-catalyst.

18. The method according to claim 16 or 17, wherein carbon dioxide comes into contact with an epoxide compound in a liquid including a catalyst system, and the liquid is a cyclic carbonate.

19. The method according to claim 18, wherein the catalyst system is the supported aluminum complex described in claim 6, and the resulting reaction mixture is a suspension.

20. The method according to any one of claims 16 to 19, wherein the epoxide compound has 2 to 8 carbon atoms.

21. The method according to claim 20, wherein the epoxide compound is ethylene oxide, propylene oxide, butylene oxide, pentene oxide, glycidol, styrene oxide, epichlorohydrin, or fluoroethylene oxide.

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