Asymmetric carbene phenol rare earth complex as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of metal organic complexes and catalytic polymerization, and particularly provides an asymmetric carbene phenol rare earth complex and a preparation method and application thereof.The asymmetric carbene phenol rare earth complex is prepared by preparing a series of monophenol substituted N-heterocyclic carbene ligand precursors and utilizing the ligands to perform coordination reaction with hexamethylsilamido rare earth metal, and the asymmetric carbene phenol rare earth complex is obtained. A series of asymmetric carbene phenol rare earth complexes with novel structures are prepared. The rare earth complex can be used as a catalyst for preparing an LED packaging adhesive. Compared with a commercially available catalyst, the rare earth complex disclosed by the invention has higher catalytic activity when being used as a catalyst, and the packaging adhesive has better strength and toughness and more excellent anti-aging performance, and can achieve a better LED packaging effect.

Description

Technical Field

[0001] The present invention relates to the technical fields of metal-organic complexes and catalytic polymerization, and particularly relates to an asymmetric carbene phenolic rare earth complex, a preparation method thereof, and an application thereof. Background Art

[0002] Rare earth elements include 17 elements in Group IIIB of the periodic table, namely scandium (Sc, 21), yttrium (Y, 39), and the lanthanide series (La-Lu, 57-71). The synthesis and application of compounds of various rare earth elements and complexes containing rare earth elements have also become one of the research hotspots in the fields of inorganic chemistry, organometallic chemistry, metal catalysis, and polymer chemistry. Currently, common rare earth compounds include halogen compounds, oxides and hydroxides, borohydrides, hexamethyldisilazanes, trimethylsilyl compounds, etc., among which hexamethyldisilazane rare earth compounds and trimethylsilyl rare earth compounds are widely used. In particular, hexamethyldisilazane rare earth compounds can not only effectively catalyze ring-opening polymerization and diene addition polymerization, but also complex with various ligands (such as phenolic ligands, N-heterocyclic carbene ligands, etc.) to form coordination compounds, which are then used as polymerization catalysts.

[0003] There are various types of ligands used in metal complexes, among which ligands containing phenolic groups account for a large proportion of applications. CN115746029A discloses a benzoxazine-functionalized amino-bridged polyaryloxy rare earth metal complex, which has high catalytic activity and can catalyze the ring-opening polymerization of racemic lactide in an organic solvent. However, due to the regularity of the coordination between its ligand and rare earth metal and the singularity of the coordination bond, it has not been successfully applied to the field of hydrosilylation catalysis.

[0004] With the continuous development and progress of LED technology, more stringent requirements are put forward for the performance of encapsulation adhesives. Ordinary LED encapsulation materials are easily exposed to extreme conditions such as light and heat for a long time, and are prone to problems such as insufficient strength and toughness, yellowing and discoloration, which seriously affect the luminous efficiency. Rare earth complex catalysts, as a kind of efficient noble metal catalysts, have not been widely used in the field of preparation of LED encapsulation materials, but their unique metal catalytic characteristics and coordination modes can efficiently catalyze hydrosilylation reactions. Therefore, there is an urgent need to develop a new type of catalyst that can achieve high catalytic efficiency in order to prepare LED encapsulation adhesives with high strength, strong toughness, and good yellowing resistance. Summary of the Invention

[0005] To solve the problems existing in the above-mentioned prior art, the present invention provides an asymmetric carbene phenol rare earth complex, a preparation method thereof and an application thereof. A series of monophenol-substituted N-heterocyclic carbene ligand precursors are prepared by an organic synthesis method, and a series of novel-structured asymmetric carbene phenol rare earth complexes are prepared by using the ligands to carry out a coordination reaction with a hexamethyldisilazide rare earth metal. The rare earth complex can be used as a catalyst to catalyze the hydrosilylation reaction.

[0006] The inventive concept of the present application is as follows:

[0007] The N-heterocyclic carbene structure is an electron-rich nucleophilic species with strong σ-donating property and weak π-acidity, and is very suitable for use as a ligand for main group or transition metals; the combination of the phenol structure and the N-heterocyclic carbene structure in the same ligand can greatly enhance the stability of the metal complex and the diversity of the spatial configuration, and is an excellent metal ligand; the asymmetry in the structure of the asymmetric rare earth metal carbene complex generates a larger coordination binding space, and has a broader application prospect compared with the catalysts of the existing structures.

[0008] The present invention provides an asymmetric carbene phenol rare earth complex having the structure of formula (I), which contains a carbene-rare earth metal structure and a phenoxy-rare earth metal bond, and its structural general formula is as follows:

[0009]

[0010] In formula (I): n = 1 or 2;

[0011] R1 is a benzene substituent, and R2 is a phenol substituent; more preferably, R 1 is β-naphthyl or 4-methylphenyl; R 2 is naphthol or 4-methylphenol.

[0012] Ln is a rare earth metal element, and more preferably any one of lanthanum, yttrium, scandium, and neodymium.

[0013] The above-mentioned asymmetric carbene phenol rare earth complex having the structure of formula (I) is obtained by carrying out a coordination reaction between a monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L and a hexamethyldisilazide rare earth metal Ln[N(SiMe 3 ) 2 3 . The chemical structure of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L includes but is not limited to the following structural types:

[0014]

[0015] ​The inventors further provided a method for preparing the above-mentioned asymmetric carbene phenol rare earth complex with the structure of formula (I), and the specific steps are as follows:

[0016] (1) Synthesis of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L

[0017] The synthesis process of the monophenol-substituted N-heterocyclic carbene ligand precursor is divided into three steps: the introduction of the benzene substituent on nitrogen, the introduction of the phenolic substituent, and the ring-forming reaction:

[0018] In the first step, a benzene substituent is introduced onto a nitrogen atom. The specific method is as follows:

[0019] The benzene-substituted amine compound and an equivalent amount of bromopropylamine hydrobromide or bromoethylamine hydrobromide are heated under reflux in water for 24 h; after the solution is cooled, it is extracted three times with ethyl acetate. The aqueous phase is rotary evaporated to obtain an oily substance, which is crystallized at low temperature in ethanol to obtain the crystal N-benzene-substituted diamine hydrobromide, and then the hydrobromic acid in the above product is neutralized with an aqueous KOH solution to obtain an oil-soluble N-substituted N-benzene-substituted diamine compound at one end;

[0020] The benzene-substituted amine compound is selected from one of naphthylamine and 4-methylaniline.

[0021] In the second step, the introduction of the phenolic substituent is obtained by the acetal reaction of an aldehyde and an amine compound, and then the carbon-nitrogen double bond therein is reduced by NaBH 4 . The specific method is as follows:

[0022] An equivalent amount of the N-benzene-substituted diamine compound and the phenol-substituted formaldehyde compound are taken in a flask, toluene is added and heated to reflux. After reacting for 2 h, the heating is stopped; after the solution is cooled, 2 equivalents of NaBH 4 relative to the diamine compound is slowly added in an ice-water bath, and the reaction is carried out overnight; then the solvent is rotary evaporated, washed three times with water and extracted with dichloromethane; after rotary evaporating to remove the dichloromethane solvent, an oily product is obtained;

[0023] The N-benzene-substituted diamine compound is selected from one of N-naphthyl-1,3-propanediamine and N-methylphenyl-ethylenediamine; the phenol-substituted formaldehyde compound is selected from one of 1-naphthaldehyde and methylbenzaldehyde.

[0024] In the third step, the ring-forming reaction uses a common hydrochloric acid / triethyl orthoformate system. The specific method is as follows:

[0025] Take the above oily product in a single-necked flask, add a mixed solvent of ethanol / ethyl acetate with a mass 5 times that of the oily product to dissolve it, where the volume ratio of ethanol to ethyl acetate is 2:1, add concentrated hydrochloric acid with a mass 0.5 times that of the oily product, stir and react for 1 h, and then rotary evaporate the solvent; dissolve the obtained product in triethyl orthoformate with a mass 2 times that of the above oily product, and heat under reflux at 120 °C overnight; a large amount of white powder precipitates during the reaction process, filter the solution, and wash the filtrate with anhydrous ether to obtain the final product, the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L.

[0026] (2) Synthesis of asymmetric carbene phenol rare earth complex LLnN 2 Synthesis

[0027] Take the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L prepared in step (1) and rare earth metal Ln[N(SiMe 3 ) 2 3 Carry out a coordination reaction in the solvent tetrahydrofuran, stir well for 10 min. Then lower the temperature, and continue the reaction under the action of potassium amide, stir overnight, remove most of the solvent, add freshly distilled n-hexane, filter, and place it at low temperature for crystallization to prepare the asymmetric carbene phenol rare earth complex LLnN 2 .

[0028] Preferably, in step (1), the substituents on the two N atoms in the monophenol-substituted N-heterocyclic carbene ligand precursor have different structures. One side of the nitrogen has a benzene-based substituent with a relatively large electron cloud density, which is convenient for the subsequent metal coordination process; the other side of the nitrogen has a phenol-based substituent, whose spatial configuration is not very different from that of the benzene-based substituent, but the oxygen on the phenol can form a bond with the rare earth metal to provide a catalytic site;

[0029] The benzene-based substituent in the monophenol-substituted N-heterocyclic carbene ligand precursor is β-naphthyl or 4-methylphenyl, and the phenol-based substituent is naphthol or 4-methylphenol; the ratio of the above benzene-based substituent to the phenol-based substituent is 1:1.

[0030] Preferably, in step (2), the molar ratio of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L, rare earth metal Ln[N(SiMe 3 ) 2 3 , potassium amide KN(SiMe 3 ) 2 is 1:1:(1.8 - 2.6).

[0031] Preferably, in step (2), the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 ​​The usage ratio of L to tetrahydrofuran is 1mmol:8-10ml; the usage ratio of n-hexane to tetrahydrofuran is 1:1.

[0032] Preferably, during the synthesis of the complex in step (2), the strongly basic potassium amine KN (SiMe 3 ) 2 The addition of can extract hydrogen from the carbene carbon in the ligand precursor, exposing the active carbene carbon, which reacts with the rare earth metal to form a carbene-rare earth coordination bond; while potassium metal itself does not undergo coordination reaction, so it will not appear in the complex structure.

[0033] Preferably, in step (2), the hexamethylsilylamine rare earth metal Ln[N(SiMe 3 ) 2 ] 3 With potassium amine KN(SiMe 3 ) 2 The order of adding materials has a great influence on the synthesis of the complex. When the silylamine rare earth metal is added first, the amine rare earth reacts with the phenolic hydroxyl group in the ligand precursor, dropping a silylamine group to form a rare earth metal-phenol oxygen bond. The addition of potassium amine removes the hydrogen on the carbene carbon and forms a bond with the rare earth metal to form an asymmetric carbene phenol rare earth complex. On the contrary, when potassium amine is added first, due to the interaction between the carbene carbon and the potassium ion, the rare earth metal cannot complete the bond with the carbene carbon.

[0034] Preferably, when potassium amide is added in step (2), the reaction temperature should be controlled at -10 to -20°C; the condition for low-temperature crystallization is to place it at -5°C for one week to complete the crystallization.

[0035] Preferably, in step (2), the asymmetric carbene phenol rare earth complex LLnN 2 It contains two coordination sites, rare earth metal-carbene carbon and rare earth metal-phenol oxygen bond, both of which can produce catalytic activity. The spatial asymmetric structure is conducive to the insertion and coordination reaction of the raw material monomers during the catalytic polymerization process, which helps to produce better catalytic effects.

[0036] The asymmetric carbene phenol rare earth complex of the present invention is used as a catalyst to catalyze the hydrosilylation reaction and can be used to prepare LED packaging adhesive. The specific operation method is as follows:

[0037] Vinyl silicone oil, hydrogen-containing silicone oil and methyl silicone resin are mixed evenly, and an asymmetric carbene phenol rare earth complex is added as a catalyst, and a defoaming agent is added. After degassing, the mixture is heated and cured. After being completely cured, the mixture can be used as an LED encapsulation adhesive.

[0038] Preferably, the formula components are calculated by weight and include 60-70 parts of vinyl silicone oil, 40-50 parts of hydrogen-containing silicone oil, 23-30 parts of methyl silicone resin, 0.0005-0.0008 parts of an asymmetric carbene phenol-based rare earth complex, and 0.0007-0.0009 parts of defoamer BYK-1790. The heating temperature is 80°C and the curing time is 10 min.

[0039] Among them, the vinyl silicone oil selected is a product with a viscosity of 12000 mPa·s at 25°C, the hydrogen-containing silicone oil selected is a product with a viscosity of 5500 mPa·s at 25°C, and the methyl silicone resin selected is a product with a viscosity of 3000 mPa·s at 25°C, all of which are directly purchased from the market.

[0040] Compared with the prior art, the asymmetric carbene phenol-based rare earth complex provided by the present invention has the structure of formula (I). By preparing a monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L, compared with the existing phenolic ligands, the introduction of the carbene structure enables one ligand to cover two different catalytic sites, which helps the catalytic reaction to proceed. At the same time, the asymmetry of the ligand structure also introduces more coordination space for the active sites, and the benzene ring structures on both sides of the ligand can also stabilize the complex structure, which helps the coordination reaction to proceed. Using this ligand to carry out a coordination reaction with a hexamethylsilylamino rare earth metal can prepare a series of asymmetric carbene phenol-based rare earth complexes with novel structures. When this rare earth complex is used as a catalyst, the amount of catalyst used is less, the reaction process can be carried out at a lower temperature and in a shorter time, the catalytic activity is higher, the LED encapsulation adhesive prepared has better strength and toughness, and more excellent anti-aging performance, and thus a better encapsulation effect can be achieved. Description of the Drawings

[0041] Figure 1 1H NMR spectrum of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L1 in Example 1;

[0042] Figure 2 13C NMR spectrum of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L1 in Example 1;

[0043] Figure 3 1H NMR spectrum of the asymmetric carbene phenol-based lanthanum metal complex L1LaN 2 in Example 1;

[0044] Figure 4 1H NMR spectrum of the asymmetric carbene phenol-based yttrium metal complex L1YN 2 in Example 1;

[0045] Figure 5 1H NMR spectrum of the monophenol-substituted N-heterocyclic carbene ligand precursor H in Example 22 1H NMR spectrum of L2;

[0046] Figure 6 For the monophenol-substituted N-heterocyclic carbene ligand precursor H in Example 2 2 13C NMR spectrum of L2;

[0047] Figure 7 For the asymmetric carbene phenol scandium metal complex L2ScN in Example 2 2 1H NMR spectrum;

[0048] Figure 8 For the asymmetric carbene phenol neodymium metal complex L2NdN in Example 2 2 1H NMR spectrum. Detailed implementation manners

[0049] The embodiments of the present invention will be further described in detail below through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention, and the implementation manners of the present invention are not limited thereto. Some non-essential adjustments and improvements made by those familiar with the relevant fields according to the above invention scheme still fall within the protection scope of the present invention.

[0050] The vinyl silicone oil used in the following examples is a product with a viscosity of 12000 mPa·s at 25 °C, the hydrogen-containing silicone oil is a product with a viscosity of 5500 mPa·s at 25 °C, and the methyl silicone resin is a product with a viscosity of 3000 mPa·s at 25 °C, all of which are directly purchased from the market.

[0051] Example 1 Preparation method of an asymmetric carbene phenol rare earth complex L1LnN 2 The specific steps are as follows:

[0052] (1) Synthesis of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 Synthesis of L1

[0053] Naphthylamine (3.29 g) and 3-bromopropylamine hydrobromide (5 g) were heated under reflux in water for 24 h. After the solution was cooled, it was extracted three times with ethyl acetate. The aqueous phase was rotary evaporated to obtain an oily substance, which was crystallized at low temperature in ethanol to obtain a pale yellow crystal of N-naphthyl-1,3-propanediamine hydrobromide. Then, the hydrobromic acid in the above product was neutralized with an aqueous KOH solution to a pH between 7 ± 0.5 to obtain an oil-soluble N-substituted N-naphthyl-1,3-propanediamine at one end.

[0054] Take the above-mentioned N-naphthyl-1,3-propanediamine (5 g) and 1-naphthaldehyde (4.5 g) in a 100 mL flask, add 50 mL of toluene and heat to reflux. The color of the solution gradually turns orange-red. After reacting for 2 h, stop heating. After the solution cools, slowly add NaBH 4 (1 g) equivalent to 2 times the amount of N-naphthyl-1,3-propanediamine in an ice-water bath. After reacting overnight, the color of the solution turns light yellow. Then, rotary evaporate to remove the solvent, wash three times with water and extract with dichloromethane. After rotary evaporating to remove the dichloromethane solvent, an oily product is obtained.

[0055] Take 5 g of the above-mentioned oily product in a single-neck flask, add 25 g of ethanol / ethyl acetate (V 乙醇 :V 乙酸乙酯 = 2:1) mixed solvent to dissolve, add concentrated hydrochloric acid (2.5 g) equivalent to 0.5 times the mass of the oily substance, stir and react for 1 h, and then rotary evaporate to remove the solvent. Dissolve the obtained product in 10 g of triethyl orthoformate and heat to reflux at 120 °C overnight. A large amount of white powder precipitates during the reaction. Filter the solution, and wash the filtrate twice with 10 mL of anhydrous ether to obtain the final product, the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L1. Yield: 85%, Purity: 95%, Elemental analysis results: C: 74%, H: 6%, N: 6.5%; Its NMR spectrum is as Figure 1 and 2 shown.

[0056] (2) Synthesis of the asymmetric carbene phenol-based lanthanum metal complex L1LaN 2 Synthesis

[0057]

[0058] Under argon protection, weigh 0.4 g of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L1 into a pre-baked 25 mL Selenk flask, add 10 mL of freshly distilled tetrahydrofuran solvent, stir well at room temperature for 10 min, and then add lanthanum hexamethysilylamide La[N(SiMe 3 ) 2 3 (0.52 g). Stir at -18 °C for half an hour in an argon atmosphere until the solution changes from turbid to clear. Then add potassium amide KN(SiMe 3 ) 2 (0.38 g) equivalent to 2 times the amount of the ligand precursor to the clear solution. As KN(SiMe 3 ) 2 ​Upon the addition of , the solution became turbid instantaneously. After stirring for 1 h, the solution became clear again. Stirring was maintained overnight at room temperature, and then most of the solvent was removed under vacuum. Then 10 mL of n-hexane was added. After centrifugation, the supernatant was taken and sealed in a long-neck glass tube and stored. Colorless crystals were obtained after standing at -5 °C for one week, which were the asymmetric carbene phenol lanthanum metal complex L1LaN 2 , Yield: 95%; Its 1H NMR spectrum is as Figure 3 shown.

[0059] (3) Synthesis of asymmetric carbene phenol yttrium metal complex L1YN 2 Synthesis

[0060] Under argon protection, 0.4 g of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L1 was weighed into a pre-baked 25 mL Selenk flask, 10 mL of freshly distilled tetrahydrofuran solvent was added, and the mixture was stirred thoroughly for 10 min at room temperature. Then yttrium hexamethyldisilazide Y[N(SiMe 3 ) 2 3 (0.56 g) was added, and the mixture was stirred at -20 °C for half an hour in an argon atmosphere until the solution changed from turbid to clear; then potassium amide KN(SiMe 3 ) 2 (0.35 g), which is 1.8 times the equivalent of the ligand precursor, was added to the clear solution. Upon the addition of KN(SiMe 3 ) 2 , the clear solution became turbid instantaneously. After stirring for about 1 h, the solution became clear again. Stirring was maintained overnight at room temperature, and then most of the solvent was removed under vacuum. Then 10 mL of n-hexane was added. After centrifugation, the supernatant was taken and sealed in a long-neck glass tube and stored. Colorless crystals were obtained after standing at -5 °C for one week, which were the asymmetric carbene phenol yttrium metal complex L1YN 2 , Yield: 90%; Its 1H NMR spectrum is as Figure 4 shown.

[0061] Example 2 Preparation method of an asymmetric carbene phenol rare earth complex L2LnN 2 The specific steps are as follows:

[0062] (1) Synthesis of monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L2

[0063] 4-Methylaniline (2.65 g) and 3-bromoethylamine hydrobromide (5 g) were heated under reflux in water for 24 h. After the solution was cooled, it was extracted three times with ethyl acetate. The aqueous phase was rotary evaporated to obtain an oily substance, which was crystallized at low temperature in ethanol, and then the hydrobromic acid in the above product was neutralized to pH 7 ± 0.5 with an aqueous KOH solution to obtain the oil-soluble N-substituted N-methylphenyl-ethylenediamine.

[0064] Take N-methylphenyl-ethylenediamine (5 g) and methylbenzaldehyde (3.96 g) in a 100 mL flask, add about 50 mL of toluene and heat to reflux. After reacting for 2 h, stop heating. After the solution cools, slowly add NaBH 4 (1 g), which is 2 times the equivalent of N-methylphenyl-ethylenediamine, dropwise in an ice-water bath. After reacting overnight, rotary evaporate to remove the solvent, wash three times with water and then extract with dichloromethane. After rotary evaporating to remove the dichloromethane solvent, an oily product is obtained.

[0065] Take 5 g of the above oily product in a single-necked flask, add 25 g of ethanol / ethyl acetate (V 乙醇 :V 乙酸乙酯 = 2:1) mixed solvent to dissolve it, add 2.5 g of concentrated hydrochloric acid, stir and react for 1 h, and then rotary evaporate to remove the solvent. Dissolve the obtained product in 10 g of triethyl orthoformate, and heat to reflux at 120 °C overnight. A large amount of white powder precipitates during the reaction. Filter the solution, and wash the filtrate twice with 10 mL of anhydrous ether to obtain the final product, the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L2. Yield: 87%, Purity: 96%, Elemental analysis results: C: 68%, H: 7%, N: 8%; Its NMR spectrum is as Figure 5 and 6 shown.

[0066] (2) Synthesis of the asymmetric carbene phenol scandium metal complex L2S C N 2 The synthesis

[0067]

[0068] The preparation method is similar to that of L1LnN 2 Under argon protection, weigh 0.3 g of the monophenol-substituted N-heterocyclic carbene ligand precursor H 2 L2 into a pre-baked 25 mL Selenk bottle, add 10 mL of freshly distilled tetrahydrofuran solvent, stir well at room temperature for 10 min, and then add scandium hexamethyldisilazide Sc[N(SiMe 3 ) 2 3 (0.51 g). Stir at -20 °C for half an hour until the solution changes from turbid to clear. Then add potassium amide KN(SiMe 3 ) 2 (0.49 g), which is 2.6 times the equivalent of the ligand precursor, to the clear solution. As KN(SiMe 3 ) 2 ​Upon the addition of , the solution immediately became turbid, and after stirring for about 1 h, the solution became clear again. Stirring was continued overnight at room temperature, and then most of the solvent was removed under vacuum. Then 10 mL of n-hexane was added, and the supernatant was taken after centrifugation and sealed in a long-neck glass tube and stored. Colorless crystals were obtained after standing at -5 °C for about one week, which were the asymmetric carbene phenol scandium metal complex L2ScN 2 , Yield: 86%; Its 1H NMR spectrum is as Figure 7 shown.

[0069] (3) Synthesis of asymmetric carbene phenol neodymium metal complex L2NdN 2 Synthesis

[0070] Under argon protection, 0.3 g of the monophenol-substituted azacyclic carbene ligand precursor H 2 L2 was weighed into a pre-baked 25 mL Schlenk flask, 10 mL of freshly distilled tetrahydrofuran solvent was added, and it was stirred thoroughly for 10 min at room temperature. Then neodymium hexamethyldisilazide Nd[N(SiMe 3 ) 2 3 (0.61 g) was added, and it was stirred at -20 °C for half an hour until the solution changed from turbid to clear; then potassium amide KN(SiMe 3 ) 2 (0.38 g) equivalent to 2 times the ligand precursor was added to the clear solution. With the addition of KN(SiMe 3 ) 2 , the clear solution immediately became turbid, and after stirring for about 1 h, the solution became clear again. Stirring was continued overnight at room temperature, and then most of the solvent was removed under vacuum. Then 10 mL of n-hexane was added, and the supernatant was taken after centrifugation and sealed in a long-neck glass tube and stored. Blue crystals were obtained after standing at -5 °C for about one week, which were the asymmetric carbene phenol neodymium metal complex L2NdN 2 , Yield: 91%; Its 1H NMR spectrum is as Figure 8 shown.

[0071] Catalytic Example 1

[0072] The asymmetric carbene phenol rare earth complex L1LaN 2 prepared in Example 1 was used as a catalyst to prepare an LED encapsulant. The formulation components were calculated by weight and included 60 parts of vinyl silicone oil, 45 parts of hydrogen-containing silicone oil, 30 parts of methyl silicone resin, 0.0005 part of the asymmetric carbene phenol rare earth complex L1LaN 2 and 0.0008 part of BYK-1790 defoamer. After vacuum degassing, it was heated and cured at 80 °C for 10 min, and cured and formed to obtain an LED encapsulant.

[0073] Catalytic Example 2

[0074] The asymmetric carbene phenol rare earth complex L1YN prepared in Example 1 2 was used as a catalyst to prepare an LED encapsulant. The formulation components were the same as those in Catalytic Example 1, and the rare earth metal catalyst was changed to the asymmetric carbene phenol rare earth complex L1YN 2 . After degassing, it was placed at 80 °C and heated and cured for 10 min, and then cured and molded to obtain an LED encapsulant.

[0075] Catalytic Example 3

[0076] The asymmetric carbene phenol rare earth complex L2ScN prepared in Example 2 2 was used as a catalyst to prepare an LED encapsulant. The formulation components were the same as those in Catalytic Example 1, and the rare earth metal catalyst was changed to the asymmetric carbene phenol rare earth complex L2ScN 2 . After degassing, it was placed at 80 °C and heated and cured for 10 min, and then cured and molded to obtain an LED encapsulant.

[0077] Catalytic Example 4

[0078] The asymmetric carbene phenol rare earth complex L2NdN prepared in Example 2 2 was used as a catalyst to prepare an LED encapsulant. The formulation components were the same as those in Catalytic Example 1, and the rare earth metal catalyst was changed to the asymmetric carbene phenol rare earth complex L2NdN 2 . After degassing, it was placed at 80 °C and heated and cured for 10 min, and then cured and molded to obtain an LED encapsulant.

[0079] Catalytic Comparative Example

[0080] A commercially available Karstedt catalyst (Beijing Innochem Science & Technology Co., Ltd.) was used as a catalyst to catalyze the hydrosilylation reaction. The formulation components were calculated by weight, including 60 parts of vinyl silicone oil, 45 parts of hydrogen-containing silicone oil, 30 parts of methyl silicone resin, 0.05 part of Karstedt catalyst, and 0.0008 part of BYK-1790 defoamer. After degassing, it was placed at 120 °C and heated and cured for 30 min, and then cured and molded to obtain an LED encapsulant.

[0081] In the experimental example, the following performance tests were carried out on the LED encapsulants prepared in the above catalytic examples and catalytic comparative example:

[0082] Refractive index (ISO 489): An Abbe refractometer was used. The uncured sample was directly dropped on the prism of the Abbe refractometer for testing, and the test temperature was (25 ± 2) °C.

[0083] Light transmittance (GB / T 2410-2008): A specimen with a length and width of 2 cm and a thickness of 3 mm was prepared with the encapsulant, and it was tested using a UV-visible spectrophotometer. The test scanning range was 300-800 nm.

[0084] Tensile strength and elongation at break test (GB / T 528 - 2009): Use the encapsulating adhesive to prepare dumbbell - shaped specimens with a length of 80 mm and a thickness of 3 mm, and test them with a universal material testing machine.

[0085] Yellowing index test (GB / T 16422.3 - 2022): Use the encapsulating adhesive to prepare specimens with a length and height of 2 cm and a thickness of 3 mm, and measure their chromaticity with a colorimeter.

[0086] Red ink experiment (IPC - TM - 650 2.4.53 - 2017): Use the encapsulating adhesive to encapsulate the SMD lamp beads, quickly cure them under a 365 nm UV lamp for 10 s, then cure them at 120 °C for 10 min. After the glue is cured, soak it in 50% red ink, boil it for 8 hours, then wash the lamp beads and observe the penetration of red ink with a microscope.

[0087] The test results are shown in Table 1:

[0088] Table 1 Performance test results of the experimental examples and comparative examples after curing

[0089]

[0090]

[0091] From the above - mentioned catalytic experiments, it can be seen that under the same raw materials of vinyl silicone oil, hydrogen - containing silicone oil, and methyl silicone resin, compared with the commercially available Karstedt catalyst, when the rare - earth complex prepared by the present invention is used as the catalyst, the catalyst dosage is only 1% of that in the comparative example, but the reaction can be carried out at a lower temperature and in a shorter time. The test results after curing show that when the rare - earth complex shown in the present invention is used as the catalyst, the refractive index, light transmittance, and yellow index values of the cured glue remain unchanged, and the red ink experiments all show no penetration, and the tensile strength and elongation at break results are both significantly improved. Comparing the effects of the four rare - earth catalysts, the cured sample prepared with the catalyst using the monophenol - substituted N - heterocyclic carbene ligand precursor H 2 L1 as the ligand has a better tensile strength than the ligand precursor H 2 L2, but the elongation at break result is slightly lower. The catalytic effects of different rare - earth metals with the same ligand are not very different.

[0092] From the above, when the rare - earth complex prepared by the present invention is used as the catalyst, the catalytic activity is higher, the encapsulating adhesive has better strength and toughness, more excellent anti - aging performance, and can achieve a better LED encapsulation effect.

[0093] The above embodiments are preferred embodiments of the present invention, mainly showing and describing the main features and basic principles of the present invention. However, the implementation schemes of the present invention are not limited by the above embodiments. Without departing from the spirit and scope of the present invention, all kinds of modifications, alterations, substitutions, combinations, and simplifications made by any person familiar with the relevant fields and technologies shall be regarded as within the scope of the present invention.

Claims

1. An asymmetric carbene phenol rare earth complex, characterized in that: The complex is an amino rare earth complex LLn[N(SiMe3)2]2 of carbene-rare earth metal structure, and its general structural formula is as follows: Wherein n=1 or 2; R1 is a benzene substituent, R2 is a phenol substituent; and Ln is a rare earth metal element.

2. The asymmetric carbene phenol rare earth complex according to claim 1, characterized in that: R1 is β-naphthyl or 4-methylphenyl; R2 is naphthol or 4-methylphenol; Ln is any one of lanthanum, yttrium, scandium and neodymium; the asymmetric carbene phenol rare earth complex is synthesized by a coordination reaction of a monophenol-substituted nitrogen heterocyclic carbene ligand H2L with a hexamethylsilylamine rare earth metal Ln[N(SiMe3)2]3 under certain conditions.

3. The method for preparing the asymmetric carbene phenol rare earth complex according to claim 1, characterized in that: The specific steps are as follows: (1) Synthesis of monophenol-substituted nitrogen heterocyclic carbene ligand precursor H2L The synthesis process of monophenol-substituted nitrogen heterocyclic carbene ligand precursors is divided into the introduction of benzene substituents on nitrogen, the introduction of phenol substituents and the ring-forming reaction. (2) Synthesis of asymmetric carbene phenol rare earth complex LLnN2 The monophenol-substituted nitrogen heterocyclic carbene ligand precursor H2L prepared in step (1) is subjected to coordination reaction with a hexamethylsilylamine rare earth metal Ln[N(SiMe3)2]3 to prepare an asymmetric carbene phenol rare earth complex LLnN2 under the action of potassium amine KN(SiMe3)2 at low temperature in tetrahydrofuran solvent.

4. The method for preparing the asymmetric carbene phenol rare earth complex according to claim 3, characterized in that: The monophenol substituted nitrogen heterocyclic carbene ligand precursor H2L is selected from the following two structures: Any one of .

5. The method for preparing the asymmetric carbene phenol rare earth complex according to claim 3, characterized in that: Step (1) Synthesis of monophenol substituted nitrogen heterocyclic carbene ligand precursor H2L, the specific steps are as follows: The first step is to introduce a benzene substituent on a nitrogen atom. The specific method is: A benzene-substituted amine compound and an equivalent amount of bromopropylamine hydrobromide or bromoethylamine hydrobromide are heated to reflux in water for 24 hours; after the solution is cooled, it is extracted with ethyl acetate three times, and the water phase is rotary evaporated to obtain an oily substance, which is crystallized in ethanol at low temperature to obtain crystalline N-benzene-substituted diamine hydrobromide, and then the hydrobromic acid in the above product is neutralized with a KOH aqueous solution to obtain an oil-soluble N-benzene-substituted diamine compound with one end N substituted; The benzene-substituted amine compound is selected from one of naphthylamine and 4-methylaniline; The second step is to introduce phenolic substituents by acetal reaction of aldehydes and amine compounds to obtain condensation products, and then reduce the carbon-nitrogen double bonds therein by NaBH4. The specific method is as follows: Take an equivalent amount of an N-benzene-substituted diamine compound and a phenol-substituted formaldehyde compound in a flask, add toluene and heat to reflux, and stop heating after reacting for 2 hours; after the solution is cooled, slowly add NaBH4 twice the equivalent of the diamine compound in an ice-water bath, and react overnight; then, remove the solvent by rotary evaporation, wash with water three times, and extract with dichloromethane; remove the solvent dichloromethane by rotary evaporation to obtain an oily product; The N-benzene-substituted diamine compound is selected from one of N-naphthyl-1,3-propylenediamine and N-methylphenyl-ethylenediamine, and the phenol-substituted formaldehyde compound is selected from one of 1-naphthaldehyde and methylbenzaldehyde; The third step of cyclization reaction uses the commonly used hydrochloric acid / triethyl orthoformate system, and the specific method is as follows: The above oily product was placed in a single-necked flask, and 5 times the volume of a mixed solvent of ethanol / ethyl acetate was added to dissolve it, wherein the volume ratio of ethanol to ethyl acetate was 2:1; 0.5 times the mass of the oily substance was added with concentrated hydrochloric acid, and the solvent was evaporated after stirring for 1 hour; the obtained product was dissolved in 2 times the mass of triethyl orthoformate of the above oily substance, and heated under reflux at 120° C. overnight; a large amount of white powder was precipitated during the reaction, and the solution was filtered, and the filtrate was washed with anhydrous ether to obtain the final product, a monophenol-substituted nitrogen heterocyclic carbene ligand precursor H2L.

6. The method for preparing the asymmetric carbene phenol rare earth complex according to claim 3, characterized in that: In step (2), the molar ratio of the monophenol-substituted nitrogen heterocyclic carbene ligand H2L, the hexamethylsilylamine rare earth metal Ln[N(SiMe3)2]3, and the amine potassium KN(SiMe3)2 is 1:1:(1.8-2.6).

7. The method for preparing the asymmetric carbene phenol rare earth complex according to claim 3 or 6, characterized in that: In step (2), the monophenol substituted nitrogen heterocyclic carbene ligand precursor H2L reacts with hexamethylsilylamine rare earth metal Ln[N(SiMe3)2]3 and potassium amide in tetrahydrofuran to obtain a transparent liquid, and then most of the solvent is removed under reduced pressure. Freshly distilled n-hexane is added, filtered, and placed at low temperature for crystallization to precipitate complex crystals, which is the asymmetric substituted nitrogen heterocyclic carbene rare earth metal complex LLnN2; the ratio of the monophenol substituted nitrogen heterocyclic carbene ligand H2L to tetrahydrofuran is 1 mmol:8-10 ml; the ratio of n-hexane to tetrahydrofuran is 1:

1.

8. Use of the asymmetric carbene phenol rare earth complex according to claim 1 as a catalyst for preparing LED packaging adhesive.

9. The use of preparing LED packaging adhesive according to claim 8, characterized in that: The specific preparation method is as follows: vinyl silicone oil, hydrogen-containing silicone oil, and methyl silicone resin are evenly mixed, an asymmetric carbene phenol rare earth complex is added as a catalyst, a defoaming agent is added, and after degassing, it is heated and cured at 80°C for 10 minutes, and after complete curing, it is used as LED packaging glue.

10. The use of the method for preparing LED packaging adhesive according to claim 9, characterized in that: By weight, it comprises 60-70 parts of vinyl silicone oil, 40-50 parts of hydrogen-containing silicone oil, 23-30 parts of methyl silicone resin, 0.0005-0.0008 parts of catalyst and 0.0007-0.0009 parts of defoaming agent.

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