Low-valence metal complex with stable N-heterocyclic germanium carbene ligand as well as preparation method and application of low-valence metal complex

Abstract

The invention provides a low-valence metal complex with a stable N-heterocyclic germanium carbene ligand as well as a preparation method and application of the low-valence metal complex, and belongs to the technical field of metal organic chemistry. According to the low-valence metal complex, aza-germanium ring carbene is taken as a center, and a series of metal complexes are obtained by changing different substituent groups and different metals on a central ligand. The preparation method comprises the following steps: uniformly mixing an NHGe ligand, a metal precursor and DMA, and stirring and reacting at 60 DEG C for 24 hours to obtain the low-valence metal complex with the stable N-heterocyclic germanium carbene ligand. The preparation route is simple, the production efficiency is high, when a substituent group with large steric hindrance and strong electron donating is introduced to the ligand, the electron donating ability of the ligand can be improved, the oxidative addition ability of metal to inert bonds can be promoted, meanwhile, the reduction elimination ability of the metal can be promoted, the method can be used in cross coupling reaction, efficient activation of phenolic derivatives is achieved, and the method is suitable for industrial production. And the catalyst has higher catalytic efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal organic chemistry, and particularly relates to a kind of nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex and a preparation method and application thereof. BACKGROUND

[0002] In the past few decades, the field of transition metal chemistry has made significant progress by incorporating new multifunctional ligands to improve the reactivity, stability and selectivity of transition metal catalysts. Among them, N-heterocyclic carbene (NHC) and its related molecules have attracted widespread attention in the field of organometallic chemistry and homogeneous catalysis. The carbon compounds based on imidazole-2-acyl framework reported by Arduengo et al. have been proven to be very successful. Their synthetic use has shown no signs of weakening, and NHC ligands have established a foothold in the field of transition metal catalysis, while also opening up new horizons in the field of organic catalysis. The success of NHCs in transition metal catalysis is largely due to their ability to form strong σ-bonds with transition metals. In contrast, as a C atom bioisostere, Ge atom has a larger atomic radius and smaller electronegativity. The differences in these properties promote the development and exploration of NHGe, and some of the reactivity of integrating NHGe as ligands with metals is extremely attractive and challenging for synthetic chemistry, so the development of new NHGe ligands and metal complexes is crucial for the study of metal-catalyzed organic reaction transformations.

[0003] As early as 1992, the first N-alkyl-substituted NHGe-Ni complex was synthesized and isolated by chemist Wagner, due to the small steric hindrance of the alkyl group, its coordination mode is a 3-NHGe complexed nickel center or a 2-NHGe complexed carbonyl nickel compound, in 2001 and 2009, N-alkyl-substituted NHGe-Mo complex and NHGe-Ni complex were reported successively. For NHGe-Mo complex, its coordination mode is a 3-NHGe complexed carbonyl Mo center, while for NHGe-Ni complex, due to the small alkyl substituent on N, it is a 4-NHGe complexed Ni center. In 2021, Vladimir K. Cherkasov reported phenanthroline type N-aryl-substituted NHGe ligand coordinated iron and nickel complexes, and their complex forms are all 1-NHGe complexed carbonyl nickel / carbonyl iron compounds. In summary, the number of NHGe metal complexes is small, and due to the larger steric hindrance of N-aryl-substituted five-membered nitrogen heterocyclic germanium carbene, the electronic effect is also significantly different compared with N-alkyl-substituted five-membered nitrogen heterocyclic germanium carbene. Due to the differences in steric hindrance and electronic effect, the form of metal complexation will also be different, thereby affecting the reactivity of the metal complex itself, and the development of this aspect has been slow and challenging.

[0004] In recent years, cross-coupling reactions have developed rapidly. The traditional cross-coupling reaction (Suzuki or Kumada) catalyzed by palladium / nickel with phosphine ligand / nitrogen heterocyclic carbine ligand has excellent performance, but in view of the use of toxic phosphine ligand, it is urgent to develop a kind of alternative ligand to meet the development goal of environment-friendly chemistry. The application of nitrogen heterocyclic carbine ligand in the above field has been developed, but due to the need for pre-activation with base, the complexing efficiency and activity with metal are low, and the dosage for catalytic reaction is large, so it is very important to develop a more active ligand to solve these problems. The coordination atom in nitrogen heterocyclic germanium carbine ligand is replaced by germanium atom with larger radius than carbon atom, which has more electrons and stronger polarization ability, and is easier to coordinate with metal, so it is very important to develop this kind of ligand for organic synthesis field to solve the previous synthesis problems.

[0005] In summary, it can be seen that in the Kumada coupling reaction reported at present, the commonly used ligands such as nitrogen ligand, phosphine ligand and nitrogen heterocyclic carbine ligand have a wide range of applications, but there are problems of large amount of ligand and catalyst required, which limits the industrial application to a certain extent, so it is very important to further develop a kind of high-efficiency and low-catalyst dosage scheme to realize the industrial synthesis production. SUMMARY

[0006] In order to solve the above problems in the prior art, the present application provides a kind of nitrogen heterocyclic germanium carbine ligand stable low valence metal complex and its preparation method and application, the main purpose of the present application is to provide a kind of nitrogen heterocyclic germanium carbine metal catalyst based on the deficiency of existing nitrogen heterocyclic germanium carbine ligand metal complex as catalyst, which takes N-heterocyclic germanium carbine as center and is modified by different substituents. The present application has the advantages of large steric hindrance, simple synthesis route, high synthesis yield, strong electron donating ability, and can also be coordinated with different metals. The catalyst has high catalytic efficiency and small catalytic amount, can effectively adjust the electronic and steric effects of the catalyst, thereby effectively activating the inert C-O bond and promoting the problems such as oxidative addition and reductive elimination in cross-coupling reaction. It can be used for the synthesis of biaryl compounds with large conjugated structure and the like. Compared with the traditional nitrogen heterocyclic germanium carbine metal catalyst, the present application has higher catalytic activity.

[0007] In order to achieve the above purpose, the present application provides the following technical scheme: One of the technical schemes of the present application: The present application provides a kind of nitrogen heterocyclic germanium carbine ligand stable low valence metal complex, the low valence metal complex takes nitrogen heterocyclic germanium carbine as center; The structural formula of the nitrogen heterocyclic germanium carbine ligand stable low valence metal complex is any of the following: .

[0008] Further, the structural formula of the NHGe ligand is: M is selected from one or a combination of 3d metal, 4d metal or 5d metal, wherein the 3d metal is any one of Cr, Mn, Fe, Co, Ni or Cu, the 4d metal is any one of Mo, Ru, Rh or Pd, and the 5d metal is Ir or Au; L is selected from any one of cyclooctadiene, enone, olefin, alkyne, carbonyl, nitrogen heterocyclic carbene ligand, pyridine, bipyridine, trialkyl phosphine or triaryl phosphine; n is in the range of 1 to 4; X is selected from any one of chloride, bromide, iodide, triflate, tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate or trifluoroacetate; R is selected from any one of hydrogen, alkyl or aryl; M-1 to M-6 represent the number of nitrogen heterocyclic germanium carbene ligands and the number of additional ligands L required; M-7 to M-8 represent the metal complexed by the nitrogen heterocyclic germanium carbene ligand is connected by M-M metal bridge bond; M-9 to M-10 represent the metal complexed by the nitrogen heterocyclic germanium carbene ligand is connected by halogen bridge bond.

[0009] Further, the precursor of the low-valent metal complex stabilized by the nitrogen heterocyclic germanium carbene ligand is the NHGe ligand, and the structural formula of the NHGe ligand includes: .

[0010] Still further, the structural formula of the NHGe ligand includes: R is any one of hydrogen, alkyl or aryl, R 1 , R 2 and R 3 are any one of H, Me, Et, i-Pr, t-Bu, OMe, F, Cl, NMe2, SMe, Ph, PhCHCH3 or chiral PhCHCH3, wherein R 1 , R 2 and R 3 are the same or different; Ar 1 is any one of phenyl, naphthyl, anthryl, pyryl or heteroaryl.

[0011] Further, the structural formula of the low-valent metal complex stabilized by the nitrogen heterocyclic germanium carbene ligand includes: .

[0012] The second technical solution of the present application: the present application also provides a preparation method of the nitrogen heterocyclic germanium carbene ligand stabilized low-valence metal complex, comprising the following steps: After the NHGe ligand, the metal precursor and N,N-dimethylacetamide (DMA) are uniformly mixed, the mixture is stirred at 60 DEG C for 24 h, and the nitrogen heterocyclic germanium carbene ligand stabilized low-valence metal complex is obtained.

[0013] Further, the molar ratio of the NHGe ligand, the metal precursor and N,N-dimethylacetamide is (0.5-3):(0.5-1):(123-246).

[0014] Further, when R in the NHGe ligand is hydrogen, a new type of NHGe ligand is obtained, and the preparation method comprises the following steps: N,N'-di(aryl)ethylenediamine and tetrahydrofuran solvent are added into a double-necked round-bottom flask, n-butyllithium is added at-78 DEG C, the mixture is stirred at 30 DEG C for 5-12 h, after cooling to room temperature, germanium dichloride dioxane is added, the mixture is stirred at room temperature for 12-24 h, after filtering the insoluble solid, the filtrate is concentrated to 5 mL under vacuum, and the new type of NHGe ligand is obtained by recrystallization at-40 DEG C.

[0015] Further, the N,N'-di(aryl)ethylenediamine has the following structural formula: ; In the formula, R 1 , R 2 and R 3 are H, Me, Et, i-Pr, t-Bu, OMe, F, Cl, NMe2, SMe, Ph, PhCHCH3 or chiral PhCHCH3, wherein R 1 , R 2 and R 3 are the same or different.

[0016] Further, the molar ratio of the N,N'-di(aryl)ethylenediamine, n-butyllithium, germanium dichloride dioxane and tetrahydrofuran solvent is 1:(2-2.5):(2-2.5):49.

[0017] The third technical solution of the present application: the present application also provides application of the nitrogen heterocyclic germanium carbene ligand stabilized low-valence metal complex as a catalyst in catalyzing Kumada coupling reaction of aryl ether.

[0018] Further, the application is that, under the condition of nitrogen, the nitrogen heterocyclic germanium carbene ligand stabilized low-valence metal complex, aryl ether, phenyl magnesium bromide (1 M in THF) and toluene are sequentially added into a 15 mL pressure-resistant sealed tube, the sealed tube is closed, heated to 40 DEG C and reacted for 18 h.

[0019] Further, the molar ratio of the aryl ether, phenyl magnesium bromide and toluene is 1:1.5:47.

[0020] Compared with the prior art, the present application has the following advantages: The present application provides a kind of nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex, classic NHCs ligand stabilized metal complex has been reported a lot, in recent years, people have realized a lot of synthesis reactions based on the ligand stabilized metal complex catalysis, however, due to the existing NHCs metal complex as catalyst is used, often synthesis yield is low, post-processing is complex etc., and the precursor raw material of synthesis NHGe ligand is relatively scarce, so for the application research of NHGe ligand is less, it is not reported for the catalytic synthesis reaction after being used to stabilize metal. Therefore, the present application designs and synthesizes NHGe stabilized metal complex, and its catalytic application research has very important significance. The present application obtains a series of NHGe stabilized metal complex with simple synthesis route and excellent yield. The raw material in the preparation method provided by the present application is cheap and easy to obtain, the aryl ether can be derived from the aryl phenol compound widely existing in nature, and the source is wide. Moreover, the synthesis is simple, the reaction conditions are mild, the catalyst usage is low, the reaction conversion efficiency is high, the nitrogen heterocyclic germanium carbene metal catalyst is easy to synthesize, and the operation is convenient. And the present application is green and clean, does not need to use toxic, poor stability, harmful to the environment phosphine ligand, and the byproduct also has no environmental pollution and toxic effect. In addition, the preparation method in the present application has certain application value for environment and industrial production, and high-purity biaryl product can be obtained by column chromatography treatment, which is suitable for industrial production and application.

[0021] The nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex of the present application is used for catalyzing Kumada coupling reaction of aryl ether, has the advantages of simple and mild reaction conditions, high reaction efficiency, and excellent yield can also be obtained under low catalyst dosage. And compared with the catalysis of NHCs metal complex on the reaction, the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex of the present application has more excellent catalytic activity, which lays a foundation for further industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0023] Figure 1A nuclear magnetic resonance hydrogen spectrum of the nitrogen heterocyclic germa carbene ligand stabilized lower valent metal complex Ni3 prepared in Example 3 of the present invention; Figure 2 A nuclear magnetic resonance carbon spectrum of the nitrogen heterocyclic germa carbene ligand stabilized lower valent metal complex Ni3 prepared in Example 3 of the present invention; Figure 3 A nuclear magnetic resonance hydrogen spectrum of the nitrogen heterocyclic germa carbene ligand stabilized lower valent metal complex Ni8 prepared in Example 8 of the present invention; Figure 4 A nuclear magnetic resonance carbon spectrum of the nitrogen heterocyclic germa carbene ligand stabilized lower valent metal complex Ni8 prepared in Example 8 of the present invention; Figure 5 A nuclear magnetic resonance hydrogen spectrum of the nitrogen heterocyclic germa carbene ligand stabilized lower valent metal complex Ni11 prepared in Example 11 of the present invention; Figure 6 A nuclear magnetic resonance carbon spectrum of the nitrogen heterocyclic germa carbene ligand stabilized lower valent metal complex Ni11 prepared in Example 11 of the present invention; Figure 7 A nuclear magnetic resonance hydrogen spectrum of the nitrogen heterocyclic germa carbene ligand stabilized lower valent metal complex Rh1 prepared in Example 15 of the present invention; Figure 8 A nuclear magnetic resonance carbon spectrum of the nitrogen heterocyclic germa carbene ligand stabilized lower valent metal complex Rh1 prepared in Example 15 of the present invention. DETAILED DESCRIPTION

[0024] Reference will now be made in detail to various exemplary embodiments of the present invention, which are illustrated in the accompanying drawings. The following detailed description is not intended to limit the present invention, but rather to explain certain aspects, features, and embodiments of the present invention.

[0025] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. Additionally, for the purpose of reading the description of the present invention, the following terms are defined herein: It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It is to be further understood that the terms "comprising," "including," and "having" are inclusive and are to be interpreted in the manner intended by the applicant, i.e., to mean "including but not limited to." It is to be further understood that the terms "comprising," "including," and "having" are inclusive and are to be interpreted in the manner intended by the applicant, i.e., to mean "including but not limited to." It is to be further understood that the terms "comprising," "including," and "having" are inclusive and are to be interpreted in the manner intended by the applicant, i.e., to mean "including but not limited to."

[0026] All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains unless otherwise specifically defined herein. Although preferred methods and materials are described herein, any method and material similar or equivalent to those described herein is also possible. Documents mentioned in this specification are incorporated herein by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict between the content of the specification and that of any document incorporated herein by reference, the content of the specification prevails.

[0027] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0028] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean including, but not limited to.

[0029] The room temperature in the following examples of the present application refers to 23±2 ℃.

[0030] Example 1 A nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex has a structural formula as follows:

[0031] The reaction formula is as follows:

[0032] The preparation method of the above-mentioned nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex comprises the following steps: A dry magnetic stirrer was added into a 50 mL round-bottom flask, followed by sequentially adding 2,6-diisopropylphenyl nitrogen heterocyclic germanium carbene ligand L1 (2.0 equiv, 2 mmol), bis-1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), and DMA 20 mL. After sealing the round-bottom flask, the glove box was removed, and the mixture was stirred at 60 ℃ for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum. Then, 10 mL of n-hexane was added in the glove box, and brick red solid was precipitated. The solid was filtered, washed with n-hexane, and then dried to obtain the nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex Ni1 (brick red solid, 743 mg, yield: 70%).

[0033] The product detection data are as follows: 1 H NMR (600 MHz, THF- d8): δ 7.14-7.05 (m, 12H), 6.37 (s, 4H), 4.08 (s, 4H), 3.12-2.92 (m, 8H), 2.35-1.97 (m, 8H), 1.18-0.92 (m, 48H). 13 C NMR (100 MHz, C6D6): δ 144.7, 141.1, 126.0, 124.7, 122.4, 80.3, 36.8, 27.1, 25.4, 22.1. Example 2 An azaheterocyclic germa-cabine ligand stabilized low-valent metal complex has a structural formula as follows:

[0034] The reaction formula is as follows:

[0035] The preparation method of the azaheterocyclic germa-cabine ligand stabilized low-valent metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particles were added, followed by 2,4,6-trimethylphenyl azaheterocyclic germa-cabine ligand L2 (2.0 equiv, 2 mmol), bis-1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), and DMA 20 mL. After sealing the round-bottom flask, the glove box was removed, and stirring was performed at 60 °C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum, 10 mL of n-hexane was then added in the glove box, and brick red solid was precipitated. The solid was filtered, washed with n-hexane, and then dried to obtain the azaheterocyclic germa-cabine ligand stabilized low-valent metal complex Ni2 (brick red solid, 536 mg, yield: 60%).

[0036] The product detection data are as follows: 1 H NMR (400 MHz, C6D6): δ 6.84 (s, 8H), 6.52 (s, 4H), 4.31 (s, 4H), 2.20 (d, J = 6.0 Hz, 36H), 2.01 (d, J = 10.0 Hz, 4H), 1.82 (d, J = 8.4 Hz, 4H). 13C NMR (100 MHz, C6D6): δ 141.4, 133.1, 127.8, 122.7, 78.8, 29.9, 19.6, 17.2. Example 3 A nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex has a structural formula as follows:

[0037] The reaction formula is as follows:

[0038] The preparation method of the above-mentioned nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particles were added, followed by 2,6-diethylphenyl nitrogen heterocyclic germanium carbene ligand L3 (2.0 equiv, 2 mmol), bis-1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), and DMA 20 mL. After sealing the round-bottom flask, the glove box was removed, and stirring was carried out at 60°C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum, and then 10 mL of n-hexane was added in the glove box to precipitate brick-red solids. The solids were filtered, washed with n-hexane, and then dried to obtain the nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex Ni3 (brick-red solid, 475 mg, yield: 50%).

[0039] The product detection data are as follows: 1 H NMR (400 MHz, C6D6): δ 7.12-7.07 (m, 12H), 6.54 (s, 4H), 4.19 (s, 4H), 2.86-2.77 (m, 8H), 2.47-2.38 (m, 8H), 1.97 (d, J = 7.2 Hz, 4H), 1.80 (d, J = 8.0 Hz, 4H), 1.19 (t, J = 72 Hz, 24H). 13 C NMR (100 MHz, C6D6): δ 143.9, 140.5, 126.2, 126.2, 124.8, 80.4, 30.7, 24.9, 15.4. Example 4 A nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex has a structural formula as follows:

[0040] The reaction formula is:

[0041] The preparation method of the above-mentioned nitrogen heterocyclic germanium carbene ligand stabilized low-valence metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particles were added, followed by 2,6-dimethylphenyl nitrogen heterocyclic germanium carbene ligand L4 (2.0 equiv, 2 mmol), bis-1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), and DMA 20 mL. After sealing the round-bottom flask, the glove box was removed, and stirring was performed at 60°C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum, and then 10 mL of n-hexane was added in the glove box to precipitate brick-red solids. The solids were filtered, washed with n-hexane, and then dried to obtain the nitrogen heterocyclic germanium carbene ligand stabilized low-valence metal complex Ni4 (brick-red solid, 475 mg, yield: 73%).

[0042] The product detection data are as follows: 1 H NMR (400 MHz, C6D6):δ 7.02-6.95 (m, 12H), 6.44 (s, 4H), 4.24 (s,4H), 2.18 (s, 24H), 1.95 (d, J = 8.8 Hz, 4H), 1.79 (d, J = 8.4 Hz, 4H). 13 C NMR (100 MHz, C6D6):δ 143.9, 133.4, 127.1, 124.6, 122.5, 79.2,29.8, 17.3. Example 5 A nitrogen heterocyclic germanium carbene ligand stabilized low-valence metal complex, whose structural formula is:

[0043] The reaction formula is:

[0044] The preparation method of the above-mentioned nitrogen heterocyclic germanium carbene ligand stabilized low-valence metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particle was added, followed by 2,6-diisopropylphenyl azacyclogermane carbene ligand L5 (2.0 equiv, 2 mmol), bis 1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), and 20 mL of DMA. After sealing the round-bottom flask, the glove box was removed, and the mixture was stirred at 60 °C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum. Then, 10 mL of n-hexane was added in the glove box, and brick red solid was precipitated. The solid was filtered, washed with n-hexane, and then dried to obtain the azacyclogermane carbene ligand stabilized low-valent metal complex Ni5 (brick red solid, 596 mg, yield: 56%).

[0045] The product detection data are as follows: 1 H NMR (600 MHz, THF- d 8):δ6.94 (d, J = 7.2 Hz, 8H), 6.87-6.85 (m, 4H),3.47-3.45 (m, 4H), 3.37-3.32 (m, 8H), 3.01 (d, J = 7.8 Hz, 8H), 1.22-1.15 (m,8H), 1.11 (d, J = 6.6 Hz, 48H). 13 C NMR (150 MHz, THF- d 8):δ143.9, 142.2, 125.4, 123.1, 122.70, 81.17,51.98, 27.03, 23.31. Example 6 An azacyclogermane carbene ligand stabilized low-valent metal complex has the following structural formula:

[0046] The reaction formula is as follows:

[0047] The preparation method of the azacyclogermane carbene ligand stabilized low-valent metal complex includes the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particle was added, followed by 2,4,6-trimethylphenylgermyl azolide ligand L6 (2.0 equiv, 2 mmol), bis 1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), and DMA 20 mL. After sealing the round-bottom flask, the glove box was removed, and the mixture was stirred at 60 °C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum. Then, 10 mL of n-hexane was added in the glove box, and brick red solid was precipitated. The solid was filtered and washed with n-hexane. After the n-hexane was removed, the brick red solid was obtained as the azolide ligand stabilized low-valent metal complex Ni6 (brick red solid, 745 mg, yield: 83%).

[0048] The product detection data are as follows: 1 H NMR (400 MHz, C6D6):δ6.88 (s, 8H), 4.16 (s, 4H), 3.50 (s, 8H), 2.20(d, J = 5.6 Hz, 36H), 2.06 (d, J = 12.0 Hz, 4H), 1.81 (d, J = 8.0 Hz, 4H). 13 C NMR (100 MHz, C6D6):δ134.7, 132.6, 130.0, 128.5, 128.1, 79.0,53.3, 30.10, 19.4, 17.60. Example 7 An azolide ligand stabilized low-valent metal complex has the following structural formula:

[0049] The reaction formula is as follows:

[0050] The preparation method of the azolide ligand stabilized low-valent metal complex includes the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particle was added, followed by 2,6-diethylphenyl azaheterocyclic germanium carbene ligand L7 (2.0 equiv, 2 mmol), bis 1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), DMA 20 mL, the round-bottom flask was sealed, then the glove box was removed, and stirred at 60 ℃ for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum, then 10 mL of n-hexane was added in the glove box, and brick red solid was precipitated. The solid was filtered, washed with n-hexane, and then dried to obtain the azaheterocyclic germanium carbene ligand stabilized low-valent metal complex Ni7 (brick red solid, 743 mg, yield: 78%).

[0051] The product detection data are as follows: 1 H NMR (600 MHz, C6D6):δ7.10 (s, 12H), 4.00 (s, 4H), 3.54 (s, 8H),2.96-2.90 (m, 8H), 2.62-2.55 (m, 8H), 2.01-1.98 (m, 4H), 1.0-1.77 (m, 4H),1.27 (t, J = 7.2 Hz, 24H). 13 C NMR (150 MHz, C6D6):δ145.5, 142.0, 128.0, 126.2, 125.3, 80.5,56.2, 30.9, 24.6, 15.7. Example 8 An azaheterocyclic germanium carbene ligand stabilized low-valent metal complex has the following structural formula:

[0052] The reaction formula is as follows:

[0053] The preparation method of the azaheterocyclic germanium carbene ligand stabilized low-valent metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particle was added, followed by 2,6-dimethylphenylgermanium azacyclopentadiene ligand L8 (2.0 equiv, 2 mmol), bis-1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), and DMA 20 mL. After sealing the round-bottom flask, the glove box was removed, and the mixture was stirred at 60°C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum. Then, 10 mL of n-hexane was added in the glove box, and brick red solid was precipitated. The solid was filtered and washed with n-hexane. After the n-hexane was removed, the low-valent metal complex Ni8 stabilized by the azacyclopentadiene ligand (brick red solid, 748 mg, yield: 89%) was obtained.

[0054] The product detection data are as follows: 1 H NMR (400 MHz, C6D6):δ7.04 (d, J = 7.6 Hz, 7H), 7.00-6.94 (m, 5H),4.09 (s, 4H), 3.43 (s, 8H), 2.28 (s, 24H), 2.00-1.98 (m, 4H), 1.81-1.75 (m,4H). 13 C NMR (100 MHz, C6D6):δ145.5, 135.1, 127.9, 127.3, 123.8, 79.3,53.10, 30.0, 17.7. Example 9 A low-valent metal complex stabilized by an azacyclopentadiene ligand has the following structural formula:

[0055] The reaction formula is as follows:

[0056] The preparation method of the above-mentioned low-valent metal complex stabilized by an azacyclopentadiene ligand comprises the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particle was added, followed by 2-ethyl-6-methylphenylgermanium azacyclic carbene ligand L9 (2.0 equiv, 2 mmol), bis 1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), DMA 20 mL, the round-bottom flask was sealed, and then the glove box was removed, and stirred at 60°C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum, then 10 mL of n-hexane was added in the glove box, and brick red solid was precipitated. The solid was filtered, washed with n-hexane, and then dried to obtain the azacyclic germanium carbene ligand stabilized low-valent metal complex Ni9 (brick red solid, 449 mg, yield: 50%).

[0057] The product detection data are as follows: 1 H NMR (400 MHz, C6D6):δ7.11-7.01 (m, 12H), 4.19-3.93 (m, 4H), 3.61(s, 2H), 3.62-3.46 (m, 4H), 3.39-3.37 (m, 2H), 2.96-2.90 (m, 4H), 2.65-2.56(m, 4H), 2.26-2.20 (m, 12H), 2.10-1.75 (m, 8H), 1.32-1.21 (m, 12H). 13 C NMR (100 MHz, C6D6):δ146.1, 142.0, 136.1, 126.4, 125.1, 80.5,55.0, 24.6, 18.5, 14.8. Example 10 An azacyclic germanium carbene ligand stabilized low-valent metal complex has the following structural formula:

[0058] The reaction formula is as follows:

[0059] The preparation method of the azacyclic germanium carbene ligand stabilized low-valent metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic bar was added, followed by 2,6-diisopropylphenyl benzazepine germanium carbene ligand L10 (2.0 equiv, 2 mmol), bis 1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), DMA 20 mL, the round-bottom flask was sealed, then removed from the glove box, stirred at 60 °C for 24 h, after the reaction was completed, the DMA was concentrated to 2 mL under vacuum, then 10 mL of n-hexane was added in the glove box, the brick red solid was precipitated, the solid was filtered, washed with n-hexane, then the n-hexane was dried to obtain the low-valent metal complex Ni10 stabilized by benzazepine germanium carbene ligand (brick red solid, 975 mg, yield: 84%).

[0060] The product detection data are as follows: 1 H NMR (600 MHz, C6D6):δ7.29-7.16 (m, 12H), 6.68-6.62 (m, 4H), 6.42-6.40 (m, 2H), 6.28-6.27 (m, 2H), 4.95 (t, J = 7.8 Hz, 2H), 4.34-4.30 (m, 2H),3.41-3.36 (m, 2H), 3.27-3.22 (m, 2H), 3.09-3.05 (m, 2H), 2.74-2.70 (m, 2H),2.43-2.38 (m, 2H), 2.07-2.03 (m, 2H), 1.56-1.52 (m, 2H), 1.39-1.36 (m, 2H),1.31 (d, J = 7.2 Hz, 6H), 1.27 (d, J = 6.6 Hz, 6H), 1.21 (d, J = 7.2 Hz, 6H), 1.16(d, J = 6.6 Hz, 6H), 0.97-0.88 (m, 12H), 0.79 (d, J = 6.6 Hz, 6H), 0.50 (d, J = 6.6Hz, 6H). 13C NMR (150 MHz, C6D6): δ 146.7, 146.3, 145.3, 145.1, 138.1, 137.5, 127.2, 123.5, 123.1, 122.7, 117.3, 117.2, 110.4, 110.3, 83.0, 82.5, 33.0, 32.2, 28.3, 27.2, 27.2, 26.4, 26.2, 24.8, 24.8, 24.6, 24.2, 23.5, 23.3, 22.6, 21.3, 20.9, 12.9. Example 11 A nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex, whose structural formula is:

[0061] The reaction formula is:

[0062] The preparation method of the above-mentioned nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic sub was added, followed by 2,4,6-trimethylphenylbenzazacyclogermane carbene ligand L11 (2.0 equiv, 2 mmol), bis-1,5-cyclooctadiene nickel (1.0 equiv, 1 mmol), and DMA 20 mL. After sealing the round-bottom flask, it was removed from the glove box and stirred at 60°C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum, and then 10 mL of n-hexane was added in the glove box to precipitate brick red solid. The solid was filtered, washed with n-hexane, and then dried to obtain the nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex Ni11 (brick red solid, 983 mg, yield: 99%).

[0063] The product detection data are as follows: 1 H NMR (600 MHz, C6D6): δ 6.86-6.82 (m, 12H), 6.56-6.55 (m, 4H), 4.32 (s, 4H), 2.21 (s, 12H), 2.00 (s, 28H), 1.79-1.77 (m, 4H). 13 C NMR (150 MHz, C6D6): δ 141.0, 138.2, 135.5, 135.4, 129.3, 118.6, 109.2, 81.7, 31.1, 20.7, 17.9. Example 12 A nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex has a structural formula of:

[0064] The reaction formula is:

[0065] The preparation method of the above-mentioned nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex comprises the following steps: In a 25 mL round-bottom flask, dry magnetic sub was added, followed by 2,6-diisopropylphenylbenzazol germanium carbene ligand L10 (1.0 equiv, 0.5 mmol), Ni(CO)4 (1.0 equiv, 0.5 mmol), and then 10 mL of DMA was added, stirred at 60 °C for 24 h, after the reaction was completed, the DMA was concentrated to 2 mL under vacuum, then 5 mL of n-hexane was added in the glove box, and yellow solid was precipitated, the solid was filtered, washed with n-hexane, and then the n-hexane was dried to obtain the nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex Ni12 (yellow solid, 128 mg, yield: 40%).

[0066] The product detection data are as follows: 1 H NMR (600 MHz, C6D6):δ7.26-7.25 (m, 2H), 7.22-7.21 (m, 4H), 6.77(dd, J = 6.0, 3.6 Hz, 2H), 6.55 (dd, J = 6.0, 3.0 Hz, 2H), 3.02-2.97 (m, 4H),1.27 (d, J = 6.6 Hz, 12H), 1.00 (d, J = 7.2 Hz, 12H). 13 C NMR (150 MHz, C6D6):δ193.8, 146.2, 141.6, 135.2, 124.0, 119.7,111.1, 28.6, 24.8, 24.0. Example 13 A nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex has a structural formula of:

[0067] The reaction formula is:

[0068] The preparation method of the above-mentioned nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic sub-particles were added, followed by the addition of 2,6-diisopropylphenyl nitrogen heterocyclic germanium carbene ligand L1 (4.0 equiv, 2 mmol), octacarbonyldicobalt (1.0 equiv, 0.5 mmol), and DMA 10 mL. After sealing the round-bottom flask, the glove box was removed, and stirring was performed at 60°C for 24 h. After the reaction was completed, the DMA was concentrated to 2 mL under vacuum, and then 10 mL of n-hexane was added in the glove box to precipitate brick-red solids. The solids were filtered, washed with n-hexane, and then dried to obtain the nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex Co1 (black solid, 406 mg, yield: 40%).

[0069] The product detection data are as follows: 1 H NMR (400 MHz, C6D6):δ7.26-7.23 (m, 24H), 6.59 (s, 8H), 3.22-3.18(m, 16H), 1.45 (d, J = 6.8 Hz, 48H), 1.12 (d, J = 6.8 Hz, 48H). 13 C NMR (100 MHz, C6D6):δ201.55, 162.1, 149.0, 140.2, 135.5, 124.2,27.0, 25.1, 22.1. Example 14 A nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex, whose structural formula is:

[0070] The reaction formula is:

[0071] The preparation method of the above-mentioned nitrogen heterocyclic germanium carbene ligand stabilized low-valent metal complex comprises the following steps: In a 50 mL round-bottom flask, dry magnetic stir bar was added, followed by 2,6-diisopropylphenylgermylazacyclopentadiene ligand L1 (6.0 equiv, 3 mmol), tris(dibenzylideneacetone)dipalladium (1.0 equiv, 0.5 mmol), DMA 10 mL, the round-bottom flask was sealed, then removed from the glove box, stirred at 60 °C for 24 h, after the reaction was completed, the DMA was concentrated to 2 mL under vacuum, then 10 mL of n-hexane was added in the glove box, the olive green solid was precipitated, the solid was filtered, washed with n-hexane, then the n-hexane was dried to obtain the low-valent metal complex Pd1 (olive green solid, 408 mg, yield: 56%) stabilized by the azacyclopentadiene ligand.

[0072] The product detection data are as follows 1 H NMR (600 MHz, C6D6):δ7.29-7.20 (m, 18H), 6.55 (s, 6H), 3.21-3.09(m, 12H), 1.21-1.16 (m, 72H). Example 15 A low-valent metal complex stabilized by an azacyclopentadiene ligand has the following structural formula:

[0073] The reaction formula is as follows:

[0074] The preparation method of the above-mentioned low-valent metal complex stabilized by an azacyclopentadiene ligand comprises the following steps: In a 25 mL round-bottom flask, dry magnetic stir bar was added, followed by 2,6-diisopropylphenylgermylazacyclopentadiene ligand L1 (2.0 equiv, 1 mmol), rhodium catalyst (1.0 equiv, 0.5 mmol), DMA 10 mL, the round-bottom flask was sealed, then removed from the glove box, stirred at 60 °C for 24 h, after the reaction was completed, the DMA was concentrated to 2 mL under vacuum, then 5 mL of n-hexane was added in the glove box, the yellow solid was precipitated, the solid was filtered, washed with n-hexane, then the n-hexane was dried to obtain the low-valent metal complex Rh1 (yellow solid, 588 mg, yield: 56%) stabilized by the azacyclopentadiene ligand.

[0075] The product detection data are as follows 1H NMR (600 MHz, C6D6): δ 7.10-7.05 (m, 24H), 6.52 (s, 8H), 3.23-3.19 (m, 16H), 1.30-1.29 (d, J = 6.6 Hz, 48H), 1.14 (d, J = 7.2 Hz, 48H). 13 C NMR (150 MHz, C6D6): δ 145.1, 140.1, 127.9, 126.1, 123.68, 28.8,24.9, 24.9. Application Example 1 Effect of different metal nickel complexes as catalysts on coupling reaction of 2- methoxynaphthalene with Grignard reagent Reaction formula:

[0076] Under the condition of nitrogen, the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex Ni1 (0.004 mmol) prepared in Example 1, 2- methoxynaphthalene (0.2 mmol), phenyl magnesium bromide (1 M in THF, 0.3 mmol) and toluene (1 mL) were sequentially added into a 15 mL pressure-resistant sealed tube, the sealed tube was placed in an oil bath, heated to 40 ℃ for 18 h, after the reaction was completed, it was cooled to room temperature, water was added to quench the reaction, extracted with ethyl acetate for three times, then dried with anhydrous sodium sulfate, concentrated under vacuum, and separated by silica gel column chromatography column (eluent: petroleum ether) to obtain 2-phenylnaphthalene; Under the condition of nitrogen, the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex Ni1 (0.004 mmol) prepared in Example 1, 2- methoxynaphthalene (0.2 mmol), phenyl magnesium bromide (1 M in THF, 0.3 mmol) and toluene (1 mL) were sequentially added into a 15 mL pressure-resistant sealed tube, the sealed tube was placed in an oil bath, heated to 40 ℃ for 18 h, after the reaction was completed, it was cooled to room temperature, water was added to quench the reaction, extracted with ethyl acetate for three times, then dried with anhydrous sodium sulfate, concentrated under vacuum, and separated by silica gel column chromatography column (eluent: petroleum ether) to obtain 2-phenylnaphthalene; The results are as follows:

[0077] From the results, among the nitrogen heterocyclic carbene (germanium carbene) metal compounds investigated, under the above reaction conditions, the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex Ni1 can more efficiently catalyze the coupling of 2-methoxynaphthalene than the nitrogen heterocyclic carbene nickel compound.

[0078] Application Example 2 Effect of different metal complexes as catalysts on the coupling reaction of 9-methoxyanthracene with Grignard reagent Reaction formula:

[0079] Under the condition of nitrogen, the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex Ni1 prepared in Example 1 (0.004 mmol), 9-methoxyanthracene (0.2 mmol), phenyl magnesium bromide (1 M in THF, 0.3 mmol) and toluene (1 mL) were sequentially added to a 15 mL pressure-resistant sealed tube, the sealed tube was placed in an oil bath, heated to 40 ℃ for 18 h, and then cooled to room temperature. After the reaction was completed, water was added to quench the reaction, extracted with ethyl acetate three times, then dried with anhydrous sodium sulfate, concentrated under vacuum, and separated by silica gel column chromatography column (eluent: petroleum ether) to obtain 9-phenylanthracene; Under the condition of nitrogen, the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex Ni1 prepared in Example 1 (0.004 mmol), 9-methoxyanthracene (0.2 mmol), phenyl magnesium bromide (1 M in THF, 0.3 mmol) and toluene (1 mL) were sequentially added to a 15 mL pressure-resistant sealed tube, the sealed tube was placed in an oil bath, heated to 40 ℃ for 18 h, and then cooled to room temperature. After the reaction was completed, water was added to quench the reaction, extracted with ethyl acetate three times, then dried with anhydrous sodium sulfate, concentrated under vacuum, and separated by silica gel column chromatography column (eluent: petroleum ether) to obtain 9-phenylanthracene; The results are as follows:

[0080] From the results, among the nitrogen heterocyclic carbene (germanium carbene) metal compounds investigated, the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex Ni1 can more efficiently catalyze the coupling of 9-methoxyanthracene than the nitrogen heterocyclic carbene nickel compound under the above reaction conditions.

[0081] Application Example 3 Effect of different metal complexes as catalysts on the coupling reaction of 9-methoxyanthracene with Grignard reagent Reaction formula:

[0082] Under nitrogen, 15 mL of pressure-resistant sealed tube was added with the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex Ni1 prepared in Example 1 (0.004 mmol), 9-methoxyphenanthrene (0.2 mmol), phenylmagnesium bromide (1 M in THF, 0.3 mmol) and toluene (1 mL) in sequence, the sealed tube was sealed, then was placed in an oil bath, heated to 40 ℃ for 18 h, after the reaction was completed, it was cooled to room temperature, water was added to quench the reaction, extracted with ethyl acetate for three times, then dried with anhydrous sodium sulfate, concentrated under vacuum, and separated by silica gel column chromatography column (eluent: petroleum ether) to obtain 9-phenylphenanthrene; Under nitrogen, 15 mL of pressure-resistant sealed tube was added with Cat-1 (0.004 mmol), 9-methoxyphenanthrene (0.2 mmol), phenylmagnesium bromide (1 M in THF, 0.3 mmol) and toluene (1 mL) in sequence, the sealed tube was sealed, then was placed in an oil bath, heated to 40 ℃ for 18 h, after the reaction was completed, it was cooled to room temperature, water was added to quench the reaction, extracted with ethyl acetate for three times, then dried with anhydrous sodium sulfate, concentrated under vacuum, and separated by silica gel column chromatography column (eluent: petroleum ether) to obtain 9-phenylphenanthrene; The results are as follows:

[0083] From the results, among the nitrogen heterocyclic carbene (germanium carbene) metal compounds investigated, under the above reaction conditions, the nitrogen heterocyclic germanium carbene ligand stabilized low valence metal complex Ni1 can more efficiently catalyze the coupling of 9-methoxyphenanthrene than the nitrogen heterocyclic carbene nickel compound.

[0084] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A class of low-valence metal complexes stabilized by nitrogen-containing heterocyclic germanium carbene ligands, characterized in that, The low-valence metal complex is centered on nitrogen heterocyclic germanium carbene; The structural formula of the low-valence metal complex stabilized by the nitrogen heterocyclic germanium carbene ligand is any one of the following: 。 2. The low-valent metal complex stabilized by the nitrogen-heterocyclic germanium carbene ligand according to claim 1, characterized in that, In the structural formula: M is selected from one or any combination of 3d metals, 4d metals or 5d metals, wherein the 3d metal is any one of Cr, Mn, Fe, Co, Ni or Cu, the 4d metal is any one of Mo, Ru, Rh or Pd, and the 5d metal is Ir or Au. L is selected from any one of cyclooctadiene, enone, alkene, alkyne, carbonyl, nitrogen-containing heterocyclic carbene ligand, pyridine, bipyridine, trialkylphosphine, or triarylphosphine; The range of n is 1 to 4; X is selected from any one of chloride ion, bromide ion, iodide ion, trifluoromethanesulfonate ion, tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroantimonate ion, or trifluoroacetate ion; R is selected from any one of hydrogen, alkyl, or aryl.

3. The low-valent metal complex stabilized by the nitrogen-heterocyclic germanium carbene ligand according to claim 1, characterized in that, The precursor of the low-valence metal complex stabilized by the nitrogen-heterocyclic germanium carbene ligand is the NHGe ligand, and the structural formula of the NHGe ligand includes: 。 4. The low-valence metal complex stabilized by the nitrogen-heterocyclic germanium carbene ligand according to claim 3, characterized in that, In the structural formula of the NHGe ligand: R is any one of hydrogen, alkyl, or aryl, R 1 R 2 and R 3 It is any one of H, Me, Et, i-Pr, t-Bu, OMe, F, Cl, NMe2, SMe, Ph, PhCHCH3 or chiral PhCHCH3, wherein R 1 R 2 and R 3 Same or different; Ar 1 It is any one of phenyl, naphthyl, anthracene, bryyl, or heteroaryl.

5. The low-valent metal complex stabilized by the nitrogen-heterocyclic germanium carbene ligand according to claim 1, characterized in that, The structural formulas of the low-valence metal complexes stabilized by the nitrogen heterocyclic germanium carbene ligands include: 。 6. The method for preparing low-valent metal complexes stabilized by nitrogen-heterocyclic germanium carbene ligands as described in any one of claims 1 to 5, characterized in that, Includes the following steps: After the NHGe ligand, metal precursor and N,N-dimethylacetamide were mixed evenly, the mixture was stirred at 60 °C for 24 h to obtain the low-valence metal complex stabilized by the nitrogen heterocyclic germanium carbene ligand.

7. The preparation method according to claim 6, characterized in that, The molar ratio of the NHGe ligand, the metal precursor, and N,N-dimethylacetamide is (0.5–3):(0.5–1):(123–246).

8. The application of the low-valent metal complex stabilized by the nitrogen heterocyclic germanium carbene ligand as described in any one of claims 1 to 5 as a catalyst in the catalytic Kumada coupling reaction of aryl ethers.

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