Silver-n-heterocyclic carbene complex, method of preparation and use thereof

Abstract

The present application relates to a kind of silver-nitrogen heterocyclic carbene complex, preparation method and its application, belong to solid propellant energetic catalysis technical field.The present application is prepared with 1,3-dimethyl imidazole salt as ligand, with silver oxide or silver salt containing oxygen acid by metathesis reaction a series of silver-nitrogen heterocyclic carbene complex.Structure contains [Ag(NHC)2] + Cation, silver center and two nitrogen heterocyclic carbene ligand form linear coordination mode, which not only ensures the spatial exposure and electronic stability of silver active center, so that it can fully contact and efficiently act when catalyzing AP decomposition, and the ordered arrangement between anion-cation lays the foundation for building stable multi-level catalytic microenvironment, thereby significantly improving its catalytic efficiency and structural stability.

Description

Technical Field

[0001] This invention relates to a silver-nitrogen heterocyclic carbene complex, its preparation method, and its application, belonging to the field of energetic catalysis technology for solid propellants. Background Technology

[0002] Solid propellants, as the core energy carriers of rocket engines, directly determine the performance ceiling of the propulsion system through their combustion efficiency. Among them, composite solid propellants (CSPs) have become the most widely used solid propellants due to their high energy density, simple structure, and excellent safety performance. CSPs are typically composed of oxidizers, metallic fuels, binders, and functional additives. Among them, the oxidizer ammonium perchlorate (AP, NH4ClO4) accounts for as much as 70 wt%, so its thermal decomposition behavior directly determines the combustion performance of the propellant. It is known that the thermal decomposition of pure AP exhibits a "two-step exothermic" characteristic: 1) Low-temperature stage (LTD, 240–330 ℃): Proton transfer first occurs inside the crystal, generating NH3 and HClO4; 2) High-temperature stage (HTD, 330–500 ℃): NH3 sublimates and is further oxidized by HClO4 and its oxidation products (ClO3·, O2), resulting in concentrated exothermic reactions. However, both stages are affected by the high bond dissociation free energy of the gas-phase N–H bonds (99.4–107.6 kcal·mol⁻¹). - The limitations of ¹) result in high decomposition temperatures and dispersed heat release, which in turn raises the propellant ignition temperature, reduces combustion efficiency, and poses safety hazards. Therefore, there is an urgent need for a technical solution that, while maintaining a high AP content, can reduce its decomposition temperature, shorten the heat release range, and increase the concentration of heat release by introducing a specific catalyst.

[0003] Metal and metal oxide catalysts are among the earliest and most thoroughly studied types of combustion rate enhancers. Studies have revealed that unsaturated 3-phase transition metal ions... d Orbitals can act as electron transfer mediators, significantly promoting intramolecular ClO4 in AP molecules. - NH4 +The directed electron transfer process. Metal and metal oxide catalysts have the following problems, including: 1) The high surface energy of metals and metal oxides makes them prone to aggregation, affecting the stability of solid propellants; 2) The aggregation effect of metals and metal oxides significantly reduces the effective specific surface area of ​​the catalyst, reduces the atomic utilization rate of active sites, and is not conducive to the adjustment of combustion pressure index and the improvement of catalytic efficiency. Another relatively mature research is on novel combustion rate promoters based on ferrocene and its derivatives. Taking cattocin ([2,2'-bis(ethylferrocenyl)propane], GFP) as an example, these compounds usually have a clear Fe 2+ The active center and unique sandwich structure can promote the redox reaction of AP through the Fe active center, accelerating its thermal decomposition. A small amount can be added to regulate the combustion performance of the propellant. The core mechanism of both types of combustion rate enhancers relies on the participation of metal active sites in the AP decomposition reaction, thereby significantly improving their catalytic efficiency. Ferrocene and its derivatives have the following problems: 1) In solid propellant systems, ferrocene and its derivatives are prone to migration during long-term storage, which can easily lead to safety accidents; 2) Ferrocene and its derivatives only participate in the catalytic decomposition of AP through the Fe center and cannot regulate subsequent key steps. This single-path catalytic approach limits its further application in high-performance propellant systems.

[0004] In recent years, hindered Lewis acid-base pairs (FLPs) have been frequently applied to the activation of small molecules (including NH3, CH4, etc.). These systems consist of a sterically hindered Lewis acid and a Lewis base, which, due to steric repulsion, cannot form a classic Lewis acid-base pair, but can synergistically activate inert chemical bonds. Studies have confirmed that phosphine (as a Lewis basic site) and aluminum (as a Lewis acidic site) constitute an FLP, achieving efficient NH bond breaking at room temperature. Aldridge's research group showed that their constructed FLP can promote proton crossing in NH3 molecules through NH bond breaking. Leung et al. successfully achieved catalytic breaking of the NH bond in NH3 molecules by confining ruthenium within a zeolite cavity and forming an FLP with oxygen atoms on the zeolite framework. Currently, there are no reports of using FLPs in the field of solid propellants. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a silver-nitrogen heterocyclic carbene complex, its preparation method and its application.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A silver-nitrogen heterocyclic carbene complex with the chemical formula Ag(C5H8N2)2]NO3 or Ag(C5H8N2)2]ClO4,

[0008] The structural formula of Ag(C5H8N2)2]NO3 is: ; The structural formula of Ag(C5H8N2)2]ClO4 is: .

[0009] Preferably, the crystal structure parameters of the complex are as follows:

[0010] A method for preparing the silver-nitrogen heterocyclic carbene complex of the present invention includes the following steps: Preparation of silver carbene nitrate: 1,3-dimethylimidazolium iodide and AgNO3 were added to dichloromethane and stirred for more than 20 minutes. The intermediate product was obtained by filtration. The intermediate product was then reacted with Ag2O in dichloromethane for 3-5 hours. After the reaction was completed, the mixture was concentrated under reduced pressure and subjected to dichloromethane-acetone gas-phase diffusion crystallization for more than 7 days to precipitate rectangular strip-shaped crystals, yielding Ag(C5H8N2)2]NO3. Preparation of silver carbene perchlorate: 1,3-dimethylimidazolium chloride, AgClO4 and Ag2O were dissolved in acetonitrile and reacted for more than 24 hours. After filtration and concentration under reduced pressure, the mixture was diffused in the gas phase of acetonitrile-diethyl ether for more than 5 days to precipitate elongated crystals, yielding Ag(C5H8N2)2]ClO4.

[0011] Preferably, the molar ratio of 1,3-dimethylimidazolium iodide to AgNO3 is 1:1 to 1.2.

[0012] Preferably, the molar ratio of the intermediate product to Ag2O is 0.9~1:1.8~2.

[0013] Preferably, the molar ratio of 1,3-dimethylimidazolium chloride, AgClO4 and Ag2O is 1:1~1.2:0.5~1.

[0014] Application of a silver-nitrogen heterocyclic carbene complex, which is used as a combustion rate catalyst for ammonium perchlorate.

[0015] Preferably, the amount of the complex added is 1% to 10% of the mass of ammonium perchlorate.

[0016] A composite solid propellant comprises aluminum powder, ammonium perchlorate, a burning rate catalyst, a binder, a plasticizer, and a curing agent, wherein the burning rate catalyst is the silver-nitrogen heterocyclic carbene complex described in this invention.

[0017] Preferably, the adhesive is hydroxyl-terminated polybutadiene (HTPB), the plasticizer is diisooctyl sebacate (DOS), and the curing agent isophorone diisocyanate (IPDI).

[0018] Beneficial effects This invention utilizes 1,3-dimethylimidazolium salt as a ligand to prepare a series of silver-nitrogen heterocyclic carbene complexes via metathesis reactions with silver oxide or oxyacid silver salts. Their structures contain [Ag(NHC)2]. + The cation, with its silver center, forms a linear coordination mode with two nitrogen-containing heterocyclic carbene ligands. This structure not only ensures the spatial exposure and electronic stability of the silver active center, enabling it to fully contact and act efficiently during the catalytic decomposition of AP, but also lays the foundation for constructing a stable multi-level catalytic microenvironment through the ordered arrangement of the anion and cation, thereby significantly improving its catalytic efficiency and structural stability. Furthermore, the energetic anion ([ClO4))... - [NO3] - ), bonded by ionic bonds with [Ag(NHC)2] + Ion binding allows it to participate in oxidation reactions during thermal decomposition, releasing more gas and heat. Thus, during AP decomposition, it not only enhances the reaction rate through the synergistic catalytic effect of Ag···N FLP, but also significantly enhances the overall exothermic effect through the energy release of the anions themselves, achieving a synergistic improvement in energy output and catalytic activity. Attached Figure Description

[0019] Figure 1 This is a synthetic route diagram for the silver-nitrogen heterocyclic carbene complex in this invention.

[0020] Figure 2 The single-crystal structures of the silver-nitrogen heterocyclic carbene complexes in the embodiments of the present invention are shown in (a) Ag-NHC-NO3 and (b) Ag-NHC-ClO4. The atomic colors are: O-pink; Ag-green; N-blue; C-gray; H-white; Cl-purple.

[0021] Figure 3 The DSC heat flux curve (a) and apparent activation energy linearity graph (b) of AP in the example are shown.

[0022] Figure 4 The DSC heat flux curve (a) and apparent activation energy linearity graph (b) of GFP (catoxine) / AP in the examples are shown.

[0023] Figure 5 The DSC heat flow curve (a) and apparent activation energy linearity graph (b) of Ag-NHC-NO3 / AP in the examples are shown.

[0024] Figure 6 The DSC heat flow curve (a) and apparent activation energy linearity graph (b) of Ag-NHC-ClO4 / AP in the examples are shown.

[0025] Figure 7This is a comparison chart of the heat release of AP, GFP / AP, Ag-NHC-ClO4 / AP and Ag-NHC-NO3 / AP in the examples.

[0026] Figure 8 Transient combustion surface recording of Ag-NHC-ClO4-based solid propellant in the examples (a); infrared imaging of the flame of Ag-NHC-ClO4-based solid propellant (b); comparison of flame structure between Ag-NHC-ClO4-based solid propellant and control sample (c); comparison of burning rate-pressure curves between Ag-NHC-ClO4-based solid propellant and control sample (d); comparison of transient intensity of luminescent flame between Ag-NHC-ClO4-based solid propellant and control sample (e).

[0027] Figure 9 The figures show the burning rate-pressure comparison curves (a) of Ag-NHC-Ag2I3-based solid propellant and control sample in the examples; and the transient intensity comparison diagram of the luminescent flame of Ag-NHC-Ag2I3-based solid propellant and control sample (b).

[0028] Figure 10 Images showing the anti-migration properties of GFP and Ag-NHC-ClO4 in the examples. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments.

[0030] Example 1 Preparation of silver-nitrogen heterocyclic carbene complexes, the synthetic route is as follows: Figure 1 As shown.

[0031] The preparation method of carbene silver nitrate is as follows: (1) 1,3-dimethylimidazolium iodide (0.224 g, 1.0 mmol) and AgNO3 (0.170 g, 1.0 mmol) were added to 25 mL of dichloromethane and stirred at room temperature for 20 min. The intermediate product was obtained by filtration. (2) The intermediate product (0.15 g, 0.9425 mmol) obtained by filtration was reacted with Ag2O (0.44 g, 1.885 mmol) in 25 mL of dichloromethane for 4 h. After concentration under reduced pressure, the product was subjected to dichloromethane-acetone gas phase diffusion crystallization. After 7 days, rectangular strip-shaped crystals were precipitated. The chemical formula is [Ag(C5H8N2)2]NO3 (denoted as Ag-NHC-NO3). m w = 362.13 (yield 0.1 g, total yield 55.23%).

[0032] The preparation method of silver carbene perchlorate is as follows: 1,3-dimethylimidazolium chloride (0.13259 g, 1.0 mmol), AgClO4 (0.20732 g, 1.0 mmol), and Ag2O (0.11587 g, 0.5 mmol) were dissolved in 10 mL of acetonitrile. After reacting for 24 h, the mixture was filtered and concentrated under reduced pressure to obtain a reddish-brown powder. After 5 days of gas-phase diffusion in acetonitrile-ether, elongated crystals precipitated. The chemical formula is [Ag(C5H8N2)2]ClO4 (denoted as Ag-NHC-ClO4). m w = 399.58, yield 0.12 g, based on C, total yield 60.06%.

[0033] The structural characterization of the obtained compound crystals using single-crystal X-ray diffraction (SC-XRD) yielded the following single-crystal visualization results: Figure 2 As shown in the figure, both compounds contain the same [Ag(NHC)2]. + The cation, with its silver center, forms a linear coordination mode with two nitrogen-containing heterocyclic carbene ligands, and the energetic anion ([ClO4)). - [NO3] - ), bonded by ionic bonds with [Ag(NHC)2] + Ion bonding. The nitrogen atom adjacent to the carbene carbon (as a Lewis basic site) can combine with the silver atom (as a Lewis acidic site) to form a fibrillated polycyclic aromatic hydrocarbon (FLP). The spatially confined silver site and nitrogen ligand can act as dual active sites, synergistically activating the NH bond in the alumina (AP) and promoting the thermal decomposition reaction of AP. Furthermore, the silver center in the Ag(I)-NHC complex is almost completely exposed, maximizing its contact with the AP molecule, thus overcoming the inaccessibility of the metal center caused by the steric hindrance of the side chain in captosine.

[0034] The crystal structure parameters of the complex are shown in Table 1 below.

[0035] Table 1

[0036] R 1 = Σ F o - F c / Σ F o . wR 2 = [Σw ( F o 2 - F c 2 ) 2 / Σ w ( F o 2 ) 2 ] 1 / 2 .

[0037] Example 2 This embodiment analyzes the combustion performance of AP, GFP / AP, Ag-NHC-NO3 / AP, and Ag-NHC-ClO4 / AP.

[0038] Accurately weigh the sample according to the mass ratio of combustion rate catalyst (GFP, Ag-NHC-NO3, Ag-NHC-ClO4):AP = 5:95, with a total sample volume of 20 mg. Add 1 to 2 drops of methanol as a co-solvent each time, and grind thoroughly at room temperature for 20 minutes to mix evenly, thus obtaining the required mixture.

[0039] At a heating rate of 10 K / min, such as Figure 3 As shown: In the low-temperature region (≤250℃), AP crystal transformation can be stably induced with a significant endothermic peak; in the temperature range of 250~500℃, the DSC curve of AP shows two distinct exothermic peaks, at 317℃ and 416℃ respectively. Adding the combustion rate catalyst GFP as a control reduces the thermal decomposition temperature of AP to 317℃ and 350℃ respectively, clearly promoting the shift of the high-temperature decomposition peak of AP to lower temperatures. The thermal decomposition of the AP composite system after adding the combustion rate accelerators Ag-NHC-NO3 and Ag-NHC-ClO4 is as follows... Figure 5 and Figure 6 As shown: the heat flow curves of AP / Ag-NHC-NO3 and AP / Ag-NHC-ClO4 both exhibit a single, sharp exothermic peak, with the exothermic temperature concentrated at ~270℃, which is nearly 140℃ lower than that of pure AP. Their AP catalytic efficiency is significantly improved compared to GFP. The apparent activation energy was calculated simultaneously (…). E a) The calculated value is: Ag-NHC-NO3 / AP (113.57 kJ·mol⁻¹) -1 ) and Ag-NHC-ClO4 / AP (112.74 kJ·mol -1 All were lower than GFP / AP (145.5 kJ·mol⁻¹). -1 ) and pure AP (199.04 kJ mol) -1This indicates that such complexes effectively lower the energy barrier of the AP thermal decomposition reaction.

[0040] Furthermore, the heat release of AP increased significantly after adding the burning rate accelerators Ag-NHC-NO3 and Ag-NHC-ClO4. Figure 7 The exothermic reactions of Ag-NHC-ClO4 / AP, Ag-NHC-NO3 / AP, GFP / AP, and pure AP were compared. The results showed that the exothermic reactions of Ag-NHC-NO3 and Ag-NHC-ClO4 mixed with AP were 1459 J g, respectively. -1 and 1488 J g -1 Much larger than GFP (703 J g) -1 ) and the heat release of AP (606 J g) -1 ).

[0041] Comprehensive data show that Ag-NHC-NO3 and Ag-NHC-ClO4, as burning rate accelerators, possess the dual advantages of strong exothermic reaction at low temperatures and low activation energy, verifying their engineering feasibility as high-efficiency burning rate accelerators in solid propellants.

[0042] Example 3 Based on the excellent thermocatalytic properties of Ag-NHC-NO3 and Ag-NHC-ClO4, a solid propellant was simulated using Ag-NHC-ClO4 as an example to test its actual burning rate performance.

[0043] A simulated composite solid propellant was prepared using a spray granulation process with the following formulation: aluminum powder (Al): AP: Ag-NHC-ClO4: hydroxyl-terminated polybutadiene (HTPB): diisooctyl sebacate (DOS): isophorone diisocyanate (IPDI) as raw materials in a ratio of 18:34:33:11.6:2.5:0.9. Methanol was used as the solvent, and the mixture was cured at 70°C for one week to obtain the final product. A control sample was prepared without the addition of a burn-up accelerator.

[0044] The combustion performance of the prepared solid propellant was tested in a sealed combustion chamber under an argon atmosphere, and the entire process was recorded by a high-speed camera. Compared with the control sample, the catalytic sample exhibited more intense combustion characteristics, with significantly increased flame brightness and a markedly expanded combustion zone. Figure 8 a and 8b). Figure 8 c. Further comparison of the flame structure of the control sample and Ag-NHC-ClO4 / AP propellant showed that the control sample exhibited an axially contracting flame, while the Ag-NHC-ClO4 / AP propellant showed a significant radial expansion characteristic, with a brighter flame and a wider combustion range, reflecting a more intense combustion process and more vigorous reaction behavior, which fully demonstrates that Ag-NHC-ClO4-based solid propellant has better combustion performance.

[0045] Infrared images of the flame were recorded using an infrared thermal imager, and the evolution curve of flame radiation intensity during propellant combustion was obtained, such as... Figure 8 As shown in e, compared with the control sample ( Figure 8 d) The Ag-NHC-ClO4 / AP composite material exhibits a larger flame radiation field area, consistent with high-speed camera observations. The Ag···NHC FLP in the Ag-NHC-ClO4 structure not only promotes AP decomposition and rapidly releases a large amount of gaseous products, but also contains energetic anions [ClO4]. - It also helps to release more heat energy, thereby improving the combustion performance of solid propellants.

[0046] Within the operational pressure range of 0.5-2.5 MPa, the burning rate of solid propellant r (mm·s) -1 The increase in ( ) is quantified by the system. Saint-Robert Law r = ap n The fitting results show that the burning rate coefficient of Ag-NHC-ClO4 based solid propellant is... a The pressure index jumped from 2.67 to 4.75. n The efficiency was reduced from 0.45 to 0.27, achieving a dual optimization of "high burning rate" and "low sensitivity." At 2.5 MPa, the burning rate of the Ag-NHC-ClO4-based solid propellant can reach 6.08 mm·s. -1 Compared with the control sample (4.12 mm·s) -1 It increased by 42% ( Figure 9 a). This gain directly lays the energy foundation for rapid response and precise delivery of rockets / missiles. Furthermore, the combustion duration of the Ag-NHC-ClO4-based solid propellant was 8.94 s, significantly shorter than the control sample (>15 s), clearly demonstrating a significant improvement in the propellant's burning rate. Figure 9 b).

[0047] Example 4 To further evaluate the safety of Ag-NHC-ClO4 as a combustion rate accelerator, its anti-migration properties were assessed, such as... Figure 10 As shown: After 24 days of storage, unlike GFP, the interface in the Ag-NHC-ClO4 tube remained clear with only slight discoloration and a migration distance of only 0.2 cm, indicating that Ag-NHC-ClO4 has good migration properties.

[0048] In this invention, the monomolecular silver-nitrogen heterocyclic carbene complexes Ag-NHC-ClO4 and Ag-NHC-NO3 exhibit a "double NHC ligand-central silver" encapsulation configuration, inhibiting silver nucleus aggregation while retaining a high-exposed surface area at the silver center, thus increasing the probability of effective collisions between the silver active sites and AP molecules. The silver-nitrogen heterocyclic carbene complex incorporates Ag···N FLP, with the Ag site providing Lewis acidity and the N site providing Lewis basicity. Used as a combustion rate catalyst for AP, it significantly promotes the breaking of NH bonds in the AP structure, leading to a significant reduction in the initial decomposition temperature of AP. Only 5% of the addition can lower the high-temperature decomposition initiation temperature of AP to 146℃; it also allows for precise control of the decomposition process, merging the originally segmented exothermic peaks into a single narrow peak, resulting in a concentrated burst of instantaneous high heat and a doubling of energy utilization. Furthermore, the energetic anion (ClO4) on the ligand... - / NO3 - During the decomposition phase, it releases additional heat instantaneously, further accelerating the AP exothermic process. This burning rate catalyst exhibits excellent resistance to migration; during the aging phase, the interface remains clear with minimal color change, and migration is unlikely to occur during long-term storage, thus improving the safety of solid propellants.

[0049] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A silver-nitrogen heterocyclic carbene complex, characterized in that: The chemical formula is Ag(C5H8N2)2]NO3 or Ag(C5H8N2)2]ClO4. The structural formula of Ag(C5H8N2)2]NO3 is: ； The structural formula of Ag(C5H8N2)2]ClO4 is: 。 2. The silver-nitrogen heterocyclic carbene complex as described in claim 1, characterized in that: The crystal structure parameters of the complex are as follows:

3. A method for preparing the silver-nitrogen heterocyclic carbene complex according to claim 1 or 2, characterized in that: The method steps include: 1,3-Dimethylimidazolium iodide and AgNO3 were added to dichloromethane and reacted for more than 20 minutes. The intermediate product was obtained by filtration. The intermediate product was then reacted with Ag2O in dichloromethane for 3-5 hours. After the reaction was completed, the mixture was concentrated under reduced pressure and subjected to dichloromethane-acetone gas-phase diffusion crystallization for more than 7 days to precipitate rectangular strip-shaped crystals, yielding Ag(C5H8N2)2]NO3. 1,3-Dimethylimidazolium chloride, AgClO4, and Ag2O were dissolved in acetonitrile and reacted for more than 24 hours. The mixture was then filtered, concentrated under reduced pressure, and diffused in the acetonitrile-diethyl ether gas phase for more than 5 days to precipitate elongated crystals, yielding Ag(C5H8N2)2]ClO4.

4. The method for preparing a silver-nitrogen heterocyclic carbene complex as described in claim 3, characterized in that: The molar ratio of 1,3-dimethylimidazolium iodide to AgNO3 is 1:1 to 1.

2.

5. The method for preparing a silver-nitrogen heterocyclic carbene complex as described in claim 3, characterized in that: The molar ratio of the intermediate product to Ag2O is 0.9~1:1.8~2.

6. The method for preparing a silver-nitrogen heterocyclic carbene complex as described in claim 3, characterized in that: The molar ratio of 1,3-dimethylimidazolium chloride, AgClO4 and Ag2O is 1:1~1.2:0.5~1.

7. An application of the silver-nitrogen heterocyclic carbene complex according to claim 1 or 2, characterized in that: The complex is used as a combustion rate catalyst for ammonium perchlorate.

8. The application as described in claim 7, wherein the amount of the complex added is 1% to 10% of the mass of ammonium perchlorate.

9. A composite solid propellant, characterized in that: It includes aluminum powder, ammonium perchlorate, a combustion rate catalyst, a binder, a plasticizer, and a curing agent, wherein the combustion rate catalyst is the silver-nitrogen heterocyclic carbene complex as described in claim 1 or 2.

10. A composite solid propellant as described in claim 9, characterized in that: The adhesive is hydroxyl-terminated polybutadiene, the plasticizer is diisooctyl sebacate, and the curing agent is isophorone diisocyanate.

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