Suzuki polycondensation catalyzed by palladium(II) diaminocarbene complexes in air

Abstract

FIELD: polymer chemistry.SUBSTANCE: production of π-conjugated polymers by Suzuki polycondensation. Synthesis method of π-conjugated polymers using the Suzuki method, in which the reaction is carried out under microwave irradiation, or with heating, in protic or aprotic solvents, their mixtures, or in two-phase systems, while the polycondensation reaction is carried out in an open system in air using acyclic and N-heterocyclic diaminocarbene complexes of palladium(II) as catalysts in an amount of 0.1-1.0 mol.%.EFFECT: development of a method of synthesis of π-conjugated polymers in air in the presence of a small amount of a catalyst, which is diaminocarbene complexes of palladium(II), which should lead to a significant improvement in electro-optical and other characteristicsof π-conjugated polymers.1 cl, 2 ex

Description

[0001] The invention relates to the chemistry of high-molecular compounds, namely, to a new method for producing π-conjugated polymers by Suzuki polycondensation using diaminocarbene (acyclic and N-heterocyclic) palladium(II) complexes in air as a catalyst.

[0002] An effective method for synthesizing π-conjugated polymers is the Suzuki cross-coupling reaction (Synthetic Communications, 1981, 11, 7, 513). This is a reaction of organoboron compounds with organic halides (or sulfonates), typically catalyzed by palladium compounds, less commonly by nickel (Macromolecules 2016, 49, 13, 4757-4762), in the presence of a base.

[0003] Patents describing the use of Suzuki polycondensation for the synthesis of π-conjugated polymers include data on the use of phosphine complexes of palladium(0) and palladium(II) as catalysts under an inert atmosphere. Although these complexes exhibit high catalytic activity, they are highly sensitive to oxygen, which poisons the catalyst.

[0004] For example, patent RU 2777171, "Molecular Polyfluorene Brushes with Polymethacrylic Acid Side Chains," mentions a method for synthesizing polyfluorene with side hydroxyl groups via Suzuki polycondensation. The authors use an inert atmosphere and a tetrakis(triphenylphosphine)palladium(0) catalyst to synthesize polyfluorenes. A similar system is also used in patent RU2800291, "Water-Soluble Molecular Polyfluorene Brushes Emitting White Light."

[0005] Patent RU 2641103 “Polymer compound and its application in photovoltaic devices”, as well as patent RU 2640810 “Polymer compound and its application in photovoltaic devices” contain only a general description of the Suzuki polycondensation reaction and a reference to publications considering the classical conditions of Suzuki polycondensation, primarily the inert atmosphere in the reaction vessel.

[0006] US Patent 7,524,923 "Suzuki Polycondensation for Preparing Aryl Polymers from Dihalide Monomers" also describes the Suzuki polycondensation process for synthesizing a wide range of polymer compounds. US Patent 005,777,070 A (Inbasekaran, Michael; Wu, Weishi; Woo, Edmund P. Process for Preparing Conjugated Polymers / / US Pat. Appl. Publ. (1998), US 005,777,070 A) describes the use of a phase-transfer catalyst, tricaprylmethylammonium chloride (Aliquat™), in carrying out the reaction in a two-phase toluene-water system.

[0007] US Patent 20090036623 (Tsuda, Yoshihiro; Morishita, Yoshii; Nomura, Satoyuki; Hoshi, Yousuke; Funyuu, Shigeaki. Progress for producing conjugated polymer / / US Pat. Appl. Publ. (2009), US 20090036625 A1) uses microwave radiation to accelerate the polycondensation reaction.

[0008] The main disadvantages of the classical method of synthesizing polymer compounds by Suzuki polycondensation are the need to use an inert atmosphere, as well as a large amount of palladium catalyst (1-10 mol%).

[0009] There are several studies where Suzuki polycondensation is carried out in air. The work (ACS Macro Lett. 2020, 9, 1167-1171) describes the synthesis using 1,1'-bis(di(tert-butyl)phosphine)ferrocene complex of palladium dichloride Pd(II)(dtbpf)Cl2 as a catalyst in a toluene-water system. Kolliphor EL surfactant was used as an interfacial agent. In the work (Angew. Chemie 2017, 129, 8551-8554), a mixture of palladium(II) acetate with sodium salt of 2-amino-4,6-dihydroxypyrimidine was used to synthesize water-soluble polyfluorenes. In the study (Green Chem. 2017, 19, 2973-2979), a solvent-free mechanochemical synthesis method was used to obtain linear and hyperbranched polyphenylenes, also using palladium(II) acetate as a catalyst. It is worth noting the high palladium content (0.5-10 mol%) in the reaction mixture.Residual palladium, which is difficult to remove, significantly degrades the luminescent properties of the polymer material (Macromolecules 2005, 38, 658-659). It is also known that even minor oxygen additions to the system at one of the numerous synthesis stages lead to uncontrollable polymerization. This affects both the behavior of the copolymers in solution and their electroluminescence, as the morphology of the solution-cast film is critical for the performance of the resulting light-emitting layer (J. Mater. Chem. Sci. 2018, 6, 1535-1542).

[0010] At the same time, diaminocarbene complexes of palladium(II) have proven themselves to be excellent catalysts for cross-coupling reactions (Chem. Soc. Rev. 2011, 40, 5151–5169; Accounts of Chemical Research 2024, 57, 22, 3343–3355), including the Suzuki reaction for the synthesis of diaryls and other small molecules, demonstrating high catalytic activity comparable to that of phosphine complexes of palladium. However, unlike phosphine complexes of palladium, diaminocarbene complexes of palladium(II) are stable in the presence of atmospheric oxygen.

[0011] These catalysts can be used in the synthesis of π-conjugated polymers by Suzuki polycondensation. This allows the reaction to be carried out in the presence of atmospheric oxygen (without an inert atmosphere), using small amounts of catalyst (<0.5 mol%), and performing the reaction in both protic and aprotic solvents, as well as mixtures of both, including two-phase systems. Small amounts of catalyst not only reduce the cost of polymer synthesis but also simplify and improve the purification of the product from traces of catalyst, which should lead to significant improvements in the electro-optical and other characteristics of π-conjugated polymers.

[0012] The objective of the proposed invention is to develop a method for synthesizing π-conjugated polymers in air in the presence of diaminocarbene complexes of palladium(II) (acyclic and N-heterocyclic) as catalysts in both protic and aprotic solvents, as well as in their mixtures and two-phase systems.

[0013] The above problem is solved by the proposed invention: the synthesis of π-conjugated polymers by the Suzuki method under microwave irradiation or heating, in protic or aprotic solvents, mixtures thereof, or in two-phase systems, characterized in that the polycondensation reaction is carried out in an open system in air using diaminocarbene complexes of palladium(II) (acyclic and N-heterocyclic) as catalysts. This work was supported by the Russian Science Foundation, project 23-43-00060.

[0014] The method for synthesizing polymer compounds proposed in this application possesses all the advantages of the classical Suzuki polycondensation method, but unlike it, the reaction occurs in air, and only 0.1-0.2 mol% palladium is used for the synthesis. The patent literature does not describe methods for producing polymer compounds by Suzuki polycondensation in an open system using such small amounts of catalyst.

[0015] The synthesis method involves conducting the Suzuki polycondensation reaction in an open system (in air) using diaminocarbene palladium(II) complexes (acyclic and N-heterocyclic) as catalysts under microwave irradiation or heating, in protic or aprotic solvents, mixtures of the two, or in two-phase systems. This method enables the production of π-conjugated polymers for LEDs, photodiodes, and other applications.

[0016] In general, the method can be described by the following diagram:

[0017]

[0018] or

[0019]

[0020] where:

[0021] one, two or more monomers of each type, different in structure, can participate in the reactions: 1a, 1b and 2a;

[0022] R 1 and R 2 - substituted or unsubstituted aryl, heteroaryl, vinyl;

[0023] Hal - Cl, Br, I;

[0024] Z - H, alkyl; moreover, if Z is H, then L is absent, and if Z is alkyl, then L is either absent or a bond;

[0025] Cat. - N-heterocyclic or acyclic diaminocarbene complex of palladium(II);

[0026] LR - a compound capable of coordinating to palladium and exhibiting reducing properties;

[0027] EG 1 - terminal group: substituted or unsubstituted aryl, heteroaryl, vinyl;

[0028] EG 2 - terminal group: substituted or unsubstituted aryl, heteroaryl, vinyl;

[0029] Y 1 - -В(ОН)2, boron;

[0030] Y 2 -Cl, Br, I;

[0031] EG 1 Y 1 may coincide with 1b;

[0032] Surf - interfacial catalyst / surfactant;

[0033] base - an organic or inorganic compound exhibiting basic properties, for example, Na2O3, K2CO3, Cs2CO3, acetates, phosphates and alcoholates of alkali metals, alkalis, trialkylamines;

[0034] MW - microwave radiation;

[0035] reflux - boiling with reflux condenser;

[0036] solvent - protic and aprotic solvents, or their mixtures, for example, water, ethanol, ethanol-water mixtures, two-phase toluene-water systems.

[0037] Examples of obtaining π-conjugated polymers

[0038] Suzuki polycondensation reaction in an ethanol-water mixture

[0039] Tetraethyl ((2,7-bis(4,4,5,5-tetramethyl-1,3,2-dio xaborolan-2-yl)-9H-fluorene-9,9-diyl)-bis(hexane-6,1-diyl))-bis(phosphonate) (107.8 mg, 0.1256 mmol), tetraethyl ((2,7-diboromo-9H-fluorene-9,9-diyl)-bis(hexane-6,1-diyl))-bis(phosphonate) (95.6 mg, 0.1250 mmol) and triphenylphosphine (5.0 mg, 0.019 mmol) are placed in a reaction vessel. Palladium(II) diaminocarbene complex (0.32 mg, 0.2 mol % (per halide group)) is dissolved in 0.5 ml of ethyl alcohol and added to the reaction mixture. A suspension of K2CO3 (276 mg, 2.0 mmol) in an ethanol-water mixture (3:1 ml) is then added to the mixture. The reaction vessel is placed in a microwave reactor. The reaction is carried out under microwave irradiation (power: 90 W) at 78°C for 2 hours.Then tetraethyl ((2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-fluorene-9,9-diyl)-bis(hexane-6,1-diyl))-bis(phosphonate) (8.6 mg in 1 ml ethyl alcohol, 0.01 mmol) is added and, after heating for another 1 h, the end group of 1-bromo-4-(tert-butyl)benzene 3.5 μl in 1.5 ml ethanol is added. Stirring and heating are continued for another 1.5 h; the resulting mixture is cooled to room temperature, then 5-10 ml of saturated aqueous NaCl solution is added. The organic phase is extracted with 3 portions of 15 ml CHCl3, filtered through 5 cm of aluminum oxide and dried over anhydrous sodium sulfate. The solution is passed through a metal-capture silica gel column and precipitated in ice-cold hexane. The precipitate is dissolved in CHCl3, passed through a Chromafil® Xtra PET-45 / 25 syringe filter, and precipitated in hexane. The yield of the product after purification is 81%.

[0040] Suzuki polycondensation reaction in a toluene-water mixture.

[0041] 1,4-Benzenediboronic acid bms(pinacolate) (84.65 mg, 0.2562 mmol), 2,7-dibromo-9,9-dihexyl-9H-fluorene (120.6 mg, 0.245 mmol), N-[6-(2,7-dibrocarbazol-9-yl)hexyl]-[(4-N',N'-diethylamino)-1,8-naphthalimide] (3.4 mg, 0.005 mmol)) and an appropriate amount of triphenylphosphine (1.9 mg, 0.007 mmol or 5.0 mg, 0.019 mmol) are charged into a reaction vessel. An appropriate amount of palladium(II) diaminocarbene complex (0.1-1 mol%) (per halide group) is dissolved in 1.5 ml of toluene and added to the reaction mixture. Methyltrioctylammonium chloride (Aliquat® 336) (10 mg, 0.019 mmol) in 1 ml of toluene, 1 ml of toluene, and 2 ml of 2 M aqueous K2CO3 solution are then added to the mixture. The reaction vessel is placed in a microwave reactor.The mixture was stirred under microwave irradiation (power: 80 W) at 92°C for 2 h, then 1,4-benzenediboronic acid bis(pinacolate) (10.3 mg in 1 mL toluene, 0.0625 mmol) was added, the mixture was heated for another 1 h and 4-bromophenyl ethyl ether (15 μL in 1 mL toluene, 0.1 mmol) was added. Stirring and heating were continued for another 1.5 h, the mixture was cooled to room temperature and poured into cold ethanol, 10-20 mL of saturated aqueous NaCl solution was added, the solution was partially evaporated, diluted with a small amount of water and extracted. The organic phase was extracted with 3 portions of 15 mL of CHCl3, filtered through 5 cm of aluminum oxide and dried over anhydrous sodium sulfate. The solution is passed through a metal-capture silica gel column and precipitated in cold methanol. The precipitate is dissolved in CHCl3, passed through a Chromafil® Xtra PET-45 / 25 syringe filter, and precipitated in cold methanol.When a precipitate forms during the first stage of precipitation in methanol, it is washed with water and methanol, dried, dissolved in CHCl3, passed through a metal-capture silica gel column, and precipitated in cold methanol. The precipitate is dissolved in CHCl3, passed through a Chromafil® Xtra PET-45 / 25 syringe filter, and precipitated in cold methanol. The product yield was up to 95%.

[0042] The resulting π-conjugated polymers of various structures for subsequent application in organic light-emitting diodes, photodiodes, and other fields were obtained by Suzuki polycondensation using diaminocarbene palladium(II) complexes as catalysts in an open system (without an inert atmosphere) in protic and aprotic solvents, as well as their mixtures and in two-phase systems under the action of microwave irradiation or heating. The synthesis utilized 0.2 mol% or less of palladium-containing catalyst—5-10 times less than in the described procedures.The optoelectronic and molecular weight characteristics of the obtained polymer compounds are not inferior to or superior (the maximum brightness of electroluminescence increases up to 3 times, the current efficiency increases up to 2 times) to the characteristics of polymer compounds obtained by the previously known and widely used Suzuki polycondensation method in an inert atmosphere using phosphine complexes of palladium.

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