JPH07196780A - Poly(alkyl substituted-2,5-pyrimidin-diyl) and its production - Google Patents

Abstract

PURPOSE:To obtain the subject pyrimidin-diyl having solubilities in various solvents, a good adhesion property to a metal surface of an electrode and to a base plate, a good film forming property and capable of manifesting an electric conductivity by n-type doping, by subjecting a condensation polymerization by adding a zero valent nickel complex as a dehalogenating agent to a specific pyrimidine compound. CONSTITUTION:This pyrimidin-diyl having a repeating unit of a substituted-2,5- pyrimidin-diyl of the formula (each one of R1 and R2 is H, a lower alkyl and at least one of R1 and R2 is an alkyl) and an average molecular degree (n) of 10-1000, is obtained by subjecting a condensation polymerization of (A) 2, 5-dihalogeno-4 and/or 6-alkyl substituted-pyrimidine by adding (B) a zero valent nickel complex as a dehalogenating agent. Further, as the component (B), e.g. bis(1,5-cyclooctadiene) nickel is preferably used.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel pi-conjugate which is soluble in an organic solvent, has excellent shapeability, has heat resistance, has high adhesion to a substrate surface, and has good n-type doping ability. The present invention relates to a conductive polymer and a method for synthesizing it.
The pi-conjugated conductive polymer has characteristic physical and electrical characteristics and is useful for various devices such as batteries, display elements, light emitting elements, photoelectric conversion elements, sensors, OPC electrodes, modified electrodes, solar cells, and transistors. is there.

[0002]

2. Description of the Related Art In a pi-conjugated conductive polymer, a p-type organic conductor in which holes play a major role in electrical conduction when oxidized by a p-type dopant or the like and electrons in which electrons are electrically conducted by reduction by an n-type dopant or the like. There is an n-type organic conductor that plays a leading role. Examples of the former include poly (2,5-thienylene),
There are many poly (2,5-pyrrolylene) s, poly (paraphenylenevinylenes), etc., and research and development are progressing, but there are few examples of the latter conductive polymers.

An n-type organic conductor, which is an electron conductor, can be expected to be used as an electron transport layer and is expected to be widely used for a light emitting device, an OPC electrode, etc., so that its development has been earnestly desired. .

Chemistry Letters, 1988, 1
Poly (2,5-pyrimidinediyl) described on pages 53 to 154 is one of the few examples of n-type organic conductors. When a pyrimidine ring is introduced into the main chain of a polymer, the nitrogen atom in the pyrimidine ring is electron-withdrawing, so that the polymer compound easily becomes n-type conductive. However, the non-alkyl-substituted poly (2,5-pyrimidinediyl) synthesized here is limited to a special solvent such as concentrated hydrochloric acid, which can dissolve it, and has poor adhesion to the electrode. There has been a problem that the use in electronic devices used as thin films is limited in terms of workability.

[0005]

DISCLOSURE OF THE INVENTION The present invention is soluble in various solvents, has good adhesion to the metal surface of an electrode and a substrate, is excellent in film-forming property, and is electrically conductive by n-type doping. It is an object to obtain a novel organic conductor exhibiting conductivity, a method for producing the same, and an electroluminescent material using the same.

[0006]

SUMMARY OF THE INVENTION The present inventors have described the above n
As a result of earnest research to solve the problems of the organic electroconductive material poly (2,5-pyrimidinediyl), the pyrimidine ring of poly (2,5-pyrimidinediyl) represented by the general formula (1) The present inventors have found that a polymer having a repeating unit in which an alkyl substituent is introduced achieves the above object, and have reached the present invention.

That is, the present invention has the general formula (1)

[Chemical 2] (Wherein R ₁ and R ₂ each represent hydrogen or a lower alkyl group, and at least one of R ₁ and R ₂ is an alkyl group), and a substituted-2,5-pyrimidinediyl represented by , Dehalogenation of zero-valent nickel complex to poly (alkyl-substituted-2,5-pyrimidinediyl) and 2,5-dihalogeno-4 and / or 6-alkyl-substituted-pyrimidine having an average degree of polymerization n in the range of 10 to 1000 A poly (alkyl-substituted-2,5-pyrimidinediyl) production method in which a polycondensation reaction is performed in addition to an agent, and n of the poly (alkyl-substituted-2,5-pyrimidinediyl)
The present invention relates to an electroluminescent material using a conductive polymer.

There are several methods for producing the poly (alkyl-substituted-2,5-pyrimidinediyl) of the present invention, and the method is not particularly limited. Examples thereof include a method of polymerizing via a Grignard reagent, an oxidative polymerization method using an oxidizing agent, and a method of dehalogenating polycondensation using a zero-valent nickel complex.

As a method for polymerizing via the Grignard reagent, for example, Chemistry Letters 353-35.
There is a method published on page 6 (1977).

Dihalogeno-magnesium was added to magnesium in an ether solvent such as tetrahydrofuran or diethyl ether.
A Grignard reagent was synthesized by reacting with alkyl-substituted-pyrimidine, and this reagent and dihalogeno-alkyl-substituted-pyrimidine were mixed with dichloro [1,3-bis (diphenylphosphino) propane] nickel, tetrakis (triphenylphosphine) nickel, bis (1 , 5-Cyclooctadiene) nickel in the presence of a catalyst.

As the oxidative polymerization method using an oxidizing agent, for example, the Cobasic method described in Tetrahydron Letters, p. 472 (1962) is generally and easily used. That is, using a Lewis acid such as aluminum trichloride or iron trichloride as a catalyst,
This is a condensation reaction using cupric chloride as an oxidizing agent. This method has a low degree of polymerization and may be branched or crosslinked.

Among these, in terms of yield, molecular weight of the polymer, etc.,
Chemistry Letters, 1988, 153-154
The method of dehalogenating polycondensation using the zero-valent nickel complex described on page is efficient and preferable. This reaction is carried out by, for example, adding 1 mol or more of bis (1,5-cyclooctadiene) nickel, bis (2,2′-bipyridyl) nickel to the raw material in a reaction vessel in an inert atmosphere,
A zero-valent nickel complex such as (2,2′-bipyridyl) (1,5-cyclooctadiene) nickel or tetrakis (triphenylphosphine) nickel is added. Depending on the nickel complex used, in order to improve reactivity,
Ligands such as 2,2'-bipyridyl and phosphine may be added. Then, N, N-dimethylformamide,
Toluene or the like is added as a solvent. Finally, a raw material such as 2,5-dihalogeno-alkyl-substituted-pyrimidine dissolved in a solvent is added, and the mixture is stirred and heated. The heating temperature is preferably 60 ° C. at which the nickel complex is not decomposed, and the heating time is preferably 12 hours or more. The reaction solution is poured into aqueous ammonia, and the obtained substance is washed with aqueous ammonia, methanol and the like.

According to this polymerization method, most of the 2,5-dihalogeno-alkyl-substituted pyrimidines can be polycondensed and the desired product can be synthesized in good yield.

The synthesis of the monomer 2,5-dihalogeno-alkyl-substituted-pyrimidines is, for example, commercially available 2
When -hydroxy-4,6-dimethylpyrimidine hydrochloride is used as a starting material, it is neutralized with a suitable base to give 2-hydroxy-4,6-dimethylpyrimidine, and bromine or N
Bromination of the 5-position with -bromosuccinimide or the like and bromination of the hydroxyl group with phosphorus tribromide, phosphorus oxybromide or the like give 2,5-dibromo-4,6-dimethylpyrimidine. Thus, the dihalogenopyrimidine derivative can be obtained.

This poly (2,5-pyrimidinediyl) derivative has chloroform, dimethylsulfoxide, tetrahydrofuran, benzene, cresol, N, etc. when the alkyl chain substituted on the pyrimidine ring has 1 to 4 carbon atoms. -Being soluble in various organic solvents such as methylpyrrolidone, the film formation becomes extremely easy. For example, a film obtained by applying this solution onto a glass plate or the like by spin coating or the like and drying it can be obtained as a flexible film by peeling from the glass plate or the like. These films are stable even when left in the air.

This poly (alkyl-substituted-2,5-pyrimidinediyl) can generate a large number of electrons in the polymer by adding an electron donor, and the electrons serve as carriers to achieve high conductivity.

This doping method includes a chemical method in which a reducing agent is brought into direct contact with a polymer in a solution or in a gas phase, and a method in which it is electrochemically reduced (doping).

Chemical n-type doping, for example, is accomplished by reacting poly (alkyl-substituted-2,5-pyrimidinediyl) with a reducing agent such as sodium naphthalenide or butyllithium in solution. It is preferable that these reducing agents have large reducing power.

In the electrochemical n-type doping, poly (alkyl-substituted-2,5-pyrimidinediyl) is supported on an electrode, and a negative potential is applied in an electrolytic solution of (CH ₃ ) ₄ NBF ₄ , LiBF ₄ or the like. By doing so, the cations in the electrolytic solution are added to the polymer to be achieved.

The n-type doped state of poly (alkyl-substituted-2,5-pyrimidinediyl) is more stable than conventional n-type conductive polymers.

As described above, poly (alkyl-substituted-2,5-pyrimidinediyl) is characterized by being a solvent-soluble n-type organic conductor.

Further, by utilizing this solubility, when a solution of the present polymer is coated on a conductive film of a single-layer electroluminescent device to form an electron transport layer, the emission brightness is higher than that of the single-layer electroluminescent device. Can be improved.

[0023]

The poly (alkyl-substituted-2,5-pyrimidinediyl) of the present invention is insoluble in an organic solvent and therefore has a problem in shapeability as a polymer and adhesion to an electrode or a substrate surface, but as a polymer. Poly (2,5-) with excellent performance
Solubility in an organic solvent is imparted by introducing a lower alkyl group having 1 to 4 carbon atoms into the pyrimidine ring of (pyrimidinediyl).

When poly (2,5-pyrimidinediyl) without alkyl substitution is dissolved in hydrochloric acid or the like and applied on a substrate such as glass and dried, a part of the film is peeled off when the film thickness is large and film formation is difficult. However, since the polymer of the present invention dissolves in an organic solvent, coating film formation is easy, and a thick film or a thin film can be easily formed. It should be noted that the polymer was 400 as a result of measurement by a thermobalance (TG).
It is a polymer with extremely high heat resistance, with no weight change observed up to about ° C.

[0025]

EXAMPLES Next, the method of the present invention will be further described with reference to typical examples. (Example 1) [Synthesis of 2-hydroxy-4,6-dimethylpyrimidine] 16.00 g (100.0 mmol) of commercially available 2-hydroxy-4,6-dimethylpyrimidine hydrochloride was dissolved in 200 ml of distilled water, And sodium hydroxide 4.
A solution obtained by dissolving 00 g (100.0 mmol) in 100 ml of distilled water was added. Water was removed by a rotary evaporator and vacuum drying was performed. Subsequently, the product was dissolved in chloroform, insoluble sodium chloride was filtered, and chloroform was removed by a rotary evaporator to obtain the desired product 2.
-Hydroxy-4,6-dimethylpyrimidine 12.02
g (96.7 mmol) was obtained. The attribution of each hydrogen peak by ¹ H-NMR measurement is as follows; 2.38
ppm (singlet) (hydrogen of methyl group), 6.4
3 ppm (singlet) (hydrogen at the 5-position of the pyrimidine ring). The result of elemental analysis of this substance was in agreement with the theoretical value within the tolerance.

[5-bromo-2-hydroxy-4,6-
Synthesis of dimethylpyrimidine] 2-hydroxy-4,6-
1.24 g (10.0 mmol) of dimethylpyrimidine was dissolved in 20 ml of chloroform, and subsequently 1.78 g (10.0 mmol) of N-bromosuccinimide was added. After stirring for 20 minutes at room temperature, chloroform was removed under reduced pressure at room temperature. After drying under reduced pressure, 2 in 20 ml of ethyl acetate
The mixture was boiled for 0 minutes, allowed to cool, and filtered. The filtered product is recrystallized from ethanol and is the desired product, 5-bromo-2.
-Hydroxy-4,6-dimethylpyrimidine 1.09 g
(5.37 mmol) was obtained. Assignment of hydrogen peaks by ¹ H-NMR measurement is as follows; 2.57 pp
m (singlet) (hydrogen of methyl group). The result of elemental analysis of this substance was in agreement with the theoretical value within the tolerance.

[Synthesis of 2,5-dibromo-4,6-dimethylpyrimidine] 4.30 g (15.0 mmol) of phosphorus oxybromide, 5-bromo-2-hydroxy-4, were placed in a reaction vessel in an inert atmosphere. 6-dimethylpyrimidine 2.0
3 g (10.0 mmol), phosphorus tribromide 5.70 ml
(60.0 mmol) was added. 130 ° C with a cooler
And refluxed for 45 minutes. The reaction solution is cooled to room temperature and then cooled to 200
It was poured into g ice. Neutralize with aqueous sodium hydroxide,
Extract with ethyl acetate, dry over anhydrous magnesium sulfate,
The solvent was removed and the residue was dried under reduced pressure. Purify with a silica gel column (ethyl acetate / hexane = 5%) to obtain the desired product, 2,5-dibromo-4,6-dimethylpyrimidine 0.1.
6 g (0.6 mmol) was obtained. Assignment of hydrogen peaks by ¹ H-NMR measurement is as follows; 2.64 p
pm (singlet) (hydrogen of methyl group). The result of elemental analysis of this substance was in agreement with the theoretical value within the tolerance.

[Synthesis of poly (4,6-dimethyl-2,5-pyrimidinediyl)] Bis (1,5-cyclooctadiene) nickel 0.74 g was placed in a reaction vessel having an inert atmosphere.
(2.69 mmol), N, N-dimethylformamide 30 ml, 2,2'-bipyridine 0.406 g (2.6
0 mmol), 1.5-cyclooctadiene 0.466
ml was added in this order and stirred. Another container was placed in an inert atmosphere, 0.5318 g (2.00 mmol) of 2,5-dibromo-4,6-dimethylpyrimidine and 10 ml of N, N-dimethylformamide were added, and the mixture was stirred and dissolved.
Mix the two solutions and keep the inert atmosphere
Heat at 0 ° C. for 48 hours. The reaction solution was poured into aqueous ammonia and washed with stirring. It was extracted with chloroform, and the chloroform layer was washed with an aqueous solution of ethylenediaminetetraacetic acid disodium. After removing chloroform, the product was dried under reduced pressure to obtain poly (4,6-dimethyl-2,5-pyrimidinediyl) 0.
18 g (yield 84.0%) was obtained. When dissolved in chloroform and measured by GPC, it was a polymer having an average molecular weight of 7,000 in terms of polystyrene. Assignment of hydrogen peaks by ¹ H-NMR measurement is as follows: 1.3 p
pm (hydrogen of methyl group). The results of elemental analysis are as follows; carbon: 66.22% (theoretical value 67.91%), hydrogen: 7.51% (theoretical value 5.70%), nitrogen: 5.38.
% (Theoretical value 26.39%), bromine: 0.01% or less.

(Example 2) [Electrochemical n-type doping] The chloroform solution of poly (4,6-dimethyl-2,5-pyrimidinediyl) obtained in Example 1 was coated on a platinum electrode (film thickness). 1μ
m) and platinum as a control electrode and silver / silver chloride as a reference electrode.
The redox potential was investigated by cyclic voltammetry in 5M (Bu) ₄ NBF ₄ / CH ₃ CN. As a result, (Bu) ₄ near −2.1 V vs Ag / Ag ^+.
An oxidation-reduction reaction accompanying N ⁺ doping and undoping was observed. The sample before doping has an electric conductivity of 1 × 10
It was less than ^-8 S / cm, whereas that after doping was 1 x 10 ^-3 S / cm.

(Example 3) [Chemical n-type doping] The poly (4,6) obtained in Example 1 was used.
-Dimethyl-2,5-pyrimidinediyl) was soaked in a solution of sodium naphthalenide in tetrahydrofuran for 8 hours, and then dried under reduced pressure at 50 ° C for 1 hour to perform n-type doping with sodium. The electrical conductivity of this doped sample was measured by the 4-terminal method. As a result, the electrical conductivity of the sample before doping was 1 × 10 ⁻³ S / cm, compared with 1 × 10 ⁻⁸ S / cm.

(Example 4) [Synthesis of poly (4-methyl-2,5-pyrimidinediyl)] [Synthesis of 2-amino-4-methyl-5-bromopyrimidine] 5.45 g of a commercial product in 150 ml of chloroform.
(50.0 mmol) 2-amino-4-methylpyrimidine was dissolved. 8.40 g (50.0 mmol) of N-bromosuccinimide was added, and the mixture was stirred at room temperature for 30 minutes. After distilling off the solvent, 50 ml of ethyl acetate was added to 1
Boiled for 5 minutes. After cooling to room temperature, the white precipitate was collected by filtration and recrystallized from ethanol to obtain 6.75 g of the desired product.
(35.9 mmol) 2-amino-4-methyl-5-
Obtained bromopyrimidine. ^The results of ¹ H-NMR measurement are as follows; 2.48 ppm (siglet)
(Hydrogen of methyl group) 4.42 ppm (siglet)
(Hydrogen of amino group), 6.24 ppm (double
t) (hydrogen at the 5-position of the pyrimidine ring), 7.51 ppm (d
doublet) (hydrogen at the 6-position of the pyrimidine ring). The result of elemental analysis was in agreement with the theoretical value within the range of allowable error.

[Synthesis of 2,5-dibromo-3-methylpyrimidine] 48% hydrobromic acid 1 was added to a reaction vessel in an inert atmosphere.
0 ml was put and it cooled at -5 degreeC. 1.88 g (10.
0 mmol) of 2-amino-4-methyl-5-bromopyrimidine was added, and the mixture was stirred for 30 minutes. 1.17 ml of bromine was added dropwise and stirred for 30 minutes. Aqueous sodium nitrite solution (1.93 g of sodium nitrite, 2.6 ml of distilled water) was added dropwise.
Stir for 1 hour. The reaction solution was returned to room temperature and further stirred for 1 hour. The solution was made weakly basic with an aqueous sodium hydroxide solution so that the solution temperature did not exceed 20 ° C. After extraction with chloroform, the organic layer was dried over anhydrous magnesium sulfate, the solvent was distilled off, and the residue was purified by column chromatography (silica gel, ethyl acetate: hexane = 1: 9) to give 1.61 g (6.4 mmo).
The yellow solid 2,5-dibromo-3-methylpyrimidine of 1) was obtained. ^The results of ¹ H-NMR measurement are as follows; 2.45 ppm (siglet) (hydrogen of methyl group) and 8.22 ppm (siglet) (hydrogen at the 6-position of the pyrimidine ring). The result of elemental analysis was in agreement with the theoretical value within the range of allowable error.

[Synthesis of poly (4-methyl-2,5-pyrimidinediyl)] Bis (1,5-cyclooctadiene) nickel 0.74 g was placed in a reaction vessel in an inert atmosphere.
(2.69 mmol), N, N-dimethylformamide 30 ml, 2,2'-bipyridine 0.406 g (2.6
0 mmol), 1,5-cyclooctadiene 0.466
ml was added in this order and stirred. Another container was placed in an inert atmosphere, 0.504 g (2.00 mmol) of 2,5-dibromo-3-methylpyrimidine and 10 ml of N, N-dimethylformamide were added, and the mixture was stirred and dissolved. This 2
The two solutions were mixed and heated at 60 ° C. for 48 hours while maintaining an inert atmosphere. The reaction solution was poured into aqueous ammonia and washed with stirring. The precipitate was collected by filtration and washed repeatedly with aqueous ammonia and methanol. It was dissolved in a minimum amount of formic acid and reprecipitated by dropping it in aqueous ammonia. The obtained solid was washed with an aqueous solution of ethylenediaminetetraacetic acid disodium. Finally, washed with methanol and dried under reduced pressure to obtain 0.15 g (80%) of poly (4-methyl-2,5-pyrimidinediyl).
%) Was obtained. When dissolved in chloroform and measured by GPC, it was a polymer having an average molecular weight of 9,500. ¹ H-N
The result of the MR measurement is as follows: 1.3 ppm
(Hydrogen of methyl group), 8.1 ppm (hydrogen at 6-position of pyrimidine ring). The results of elemental analysis are as follows: carbon 64.8
3% (theoretical value 65.21%), hydrogen 4.97% (theoretical value 4.38%), nitrogen 29.69% (theoretical value 30.41)
%), Bromine 0.01% or less.

Example 5 [Electrochemical Doping] A 3% by weight chloroform solution of the poly (4-methyl-2,5-pyrimidinediyl) obtained in Example 4 was coated on a platinum electrode (about 1 μm). , Platinum as a control electrode and silver / silver chloride as a reference electrode, 0.5M (Bu) ₄ N
The redox potential was investigated by the cyclic voltammetry method in BF ₄ / CH ₃ CN. As a result, -2.3
Vvs. Ag / Ag ⁺ in the vicinity of (Bu) ₄ ⁺ doping,
An oxidation-reduction reaction associated with undoping was observed.

(Example 6) [Chemical n-type doping] The poly (4-methyl-2,5-pyrimidinediyl) obtained in Example 4 was processed into a uniform film having a thickness of 1 µm, and sodium naphthalene was added thereto. It was permeated into a tetrahydrofuran solution of sodium chloride for 8 hours and then dried under reduced pressure at 50 ° C. for 1 hour to perform n-type doping with sodium. The electrical conductivity of this doped sample was measured by the 4-terminal method. As a result, while the electric conductivity of the sample before doping is 1 × 10 ⁸ S / cm or less,
The sample after doping was 1 × 10 ³ S / cm.

(Example 7) [Production of electroluminescent material] As an electroluminescent material, a method described in the literature (FEk) was used.
arasz et al .; Polymer Sci. Poly
mer Chemistry, 26 , 3241 (198)
8)) synthesized poly (paraphenylene vinylene)
A 1% by weight aqueous solution of poly (paraxylylenedimethylsulfonium chloride), which is the precursor of 1., was applied on ITO glass and then heated at 150 ° C. for 2 hours in a nitrogen atmosphere to form a poly (paraphenylene vinylene) film. . On top of this, the poly (4,6-dimethyl-
A 3 wt% chloroform solution of 2,5-pyrimidinediyl) was spin-coated at 1000 rpm and dried under reduced pressure to form an electron transport layer. Aluminum was vacuum-deposited on this as an electrode to prepare an electroluminescence element. 5 with ITO glass as positive electrode and aluminum as negative electrode
When a DC voltage of V was applied, the light emission luminance was improved by about 20% as compared with the single-layer electroluminescent device containing only poly (paraphenylene vinylene).

Example 8 [Production of Electroluminescent Material] As an electroluminescent material, ITO was used in the same manner as in Example 7.
After forming a poly (paraphenylene vinylene) film on the glass, the poly (4-methyl-vinyl) obtained in Example 4 was formed thereon.
A 3 wt% chloroform solution of 2,5-pyrimidinediyl) was spin-coated at 1000 rpm and dried under reduced pressure to form an electron transport layer. Aluminum was vacuum-deposited on this as an electrode to prepare an electroluminescent element. 5 with ITO glass as positive electrode and aluminum as negative electrode
When a DC voltage of V was applied, the emission luminance was improved by about 20% as compared with the single-layer electroluminescent device containing only poly (paraphenylene vinylene).

[0038]

As described above, according to the present invention, poly (alkyl-substituted-2,5-pyrimidinediyl) capable of n-type doping and a conductive polymer doped with the same can be obtained. Furthermore, the obtained polymer is soluble in many organic solvents, has good adhesiveness to electrodes, substrates, etc., and is easy to form a film, and is a functional material such as conductor, semiconductor, optical material, antistatic material, etc. Can be used as a battery, a display element, an OPC electrode, a modified electrode, an electrochromic element, an electroluminescent element, a non-linear optical element,
It can be applied to various devices such as organic solar cells and organic transistors.

In particular, the electroluminescent material using the n-type conductive polymer has a high emission brightness and has useful performance.

Claims (4)

[Claims] 1. A compound represented by the general formula (1): (Wherein R ₁ and R ₂ each represent hydrogen or a lower alkyl group, and at least one of R ₁ and R ₂ is an alkyl group), and a substituted-2,5-pyrimidinediyl represented by , Poly (alkyl-substituted-2,5-pyrimidinediyl) having an average degree of polymerization n of 10 to 1000. 2. The poly (alkyl-substituted- according to claim 1.
An n-type conductive polymer chemically or electrochemically n-doped with 2,5-pyrimidinediyl). 3. A poly (alkyl-substituted-2,5) which is characterized in that a zero-valent nickel complex is added to 2,5-dihalogeno-4 and / or 6-alkyl-substituted-pyrimidine as a dehalogenating agent to cause polycondensation reaction. -Pyrimidinediyl) production method. 4. The poly (alkyl-substituted- according to claim 1.
An electroluminescent material using a conductive polymer of 2,5-pyrimidinediyl).