WO2015068958A1

WO2015068958A1 - Novel alkyl halide compound and method for preparing same

Info

Publication number: WO2015068958A1
Application number: PCT/KR2014/009717
Authority: WO
Inventors: 김윤희; 권순기; 윤희준
Original assignee: 경상대학교산학협력단
Priority date: 2013-11-11
Filing date: 2014-10-16
Publication date: 2015-05-14
Also published as: KR101547843B1; KR20150054136A

Abstract

The present invention relates to a novel alkyl halide compound and a method for preparing the same. The alkyl halide compound according to the present invention can be applied to all polymers and single molecules used in an organic semiconductor, and thus the organic semiconductor materials incorporating the novel alkyl group have an improved solubility due to the novel alkyl group, thereby facilitating fabrication of a device via solution processes of spin coating, dye casting, printing, etc. In addition, the alkyl halide compound can improve properties of the device by adjusting the form and crystallinity of a film.

Description

Novel alkyl halide compounds and preparation methods thereof

The present invention relates to a novel alkyl halide compound and a method for preparing the same, wherein the alkyl halide compound according to the present invention is applied to all polymers and monomolecules used in organic semiconductors, so that the organic semiconductor material into which the new alkyl group is introduced is soluble due to the new alkyl group. It is possible to improve the device characteristics by adding various solvents to facilitate the fabrication of the device through a solution process such as spin coating, die casting, printing, etc., and to improve the device characteristics by controlling the form and crystallinity of the film.

Organic thin film transistor is an electronic device that has been actively researched and developed recently due to its many advantages. Especially, the organic thin film transistor is easy for flexible electronic circuit boards that can be bent or folded without breaking due to the simple manufacturing process and low cost. Can be applied.

In addition, compared with conventional thin film transistors using amorphous silicon and polysilicon, organic thin film transistors have a large number of researches due to the simple manufacturing process, low cost production, and high compatibility with other electronic components. Is being done.

The organic thin film transistor element includes a substrate, a gate electrode, an insulating layer, a channel layer, a source / drain electrode, and a protective layer that prevents external moisture and oxygen transmission. Organic thin film transistors are fabricated by replacing organic silicon or organic materials exhibiting semiconductor characteristics by replacing conventional silicon-based inorganic materials in the channel layer, which has the greatest effect on device characteristics and is the key part of charge transfer.

The organic semiconductor compound constituting the organic thin film transistor can be classified into low molecules and polymers according to molecular weight, and classified into n-type organic semiconductors or p-type organic semiconductors depending on whether electrons or holes are transferred.

In general, when a low molecular organic semiconductor is used to form an organic semiconductor layer, the low molecular organic semiconductor is easy to purify and almost removes impurities, so the charge transfer characteristics are excellent. However, spin coating and printing are not possible, so that the thin film is deposited by vacuum deposition. Since it is necessary to manufacture, the manufacturing process is complicated and expensive compared to the polymer organic semiconductor has a disadvantage. In the case of the polymer organic semiconductor, it is difficult to purify the high purity, but excellent heat resistance, spin coating and printing is possible, there is an advantage in the manufacturing process, cost, mass production.

In particular, the use of a polymer organic semiconductor has the advantage that the manufacturing cost can be reduced compared to the low molecular organic semiconductor compound because of the advantage that the thin film can be easily formed by the solution process.

Representative semiconductor compounds for polymer-based organic thin film transistors developed to date include P3HT [poly (3-hexylthiophene)] and F8T2 [poly (9,9-dioctylfluorene-co-bithiophene)]. There are many performances of OTFT, but the most important evaluation scale is charge mobility and on / off ratio, and the most important evaluation scale is charge mobility. The charge mobility varies depending on the type of semiconductor material, thin film formation method (structure and morphology), driving voltage, and the like.

On the other hand, the polymer organic semiconductor compound has a disadvantage of low charge mobility, which is an important evaluation measure of OTFT performance, and in order to overcome such disadvantages, the polymer organic semiconductor incorporating a thiophene group substituted with an alkyl group in a side chain is disclosed in Korean Patent No. 1082477. Compounds are disclosed.

However, there is still a need for the development of a polymer organic semiconductor having high charge mobility and low flashing ratio, which are advantages of low molecular organic semiconductors, and which is advantageous in terms of manufacturing process and cost and is capable of solution process.

The present inventors applied various substituents to polymers and single molecules used in organic semiconductors to improve the solubility of organic semiconductor materials and improve device characteristics, and at the ends of long carbon chains of at least five carbons. A morphology and crystal that can increase solubility and improve device characteristics when an alkyl halide compound having a halogen atom substituted at one end and two alkyls at the other end react with a polymer or a single molecule used in an organic semiconductor The present invention was accomplished by finding a sex.

Accordingly, an object of the present invention is to provide a novel alkyl halide compound that can be applied to an organic semiconductor material to improve solubility and device characteristics, and a method for preparing the same.

Hereinafter, the present invention will be described in detail.

The present invention provides an alkyl halide compound represented by the following formula (1).

[Formula 1]

In Chemical Formula 1,

R ₁ and R ₂ independently of one another are (C5-C50) alkyl, (C5-C50) alkoxy, (C5-C50) alkoxycarbonyl, (C6-C50) aryl or (C6-C50) aryl (C5-C50) Alkyl;

L is a single bond or O;

X is I, Br or Cl; And

n is an integer from 2 to 50.

In addition, the alkyl halide compound of Formula 1 of the present invention is characterized by a structure in which halogen is substituted on carbon ₁ and R ₁ and R ₂ are substituted on carbon (n + 3). Compared to a structure in which R ₁ and R ₂ are substituted with a conventional carbon 3, a halogen atom is substituted at one of both ends of a long carbon chain having at least 5 carbons, and R ₁ and R ₂ are substituted at the other end. Therefore, when the alkyl group of the alkyl halide compound of Formula 1 is introduced into the organic semiconductor material, it is possible to obtain morphology and crystallinity which can increase solubility and improve device properties.

In the alkyl halide compound of the general formula (1) of the present invention, preferably, R ₁ and R ₂ are each independently (C5-C50) alkyl or (C6-C50) aryl (C5-C50) alkyl, and are introduced into an organic semiconductor material to improve In terms of solubility and excellent morphology and crystallinity, linear alkyl having 20 or more of the sum of the carbon atoms of R ₁ and R ₂ is more preferable.

Specifically, the alkyl halide compound of Formula 1 according to the present invention may be represented by the following compounds, but is not limited thereto.

X is I, Br or Cl.

The alkyl halide compound of formula 1 according to the present invention can be applied to all polymers and single molecules used in organic semiconductor materials, and can exhibit excellent properties such as increased solubility and improved device properties due to the alkyl of the alkyl halide compound of formula 1 . In particular, since the solubility is greatly improved due to the long carbon chain and the substituted R ₁ and R ₂ at the terminal, mass production at low cost is possible when manufacturing organic thin film transistor through solution process such as spin coating, die casting, printing, etc. It has the effect of cost reduction.

In addition, since the alkyl of the alkyl halide compound of Formula 1 of the present invention enters into a long alkyl spacer form when applied to all polymers and single molecules used in organic semiconductor materials, it is even more than conventional organic semiconductor materials. By improving the solubility, the device fabrication process can be easily performed, and the performance of the organic semiconductor material can be improved. Specifically, it has high arrangement and crystallinity between organic semiconductor materials and at the same time induces interdigitation and improves pi-pi stacking (π-π staking) to improve charge and hole transfer between molecules and molecules. Since the properties are further improved, the organic semiconductor properties can be significantly improved.

The present invention also provides a method for preparing an alkyl halide compound represented by the formula (1).

The present invention provides a method for producing an alkyl halide compound which is simpler and more industrially applicable.

There are two methods for preparing the alkyl halide compound represented by Formula 1 according to L.

One method is to prepare an alkyl halide compound in which L is a single bond, comprising the following steps:

a) reacting a metal magnesium compound with a monohalide compound of Formula 2 to prepare an alkylmagnesium halide compound of Formula 3; And

b) preparing an alkyl halide compound of Formula 1-1 by performing a metal substitution reaction of the prepared alkylmagnesium halide compound of Formula 3 with a dihalide compound of Formula 4 below.

[Formula 1-1]

[Formula 2]

[Formula 3]

[Formula 4]

In Chemical Formulas 1-1, 2, 3, and 4,

L is a single bond or O;

X is I, Br or Cl; And

n is an integer from 2 to 50.

The present invention is to prepare an alkyl halide compound of Formula 1-1, by reacting the monohalide compound of Formula 2 with metal magnesium, an alkylmagnesium halide compound of Formula 3 as a Grignard reagent (organometallic reagent) After the preparation, a metal halide reaction with the dihalide compound of Chemical Formula 4 was added to an acid, extracted with an organic solvent, concentrated, and column purified to prepare an alkyl halide compound of Chemical Formula 1-1.

The amount of magnesium used in step a) is related to the reaction time. The higher the amount used, the shorter the reaction time, but a large amount of acid is required for removal after completion of the reaction. In addition, the reaction temperature is also related to the reaction time. When the reaction proceeds at a high temperature, the reaction time is shortened, but it is preferable to use an appropriate amount because a number of side reactions are generated due to the violent reaction and the yield is reduced. Therefore, the amount of magnesium used in the present invention is used in 0.5 to 5 equivalents, preferably 0.8 to 1.5 equivalents, based on the monohalide compound of Formula 2. In addition, the reaction temperature of step a) is 25 to 100 ℃, preferably carried out at 50 to 80 ℃.

The reaction of step a) is carried out in an inert reaction medium, the inert reaction medium is diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, t-butyl- methylether, diisopropyl ether, diphenyl ether methylene Chloride, 1,2-dimethoxyethane or bis (2-methoxyethyl) ether or any mixture thereof.

In addition, the amount of the dihalide compound represented by Chemical Formula 4 in step b) is preferably used in an amount of 1 to 5 equivalents based on the monohalide compound represented by Chemical Formula 2. In addition, the reaction of step b) is preferably carried out at a temperature of -10 to 30 ℃.

In addition, the reaction of step b) may be carried out further comprising a catalytic amount of copper salts, lithium salts or mixtures thereof, the catalytic amount of copper salts, lithium salts or mixtures thereof to improve the yield in the metal substitution reaction It acts as a catalyst to help metal replacement reactions occur well. Copper bromide (CuBr) and lithium chloride (LiCl) are preferably used.

In addition, the reaction of step b) is carried out in an inert reaction medium, the inert reaction medium is diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, t-butyl-methylether, diisopropyl ether, diphenyl Ether methylene chloride, 1,2-dimethoxyethane or bis (2-methoxyethyl) ether or any mixture thereof.

Upon completion of the reaction, an acid was added to the reaction solution, extracted with an organic solvent, concentrated, and column purified to obtain an alkyl halide compound of Chemical Formula 1-1. The acid used may be sulfuric acid, hydrochloric acid, acetic acid, and the like, and the extraction solvent may be ethyl acetate, ether, benzene, toluene, nitrobenzene, methylene chloride, chloroform, or the like.

Another method is to prepare an alkyl halide compound of Formula 1-2 by reacting metal sodium with a monool compound of Formula 5 and then reacting with a dihalide compound of Formula 4 when L is oxygen. to be.

[Formula 1-2]

[Formula 5]

[Formula 4]

In Formulas 1-2, 4, and 5, R ₁ and R ₂ are each independently of (C5-C50) alkyl, (C5-C50) alkoxy, (C5-C50) alkoxycarbonyl, (C6-C50) aryl or (C6-C50) aryl (C5-C50) alkyl;

L is a single bond or O;

X is I, Br or Cl; And

n is an integer from 2 to 50.

The amount of sodium used is 0.5 to 5 equivalents, preferably 0.8 to 1.5 equivalents, based on the monool compound of Formula 5. The reaction is also carried out in a reflux reaction, in an inert reaction medium, the inert reaction medium is diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, t-butyl-methyl ether, diisopropyl ether, diphenyl ether Methylene chloride, 1,2-dimethoxyethane or bis (2-methoxyethyl) ether or any mixture thereof. In addition, the dihalide compound of Formula 4 is preferably used in an amount of 1 to 5 equivalents based on the monool compound of Formula 5.

When the reaction is completed, the reaction solution is extracted with an organic solvent, concentrated and purified by column to obtain the alkyl halide compound of Formula 1-1. The extraction solvent may be ethyl acetate, ether, benzene, toluene, nitrobenzene, methylene chloride, chloroform and the like.

The present invention relates to a novel alkyl halide compound and a method for preparing the same, wherein the alkyl halide compound according to the present invention has a halogen atom substituted at one of both ends of a long carbon chain consisting of 5 carbons and R ₁ at the other end thereof. When R ₂ is substituted and the alkyl group of the alkyl halide compound of Formula 1 is introduced into the organic semiconductor material, morphology and crystallinity can be obtained to increase solubility and improve device properties. In particular, since the solubility is greatly improved due to the long carbon chain and R ₁ and R ₂ substituted at the terminal, mass production at low cost is possible when manufacturing organic thin film transistor through solution process such as spin coating, die casting, printing, etc. In addition to the cost reduction effect, it is possible to improve the device characteristics by adjusting the shape and crystallinity of the film.

Hereinafter, the present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples.

[실시예 1] 15-(6-브로모헥실)헨트리아콘탄 (15-(6-bromohexyl)hentriacontane)의 합성Example 1 Synthesis of 15- (6-bromohexyl) hentriacontane (15- (6-bromohexyl) hentriacontane)

2-테트라데실옥타데칸-1-올 (2-tetradecyloctadecan-1-ol )의 합성Synthesis of 2-tetradecyloctadecan-1-ol (2-tetradecyloctadecan-1-ol)

In a well-dried 500 mL three neck round bottom flask, hexadecan-1-ol (50.0 g, 0.1032 mol), KOH (0.32 g, 0.0057 mol) and Ni powder (0.0625 g, 1.0645 mmol) were added. Put, and raise the temperature to 250 ^o C. After stirring for 1 hour under a nitrogen stream, water was removed using simple distillation. The temperature was maintained at 250 ^° C. for 3 hours, after which the temperature was lowered to room temperature, extracted with methylene chloride (MC), the organic layer was washed several times with water, and the solvent was removed using a rotary evaporator. The starting material was then removed using vacuum distillation to yield the product 2-tetradecyloctadecane-1-ol (34 g, 70.62%).

¹ H-NMR (300 MHz, CDCl ₃ ): δ 4.86-4.85 (s, 1 H), 3.67-3.53 (m, 2 H), 1.58-155 (d, 1 H), 1.28-1.21 (m, 56 H), 0.91-0.87 (t, 6H)

15-(브로모메틸)헨트리아콘탄 (15-(bromomethyl)hentriacontane)의 합성Synthesis of 15- (bromomethyl) hentriacontane

Triphenylphosphine (17.9 g, 0.06544 mol) was added to MC in a well-dried 500 mL three-neck round bottom flask, and the temperature was lowered to 0 ^o C and bromine (10.5 g, 0.06544 mol). Was dropped and stirred for 10 minutes. Then, 2-tetradecyloctadecan-1-ol (25.5 g, 0.05462 mol) dissolved in MC was dropped and stirred for 16 hours. Extraction with MC, the organic layer was washed with water, dried over MgSO ₄ and the solvent was removed using a rotary evaporator. The solvent was dissolved in hexane to filter free solids (triphenylphosphine side reactions) as impurities, and the solvent dissolved in hexane was removed using a rotary evaporator. Separation by column chromatography using n -hexane afforded 15- (bromomethyl) hentracontane as a target compound (22.56 g, 78%).

¹ H-NMR (300 MHz, CDCl ₃ ): δ 3.67-3.53 (m, 2H), 1.58-155 (d, 1H), 1.28-1.21 (m, 56H), 0.91-0.87 (t, 6H )

15-(6-브로모헥실)헨트리아콘탄 (15-(6-bromohexyl)hentriacontane)의 합성Synthesis of 15- (6-bromohexyl) hentriacontane

Magnesium Mg (0.78 g, 32.24 mmol, 1.4 equiv) was added to a well-dried three-necked flask, and 15- (bromomethyl) hentricontane (12.2 g, 23.02 mmol, 1 equiv) and THF (30 mL) were slowly added dropwise. Refluxing at 80 ^° C. for 1 hour while producing 1- (2-tetradecyloctadecyl) magnesium bromide (1- (2-tetradecyloctadecyl) magnesium bromide) (under THF (30 mL) solution) (preparation of organic metal reagent) ).

In another well-dried three-necked flask, 1,5-dibromopentane (12.18 g, 52.96 mmol, 3 equiv), CuBr (33 mg, 0.23 mmol, 0.01 equiv) and LiCl (20 mg, 0.46 mmol, 0.02 equiv) were THF Dissolve in (50 mL) and slowly add dropwise the organometallic reagent prepared above while maintaining -10 ° C. The temperature was then raised to room temperature and stirred for 16 hours. Then, NH ₄ Cl aqueous solution (50 mL) was added thereto, stirred for 10 minutes, extracted with ether, 2M hydrochloric acid, and 10% Na ₂ CO ₃ aqueous solution, dried over MgSO ₄ , and the solvent was removed using a rotary evaporator. Thereafter, the starting material was removed by vacuum distillation, followed by column chromatography using hexane, thereby obtaining 15- (6-bromohexyl) hentracontane (9.27 g, 67.11%).

¹ H-NMR (300 MHz, CDCl ₃ ): δ 3.44-3.40 (m, 2H), 1.90-1.86 (m, 2H), 1.46-1.13 (m, 65H), 0.91-0.87 (t, 6H)

[실시예 2] 11-(6-브로모헥실) 트리코산 (11-(6-bromohexyl)tricosane)의 합성Example 2 Synthesis of 11- (6-bromohexyl) trichoic acid (11- (6-bromohexyl) tricosane)

11-(브로모메틸)트리코산 (11-(bromomethyl)tricosane)의 합성Synthesis of 11- (bromomethyl) trichoic acid (11- (bromomethyl) tricosane)

Triphenylphosphine (23.72 g, 0.0862 mol) was dissolved in MC in a well-dried 500 mL three neck round bottom flask, and the temperature was lowered to 0 ^o C and bromine (13.84 g, 0.06544 mol). Was dropped and stirred for 10 minutes. Then, 2-decyltetradecan-1-ol (25.5 g, 0.0719 mol) dissolved in MC was dropped and stirred for 16 hours. Extraction with MC, the organic layer was washed with water, dried over MgSO ₄ and the solvent was removed using a rotary evaporator. The solvent was dissolved in hexane to filter free solids (triphenylphosphine side reactions) as impurities, and the solvent dissolved in hexane was removed using a rotary evaporator. Column chromatography using n -hexane afforded the title compound 11- (bromomethyl) trichoic acid (27.2 g, 75.5%).

¹ H-NMR (300 MHz, CDCl ₃ ): δ 3.47-3.33 (m, 2H), 1.57-153 (d, 1H), 1.29-1.21 (m, 40H), 0.91-0.86 (t, 6H )

11-(6-브로모헥실) 트리코산 (11-(6-bromohexyl)tricosane)의 합성Synthesis of 11- (6-bromohexyl) trichoic acid (11- (6-bromohexyl) tricosane)

Magnesium Mg (6.50 g, 0.268 mol, 1.4 equiv) was added to a well-dried three neck flask and 11- (bromomethyl) trichoic acid (80.0 g, 0.191 mol, 1 equiv) and THF (270 mL) were slowly added dropwise. It was refluxed at 80 ^° C. for 1 hour to give 1- (2-decyltetradecyl) magnesium bromide (under THF (270 mL) solution) (preparation of organic metal reagent).

In another well-dried three-necked flask, 1,5-dibromopentane (110.13 g, 0.478 mol, 2.5 equiv), CuBr (0.27 g, 1.915 mmol, 0.01 equiv) and LiCl (0.162 g, 3.383 mmol, 0.02 equiv) were THF (320 mL) was slowly added dropwise to the previous organometallic reagent prepared while maintaining -10 ° C. The temperature was then raised to room temperature and stirred for 16 hours. Then, NH ₄ Cl aqueous solution (50 mL) was added thereto, stirred for 10 minutes, extracted with ether, 2M hydrochloric acid, and 10% Na ₂ CO ₃ aqueous solution, dried over MgSO ₄ , and the solvent was removed using a rotary evaporator. Thereafter, the starting material was removed by vacuum distillation, and then column chromatography using hexane gave 11- (6-bromohexyl) trichoic acid as a target compound (76.25 g, 81.85%).

[실시예 3] 11-((6-브로모헥실옥시)메틸)트리코산 (11-((6-bromohexyloxy)methyl)tricosane)의 합성Example 3 Synthesis of 11-((6-bromohexyloxy) methyl) trichoic acid (11-((6-bromohexyloxy) methyl) tricosane)

In a well-dried 500 mL three neck round bottom flask, 2-decyltetradecan-1-ol (30 g, 0.085 mol) was dissolved in THF (270 mL) and the metal Na (2.1 g 0.0913 mol) ) Was refluxed at 70 ^° C. for 2 hours. Then, 1,6-dibromohexane (1,6-dibromohexane) (41 g, 0.168 mol) was slowly added dropwise, and the temperature was raised to 80 ^° C. and refluxed for 8 hours. After the reaction was completed, the mixture was extracted with an ether and Na ₂ CO ₃ aqueous solution, dried over anhydrous MgSO _4, and then the solvent was removed using a rotary evaporator. Column chromatography gave the target compound 11-((6-bromohexyloxy) methyl) trichoic acid (31 g, 70.44%).

¹ H-NMR (300 MHz, CDCl ₃ ): δ 3.45-3.39 (m, 6 H), 1.92-186 (m, 4 H), 1.51-1.47 (m, 5H), 1.32-1.27 (m, 40 H ), 0.92-0.87 (t, 6H)

The present invention relates to a novel alkyl halide compound and a method for preparing the same, wherein the alkyl halide compound according to the present invention has a halogen atom substituted at one of both ends of a long carbon chain consisting of 5 carbons and R ₁ at the other end thereof. And R ₂ is substituted so that when the alkyl group of the alkyl halide compound of Formula 1 is introduced into the organic semiconductor material, morphology and crystallinity can be obtained to increase solubility and improve device characteristics. In particular, since the solubility is greatly improved due to the long carbon chain and the substituted R ₁ and R ₂ at the terminal, mass production at low cost is possible when manufacturing organic thin film transistor through solution process such as spin coating, die casting, printing, etc. In addition to the cost reduction effect, it is possible to improve the device characteristics by adjusting the shape and crystallinity of the film.

Claims

Alkyl halide compounds represented by the following formula (1):

[Formula 1]

In Chemical Formula 1,

R 1 and R 2 independently of one another are (C5-C50) alkyl, (C5-C50) alkoxy, (C5-C50) alkoxycarbonyl, (C6-C50) aryl or (C6-C50) aryl (C5-C50) Alkyl;

L is a single bond or O;

X is I, Br or Cl; And

n is an integer from 2 to 50.
The method of claim 1,

Alkyl halide compound selected from the following compounds.

X is I, Br or Cl.
a) reacting a metal magnesium compound with a monohalide compound represented by the following Chemical Formula 2 to prepare an alkylmagnesium halide compound represented by the following Chemical Formula 3,

b) a method of preparing an alkyl halide compound of Formula 1-1 by performing a metal substitution reaction of the prepared alkylmagnesium halide compound of Formula 3 with a dihalide compound of Formula 4.

[Formula 1-1]

[Formula 2]

[Formula 3]

[Formula 4]

In Formulas 1-1, 2, 3, and 4, R 1 , R 2 , X, and n are the same as defined in claim 1.
The method of claim 3, wherein

The use amount of magnesium in step a) is 0.5 to 5 equivalents based on the monohalide compound of Formula 2.
The method of claim 3, wherein

The reaction of step a) is characterized in that the production method is carried out at a temperature of 25 to 100 ℃.
The method of claim 3, wherein

The amount of the dihalide compound of Formula 4 of step b) is 1 to 5 equivalents based on the monohalide compound of Formula 2.
The method of claim 3, wherein

The reaction of step b) is characterized in that carried out at a temperature of -10 to 30 ℃.
The method of claim 3, wherein

Each reaction of steps a) and b) is carried out in an inert reaction medium.
The method of claim 3, wherein

The metal substitution reaction of step b) is characterized in that the production method further comprises a catalytic amount of copper salt, lithium salt or a mixture thereof.
A method of preparing an alkyl halide compound of formula 1-2 by reacting a metal sodium with a monool compound of formula 5 and then reacting with a dihalide compound of formula 4 below.

[Formula 1-2]

[Formula 5]

[Formula 4]

In Formulas 1-2, 4, and 5, R 1 , R 2 , X, and n are the same as defined in claim 1.