Methods for preparing benzodithiophenes
Methods of adding substituents to a benzodithiophene are disclosed. A benzodithiophene is reacted with a reagent to directly add the substituent to the benzene core of the benzodithiophene. This method eliminates steps from prior process and eliminates the need for hydrogenation, allowing for a safer and more scaleable process. The resulting benzodithiophenes are suitable for use in semiconductor polymers and have no loss of performance.
1. A method of producing a semiconductor polymer of Formula (II):
wherein R 1 and R 2 are independently selected from alkyl, aryl, and heteroaryl; and n is from 2 to about 5,000; the method comprising:
reacting a benzoquinone-dithiophene with a reagent of the formula M-R 1 , wherein M is MgX or Li, X is a halogen, and R 1 is alkyl, aryl, or heteroaryl;
reducing the resulting intermediate to form the 4,8-disubstituted benzodithiophene of Formula (I):
coupling a 3-R 2 -thiophene to the 2 and 6 positions of the benzodithiophene, wherein R 2 is alkyl, aryl, or heteroaryl, to obtain a repeating unit; and
polymerizing the repeating unit to obtain the polymer of Formula (II).
2. The method of claim 1 , wherein R 1 and R 2 independently have from 1 to about 24 carbon atoms.
3. The method of claim 1 , wherein the 4,8-disubstituted benzodithiophene of Formula (I) is coupled to 3-R 2 -thiophene at the 2 and 6 positions using a palladium, nickel, or iron catalyzed cross-coupling reaction.
4. The method of claim 1 , further comprising purifying the repeating unit of Formula (II) (n=1) to a minimum HPLC purity of 94% using column chromatography through silica gel, alumina, or combinations thereof; recrystallization; and combinations thereof.
5. The method of claim 1 , wherein R 1 and R 2 are each alkyl having from 1 to about 24 carbon atoms.
6. The method of claim 5 , wherein R 1 and R 2 are identical.
7. The method of claim 1 , wherein R 1 is linear alkyl or branched alkyl.
8. The method of claim 1 , wherein the reduction of the intermediate is performed using a metal chloride in an acidic solution, the metal chloride being selected from the group consisting of tin chloride, zinc chloride, or iron chloride.
9. The method of claim 1 , wherein the reagent is dissolved in a solvent selected from hydrocarbon solvents, aromatic solvents, diethyl ether, tert-butylmethyl ether, tetrahydrofuran, 1,4-dioxane, and mixtures thereof to form a reagent solution.
10. The method of claim 1 , further comprising adding a salt or organic additive to the reagent solution to modify the reactivity of the reagent.
11. The method of claim 10 , wherein the salt is LiCl or LiBr.
12. The method of claim 1 , wherein the reacting is performed by adding the benzoquinone-dithiophene to the reagent solution.
13. The method of claim 1 , wherein the reacting comprises combining the benzoquinone-dithiophene with the reagent and heating to a temperature of from about 20° C. to about 140° C.
14. The method of claim 13 , wherein the heating occurs for a period of at least 30 minutes.
15. The method of claim 1 , wherein the molar ratio of the reagent to the benzoquinone-dithiophene is from about 2:1 to about 4:1.
16. The method of claim 1 , wherein the reducing comprises heating to a temperature of from about 20° C. to about 140° C.
17. The method of claim 16 , wherein the heating occurs for a period of at least 30 minutes.
18. The method of claim 1 , further comprising purifying the 4,8-disubstituted benzodithiophene using column chromatography through silica gel, alumina, or combinations thereof; recrystallization; and combinations thereof.