A Scalable and Chromatography‐Free Synthesis of N,N‐Bis(9,9‐dimethyl‐9H‐fluoren‐2‐yl)‐3′,3′,4′,7′‐tetramethyl‐2′,3′‐dihydrospiro[fluorene‐9,1′‐indene]‐2‐amine, a new Hole Transport Material for Organic Solar Cells

• Published in: Helvetica chimica acta Vol. 107; no. 3
• Main Authors: Aeschi, Yves, Beck, Thorsten M., Berens, Ulrich, Ernst, Alexander
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 01.03.2024; Wiley Subscription Services, Inc
• Subjects: Alkylation; Buchwald-Hartwig coupling; Chemistry; Chemistry, Multidisciplinary; Chromatography; diaminophenylindane (DAPI); Fluorene; Grignard reactions; Hole Transport Material; Indene; intramolecular Friedel-Crafts alkylation; Organic Electronic Material; Organic Light Emitting Diodes; Organic Solar Cells; Photovoltaic cells; Physical Sciences; Science & Technology; Solar cells; Spirofluorene indene; Synthesis; Triarylamine; Organic Electronic Material; Buchwald-Hartwig coupling; Organic Light Emitting Diodes; intramolecular Friedel-Crafts alkylation; diaminophenylindane (DAPI); METRICS; Triarylamine; Organic Solar Cells; Spirofluorene indene; Hole Transport Material
• DOI: 10.1002/hlca.202300220
• ISSN: 0018-019X

The title triarylamine N,N‐bis(9,9‐dimethyl‐9H‐fluoren‐2‐yl)‐3′,3′,4′,7′‐tetramethyl‐2′,3′‐dihydrospiro[fluorene‐9,1′‐indene]‐2‐amine is a new hole transport material for organic solar cells. After investigating different discovery approaches (Schemes 1 + 2), a multi gram‐scale synthetic sequence was developed (Scheme 4). The key intermediate 2‐bromo‐9‐(2,5‐dimethylphenyl)‐9H‐fluorene was accessible from 2‐bromo‐9‐fluorenone by either the sequence Grignard reaction, Et3SiH/BF3 reduction or by direct arylation of the corresponding 2‐bromo‐9‐fluorenol. Alkylation at C(9) of 2‐bromo‐9‐(2,5‐dimethylphenyl)‐9H‐fluorene with methallyl chloride and cyclization by an intramolecular Friedel‐Crafts alkylation led to the key building block 2‐bromo‐3′,3′,4′,7′‐tetramethyl‐2′,3′‐dihydrospiro[fluorene‐9,1′‐indene] (Scheme 4). A Buchwald‐Hartwig coupling was employed (Scheme 3 + 4) for the assembly of the final triarylamines. The developed gram‐scale synthesis of the title compound is scalable and chromatography‐free with an overall yield >25 % over 5 steps. Triarylamine 17 represents a new class of hole transport material for organic solar cells (OSC) and organic light emitting diodes (OLED). The scalable and chromatography‐free synthesis comprises five steps starting from commercially available 2‐bromo‐9‐fluorenone (5). An intramolecular Friedel‐Crafts alkylation is the key reaction for the formation of the bromo‐spirofluorene scaffold 16; subsequent Buchwald‐Hartwig cross‐coupling leads to the title triarylamine as crystalline solid.