Direct borylation of terrylene and quaterrylene.

Haruka Kano,Keiji Uehara,Kyohei Matsuo,Naoki Aratani,Hironobu Hayashi,Hiroko Yamada

doi:10.3762/bjoc.16.58

Haruka Kano, Keiji Uehara + Show 4 more

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The preparation of large rylenes often needs the use of solubilizing groups along the rylene backbone, and all the substituents of the terrylenes and quaterrylenes were introduced before creating the rylene skeleton. In this work, we successfully synthesized 2,5,10,13-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)terrylene (TB4) by using an iridium-catalyzed direct borylation of C–H bonds in terrylene in 56% yield. The product is soluble in common organic solvents and could be purified without column chromatography. Single crystal X-ray diffraction analysis revealed that the terrylene core is not disturbed by the substituents and is perfectly flat. The photophysical properties of TB4 are also unchanged by the substituents because the carbon atoms at 2,5,10,13-positions have less coefficients on its HOMO and LUMO, estimated by theoretical calculations. Finally, the same borylation reaction was applied for quaterrylene, resulting in the formation of soluble tetra-borylated quaterrylene despite a low yield. The post modification of rylenes enables us to prepare their borylated products as versatile units after creating the rylene skeletons.

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Compared with fruitful researches of oligorylene-bisimides for organic devices and single molecular spectroscopy [1,2,3,4,5,6], genuine oligorylenes have been sporadically investigated mainly because of their synthetic difficulty and low solubility (Figure 1) [7]
Scholl reaction using a superacid catalyst in combination with 2,3-dichloro-5,6-dicyano-1,4benzoquinone (DDQ) as oxidant provides a scalable preparation of quaterrylene [9], but the low solubility prevents 1H NMR characterization
In light of the above, we plan to perform the Ir-catalyzed direct borylation of C–H bonds in terrylene because 1) the regioselectivity of the reaction is unique and should be remarkably high, terrylene will be borylated at the 2, 5, 10, and 13 positions, which don’t deform the rylene cores, 2) the product obtained is soluble in common organic solvents so that the separation and characterization would be readily performed, and 3) the resultant pure soluble terrylene derivative as a versatile unit can be functionalized by using conventional metal-catalyzed coupling reactions

Summary

Introduction

Compared with fruitful researches of oligorylene-bisimides for organic devices and single molecular spectroscopy [1,2,3,4,5,6], genuine oligorylenes have been sporadically investigated mainly because of their synthetic difficulty and low solubility (Figure 1) [7]. In light of the above, we plan to perform the Ir-catalyzed direct borylation of C–H bonds in terrylene because 1) the regioselectivity of the reaction is unique and should be remarkably high, terrylene will be borylated at the 2, 5, 10, and 13 positions, which don’t deform the rylene cores, 2) the product obtained is soluble in common organic solvents so that the separation and characterization would be readily performed, and 3) the resultant pure soluble terrylene derivative as a versatile unit can be functionalized by using conventional metal-catalyzed coupling reactions. Note that the terrylene is slightly soluble in halogenated solvents, a 1H NMR spectrum in CDCl3 at room temperature can be measured.

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