Base‐Assisted Imidization: A Synthetic Method for the Introduction of Bulky Imide Substituents to Control Packing and Optical Properties of Naphthalene and Perylene Imides

Abstract We report the direct imidization of naphthalene and perylene dicarboxylic anhydrides/esters with bulky ortho,ortho‐diaryl‐ and ortho,ortho‐dialkynylaniline derivatives. This imidization method uses n‐butyllithium as a strong base to increase the reactivity of bulky amine derivatives, proceeds under mild reaction conditions, requires only stoichiometric amounts of reactants and gives straightforward access to new sterically crowded rylene dicarboximides. Mechanistic investigations suggest an isoimide as intermediary product, which was converted to the corresponding imide upon addition of an aqueous base. Single‐crystal X‐ray diffraction analyses reveal dimeric packing motifs for monoimides, while two‐side shielded bisimides crystallize in isolated molecules without close π–π‐interactions. Spectroscopic investigations disclose the influence of the bulky substituents on the optical properties in the solid state.

4 Optimization Table S1. Additional optimization for the reaction conditions for 6d. [a] entry base solvent additive (equiv) yield [%] [b]   6 Synthesis Perylene-3,4-dicarboxylic acid dimethyl ester (4) Synthesis of this compound is already reported in literature. [S6] We used an alternative route for the synthesis of 4.
Subsequently, methyl iodide (2.09 g, 14.7 mmol, 5.0 equiv) was added and the reaction mixture was cooled to 0 °C and 1, 8-diazabicyclo[5.4.0]undec-7-ene (DBU) (1.79 g, 11.8 mmol, 4.0 equiv) was added dropwise. The reaction mixture was allowed to warm-up to room temperature and then heated to 65 °C for 6 d. The mixture was cooled to room temperature and carefully added 10% NH3(aq)-solution (25 mL) to destroy excess of methyl iodide. The resulting mixture was extracted with dichloromethane. The organic phases were washed with water, dried over MgSO4 and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography (chloroform) to yield 4 (831 mg, 2.26 mmol, 77%) as an orange solid. 1  Perylene-3,4,9,10-tetracarboxylic acid tetramethyl ester (5) Synthesis of this compound is already reported in literature. [S7] We used an alternative route for the synthesis of 5.

General method A
In a Schlenk-tube the respective amine 1a-d (1.0 equiv) was dissolved in dry THF under a nitrogen atmosphere and cooled to -78 °C. Subsequently, 1.6 M n-BuLi solution in n-hexane (2.0 equiv) was added and the reaction mixture was stirred for 1 h at -78 °C. The solution was allowed to warm-up to room temperature and the respective anhydride 2-3 (1.0 equiv) was added. The mixture was heated to 75 °C for 6 h and water (5.0 equiv) was added. The reaction mixture was stirred for another 12 h at 75 °C and then cooled to room temperature. The resulting mixture was concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography to obtain the respective product. For two-fold imidization equivalents of amine 1a-d, n-BuLi and water were doubled.

General method B
In a pressure-stable Schlenk-tube the respective amine 1a-d (1.0 equiv) was dissolved in dry THF under a nitrogen atmosphere and cooled to -78 °C. Subsequently, 1.6 M n-BuLi solution (2.0 equiv) was added and the reaction mixture was stirred for 1 h at -78 °C. The solution was allowed to warm-up to room temperature and the respective ester 4-5 (1.0 equiv) was added. The mixture was heated to 90 °C for 72 hours (caution: Schlenk-tube under pressure) and then cooled to room temperature. The resulting mixture was concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography to obtain the respective product. For two-fold imidization equivalents of amine 1a-d and n-BuLi were doubled.

Conversion of isoimide 10a to imide 6a
In a Schlenk-tube 10a (10.0 mg, 23.5 µmol, 1.0 equiv) was dissolved in THF (1.0 mL) under a nitrogen atmosphere and heated to 75 °C. Subsequently, tert-BuOK solution (0.24 mL, 0.5 M in water, 118 µmol, 5.0 equiv) was carefully added and heated for 6 h at 75 °C. The reaction mixture was cooled to room temperature and 20 mL dichloromethane and 20 mL water was added. The mixture was extracted with dichloromethane. The combined organic layers were washed with water, dried over MgSO4 and concentrated under reduced pressure. The product was dried under high vacuum to give 6a (9.9 mg, 23.5 µmol, 99%) as a white solid. 1 H NMR spectrum was in accordance with product identity of one-pot procedure.

Single crystal X-ray analysis
Crystals suitable for single x-ray diffraction were grown by slow evaporation of concentrated dichloromethane or chloroform solutions or slow diffusion of n-hexane or methanol into dichloromethane or chloroform solutions.                        Effective fluorescence quantum yields of bulk powder samples were determined using an integration sphere. Represent the lower limit of the intrinsic fluorescence quantum yields due to reabsorption effects.
[d] Precise determination not possible due to weak resolution of absorption spectra (low solubility of substrate).