Synthesis and Columnar Organization of Partially Fluorinated Dehydrobenz[18]annulenes

Two diamond-shaped and partially fluorinated dehydrobenz[18]annulene macrocycles have been synthesized through a one-pot synthesis relying on fourfold Sonogashira coupling. Single crystal structures of the prepared macrocycles show continuous columnar stacks of these molecules that are mediated by the fluoroarene–alkyne, arene–alkyne, fluoroarene–fluoroarene, and alkyne–alkyne [π···π] interactions instead of the expected fluoroarene–arene [π···π] interaction.


Syntheses of Dehydrobenz[18]annulene (DBA) 1
A one-liter two-neck round bottom flask was equipped with a stir bar and charged with PdCl2(PPh3)2 (0.175 g, 0.25 mmol) and CuI (0.048 g, 0.25 mmol). One neck of the flask was sealed with a septum and the other neck was connected to the condenser. The flask was then evacuated and backfilled with nitrogen three times and left under nitrogen. Dry NEt3 (500 mL) and dry PhMe (550 mL) were transferred via cannula into the round bottom flask and the reaction mixture was stirred at 80 °C. A homogenous solution of 1,2-diiodotetrafluorobenzene (3, 2.01 g, 5 mmol) and 1,3diethynylbenzene (4, 0.69 mL, 5.25 mmol) was made in dry PhMe (20 mL). This solution was slowly added to the flask via a syringe pump at the rate of 2 mL h −1 , and the reaction was stirred at 80 °C for additional 3 days. After that, the hot solution was filtered to remove the salts and catalyst. The filtrate was washed with water, saturated aqueous solution of NH4Cl, and brine, and dried over MgSO4. Then it was passed through a Celite pad and washed with PhMe. The solvent was removed using rotary evaporator to give a viscous crude product. Acetone was added to that crude material and the suspension was filtered off to remove most side products. The filtrate was then evaporated and the obtained solid was recrystallized in PhMe/Me2CO, followed by PhMe/MeCN mixture to get the pure macrocycle 1 in 22% yield (297 mg, 0.54 mmol) as a light brown solid. mp 305-310°C (decomp). 1  A one-liter two-neck round bottom flask equipped with a stir bar was charged with PdCl2(PPh3)2 (0.175 g, 0.25 mmol) and CuI (0.048 g, 0.25 mmol). One neck of the flask was sealed with a septum and the other neck was connected to the condenser. The flask was then evacuated and backfilled with nitrogen three times and left under nitrogen. Dry NEt3 (200 mL) and dry PhMe (550 mL) were then added via a cannula into the round bottom flask and the reaction mixture was stirred at 80 °C. A homogenous solution of 1,2-diiodo-3,4,5,6-tetrafluorobenzene (3, 2.01 g, 5 mmol) and methyl 1,3diethynylbenzoate (5, 0.97 g, 5.25 mmol) was made in dry PhMe (20 mL). Then the solution was slowly added to the flask via a syringe pump at the rate of 2 mL h −1 , and the reaction was stirred at 80 °C for 3 additional days. After that, the hot solution was filtered to remove the salts and catalyst. The filtrate then was washed with water, saturated aqueous solution of NH4Cl, brine, and dried over MgSO4. The solvent was removed using a rotatory evaporator. Acetone was added to the crude mixture and the suspension filtered off to remove most side products. Column chromatography of residue in DCM/hexane (1:1) gave a pure macrocycle 2. Some was also recovered from column chromatography of filtrate in DCM/hexanes (1:9). Together, macrocycle 2 was isolated in a 5% yield (79 mg, 0.12 mmol, Rf: 0.35) as a white solid. mp 308-311°C (decomposed). 1

Single Crystal Structures and Analyses
All measurements were performed on a Bruker DUO platform diffractometer equipped with a 4K CCD APEX II detector and an Incoatec 30-Watt Cu microsource with compact multilayer optics.
Data were collected using a narrow-frame algorithm with scan widths of 0.5% in omega and an exposure time of 20 s/frame at 4 cm detector distance. The data were integrated using the Bruker SAINT program, with the intensities corrected for Lorentz factor, polarization, air absorption, and absorption due to variations in the path length through the detector faceplate. The data were scaled, and an absorption correction was applied using SADABS. The structure was solved with SHELXT 2014 and refined with SHELXL 2018 using full-matrix least-squares refinement. The non-H atoms were refined with anisotropic thermal parameters, and all the H atoms were calculated in idealized positions and refined riding on their parent atoms. Figure S5. Single crystal structure of DBA 1. Thermal ellipsoids are shown at 50% probability levels.

Computational Analyses
The calculations were carried out at the TD-B3LYP-D3/6-311+G(d,p) level of theory using the Gaussian16 software. 3 Figure S7 . Computed HOMO-LUMO gap for DBA 1.

S17
Absorption and Emission Spectra in Solution of DBAs 1 and 2 With limited solubility of these macrocycles in hexanes and pentanes, the UV-vis absorption and fluorescence were investigated in chloroform. The absorption spectra in Figure S9A show the absorption band range for both DBAs between 250 and 375 nm, with λmax of 277 nm for DBA 1 and 275 nm for DBA 2. When excited at 342 nm at 1% transmission ( Figure S9B), both macrocycles showed the similar peaks with the λem for the DBA 1 at 381 nm and at 382 nm for DBA 2.