The Crystal Structures and application research of 9,10-Dibromoanthracene

Introduction

9,10-Dibromoanthrene (Figure 1) is an important intermediate in organic synthesis, which is widely used in chemical industry, medicine and other fields. The first molecule which was examined in the present series of investigations of anthracene derivatives was 9:10-dibromoanthracene. The structure of this molecule has been investigated previously but as no details of the structure or coordinates of the atoms are given, a full analysis by X-ray diffraction methods has been carried out.

The Crystal Structures of 9,10-Dibromoanthracene

9,10-Dibromoanthracene, C₁₄H₈Br₂; M=336.0; m.p. 226°C. Triclinic, a=4.06±0.01, b= 8.88±0.02, c=16.15±0.04Å, ɑ= 98°50'±10', β=97°05'±10', γ=100°21'±10'. Volume of the unit cell =559.3Å. Density, calculated (Z=2)=1.983g/cm3, measured=1.981g/cm3. Absorption coefficient for X-rays, ‌λ‌=1.542Å,μ=92.7cm.^-1; ‌λ= 0.7107Å, μ= 78.2cm.^-1. Total number of electrons per unit cell=F(000)=324. The unit-cell dimensions determined by Kitajgorod skij are referred to an A-centred cell. The standard deviations of the atomic coordinates,calculated from Cruiekshank's formulae are 0.005Å for the bromine atoms and 0-038Å for the carbon utoms, so that the standard deviations of the mean bond lengths are about 0.025 Å for a Br-C bond,and 0.03 Å for a C-C bond.The molecule is completely planar within the limits of experimental error, the Br-C distance (1.93Å)corresponds to a single bond, and the C-C bond lengths do not differ significantly from the corresponding bond lengths in anthracene. All the intermolecular distances correspond to normal van der Waals interactions. The mean perpendicular distance between the planes of molecules related by translation a is 3.55Å.[1]

Application research examples

Diborylated magnesium anthracene as precursor for B₂H₅^--bridged 9,10-dihydroanthracene

9,10-(Bpin)₂-anthracene (3, HBpin = pinacolborane) was synthesized from 9,10-dibromoanthracene in a stepwise lithiation/borylation sequence. The reaction of 3 with highly activated magnesium furnished the diborylated magnesium anthracene 4, which was quenched in situ with ethereal HCl to yield cis-9,10-(Bpin)₂-DHA (cis-5, DHA = 9,10-dihydroanthracene). Compound cis-5, in turn, can be reduced with Li[AlH4] in THF to give its diborate Li₂[cis-9,10-(BH₃)₂-DHA] (Li₂ [cis-6]). In the crystal lattice, the THF solvate Li₂[cis-6]⋅₃ THF establishes a dimeric structure with Li-(μ-H)-B coordination modes. Hydride abstraction from Li₂[cis-6] with Me₃SiCl yields the B-H-B-bridged DHA Li[7]. This product can also be viewed as a unique cyclic B₂H₇^- derivative with a hydrocarbon backbone. Treatment of Li₂[cis-6] with the stronger hydride abstracting agent Me₃SiOTf (HOTf=trifluoromethanesulfonic acid) in THF affords the THF diadduct of cis-9,10-(BH(OTf))₂-DHA.[2]

9,10-Dibromoanthracene were used as representative π-conjugated molecules

Crystal engineering for single crystallization of π-conjugated molecules has attracted much attention because of their electronic, photonic, and mechanical properties. However, reproducibility is a problem in conventional printing techniques because control of solvent evaporation is difficult. Researchers investigated the phase diagrams of two anthracene derivatives in synthesized ionic liquids for non-volatile crystal engineering to determine the critical points for nucleation and crystal growth. Anthracene and 9,10-dibromoanthracene were used as representative π-conjugated molecules that form crystal structures with different packing types. Ionic liquids with an alkylpyridinium cation and bis(fluorosulfonyl)amide were good solvents for the anthracene derivatives from ca. 0 °C to 200 °C. The solubilities (critical points for crystal growth) of the anthracene derivatives in the ionic liquids reached the 100 mM level, which is similar to those in organic solvents. Ionic liquids with phenyl and octyl groups tended to show high-temperature dependence (a high dissolution entropy) with 9,10-dibromoanthracene. The precipitation temperature (critical point for crystal nucleation) at each 9,10-dibromoanthracene concentration was lower than the dissolution temperature. The differences between the dissolution and precipitation temperatures (supersaturated region) in the ionic liquids were greater than those in an organic solvent.[3]

The fluorescent probe diethyl-3,3'-(9,10-anthracenediyl)bisacrylate synthesized

Singlet molecular oxygen O₂¹Δ_g is a potent oxidant that can react with different biomolecules, including DNA, lipids and proteins. Many polycyclic aromatic hydrocarbons have been studied as O₂¹Δ_g chemical traps. Nevertheless, a suitable modification in the polycyclic aromatic ring must be made to increase the yield of O₂¹Δ_g chemical trapping. With this goal, an anthracene derivative, diethyl-3,3'-(9,10-anthracenediyl)bisacrylate (DADB), was obtained from the reaction of 9,10-dibromoanthracene and ethyl acrylate through the Heck coupling reaction. The coupling of ethyl acrylate with the anthracene ring produced a new lipophilic, esterified, fluorescent probe reactive toward O₂¹Δ_g. This compound reacts with O₂¹Δ_g at a rate of k(r)=1.69 ×10⁶ M^-1s^-1 forming a stable endoperoxide (DADBO₂), which was characterized by UV-Vis, fluorescence, HPLC/MS and ¹H and ¹³C NMR techniques. The photophysical, photochemical and thermostability features of DADB were also evaluated. Furthermore, this compound has the potential for great application in biological systems because it is easily synthetized in large amount and generates specific endoperoxide (DADBO₂), which can be easily detected by HPLC tandem mass spectrometry (HPLC/MS/MS).[4]

Conjugated Ladder Polymers synthesized

Bheemireddy and his colleagues reported a nontraditional synthesis of cyclopentafused-polycyclic aromatic hydrocarbon embedded ladder polymers using a palladium catalyzed cyclopentannulation polymerization followed by a cyclodehydrogenation reaction. Donor-acceptor type polymers containing a cyclopenta[hi]aceanthrylene acceptor groups can be synthesized by a palladium catalyzed copolymerization between 9,10-dibromoanthracene and a variety of bis(arylethynyl)arenes to give polymers with molecular weights (Mn) of 9-22 kDa. The bis(arylethynyl)arenes were composed of benzene, thiophene, or thieno[3,2-b]thiophene moieties, which provided access to a series of four donor-acceptor copolymers. The polymers were subjected to cyclodehydrogenation with FeCl₃ to access rigid ladder type polymers with the conversion investigated by ¹³C NMR of isotopically labeled polymers. The ladder polymers possess broad UV-Vis absorptions and narrow optical band gaps of 1.17-1.29 eV and are p-type semiconductors in organic field effect transistors.[5]

References

[1] Trotter, J. (1958). The Crystal Structures of Some Anthracene Derivatives. II. 9:10-Dibromoanthracene. Acta Crystallographica, 11, 803–807.

[2] Pospiech S, Bolte M, Lerner HW, Wagner M. Diborylated magnesium anthracene as precursor for B2H5(-)-bridged 9,10-dihydroanthracene. Chemistry. 2015;21(22):8229-8236. doi:10.1002/chem.201500541

[3] Watanabe S, Ono K, Nakayama R, et al. Phase Diagrams of Anthracene Derivatives in Pyridinium Ionic Liquids. Chemphyschem. 2024;25(11):e202300867. doi:10.1002/cphc.202300867

[4] Oliveira MS, Severino D, Prado FM, et al. Singlet molecular oxygen trapping by the fluorescent probe diethyl-3,3'-(9,10-anthracenediyl)bisacrylate synthesized by the Heck reaction. Photochem Photobiol Sci. 2011;10(10):1546-1555. doi:10.1039/c1pp05120b

[5] Bheemireddy SR, Hautzinger MP, Li T, Lee B, Plunkett KN. Conjugated Ladder Polymers by a Cyclopentannulation Polymerization. J Am Chem Soc. 2017;139(16):5801-5807. doi:10.1021/jacs.6b12916

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