Synthesis and Molecular Structures of Two Novel π-Conjugation Extended Dithia [ 3 . 3 ] metacyclophanes

Two novel dithia[3.3]metacyclophanes substituted with ethynyl groups were synthesized as small-sized metacyclophanes from the corresponding brominated dithia-metacyclophanes via C-C bond formation reaction. These compounds were characterized by using H NMR, mass spectrometry and elemental analyses. The exact structures were determined by using X-ray diffraction analyses. X-ray diffraction analysis results revealed that these compounds have anti conformations because of existence of intermolecular π-π interaction and some short contacts in the crystal. The long wavelength fluorescence was observed for one of the compound having a pyrene moiety in solid state because of the existence of the intermolecular π-π interaction between two pyrene units.


Introduction
Cyclophanes are cyclic compounds consisting of aromatic rings and bridge chains.
Over the years, synthesis and molecular structures of short-bridged cyclophanes have been attracting many researcher in supramolecular chemistry due to the interesting conformations of these molecules [1].The understanding of the preferred conformations of cyclophane is of importance in the design of various supramolecular systems.On the other hand, small-sized cyclophane molecules act as a model to explore the flexibility of such cyclophanes, due to the presence of various conformational processes including ring flipping, ring-tilting and synanti isomerization.Tsuge et al., have reported the small-sized cyclophane units How to cite this paper: Moriguchi, T., Yakeya, D., Jalli, V., Tsuge, A. and Yoza, K. (2017) Synthesis and Molecular Structures of Two Novel π-Conjugation Extended Di-as a platform to build cofacial bisporphyrins [2].
Although thia-metacyclophanes considered as a member of the metacyclophane family, readily synthesized from base-induced condensation of bis-halomethylarenes with bis-mercaptomethylarenes in the existence of alkaline catalyst using high-dilution technique [3].Varieties of [3.3]metacyclophanes containing oxygen [4] and nitrogen [5] as a hetero atom have also been reported.In general, cyclic compounds such as small sized metacyclophanes have various conformations derived from their orientations of the aromatic parts [6].As part of our ongoing research towards the synthesis and conformational analysis of various substituted [3.3]metacyclophanes [7] [8], in this study, we report the synthesis and absolute structure determination of two novel small-sized metacyclophanes having thiaether bridges and ethynyl substituents.

Materials and Methods
All reagents and solvents were obtained from commercial sources and are used without further purification.The 1 H-NMR spectra were recorded on a Bruker ABANCE 400 spectrometer in CDCl 3 with tetramethylsilane (Me 4 Si) as the internal reference.The electron impact (EI) mass spectra (MS) of the compounds were obtained on a JEOL JMS-SX102A spectrometer using dichloromethane (DCM) as the solvent.The instrument was operated in positive ion mode over an m/z range of 100 -1200.Elemental analyses were performed on a YANAKO MT-5 CHN analyzer.Column chromatography was carried out on silica gel (5 -50 g, Wako gel C-300).

Single-Crystal X-Ray Analysis and Structure Determination
The structure was solved using SHELXS-2014/7 direct method [12], and subsequent structure refinements were performed using SHELXL-2014/7 [12].All non-hydrogen atoms were refined with anisotropic displacement parameters.
Hydrogen atoms at carbon atoms were added geometrically and refined using a riding model (constrained).The final cycle of full-matrix least-squares refinement on F 2 was based on 3587 observed reflections and 100 variable parameters and converged with un-weighted and weighted agreement factors of: , respectively.The standard deviation for the observations of the unit weights was 1.227 [13], and the sigma weights were used in the LS calculation [14].
The data were collected at a temperature of 90 K to a maximum 2θ value of 25.04˚ (0.84 Å resolution).APEX2 software was used for preliminary determination of the unit cell [10].Determination of the integrated intensities and unit cell refinement were performed using the SAINT program [11].Out of the 10028 reflections that were collected, 4233 were unique (Rint = 0.0121); equivalent reflections were merged.The linear absorption coefficient, μ, for Mo-Kα radiation was 0.240 cm −1 .
An empirical absorption correction was applied that resulted in transmission factors ranging from 0.900 to 0.960 [10].The data were corrected for Lorentz and polarization effects.
The structure was solved using SHELXS-2014/7 direct method [12], and subsequent structure refinements were performed using SHELXL-2014/7 [12].All non-hydrogen atoms were refined with anisotropic displacement parameters.Hydrogen atoms at carbon atoms were added geometrically and refined using a riding model (constrained).The final cycle of full-matrix least-squares refinement on F 2 was based on 4233 observed reflections and 311 variable parameters and converged with un-weighted and weighted agreement factors of:  , respectively.The standard deviation for the observations of the unit weights was 1.215 [13], and the sigma weights were used in the LS calculation [14].
The results are summarized in Table 1.
In the EI mass spectra of the compounds 2a and 2b using 50 eV ionization voltage, only one intensive signal with characteristic isotopic patterns for [M] + were detected.
In the 1 H NMR spectra, quite simple aromatic proton signals corresponding to the phenyl groups of the compounds 2a and 2b were observed.Therefore, it was quite easy to determine the exact structure of the molecule via simple 1 H NMR analysis.In addition, the bridge ether protons appeared as simple singlet(s), germinal coupling pattern(s) are not observed.Therefore, the molecular structures are readily moved in the chloroform-d solution at 297 K, in other words, the molecules are not rigid completely in solution.
A single-crystal X-ray diffraction study was performed to determine the structures of the compounds 2a and 2b in the solid state.To the best of our knowledge, the exact structures and crystal packing of these cyclophane compounds have not been previously characterized by X-ray analysis.
The compound 2a crystallizes in the space group P2 1 /c (Z = 2, Figure 2).Molecules 2a exist in anti conformation structure in the crystal (Figure 1).
The orientation of the two ethynyl substituents are effectively stabilized by intermolecular short contacts between the hydrogen atoms of the ethynyl groups and the lone pairs of the bridge sulfur atoms (Figure 2).
On the other hand, the compound 2b crystallizes in the space group P − 1 (No.2) with the anti conformer in the unit cell (Z = 2, Figure 3).In the crystal packing of molecule 2b, there existed intermolecular π-π interaction between pyrene units resulted in complex packing (Figure 4).
We have also evaluated the photochemical properties of the two compounds 2a and 2b.UV-visible and fluorescence spectral measurements were performed, and the results are summarized in Table 2.
In general, the compounds, such as pyrene derivatives exhibit quite strong emission both in solutions and in the solid state.The emission peak maxima in solutions were observed at 334 nm for 2a and at 410 nm for 2b, respectively.
In the solid state, however, the emission maxima shifted to a much longer wavelength region.This phenomenon can be explained by the intermolecular interactions existing between the molecules when the compound 2b is in the solid form.This explanation is strongly supported by the results of the single crystal X-ray single crystal analysis.Furthermore, HOMO and LUMO energy level calculations of the π systems of the compounds were carried out using density functional theory (DFT) B3-LYP 6-31G** level on SPARTAN14 Suite program [15].The atomic coordinate data (x, y, z) of the X-Ray analyses were used in calculations.The calculation results were HOMO −6.05 eV LUMO −0.95 eV for 2a and HOMO −5.15 eV LUMO −1.54 eV for 2b, respectively (Figure 5).

Conclusion
In conclusion, two novel π-conjugation extended dithia [3.3]     and 2b were synthesized using Suzuki coupling reaction and their absolute structures were determined via X-ray diffraction analysis.Further, we have also evaluated the UV-Visible and Fluorescence spectral properties of these compounds.The long wavelength fluorescence was observed for the compound 2b in solid state because of the existence of the intermolecular π-π interaction between two pyrene units.

A
colorless prismatic crystal of 6,15-diethynyl-2,11-dithia[3.3]metadibenzenophane (2a) with the approximate dimensions 0.50 × 0.15 × 0.10 mm was mounted on a glass fiber.The data collection was performed on a Bruker APEX II KY CCD diffractometer using graphite monochromatized Mo-Kα radiation (λ = 0.71073Å) and a nominal crystal-to-area detector distance of ca.83 mm.The data were collected at a temperature of 90 K to a maximum 2θ value of 25.02˚ (0.84 Å resolution).APEX2 software was used for preliminary determination of the unit cell [10].Determination of the integrated intensities and unit cell refinement were performed using the SAINT program [11].Out of the 3587 ref-lections that were collected, 1249 were unique (Rint = 0.0151); equivalent reflections were merged.The linear absorption coefficient, μ, for Mo-Kα radiation was 0.337 cm −1 .