Oxacalix[2]arene[2]triazine Derivatives with Halogen Bond Donors

Article pubs.acs.org/crystal

Oxacalix[2]arene[2]triazine Derivatives with Halogen Bond Donors: Synthesis, Structure, and Halide Binding in the Solid State Sen Li,†,§ Xu-Dong Wang,†,∥,§ Qi-Qiang Wang,† Yu-Fei Ao,† De-Xian Wang,*,†,∥ and Mei-Xiang Wang*,‡ †

Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡ The Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China ∥ University of Chinese Academy of Sciences, Beijing 100049, China S Supporting Information *

ABSTRACT: By means of post-macrocyclization functionalization, a series of oxacalix[2]arene[2]triazine derivatives 3a− d, bearing mono- and dihalogen (Br, I) substituted phenyl moieties on the larger rim of the triazine rings were very efficiently synthesized with yields of 85−89%. The binding of 3a−d toward halide anions in the solid state was investigated by X-ray crystallography. For complexation of 3c (X = H, X′ = I) with chloride, a Cl−···H2O···Cl−···H2O···H2O pentagonal hydrogen bond network was found included in the cavity of the host molecule, as stabilized by cooperative anion-π interaction and halogen and hydrogen bonding. In contrast, with iodide only intermolecular halogen bonding between 3c and iodide was observed. On the other hand, 3d (X = X′ = I) forms a series of very similar chelating halogen bonding motifs with chloride, bromide, and iodide, respectively.

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INTRODUCTION Because of the important roles that anions play in biological and environmental processes, anion recognition is one of the central themes in supramolecular chemistry.1−3 To conquer the challenge caused by the inherent properties of anions such as varied geometries, low charge density, high solvation free energies, and a narrow pH window, a variety of complementary noncovalent interactions including electrostatic interaction,4−9 hydrogen bonding,10−20 and Lewis acid−base interaction21−26 have been developed for efficient recognition of anions. Recently, the intensive studies based on halogen bonding and anion-π interactions are remarkable.27−33 For instance, typical examples of anion receptors such as iodo-perfluoroaromatics based tripodal receptors,34−36 calix[4]arene derivatives,37,38 and haloimidazolium-containing receptors39−42 have demonstrated the promising halogen bonding contribution for anion recognition. In context of anion-π interactions, charge-neutral anion receptors incorporating both hydrogen bonding and anion-π motifs,43−48 planar electron-deficient aromatics49−55 such as tetracyanopyrazine (TCP),49,50 naphthalenediimides (NDI),51,52 and 1,4,5,8,9,12-hexaazatriphenylene-hexacarbonitrile (HAT(CN)6),54,55 and electron-deficient cavity containing oxacalix[2]arene[2]triazine hosts56−63 have been reported. Inspired by the anion-binding ability of both halogen bonding and anion-π interactions, exploration of cooperative anion-π interactions with halogen bonding by tailor-made dual hosts would be attractive. One of the salient structural features of oxacalix[2]arene[2]triazines is the formation of shape-persistent 1,3-alternate © XXXX American Chemical Society

conformation, in which two triazine rings form a V-shaped cleft. 64 The unique conformational structure renders oxacalix[2]arene[2]triaiznes useful platforms for fabrication of sophisticated molecular architectures.60,65−71 Therefore, we envisioned introducing halogen donors onto the larger rim of triazine rings. The halogen donors, together with the intrinsic electron-deficient V-shaped cleft formed by the two triazine rings, would construct a expanded V-shaped cavity bearing multiple distinct anion binding sites and thus can provide the potentiality for cooperative anion-π interaction and halogen bonding. Reported herein is the synthesis, structure, and anion binding properties of oxacalix[2]arene[2]triazine derivatives with the decorated halogen donors. Structural evidence of cooperative anion-π interaction and halogen bonding is demonstrated in the complex of 3c and chloride in the solid state. In addition to this, a series of intriguing chelating halogen bonding motifs are formed between 3d and chloride, bromide, and iodide as facilitated by the unique 1,3-alternate conformational host platform.

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EXPERIMENTAL SECTION

X-ray Crystallography. Single crystals were obtained through slow diffusion of diethyl ether into acetone or chloroform solutions of 3, or a mixture of 3 and different halides (as tetraethylammonium or tetrabutylammonium salts). Received: June 15, 2016 Revised: July 30, 2016

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DOI: 10.1021/acs.cgd.6b00916 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Single crystal X-ray diffraction data were collected on a MM007HF + CCD (Saturn724+) diffractometer for structures 3a, 3c·Cl−, 3c·I−, 3d·Cl−, 3d·I− and on a Saturn724 + CCD diffractometer for structures 3b, 3d, 3d·Br− using MoK/α radiation (λ = 0.71073 Å) at a temperature of 173 K. The intensity data were collected by the omega scans technique, scaled, and reduced with CrystalClear. The correction of the collected intensities for absorption was done using the CrystalClear program. The structures were solved by direct methods using SHELXS and refined using full-matrix least-squares methods in ShelXL. All nonhydrogen atoms were refined anisotropically depending on the occurrence of disorder in the structures. All hydrogen atoms were placed geometrically and with a riding model for their isotropic temperature factors. General Procedure for Synthesis of 3a−d. 2 (191 mg for 2a, 277 mg for 2b, 242 mg for 2c, 381 mg for 2d, 1.1 mmol), potassium carbonate (152 mg, 1.1 mmol), and acetone (25 mL) were added to a flask, and the mixture was heated to reflux for 0.5 h. Then a solution of 1 (222 mg, 0.5 mmol) in acetone (25 mL) was added dropwise during 0.5 h. The resulting mixture was refluxed for another 15 min. After being cooled down to room temperature, the solid was removed by filtration. The filtrate was concentrated, and the residue was chromatographed on a silica gel column eluted with a mixture of petroleum ether, dichloromethane, and acetone (10:2:1, v/v/v) as the mobile phase to give pure product 3. 3a (White Solid, 306 mg, Yield 85%). mp 182−183 °C; 1H NMR (CDCl3/300 MHz) δ 7.68 (dd, J = 1.4, 8.0 Hz, 2H), 7.42 (td, J = 1.4, 8.1 Hz, 2H), 7.30−7.18 (m, 6H), 6.86 (dd, J = 2.2, 8.2 Hz, 4H), 6.72 (t, J = 2.2 Hz, 2H); 13C NMR (CDCl3/75 MHz) δ 173.8, 173.6, 151.8, 148.8, 133.6, 130.3, 128.8, 127.8, 123.5, 119.2, 116.4, 115.9; IR (KBr) ν 1563, 1362, 1214 cm−1; MS (EI-MS) m/z (%): 635 [M − Br]+ (100), 637 [M − Br + 2]+ (95). HRMS (EI): m/z [M]+ calcd. for C30H16Br2N6O6: 713.9498. Found: 713.9490. 3b (White Solid, 389 mg, Yield 89%). mp 232−233 °C; 1H NMR (CDCl3/300 MHz) δ 7.63 (d, J = 8.0 Hz, 4H), 7.25 (t, J = 8.1 Hz, 2H), 7.09 (t, J = 8.1 Hz, 2H), 6.89 (dd, J = 2.1, 8.1 Hz, 4H), 6.784− 6.777 (m, 2H); 13C NMR (CDCl3/75 MHz) δ 173.9, 173.1, 152.0, 146.7, 132.8, 130.4, 128.7, 119.4, 117.7, 116.5; IR (KBr) ν 1576, 1360, 1223 cm−1; MS (EI-MS) m/z (%):791 [M − Br]+ (20), 793 [M − Br + 2]+ (100), 795 [M − Br + 4]+ (98), 797 [M − Br + 6]+ (20). Anal. Calcd for C30H14Br4N6O6: C, 41.22; H, 1.61; N, 9.61. Found: C, 41.60; H, 1.94; N, 9.40. 3c (White Solid, 362 mg, Yield 89%). mp 189−190 °C; 1H NMR (CDCl3/300 MHz) δ 7.90 (d, J = 7.9 Hz, 2H), 7.45 (t, J = 8.0 Hz, 2H), 7.26−7.22 (m, 4H), 7.06 (t, J = 7.8 Hz, 2H), 6.87 (dd, J = 2.0, 8.1 Hz, 4H), 6.734−6.727 (m, 2H); 13C NMR (CDCl3/75 MHz) δ 173.8, 173.7, 151.8, 139.8, 130.3, 129.8, 128.2, 122.9, 119.3, 116.4, 90.0; IR (KBr) ν 1565, 1363, 1207 cm−1; MS (EI-MS) m/z (%): 683 [M − I]+ (100), 684 [M − I + H]+ (40). Anal. Calcd for C30H16I2N6O6: C, 44.47; H, 1.99; N, 10.37. Found: C, 44.31; H, 2.22; N, 10.33. 3d (White Solid, 448 mg, Yield 85%). mp 251−252 °C; 1H NMR (CDCl3/300 MHz) δ 7.86 (d, J = 7.9 Hz, 4H), 7.26 (t, J = 8.1 Hz, 2H), 6.76 (dd, J = 2.0, 7.9 Hz, 4H), 6.79−6.73 (m, 4H); 13C NMR (CDCl3/75 MHz) δ 173.9, 173.0, 152.0, 151.9, 140.0, 130.4, 129.7, 119.5, 116.6, 90.3; IR (KBr) ν 1571, 1358, 1217 cm−1; MS (MALDITOF) m/z (%): 935.5 [M − I + H]+ (100). Anal. Calcd for C30H14I4N6O6: C, 33.93; H, 1.33; N, 7.91. Found: C, 34.20; H,1.58; N, 7.72.

Scheme 1. Synthesis of Oxacalix[2]arene[2]triazine Derivatives 3 Bearing Halogen Bond Donors

base amount and the reactant concentration, 3 can be obtained in as high as 85−89% yields. Compounds 3a−d were fully characterized by 1H, 13C NMR spectroscopy, MS and elemental analysis (see Supporting Information). To get insight into the structural information from the molecular level, single crystals of compounds 3 were cultivated. Through slow diffusion of diethyl ether into an acetone or chloroform solution of 3, single crystals of 3a, 3b, and 3d suitable for X-ray analysis were obtained. The crystal structures are illustrated in Figures 1, 2, and 3 and Figures S1− S3. As anticipated, all the oxacalix[2]arene[2]triazine derivatives adopt 1,3-alternate conformations, similar to the parent macrocycle 1,67 indicating that the introduced substituents on the triazine rings do not affect the conformation of the macrocyclic backbone. In the case of 3b and 3d, each dihalogen substituted benzene ring plane is almost orthogonal to the attached triazine ring plane, with two halogen atoms directed inward and the other two outward from the macrocyclic cavity, respectively (Figures 2 and 3 and Figures S2 and S3). The two inwardly oriented halogen bond donor sites hence form a new convergent cavity with the V-shaped cleft of the two triazine rings. Interestingly, in 3a the two mono-bromo-substituted benzene rings adopt a trans-orientation (relative to the Vshaped cavity) with only one bromine atom pointing inward the cavity (Figure 1 and Figure S1). As only one set of distinct proton and carbon signals in the NMR spectra was observed, which indicates a fast conformational interconversion exists in solution within the NMR time scale, the above trans-orientation of the two substituted benzene rings in 3a in the solid state is hence probably caused by the crystal lattice packing. Crystallographic Study of the Binding between Oxacalix[2]Arene[2]Triazine Derivatives and Halides. Having the oxacalix[2]arene[2]triazine derivatives bearing halogen bonding donors in hand, we next examined their binding toward halides in the solid state. Through slow diffusion of diethyl ether to a solution of oxacalix[2]arene[2]triazine derivatives in chloroform in the presence of different halides (as tetraethylammonium or tetrabutylammonium salts), single crystals of the complexes of 3c·Cl− and 3c·I−, 3d·Cl−, 3d·

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RESULTS AND DISCUSSION Synthesis and Structure of the Oxacalix[2]arene[2]triaizne Derivatives. We initiated our synthesis through a post-macrocyclization functionalization protocol, as illustrated in Scheme 1. In the presence of base, the aryl nucleophilic substitution reaction of oxacalix[2]arene[2]triazine 167 with mono- or dihalogen substituted phenols 2 in acetone under reflux smoothly gave the target macrocyclic products 3. After the simple optimization of the reaction conditions including the B

DOI: 10.1021/acs.cgd.6b00916 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 1. Crystal structure of 3a.

Figure 2. Crystal structure of 3b.

Figure 3. Crystal structure of 3d.

Figure 4. Crystal structure of the 3c-Cl−-H2O complex. Hydrogen atoms and cations are omitted for clarity.

Br−, and 3d·I− were obtained. The structural details are illustrated in Figures 4−6 and Figures S4−S8.

The interaction of 3c and tetraethylammonium chloride gives an interesting complex structure (Et4N+)2[3c·2Cl−· C

DOI: 10.1021/acs.cgd.6b00916 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 5. Crystal structure of the 3c-I−-CHCl3 complex. Hydrogen atoms and cations are omitted for clarity.

Figure 6. Crystal structures of the complexes of 3d with (A) chloride, (B) bromide, and (C) iodide. Hydrogen atoms and cations are omitted for clarity.

and its phenoxylated analogue, two host molecules in the absence of halogen donors in the structures.56,63 Hence, the included Cl1···O7···Cl2···O8···O9 pentagonal hydrogen bond network formed within the cavity of 3c is most probably stabilized by the cooperative anion-π interaction and halogen bonding. Moreover, such binding motifs further interact with each other through an O8−O8 hydrogen bonding bridge and it leads to a dimeric structure (Figure 4B). Interestingly, the 3c·I− complex obtained from 3c and tetrabutylammonium iodide shows a different structure with the 3c-Cl−-H2O complex. For example, although the host adopts a similar conformation, the guest iodide anion (I3), however, resides outside the V-shaped host cavity (Figure 5). Each iodide interacts with two iodine atoms (I1 and I2) on the two adjacent host molecules through intermolecular halogen bonding (dI3−I1 = 3.607 Å, dI3−I2 = 3.725 Å). With the help of four halogen bonds and π−π stacking between the benzene rings of the host molecules, two iodides and two host molecules form a 2 + 2 complex. Such 2 + 2 complex results in two pseudo intermolecular V-shaped cavities (across from C7 to C17), and within each pseudo cavity a chloroform molecule is included and forms a lone-pair electron-π interaction with one of the triazine rings (dCl3‑plane = 3.362 Å). The distinguished structural difference between 3c-I−-CHCl3 complex and 3cCl−-H2O complex is that iodide forms a sole halogen bonding,

(H2O)3] as shown in Figure 4. The host molecule adopts a shape-persisted 1,3-alternate conformation. The two iodine atoms on the phenyl substituents, however, point outward from the cavity instead of forming a convergent cavity with the two triazine rings. A unique pentagonal hydrogen bond network composed of two chloride anions and three water molecules is included within the V-shaped host cavity. One chloride (Cl1) locates above one of the triazine rings with a distance of 3.149 Å to the triazine plane, forming a typical anion-π interaction.11 Meanwhile, a water molecule (O7) resides over the other triazine ring forming a lone-pair electron-π interaction as judged by the short distance from O7 to the triazine plane (dO7‑plane = 2.917 Å). These two species hydrogen bond to each other with a distance of 3.125 Å between Cl1 and O7. Moreover, the chloride (Cl1) and water molecule (O7) form hydrogen bonds with another water molecule (O9) and chloride (Cl2), respectively, and the latter two bind a third water molecule (O8), furnishing a Cl1···O7···Cl2···O8···O9 pentagonal hydrogen bond network. Noticeably, in addition to hydrogen bonding with the two water molecules (O7 and O8), Cl2 also interacts with an iodine atom (I2) from another adjacent host molecule through halogen bonding (dCl2−I2 = 3.415 Å). It is worth addressing that such an interaction mode of 3c-Cl−-H2O complex is quite different from the host−Cl−− H2O ternary complexes formed with the parent macrocycle 1 D

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chloride, bromide, and iodide through halogen bonding, hence representing rare examples of charge neutral halogen bonding host molecules. The current study therefore provides the promising future for tailor-made dual anion-π and halogen bonding hosts utilizing the unique shape-persistent 1,3alternate oxacalix[2]arene[2]triazine platform.

whereas chloride forms cooperative anion-π interaction and halogen bonding with the hosts. This finding is consistent with the fact that iodide usually acts as a stronger halogen bonding acceptor rather than an anion-π donor. Figure 6 and Figures S6−S8 illustrate the structures of the complexes of 3d with chloride, bromide, and iodide, respectively. In all three cases, an intriguing chelating halogen bonding motif between the host and guest anions is observed in the structures. Each diiodine substituted benzene ring plane is almost orthogonal to the attached triazine ring plane, with two iodine (I1 and I3) atoms directed inward and the other two (I2 and I4) outward from the cavity, respectively. As a result, the two inwardly oriented iodine atoms (I1 and I3) form a new convergent cavity with the two triazine rings. Halide anion (Cl−, Br−, or I−) locates in between the two inwardly oriented iodine atoms through halogen bonding, and a solvent molecule (chloroform or water) resides within the enclosed cavity formed and locates above one of the triazine rings forming lone-pair electron-π interactions (dCl3‑plane = 3.382 Å, dCl6‑plane = 3.418 Å, dO7‑plane = 3.090 Å, respectively). Noticeably, the distances between halides and the two iodine atoms (I1, I3) vary depending on the type of anions accommodated in the cavity (dCl1−I1 = 3.523 Å, dCl1−I3 = 4.143 Å for chloride; dBr1−I3 = 3.584 Å, dBr1−I1 = 4.067 Å for bromide; dI5−I1 = 3.557 Å, dI5−I3 = 3.534 Å for iodide). These different distances indicate that chloride (Cl1) and bromide (Br1) tend to form halogen bonding with one of the inwardly directed iodine atoms, while iodide (I5) forms halogen bonding with both of the iodine atoms. Following the order of chloride, bromide, and iodide, the localization of the halide tends to shift to the middle of the two iodine atoms, which is consistent with the strength order of I− > Br− > Cl− as halogen bonding acceptors5 and their radius sequence. Interestingly, the larger rim distance between the two triazine rings follows a decreasing order of 9.132 Å (free host 3d), 8.412 Å (3d·Cl−), 8.367 Å (3d·Br−), and 8.308 Å (3d·I−). The variations of the cleft size indicate that the host molecule is able to self-tune its cavity in response to the guest halides in order to achieve strongest halogen bonding. It is worth addressing that though the electron-deficient triazine ring shows affinity to electron-rich species (chloride or oxygen of the solvents) through long pair electron-π interactions, only halogen bonds between host and halides rather than cooperative halogen bonding and anion-π interaction are observed. The probable reason can be that the strict directionality of halogen bonding disfavors the intramolecular cooperative halogen bonding and anion-π interaction but benefits the intermolecular halogen bonding in the crystal lattice packing (Supporting Information).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b00916. Experimental details and characterization of products, 1H and 13C NMR spectra for new compounds (PDF) Accession Codes

CCDC 1485664−1485671 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*(D.-X.W.) Tel: +86 10 62565610. Fax: +86 10 62564723. Email: [email protected]. *(M.-X.W.) Tel: +86 10 62796761. E-mail: wangmx@mail. tsinghua.edu.cn. Author Contributions §

S.L. and X.-D.W. contributed equally to this paper.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank NSFC (21272239, 91427301, 21521002) and MOST (2013CB834504). Q.-Q.W. thanks NSFC (21502200) for financial support.

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REFERENCES

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CONCLUSIONS In summary, we have synthesized oxacalix[2]arene[2]triazine derivatives 3a−d bearing mono- and dihalogen substituted benzene rings on the larger rim of triazine rings through very efficient aromatic nucleophilic reactions. The resulting halogen substituted macrocycles adopt 1,3-alternate conformation, therefore yielding an expanded convergent cavity composed of two triazine rings and two additional halogen bonding donors. The outcome of X-ray crystallographic study showed the structural evidence of the cooperative anion-π interaction and halogen bonding in the complex of 3c and chloride, whereas only intermolecular halogen bonding between 3c and iodide was observed. The tetra-iodine substituted macrocyclic molecule 3d formed a series of chelating complexes with E

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DOI: 10.1021/acs.cgd.6b00916 Cryst. Growth Des. XXXX, XXX, XXX−XXX