Synthesis and characterization of a new triptycene based tripod

Herein, we report an efficient and facile synthesis of a new triptycene based tripodal ligand containing both imine functionality and phenolic pendant arms. This tripodal unit is a potential building block for constructing novel supramolecular architectures. The newly synthesized 2,6,14-triaminotriptycene derivative, which was characterized by FT-IR, UV−Vis absorption, mass and NMR spectroscopic techniques has interesting properties such as high solubility in common organic solvents and fluorescence emission in THF solution (λ = 550 nm).

The directional bonding approach dictates that the design of a polyhedral supramolecular structure necessitates one of the building blocks to possess at least three binding sites.
Herein, we report an efficient and facile synthesis of a new triptycene-based tripodal ligand containing both imine functionality and phenolic pendant arms, and therefore, it can act as trisbidentate N,O-donor in neutral metal complexes of the type M 3 L 2 .
Scheme 1.Some of the metallacages that can be formed by reaction of a tripodal ligand (black) and a cis-protected metal acceptor with preference for square-planar coordination (green).

Results and discussion
Synthesis of the tripod.The triptycene-based tripodal ligand was synthesized by reacting 2-hydroxybenzaldehyde with 2,6,14-triaminotriptycene [6] in ethanol at room temperature (Scheme 2).The obtained tripod is very soluble in common organic solvents, such as chloroform, dichloromethane and toluene as well as other aromatic solvents, but it is rather insoluble in MeOH and EtOH.

Conclusions
We report the synthesis of a supramolecular donor building block having a central triptycene unit and decorated with three phenolic pendant arms.The new molecule has been characterized by elemental analysis, FT-IR, NMR, UV-Vis and MALDI-TOF spectrometries.The triptycene-based tripodal ligand acting as trisbidentate N,O-donor drives self-assembly processes with naked Zn(II) ions that leads to a TBP metallacage.
Interestingly, the triptycene-based tripod is soluble in common organic solvents and emits fluorescence in solution.

Syntheses of the tbp cage
Self-assembly of the triptycene tripod (0.030 g, 4.9 10 -5 mol in 7 mL of DCM) with Zn(OAc) 2 •2H 2 O (0.016 g, 7.4 10 -5 mol in 7 mL of MeCN) in a 2:3 ratio was carried out at room temperature for overnight and the resulting solution was evaporated and washed with diethyl ether to obtain the cage Zn 3 L 2 as yellow coloured powdered solid. 1

Scheme 2 .
Scheme 2. Synthetic approach for obtaining the triptycene-based tripod for constructing TBP metallacages.The tripodal/trisbidentate N,O-donor ligand has been represented in black, while the four-coordinate metal acceptor has been represented in green.

1 H
NMR spectrum of the triptycene-based tripod (Fig.1) revealed the presence of three characteristic non-aromatic signals at about 13.0, 9.0 and 5.8 ppm that were assigned to phenol (3H), imino (3H) and 9,10 protons of dihydroanthracene (2H), respectively.It must be noted that both phenol and imino proton signals of the arms in 2,6-positions appear as unique singlets at about 13.04 and 8.88 ppm, respectively, while the corresponding proton signals of the arm in 14-position are slightly shifted to lower field, which matches up almost exactly with the expected results.NMR assignment of each aromatic proton signal, which is shown in Fig.1(bottom), was made by a combination of COSY and NOESY experiments.The IR spectrum of the above triptycene-based tripod shows two strong absorption bands at about 1620 and 1610 cm -1 corresponding to the vibrations of the different imine groups of the molecule.Besides, a broad band corresponding to OH vibrations is observed at about 3430 cm -1 .A MALDI-TOF mass spectrum shows the molecular peak ion at 611.7 m/z.

Fig. 1 .
Fig. 1.View of the 1 H NMR spectrum of the triptycene-based tripod in dmso-d 6 (top) with magnification of the aromatic region (bottom)