(E)-2-tert-Butyl-6-[(naphthalen-1-yl)iminomethyl]phenol

The asymmetric unit of the title Schiff base compound, C21H21NO, contains two crystallographicaly independent molecules. The dihedral angles between the naphthalene mean plane and the benzene ring are 29.28 (8) and 26.92.(8)° in the two molecules. An intramolecular O—H⋯N hydrogen bond and weak intramolecular C—H⋯O hydrogen bonds stabilize the structure of each independent molecule.

The asymmetric unit of the title Schiff base compound, C 21 H 21 NO, contains two crystallographicaly independent molecules. The dihedral angles between the naphthalene mean plane and the benzene ring are 29.28 (8) and 26.92.(8) in the two molecules. An intramolecular O-HÁ Á ÁN hydrogen bond and weak intramolecular C-HÁ Á ÁO hydrogen bonds stabilize the structure of each independent molecule.

Related literature
For general background to the synthesis and catalytic activity of FI catalysts, see: Matsui & Fujita (2001); Matsui et al. (1999Matsui et al. ( , 2001.  Table 1 Hydrogen-bond geometry (Å , ). In FI catalysts, the ligand systems can be produced by using condensation reaction of salicylaldehydes and primary amines, under standard conditions. These reactions produce Schiff bases with high selectivity, in high yield. Amines and some salicylaldehyde derivatives are commercially available. The presence of salicylaldimine unit allows for easy variation of the system on both the phenol and amine functionalities, for instance the variations of the mentioned compounds lead to profound effects on polymers.
X-ray crystallographic analysis reveals that there are two molecules in the asymmetric unit of the title Schiff base compound ( Fig. 1). In both molecules, the C═N bond distances are 1.289 (3) and 1.290 (3) Å, respectively. The angle between naphthalene mean plane and phenyl rings are equal to 29.28 (8) and 26.92.(8)°, respectively. Bond distances and angles are in the normal ranges reported for Schiff base compounds (Hiller et al., 1993;Darensbourg et al., 2005;Jamjah et al., 2011). There are intramolecular O-H···N hydrogen bonding between hydroxyl and imine groups. There are also weak intramolecular C-H···O hydrogen bonding which play important role in the stabilization of the crystal structure of the title compound ( Fig. 1 & Table 1).

Experimental
Synthesis of 3-tert-butyl-2-hydroxybenzaldehyde 2,6-dimethylpyridine (50.0 mmol, 5.4 g) and SnCl 4 (10.0 mmol, 2.6 g) were added into 2-tert-butylphenol (40.0 mmol, 6 g) in toluene (125 ml) into a 250 ml round-bottom flask which had been already dried and purged with nitrogen and equipped with a stirrer bar. White fumes appeared immediately during the addition and stirring was continued at room temperature for 30 min. The mixture turned yellow, and then dry paraformaldehyde (160.0 mmol, 4.8 g) was added into the reaction solution and stirred at 100°C for 12 hrs. After cooling to room temperature, the yellow reaction mixture was poured into a mixed solution of water (3×100) and diethyl ether (3×50). The yellow precipitate was removed via filtration. The filtrate was extracted with diethyl ether (2×100 ml) and the organic layer was washed further with saturated NaCl (aq) (brine) (50 ml). The solution was then dried over anhydrous sodium sulfate. After that, it was concentrated under reduced pressure (in a rotary evaporator) and the residue was purified via column chromatography on silica gel, using a mixed solvent of ethylacetate/hexane (v/v, 5/100) as the mobile phase. The product was isolated as pale yellow oil and characterized by 1 H-NMR, 13 C-NMR and FTIR as follows. Synthesis of (E)-2-tert-butyl-6-((naphthalen-1-ylimino)methyl)phenol: Into a 100 ml round-bottom flask which had been dried and purged with nitrogen, ethanol (30 ml), α-naphthylamine (9.99 mmol, 1.34 g), 3-tert -butyl-2-hydroxybenzaldehyde (7.86 mmol, 1.40 g) and molecular sieve 3Å (5 g) were added.
This mixture was refluxed at 78°C for 8 hrs and then stirred at ambient temperature for another 12 hrs. The reaction solution was concentrated under reduced pressure (in a rotary evaporator). The residue was purified via column chromatography on silica gel, using a mixed solvent of ethylacetate/hexane (v/v, 2/98) as the mobile phase to obtain a yellow-orange crystalline solid (yield: 98%).

Refinement
All H atoms were positioned geometrically and refined as riding atoms with O-H = 0.82, U iso (H) = 1.5U eq (O) and C-H = 0.93 to 0.96 Å, U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for the others. Fig. 1. The molecular structure of the title compound with displacement ellipsoids drawn at 50% probability level. The intramolecular O-H···N and C-H···O hydrogen bonds are shown as dashed lines.  (17)