2,2′-[(2S*,6R*)-Piperidine-2,6-diyl]dipropan-2-ol

In the title compound, C11H23NO2, the piperidine ring has a chair conformation. The two hydroxy H atoms are disordered over two positions with fixed occupancy ratios of 0.57:0.43 and 0.63:0.37. In the molecule, there are two short N—H⋯O interactions. In the crystal, four symmetry-related molecules are linked by O—H⋯O hydrogen bonds to form a cage-like arrangement, centered about the point of intersection of three twofold axes. These cages stack along the [100] direction.

In the title compound, C 11 H 23 NO 2 , the piperidine ring has a chair conformation. The two hydroxy H atoms are disordered over two positions with fixed occupancy ratios of 0.57:0.43 and 0.63:0.37. In the molecule, there are two short N-HÁ Á ÁO interactions. In the crystal, four symmetry-related molecules are linked by O-HÁ Á ÁO hydrogen bonds to form a cage-like arrangement, centered about the point of intersection of three twofold axes. These cages stack along the [100] direction.
The modification of these ligands by the hydrogenation of the pyridine ring installs chirality into the structure and increases the basicity and the strength of the ligand. In contrast to the 2,6-pyridinedicarboxylic acids and its derivatives, which have been extensively used, studies on the corresponding tridentate ONO-piperidine ligands containing the bisalcohols have been very rare so far. The title compound (2) was prepared by the stereoselective cis-reduction of 2,2′-(pyridine-2,6-diyl)dipropan-2-ol (1). Herein we report on the synthesis and the crystal structure of the title compound, (2).
In the molecule the amine (N1) H atom is involved in two short interactions with the hydroxyl O atoms, O1′ and O1′′ (Table 1). The hydroxyl H atoms are each disordered over two positions, H1A/H1B and H1C/H1D. Their occupancies were initially refined before being fixed at 0.57/0.43 and 0.63/0.37, respectively. The 1 H NMR signal for the hydroxyl H atoms [δ 2.88 (bs, 2 H, OH); see archived CIF] is a broad singlet, which indicates some fluxionality of these protons in solution.
In the crystal, four symmetry related molecules are linked by O-H···O hydrogen bonds to form a cage-like arrangement, centered about the point of intersection of three 2-fold axes (Fig 2). These cages are arranged in stacks along direction [100], as shown in Fig. 3.

Experimental
The synthesis of the title compound (2) is illustated in Fig. 4. The starting material, 2,2′-(pyridine-2,6-diyl)dipropan-2-ol (1), was prepared in one step from the commercially available dimethyl pyridine-2,6-dicarboxylate, according to the method described by (Klein et al., 2009). The title compound (2), was synthesized by heating 0.5 g (2.56 mmol) of compound (1), together with 10% Pd/C (430 mg), methanol (10 ml) and acetic acid (10 ml), in an autoclave under hydrogen (50 atm), with stirring at 323 K for 12 h. For workup the reaction was filtered through a pad of celite and washed three times with dichloromethane. The solution was concentrated under vacuum to give a colourless slurry. The slurry was dissolved in dichloromethane and washed with 5% sodium hydroxide and the mixture was stirred for 5 min. The organic layer was separated and the aqueous layer was extracted three times with dichloromethane. The combined organic layers were washed with brine, dried with sodium sulfate and concentrated under vacuum to yield 0.494 g (96%) of compound (2). Melting point: 345.3 K. HRMS calcd. for [C 11 H 23 NO 2 + H + ] 224.1621; found 224.1621. Colourless rodlike crystals were obtained by slow evaporation of a solution of (2) in dichloromethane. Spectroscopic data for the title compound (2), are given the archived CIF.

Refinement
The NH H-atom was located in a difference Fourier map and was freely refined. The OH H atoms are disordered over two positions. They were located in a difference Fourier map and were initially freely refined, including their occupancies, before being refined with distance restraints of 0.84 (2) Å. In the final cycles of refinement they were refined with fixed occupancies of 0.57/0.43 and 0.63/0.37, and allowed to ride on the parent O atom with U iso (H) = 1.5U eq (O). The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.98, 0.99 and 1.00 Å for CH 3 , CH 2 and CH H-atoms, respectively, with U iso (H) = k × U eq (parent C-atom), where k = 1.5 for CH 3 Hatoms and k = 1.2 for all other H-atoms.    Table 1 for details).   Table 1 for details).

Figure 4
Reaction scheme for the synthesis of the title compound, (2). Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. The NH H-atom was located in a difference Fourier map and was freely refined. The OH H atoms are disordered over two positions with fixed occupancies of 0.57/0.43 and 0.63/0.37. They were located in a difference Fourier map and were initially freely refined, including their occupancies, before being refined with distance restraints of 0.84 (2) Å. In the final cycles of refinement they were refined with fixed occupancies of 0.57/0.43 and 0.63/0.37, and allowed to ride on the parent O atom with U iso (H) = 1.5U eq (O). The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.98, 0.99 and 1.00 Å for CH 3 , CH 2 and CH H-atoms, respectively, with U iso (H) = k × U eq (parent C-atom), where k = 1.5 for CH 3 H-atoms and k = 1.2 for all other H-atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (