(2R,2′S)-2,2′-Bi­piperidine-1,1′-diium dibromide

The title compound, C₁₀H₂₂N₂²⁺·2Br⁻, was synthesized via reduction of 2,2′-dipyridyl with Ni–Al alloy/KOH, followed by separation of diastereoisomers (meso and rac) by recrystallization from ethanol. Although the two bridging C atoms are optically active, these two chiral centers adopt an (S,R) configuration; thus, the title compound contains an achiral meso form of 2,2′-bi­piperidine. Both of the piperidinium rings adopt chair conformations, and the two N atoms are trans to each other; an inversion center is located in the mid-point of the central C—C bond. The conformation of the organic moiety resembles that of 1,1′-bi(cyclo­hexa­ne). The organic di­ammonium cations are linked to each other through hydrogen bonding with bromide counter-ions, each of which forms two hydrogen bonds (N—H⋯Br) with two adjacent organic cations, thus linking the latter together in sheets parallel to (100).

Related literature

For more details about synthetic and characterization methods, see: Denmark et al. (2006); Herrmann et al. (2006). For the chemistry of related complexes, see: Mikhalyova et al. (2012); Lyakin et al. (2012). For a related structure (the racemic isomer of the title compound), see: Laars et al. (2011).

Experimental

Crystal data

• C₁₀H₂₂N₂²⁺·2Br⁻

• M_r = 330.11

• Monoclinic, C 2/c

• a = 17.9719 (9) Å

• b = 9.7654 (5) Å

• c = 7.3637 (3) Å

• β = 92.134 (1)°

• V = 1291.45 (11) ų

• Z = 4

• Mo Kα radiation

• μ = 6.25 mm⁻¹

• T = 100 K

• 0.55 × 0.23 × 0.10 mm

Data collection

• Bruker D8 QUEST CMOS diffractometer

• Absorption correction: multi-scan (SADABS; Sheldrick, 2012) T_min = 0.13, T_max = 0.57

• 12426 measured reflections

• 2155 independent reflections

• 1955 reflections with I > 2σ(I)

• R_int = 0.021

Refinement

• R[F² > 2σ(F²)] = 0.018

• wR(F²) = 0.045

• S = 1.11

• 2155 reflections

• 70 parameters

• H atoms treated by a mixture of independent and constrained refinement

• Δρ_max = 0.88 e Å⁻³

• Δρ_min = −0.24 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯Br1^i	0.913 (16)	2.408 (16)	3.2670 (10)	156.7 (13)
N1—H1B⋯Br1	0.880 (18)	2.359 (18)	3.2311 (10)	170.9 (14)
Symmetry code: (i) .

Data collection: APEX2 and Bruker Instrument Service (Bruker, 2013); cell refinement: SAINT (Bruker, 2011); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2.

Supporting information

S1. Comment

N-substituted 2-picolyl derivatives of the title compound, and related tetradentate aminopyridine ligands (Mikhalyova et al., 2012; Lyakin et al., 2012), in the form of Fe(II) and Mn(II) complexes, are good catalysts for selective olefin epoxidation, as well as aromatic or aliphatic hydroxylation reactions, with peroxides or peracids as oxidants. Rigid cyclic diamine scaffolds increase thermodynamic and kinetic stability of the catalysts and orient picolyl groups in the pseudo-octahedral complexes which also contain two labile solvent-occupied sites essential for hydrogen peroxide activation (Mikhalyova et al., 2012). Understanding the molecular structure of these diamine scaffolds is important for catalyst design.

The title compound, which consists of organic diammonium cations and bromide counteranions (Figure 1), crystallizes in the monoclinic space group C2/c. The structure of the organic moiety resembles that of 1,1'-bi(cyclohexane), with both piperidinium rings adopting chair conformations. Two nitrogen atoms are trans to each other. The least square planes passing through the heavy (non-hydrogen) atoms of the two piperidinium rings in the centrosymmetric molecule are coplanar. This conformation differs from the twisted orientation of the piperidinium rings in the racemic isomer of the title compound (the angle between their least-square planes was found to be 77 °) (Laars et al., 2011). Two stereocenters (bridging carbon atoms, C1 and C1') adopt different configurations (R and S, respectively) and are symmetry-related. The centrosymmetric meso form of C₁₀H₂₂N₂Br₂ described herein is achiral.

The organic diammonium cations are linked to each other through hydrogen bonding with bromide counter ions, each of which forms two hydrogen bonds (N—H···Br) with two adjacent organic cations, thus linking the latter together in sheets parallel to the (100) plane (Figure 2).

Related literature

For more details about synthetic and characterization methods, see: Denmark et al. (2006); Herrmann et al. (2006). For the chemistry of related complexes, see: Mikhalyova et al. (2012); Lyakin et al. (2012). For a related structure (the racemic isomer of the title compound), see: Laars et al. (2011).

S2. Experimental

The synthesis of the title compound followed the procedure published by Herrmann et al. (2006). 2,2'-Dipyridyl (8.25g, 0.053mol, in 100ml methanol) was mixed with 3M aqueous solution of KOH (16.8g, 0.3mol); Raney type Ni/Al alloy (1:1, v/v, 30g) was then added in portions and this mixture was stirred and refluxed for 4 days. The solution was separated from nickel mud, concentrated and extracted with 15ml dichloromethane (DCM) 3 times. The combined DCM extracts were evaporated to a faint yellow oil, which was then dissolved in 20ml ethanol. 9 ml of concentrated hydrobromic acid were added dropwise into the ethanolic solution; clear colorless hexagonal plate crystals of meso-C₁₀H₂₂N₂Br₂ were formed upon slow evaporation of the solution (one of these crystals was selected for X-Ray diffraction analysis).

Further evaporation (no less than 5ml) of the solvent liberated additional amount of meso-C₁₀H₂₂N₂Br₂. Yield: 6.2g (35%). More meso-C₁₀H₂₂N₂Br₂ was obtained by separation of meso- and rac-diastereomers of C₁₀H₂₂N₂Br₂ (from the remaining ethanolic solution) according to W.A. Herrmann et al. (2006) in 55% recovery. ¹H NMR (500 MHz, D₂O): δ 1.64 (m, 6, CH₂), 1.96 (d, J = 14.5 Hz, 2, CH₂), 2.02 (d, J = 10.5 Hz, 2, CH₂), 2.14 (d, J = 11.5Hz, 2, CH₂), 3.11 (t, J = 13.0 Hz, 2, CH₂), 3.45 (d, J = 8.5 Hz, 2, CH), 3.56 (d, J = 12.5 Hz, 2, CH₂). ¹³C NMR (500 MHz, D₂O): δ 21.26, 21.49, 24.99, 46.02, 58.12. IR ν_max /cm^-1: 2907, 2714, 2390, 1573, 1413, 1358, 1307, 1010, 901, 605.

S3. Refinement

Except where noted, hydrogen atoms were placed at calculated geometries and allowed to ride on the position of the parent atom. C–H distances were constrained to 1.00 Å for tertiary CH groups and to 0.99 Å for methylene groups (CH₂). Isotropic thermal parameters were set to 1.2× the equivalent isotropic thermal parameter of the parent atom. Hydrogens H1A and H1B, bound to N1, were located in difference density Fourier synthesis maps. The positions of these two H atoms were freely refined. Isotropic thermal parameters for H1A and H1B were set to 1.2× the equivalent isotropic U of N1.

Computing details

Data collection: APEX2 and Bruker Instrument Service (Bruker, 2013); cell refinement: SAINT (Bruker, 2011); data reduction: SAINT (Bruker, 2011); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Figures

	Fig. 1. A view of the title compound, with displacement ellipsoids shown at the 50% probability level. Symmetry transformations used to generate equivalent atoms: (i) -x + 1/2, -y + 3/2, -z + 1.
	Fig. 2. A fragment of the packing diagram of the title compound, with displacement ellipsoids shown at the 50% probability level (H atoms, except H atoms attached to N1 atom, are omitted for clarity). Symmetry transformations used to generate equivalent atoms: (i) -x + 1, -y + 1, -z; (ii) x, -y + 1, z + 1/2; (iii) -x + 1/2, y, -z + 1/2.

(2R,2'S)-2,2'-Bipiperidine-1,1'-diium dibromide

Crystal data

C10H22N2^2+·2Br^−	F(000) = 664
Mr = 330.11	Dx = 1.698 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 17.9719 (9) Å	Cell parameters from 8775 reflections
b = 9.7654 (5) Å	θ = 2.3–31.5°
c = 7.3637 (3) Å	µ = 6.25 mm^−1
β = 92.134 (1)°	T = 100 K
V = 1291.45 (11) Å^3	Plate, clear colorless
Z = 4	0.55 × 0.23 × 0.10 mm

Data collection

Bruker D8 QUEST CMOS diffractometer	2155 independent reflections
Radiation source: sealed tube, Siemens KFFMO2K-90	1955 reflections with I > 2σ(I)
Curved graphite monochromator	Rint = 0.021
ϕ and ω scans	θmax = 31.5°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 2012)	h = −26→26
Tmin = 0.13, Tmax = 0.57	k = −14→12
12426 measured reflections	l = −10→10

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.018	Hydrogen site location: mixed
wR(F^2) = 0.045	H atoms treated by a mixture of independent and constrained refinement
S = 1.11	w = 1/[σ^2(Fo^2) + (0.0237P)^2 + 0.7137P] where P = (Fo^2 + 2Fc^2)/3
2155 reflections	(Δ/σ)max = 0.001
70 parameters	Δρmax = 0.88 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2sigma(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.15631 (5)	0.83374 (10)	0.52604 (14)	0.00987 (17)
H1A	0.1668 (8)	0.9229 (17)	0.500 (2)	0.012*
H1B	0.1566 (9)	0.8270 (15)	0.645 (2)	0.012*
C1	0.21196 (6)	0.73540 (11)	0.45193 (15)	0.00905 (18)
H1	0.2159	0.7519	0.3186	0.011*
C2	0.18497 (6)	0.58942 (11)	0.48165 (17)	0.0123 (2)
H2A	0.1854	0.5699	0.6136	0.015*
H2B	0.2195	0.5245	0.4249	0.015*
C3	0.10648 (6)	0.56754 (12)	0.40071 (17)	0.0136 (2)
H3A	0.0903	0.4725	0.4243	0.016*
H3B	0.1063	0.5813	0.2675	0.016*
C4	0.05255 (6)	0.66795 (12)	0.48479 (17)	0.0133 (2)
H4A	0.002	0.6545	0.4298	0.016*
H4B	0.0505	0.6505	0.6169	0.016*
C5	0.07765 (6)	0.81376 (12)	0.45314 (16)	0.0126 (2)
H5A	0.0749	0.8341	0.3213	0.015*
H5B	0.0441	0.8779	0.5144	0.015*
Br1	0.14264 (2)	0.83601 (2)	0.96230 (2)	0.01383 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0097 (4)	0.0102 (4)	0.0097 (4)	−0.0001 (3)	0.0005 (3)	−0.0007 (3)
C1	0.0087 (4)	0.0093 (4)	0.0092 (4)	0.0003 (4)	0.0004 (3)	−0.0005 (4)
C2	0.0110 (5)	0.0093 (5)	0.0165 (5)	−0.0010 (4)	−0.0010 (4)	0.0000 (4)
C3	0.0104 (5)	0.0128 (5)	0.0176 (5)	−0.0025 (4)	−0.0005 (4)	−0.0009 (4)
C4	0.0095 (5)	0.0147 (5)	0.0158 (5)	−0.0018 (4)	0.0016 (4)	0.0004 (4)
C5	0.0090 (5)	0.0142 (5)	0.0144 (5)	0.0008 (4)	−0.0006 (4)	0.0002 (4)
Br1	0.01971 (7)	0.01159 (7)	0.01027 (6)	−0.00222 (4)	0.00163 (4)	−0.00018 (4)

Geometric parameters (Å, º)

N1—C1	1.5036 (14)	C2—H2B	0.99
N1—C5	1.5060 (15)	C3—C4	1.5260 (17)
N1—H1A	0.913 (16)	C3—H3A	0.99
N1—H1B	0.880 (18)	C3—H3B	0.99
C1—C2	1.5243 (16)	C4—C5	1.5143 (16)
C1—C1^i	1.543 (2)	C4—H4A	0.99
C1—H1	1.0	C4—H4B	0.99
C2—C3	1.5259 (16)	C5—H5A	0.99
C2—H2A	0.99	C5—H5B	0.99
C1—N1—C5	114.59 (9)	C2—C3—C4	110.09 (9)
C1—N1—H1A	112.7 (10)	C2—C3—H3A	109.6
C5—N1—H1A	104.3 (10)	C4—C3—H3A	109.6
C1—N1—H1B	109.6 (10)	C2—C3—H3B	109.6
C5—N1—H1B	108.4 (11)	C4—C3—H3B	109.6
H1A—N1—H1B	106.8 (13)	H3A—C3—H3B	108.2
N1—C1—C2	109.01 (9)	C5—C4—C3	110.15 (9)
N1—C1—C1^i	107.79 (11)	C5—C4—H4A	109.6
C2—C1—C1^i	112.85 (11)	C3—C4—H4A	109.6
N1—C1—H1	109.0	C5—C4—H4B	109.6
C2—C1—H1	109.0	C3—C4—H4B	109.6
C1^i—C1—H1	109.0	H4A—C4—H4B	108.1
C1—C2—C3	111.68 (9)	N1—C5—C4	110.36 (9)
C1—C2—H2A	109.3	N1—C5—H5A	109.6
C3—C2—H2A	109.3	C4—C5—H5A	109.6
C1—C2—H2B	109.3	N1—C5—H5B	109.6
C3—C2—H2B	109.3	C4—C5—H5B	109.6
H2A—C2—H2B	107.9	H5A—C5—H5B	108.1
C5—N1—C1—C2	−54.03 (12)	C1—C2—C3—C4	−58.25 (13)
C5—N1—C1—C1^i	−176.84 (11)	C2—C3—C4—C5	58.08 (13)
N1—C1—C2—C3	54.76 (12)	C1—N1—C5—C4	55.44 (12)
C1^i—C1—C2—C3	174.49 (11)	C3—C4—C5—N1	−55.86 (13)

Symmetry code: (i) −x+1/2, −y+3/2, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Br1^ii	0.913 (16)	2.408 (16)	3.2670 (10)	156.7 (13)
N1—H1B···Br1	0.880 (18)	2.359 (18)	3.2311 (10)	170.9 (14)

Symmetry code: (ii) x, −y+2, z−1/2.