N,N′-Di­acetyl-1,13-di­aza-24-crown-8

Half of the title compound (N,N′-di­acetyl-1,4,7,13,16,19-hexaoxa-10,22-di­aza­cyclo­tetra­cosane), C₂₀H₃₈N₂O₈, makes up the asymmetric unit. The crown ring is relatively flat, and though collapsed in on itself, would require little change to adopt a binding conformation. C—H...O bonding is also observed.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.032
• wR factor = 0.087
• Data-to-parameter ratio = 19.3

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

As part of a continuing research program that involves the synthesis of cage-annulated crown ethers, cryptands, and molecular boxes (Macias et al., 2000; Watson et al., 2000; Marchand et al., 1998), we prepared N,N'-diacetyl-1,13-diaza-24-crown-8, (I), as a precursor to N,N'-ethyl-1,13-diaza-24-crown-8.

Half of the molecule makes up the asymmetric unit, the other half is generated through the crystallographic inversion center. The crown rings lies in a rough plane with the acetyl groups roughly orthogonal to that plane, but placed on opposite sides. The crown ether is collapsed in on itself, as is commonly observed in the structures of large, uncomplexed crown ethers (Bryan et al., 2000). Its conformation can be described in terms of the torsion angles around ring (Dale, 1980) where g and a represent gauche and anti respectively, and a superscript following the g indicates the sign. Starting with N—C1—C2—O1, the conformation is g^-aa g^-aa g(a)(a) g^-gg, which is then repeated, although inverted, for the other half of the molecule. The "(a)" values refer to C7—O3—C6—C5ⁱ [symmetry code: (i) 1 - x, 2 - y, 1 - z] and C6—O3—C7—C8 which are 143.41 (9) and -148.26 (9)°, respectively. They are marked in parenthesis because of their proximity to the intermediate torsion value of 120°. To bind a cation, the pattern g^±aa should repeat around the ring. This structure only needs to change two torsion angles to meet this criterion.

This is the first X-ray structure of a 24-crown-8 ether without sterically constraining groups on the crown backbone (such as benzo or cyclohexano). As such, it may represent a relatively low energy conformation for 24-crown-8.

The collapse of an uncomplexed crown ring typically leads to favorable intramolecular C—H···O bonding (Bryan, et al., 1999; Steiner, 1996), which may influence the observed conformation. Only one such bond is observed here (C1—H1B···O3), but an intramolecular H bond is also observed between one of the acetyl methyl H atoms and O1 (Table 2). The orientation of the acetyl group may also be affected by a short contact between O4 and H8B (2.42 Å, see Table 2).

S2. Experimental

To a solution of 1,13-diaza-24-crown-8 (Dietrich et al., 1973; Johnson et al., 1985) (820 mg, 2.34 mmol), 4-dimethylaminopyridine (DMAP, 57 mg, 0.468 mmol), Et₃N (824 mg, 8.1 mmol) in dry CH₂Cl₂ (40 ml) was added freshly distilled Ac₂O (529 mg, 5.2 mmol), and the resulting mixture was refluxed for 2 d. The reaction mixture was allowed to cool gradually to ambient temperature and then was washed with water (3 × 50 ml). The organic layer was dried (MgSO₄) and filtered, and the filtrate concentrated in vacuo. The residue was purified via column chromatography on silica gel by eluting with 5% MeOH–CHCl₃. Workup of the eluate afforded the title compound (280 mg, 27%) as a colorless waxy solid. Single crystals were obtained via fractional recrystallization from CH₂Cl₂-hexane. IR (KBr) 2880 (m), 2865 (m), 1638 (s), 1100 cm^-1 (s); ¹H NMR (CDCl₃) δ 2.09 (s, 6 H), 3.48–3.65 (m, 32 H); ¹³C NMR (CDCl₃) δ 21.6 (q, 2 C), 46.6 (t), 46.8 (t), 49.9 (t, 2 C), 69.4 (t), 69.6 (t), 69.7 (t), 70.0 (t), 70.3 (t), 70.4 (t), 70.5 (t), 70.56 (t, 2 C), 70.62 (t), 70.8 (t), 71.0 (t), 171.0 (t, 2 C). Analysis calculated for C₂₀H₃₈N₂O₈: C 55.26, H 8.82%; found: C 55.35, H 8.76%. Elemental microanalyses were performed by M. H. W. Laboratories, Phoenix, AZ.

S3. Refinement

A 1.1 mm collimator was used. All C-bound H atoms were placed in calculated positions, refined using a riding model, and given an isotropic displacement parameter equal to 1.2 (CH₂) or 1.5 (CH₃) times the equivalent isotropic displacement parameter of the atom to which they were attached. The C—H distances used depend on the type of C atom: C_methylene—H = 0.99 and C_methyl—H = 0.98 Å. Methyl H atoms were allowed to rotate about the adjacent C—C bond.

Computing details

Data collection: CAD-4-PC (Nonius, 1996); cell refinement: CAD-4-PC; data reduction: XCAD4 (Harms, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: PLATON (Spek, 2000).

N,N'-Diacetyl-1,4,7,13,16,19-hexaoxa-10,22-diazacyclotetracosane

Crystal data

C20H38N2O8	Z = 1
Mr = 434.5	F(000) = 236
Triclinic, P1	Dx = 1.311 Mg m^−3
Hall symbol: -P 1	Melting point = 358.5–359.5 K
a = 7.4145 (12) Å	Mo Kα radiation, λ = 0.71073 Å
b = 8.145 (2) Å	Cell parameters from 25 reflections
c = 10.299 (3) Å	θ = 10.2–15.8°
α = 98.95 (2)°	µ = 0.10 mm^−1
β = 105.103 (18)°	T = 100 K
γ = 108.424 (17)°	Prism, colourless
V = 550.2 (3) Å^3	0.52 × 0.43 × 0.30 mm

Data collection

Nonius CAD4 diffractometer	Rint = 0.015
Radiation source: fine-focus sealed tube	θmax = 28.0°, θmin = 2.1°
Graphite monochromator	h = −9→9
ω scans	k = −10→10
5289 measured reflections	l = −13→13
2644 independent reflections	3 standard reflections every 120 min
2357 reflections with I > 2σ(I)	intensity decay: 4%

Refinement

Refinement on F^2	0 constraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.032	Secondary atom site location: difference Fourier map
wR(F^2) = 0.087	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0475P)^2 + 0.1429P] where P = (Fo^2 + 2Fc^2)/3
2644 reflections	(Δ/σ)max < 0.001
137 parameters	Δρmax = 0.34 e Å^−3
0 restraints	Δρmin = −0.23 e Å^−3

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All e.s.d.'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. Refinement on F² for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating -R-factor-obs 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
O1	0.26570 (10)	0.77430 (9)	0.34109 (6)	0.0164 (2)
O2	0.46987 (10)	0.80497 (8)	0.12633 (7)	0.0163 (2)
O3	0.11420 (10)	0.96450 (8)	0.82183 (7)	0.0172 (2)
O4	0.29345 (10)	0.53700 (9)	0.71423 (7)	0.0206 (2)
N	0.20366 (11)	0.74295 (10)	0.61983 (8)	0.0137 (2)
C1	0.24304 (13)	0.89708 (12)	0.55960 (9)	0.0154 (2)
C2	0.14525 (13)	0.84522 (12)	0.40288 (9)	0.0156 (2)
C3	0.17618 (14)	0.70797 (13)	0.19402 (9)	0.0170 (2)
C4	0.31979 (14)	0.65125 (12)	0.13492 (9)	0.0169 (2)
C5	0.60617 (14)	0.75714 (12)	0.06703 (9)	0.0166 (2)
C6	0.25306 (14)	1.07754 (12)	0.95372 (9)	0.0166 (2)
C7	0.05968 (14)	0.77732 (12)	0.80703 (9)	0.0159 (2)
C8	0.01895 (13)	0.68811 (12)	0.65594 (9)	0.0145 (2)
C9	0.33297 (13)	0.65967 (12)	0.65679 (9)	0.0157 (2)
C10	0.52950 (14)	0.72165 (14)	0.62766 (11)	0.0220 (3)
H1A	0.39030	0.95820	0.58320	0.0180*
H1B	0.19230	0.98310	0.60200	0.0180*
H2A	0.00740	0.75410	0.37560	0.0190*
H2B	0.13600	0.95150	0.37060	0.0190*
H3A	0.14580	0.80240	0.15320	0.0200*
H3B	0.04830	0.60440	0.17050	0.0200*
H4A	0.38390	0.58810	0.19550	0.0200*
H4B	0.24510	0.56800	0.04110	0.0200*
H5A	0.53010	0.66650	−0.02340	0.0200*
H5B	0.68410	0.70490	0.12990	0.0200*
H6A	0.33110	1.01240	1.00080	0.0200*
H6B	0.17880	1.11200	1.01340	0.0200*
H7A	−0.06230	0.72920	0.83320	0.0190*
H7B	0.17030	0.75350	0.86860	0.0190*
H8A	−0.03540	0.55630	0.64040	0.0170*
H8B	−0.08340	0.72140	0.59480	0.0170*
H10A	0.61980	0.83730	0.69340	0.0330*
H10B	0.50390	0.73480	0.53230	0.0330*
H10C	0.59240	0.63310	0.63830	0.0330*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0152 (3)	0.0205 (3)	0.0120 (3)	0.0057 (3)	0.0037 (2)	0.0033 (2)
O2	0.0182 (3)	0.0124 (3)	0.0188 (3)	0.0043 (3)	0.0087 (3)	0.0039 (2)
O3	0.0205 (3)	0.0125 (3)	0.0157 (3)	0.0061 (3)	0.0024 (3)	0.0023 (2)
O4	0.0209 (3)	0.0188 (3)	0.0228 (3)	0.0071 (3)	0.0062 (3)	0.0097 (3)
N	0.0137 (3)	0.0132 (3)	0.0145 (3)	0.0033 (3)	0.0063 (3)	0.0049 (3)
C1	0.0172 (4)	0.0118 (4)	0.0168 (4)	0.0036 (3)	0.0067 (3)	0.0048 (3)
C2	0.0148 (4)	0.0158 (4)	0.0170 (4)	0.0052 (3)	0.0059 (3)	0.0067 (3)
C3	0.0159 (4)	0.0177 (4)	0.0126 (4)	0.0021 (3)	0.0021 (3)	0.0042 (3)
C4	0.0196 (4)	0.0125 (4)	0.0145 (4)	0.0018 (3)	0.0045 (3)	0.0031 (3)
C5	0.0193 (4)	0.0143 (4)	0.0160 (4)	0.0068 (3)	0.0061 (3)	0.0021 (3)
C6	0.0177 (4)	0.0171 (4)	0.0139 (4)	0.0058 (3)	0.0057 (3)	0.0018 (3)
C7	0.0185 (4)	0.0138 (4)	0.0168 (4)	0.0055 (3)	0.0083 (3)	0.0050 (3)
C8	0.0135 (4)	0.0136 (4)	0.0158 (4)	0.0031 (3)	0.0060 (3)	0.0040 (3)
C9	0.0146 (4)	0.0158 (4)	0.0131 (4)	0.0036 (3)	0.0025 (3)	0.0019 (3)
C10	0.0154 (4)	0.0282 (5)	0.0242 (5)	0.0085 (4)	0.0072 (4)	0.0100 (4)

Geometric parameters (Å, º)

O1—C2	1.4297 (13)	C2—H2A	0.99
O1—C3	1.4218 (11)	C2—H2B	0.99
O2—C4	1.4209 (13)	C3—H3A	0.99
O2—C5	1.4292 (14)	C3—H3B	0.99
O3—C6	1.4268 (12)	C4—H4A	0.99
O3—C7	1.4202 (12)	C4—H4B	0.99
O4—C9	1.2342 (12)	C5—H5A	0.99
N—C1	1.4666 (13)	C5—H5B	0.99
N—C8	1.4642 (14)	C6—H6A	0.99
N—C9	1.3511 (14)	C6—H6B	0.99
C1—C2	1.5145 (13)	C7—H7A	0.99
C3—C4	1.5096 (16)	C7—H7B	0.99
C5—C6^i	1.5052 (15)	C8—H8A	0.99
C7—C8	1.5183 (13)	C8—H8B	0.99
C9—C10	1.5094 (16)	C10—H10A	0.98
C1—H1A	0.99	C10—H10B	0.98
C1—H1B	0.99	C10—H10C	0.98
C2—O1—C3	112.18 (8)	O2—C4—H4A	110
C4—O2—C5	111.43 (7)	O2—C4—H4B	110
C6—O3—C7	115.90 (7)	C3—C4—H4A	110
C1—N—C8	116.92 (8)	C3—C4—H4B	110
C1—N—C9	125.10 (9)	H4A—C4—H4B	108
C8—N—C9	117.65 (8)	O2—C5—H5A	110
N—C1—C2	112.95 (8)	O2—C5—H5B	110
O1—C2—C1	108.27 (8)	H5A—C5—H5B	108
O1—C3—C4	109.16 (8)	C6^i—C5—H5A	110
O2—C4—C3	109.46 (8)	C6^i—C5—H5B	110
O2—C5—C6^i	108.89 (8)	O3—C6—H6A	110
O3—C6—C5^i	109.48 (7)	O3—C6—H6B	110
O3—C7—C8	108.01 (8)	H6A—C6—H6B	108
N—C8—C7	110.81 (8)	C5^i—C6—H6A	110
O4—C9—N	121.24 (10)	C5^i—C6—H6B	110
O4—C9—C10	120.40 (10)	O3—C7—H7A	110
N—C9—C10	118.36 (9)	O3—C7—H7B	110
N—C1—H1A	109	C8—C7—H7A	110
N—C1—H1B	109	C8—C7—H7B	110
C2—C1—H1A	109	H7A—C7—H7B	108
C2—C1—H1B	109	N—C8—H8A	109
H1A—C1—H1B	108	N—C8—H8B	109
O1—C2—H2A	110	C7—C8—H8A	110
O1—C2—H2B	110	C7—C8—H8B	109
C1—C2—H2A	110	H8A—C8—H8B	108
C1—C2—H2B	110	C9—C10—H10A	109
H2A—C2—H2B	108	C9—C10—H10B	109
O1—C3—H3A	110	C9—C10—H10C	109
O1—C3—H3B	110	H10A—C10—H10B	109
C4—C3—H3A	110	H10A—C10—H10C	110
C4—C3—H3B	110	H10B—C10—H10C	109
H3A—C3—H3B	108
C3—O1—C2—C1	175.08 (8)	C8—N—C9—C10	−176.60 (8)
C2—O1—C3—C4	174.85 (8)	C8—N—C1—H1B	34
C5—O2—C4—C3	−178.31 (7)	C9—N—C1—H1A	−22
C4—O2—C5—C6^i	173.89 (7)	C8—N—C1—H1A	152
C7—O3—C6—C5^i	143.41 (9)	C9—N—C8—H8A	−40
C6—O3—C7—C8	−148.26 (9)	C9—N—C8—H8B	−158
C9—N—C1—C2	99.78 (11)	C1—N—C8—H8A	146
C1—N—C8—C7	−93.00 (9)	C1—N—C8—H8B	28
C9—N—C8—C7	80.71 (10)	C9—N—C1—H1B	−139
C8—N—C1—C2	−87.04 (10)	N—C1—C2—O1	−78.49 (10)
C1—N—C9—O4	175.83 (8)	O1—C3—C4—O2	−79.18 (9)
C1—N—C9—C10	−3.47 (13)	O2—C5—C6^i—O3^i	72.09 (10)
C8—N—C9—O4	2.70 (13)	O3—C7—C8—N	66.01 (10)

Symmetry code: (i) −x+1, −y+2, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1B···O3	0.99	2.49	3.1181 (15)	121
C2—H2A···O4^ii	0.99	2.52	3.4804 (16)	163
C6—H6A···O2^iii	0.99	2.58	3.5592 (16)	169
C8—H8A···O4	0.99	2.42	2.6822 (15)	94
C10—H10B···O1	0.98	2.42	3.2613 (16)	144

Symmetry codes: (ii) −x, −y+1, −z+1; (iii) x, y, z+1.