1,4-Bis(2-diazo­acet­yl)piperazine

The asymmetric unit of the title compound, C₈H₁₀N₆O₂, contains one-half mol­ecule, which is completed by a crystallographic center of symmetry. The piperazine ring adopts a chair conformation. In the crystal, weak C—H⋯O inter­actions link the mol­ecules into layers parallel to the bc plane. The crystal packing also exhibits short N⋯N contacts of 3.0467 (16) Å between the terminal diazo N atoms from neighbouring mol­ecules.

Related literature

For related structures in the Cambridge Structural Database (Version 5.34 of November 2012; Allen, 2002), see: Kaupang (2010); Kaupang et al. (2010, 2011); Aliev et al. (1980); Fitzgerald & Jensen (1978); Hope & Black (1972). For normal bond lengths in organic compounds, see: Allen et al. (1987). For synthetic details, see: Kaupang & Bonge-Hansen (2013); Kaupang (2010); Toma et al. (2007). For the synthesis of other diazo­acetamides with a 1,4-di­aza six-membered ring, see: Kaupang (2010); Mickelson et al. (1996). For the synthesis of other diazo­acetamides, see: Ouihia et al. (1993). For the Chemical Abstracts Service, see: American Chemical Society (2008). For graph-set notation for hydrogen-bonding patterns, see: Etter et al. (1990).

Experimental

Crystal data

• C₈H₁₀N₆O₂

• M_r = 222.22

• Monoclinic, P 2₁ /c

• a = 4.0630 (7) Å

• b = 9.0941 (15) Å

• c = 13.230 (2) Å

• β = 94.453 (2)°

• V = 487.38 (14) ų

• Z = 2

• Mo Kα radiation

• μ = 0.12 mm⁻¹

• T = 105 K

• 1.4 × 0.2 × 0.2 mm

Data collection

• Bruker APEXII CCD diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2007) T_min = 0.859, T_max = 0.977

• 4255 measured reflections

• 1190 independent reflections

• 1013 reflections with I > 2σ(I)

• R_int = 0.021

Refinement

• R[F² > 2σ(F²)] = 0.034

• wR(F²) = 0.090

• S = 1.04

• 1190 reflections

• 82 parameters

• 3 restraints

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

• Δρ_max = 0.30 e Å⁻³

• Δρ_min = −0.22 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H21⋯O1^i	0.92 (1)	2.39 (1)	3.2219 (15)	151 (1)
Symmetry code: (i) .

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT-Plus (Bruker, 2007); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supporting information

S1. Comment

The N,N'-bis(2-diazoacetyl)piperazine (I) was prepared as part of a series of diazoacetamides (Kaupang et al., 2010; 2011) used in the intramolecular C—H insertion reactions taking place upon thermolysis of their corresponding α-bromodiazoacetamides (Kaupang, 2010). The title compound was synthesized from N,N'-bis(2-bromoacetyl)piperazine following a procedure reported by Toma et al. (2007), modified to employ 1,1,3,3-tetramethylguanidine as the base instead of 1,8-diazabicyclo[5.4.0]undec-7-ene. No previous reports of this compound were found in the Chemical Abstracts Service (CAS; American Chemical Society, 2008).

In (I) (Fig. 1), the piperazine ring is in a normal chair conformation, with one half of the molecule constituting the asymmetric unit. In the Scheme the diazoacetyl group is illustrated in the normal way with C═N⁺ and N⁺═N^- double bonds, but sometimes a C—N single bond and a N≡N triple bond is used. N2—N3 = 1.1239 (14) Å is actually close in length to the triple bond in N₂(g) = 1.0976 Å, but N2—C2 = 1.3099 (14) Å is clearly shorter than a normal N═N—C(sp³) single bond = 1.493 Å (Allen et al., 1987), illustrating clearly the double bond nature.

As pointed out previously (Kaupang et al., 2010), the ring N atoms have an amide rather than amine character and display an almost planar configuration [sum of C—N1—C angles 358.86 (15)°] due to the double bond character of N1—C1 = 1.3621 (13) Å. There are two interesting intermolecular interactions in the crystal packing (Fig. 2) - a C2—H21···O1 contact (Table 1) giving rise to chains and rings, and a 3.047 (14) Å N3···N3(1 - x,-y,-z) contact between the diazo groups with an associated N2—N3···N3 angle of 115.56 (10)° and N2—N3···N3—N2 torsion angle 180.0°. The diazoacetyl moiety is a relatively rare functional group occurring in 20 different organic molecules in the Cambridge Structural Database (CSD, Version 5.34 of November 2012; Allen 2002), and only three (Aliev et al., 1980; Fitzgerald & Jensen, 1978; Hope & Black, 1972) participate in this type of interaction. Among more general compounds with a diazo group, 40 structures with 53 N···N distance < 3.5 Å were found in the CSD. Most contacts are within the 3.0 to 3.4 Å range. N—N···N angles have a wide distribution, but 45 are in the range 75 - 140° with average value 107°. A trans orientation for the N—N···N—N torsion angle is preferred; 36 out of 53 contacts have values in the range 180 ±20°. Almost all structures with N···N contacts < 3.2 Å fall into this group.

Related literature

For related structures in the Cambridge Structural Database (Version 5.34 of November 2012; Allen, 2002), see: Kaupang (2010); Kaupang et al. (2010, 2011); Aliev et al. (1980); Fitzgerald & Jensen (1978); Hope & Black (1972). For normal bond lengths in organic compounds, see: Allen et al. (1987). For synthetic details, see: Kaupang & Bonge-Hansen (2013); Kaupang (2010); Toma et al. (2007). For the synthesis of other diazoacetamides with a 1,4-diaza six-membered ring, see: Kaupang (2010); Mickelson et al. (1996). For the synthesis of other diazoacetamides, see: Ouihia et al. (1993). For the Chemical Abstracts Service, see: American Chemical Society (2008). For graph-set notation for hydrogen-bonding patterns, see: Etter et al. (1990).

S2. Experimental

A solution of 4.0 mg of the title compound in 500 µL of MeCN was placed in a vial measuring 30 × 6 mm and the open vial stored in the dark, exposed to air and at ambient temperature. Slow evaporation afforded yellow needles after 48 h. Crystals are rather fragile and easily fracture if cut with a scalpel. A rather long needle, 1.4 × 0.2 × 0.2 mm, was thus used for data collection.

S3. Refinement

H atoms bonded to C4 were positioned with idealized geometry and with fixed C—H distances at 0.99 Å, while positional coordinates were refined for H atoms bonded to C2 and C3, as too short intramolecular H···H distances resulted from putting these H atoms in theoretical positions. Distance restraints were imposed on the C2—H21 and C3—H31/H32 bonds utilizing SHELX DFIX 0.95 0.02 and DFIX 0.99 0.02 commands, respectively.

Computing details

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT-Plus (Bruker, 2007); data reduction: SAINT-Plus (Bruker, 2007); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

Fig. 1. The molecular structure of (I) showing the atomic numbering and 50% probability displacement ellipsoids [symmetry code: (') -x, -y, 1 - z].

Fig. 2. The unit cell and crystal packing of (I) viewed approximately along the a axis with the asymmetric unit covered by a grey ellipse. H atoms not involved in short intermolecular contacts (indicated by dotted lines) have been omitted for clarity. The molecules are connected by C21—H21···O1"(-x, y-1/2-y, 1/2-z) hydrogen bonds into two-dimensional sheets with C(4) chain and R4^4(26) ring motifs (for graph set notation, see Etter et al., 1990). An intermolecular N3···N3^#(1-x,-y,-z) contact has been highlighted in orange.

1,4-Bis(2-diazoacetyl)piperazine

Crystal data

C8H10N6O2	F(000) = 232
Mr = 222.22	Dx = 1.514 Mg m^−3
Monoclinic, P21/c	Melting point: 382 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 4.0630 (7) Å	Cell parameters from 1727 reflections
b = 9.0941 (15) Å	θ = 2.7–28.7°
c = 13.230 (2) Å	µ = 0.12 mm^−1
β = 94.453 (2)°	T = 105 K
V = 487.38 (14) Å^3	Needle, yellow
Z = 2	1.4 × 0.2 × 0.2 mm

Data collection

Bruker APEXII CCD diffractometer	1190 independent reflections
Radiation source: fine-focus sealed tube	1013 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
Detector resolution: 8.3 pixels mm^-1	θmax = 28.7°, θmin = 2.7°
Sets of exposures each taken over 0.5° ω rotation scans	h = −5→5
Absorption correction: multi-scan (SADABS; Bruker, 2007)	k = −11→11
Tmin = 0.859, Tmax = 0.977	l = −17→17
4255 measured reflections

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)] = 0.034	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.090	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0478P)^2 + 0.1317P] where P = (Fo^2 + 2Fc^2)/3
1190 reflections	(Δ/σ)max < 0.001
82 parameters	Δρmax = 0.30 e Å^−3
3 restraints	Δρmin = −0.22 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 2σ(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
C1	0.1936 (3)	0.09488 (12)	0.31650 (8)	0.0164 (2)
C2	0.2433 (3)	−0.01250 (13)	0.23807 (8)	0.0206 (3)
H21	0.165 (3)	−0.1064 (14)	0.2306 (11)	0.025*
C3	−0.0658 (3)	−0.10152 (12)	0.41721 (8)	0.0168 (2)
H31	0.016 (3)	−0.1708 (14)	0.3686 (10)	0.020*
H32	−0.308 (3)	−0.1005 (15)	0.4067 (10)	0.020*
C4	−0.0370 (3)	0.15403 (11)	0.47597 (8)	0.0169 (2)
H41	−0.2791	0.1688	0.4685	0.020*
H42	0.0701	0.2495	0.4638	0.020*
N1	0.0575 (2)	0.04673 (10)	0.40139 (7)	0.0165 (2)
N2	0.4038 (2)	0.03769 (10)	0.16317 (7)	0.0208 (2)
N3	0.5432 (3)	0.08327 (13)	0.10006 (8)	0.0295 (3)
O1	0.2787 (2)	0.22436 (9)	0.30680 (6)	0.0208 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0158 (5)	0.0172 (5)	0.0158 (5)	0.0018 (4)	−0.0009 (4)	0.0016 (4)
C2	0.0285 (6)	0.0176 (5)	0.0162 (5)	−0.0020 (4)	0.0047 (4)	0.0010 (4)
C3	0.0204 (5)	0.0141 (5)	0.0162 (5)	−0.0021 (4)	0.0026 (4)	−0.0006 (4)
C4	0.0202 (5)	0.0142 (5)	0.0167 (5)	0.0009 (4)	0.0030 (4)	−0.0012 (4)
N1	0.0221 (4)	0.0131 (4)	0.0145 (4)	−0.0008 (3)	0.0035 (3)	−0.0006 (3)
N2	0.0264 (5)	0.0189 (5)	0.0171 (5)	0.0024 (4)	0.0021 (4)	−0.0006 (4)
N3	0.0395 (6)	0.0282 (6)	0.0222 (5)	−0.0010 (5)	0.0110 (5)	0.0007 (4)
O1	0.0282 (4)	0.0154 (4)	0.0193 (4)	−0.0016 (3)	0.0047 (3)	0.0017 (3)

Geometric parameters (Å, º)

C1—O1	1.2367 (14)	C3—H31	0.978 (12)
C1—N1	1.3621 (13)	C3—H32	0.985 (12)
C1—C2	1.4504 (16)	C4—N1	1.4602 (13)
C2—N2	1.3099 (14)	C4—H41	0.9900
C2—H21	0.915 (12)	C4—H42	0.9900
C3—N1	1.4589 (13)	N2—N3	1.1239 (14)
C3—C4^i	1.5193 (15)
O1—C1—N1	121.76 (10)	H31—C3—H32	107.6 (11)
O1—C1—C2	120.75 (10)	N1—C4—C3^i	110.54 (9)
N1—C1—C2	117.48 (10)	N1—C4—H41	109.5
N2—C2—C1	114.31 (10)	C3^i—C4—H41	109.5
N2—C2—H21	115.7 (9)	N1—C4—H42	109.5
C1—C2—H21	129.7 (9)	C3^i—C4—H42	109.5
N1—C3—C4^i	110.57 (9)	H41—C4—H42	108.1
N1—C3—H31	111.3 (8)	C1—N1—C3	125.53 (9)
C4^i—C3—H31	109.1 (8)	C1—N1—C4	119.16 (9)
N1—C3—H32	108.8 (8)	C3—N1—C4	114.17 (8)
C4^i—C3—H32	109.5 (8)	N3—N2—C2	178.58 (12)
O1—C1—C2—N2	4.86 (16)	C2—C1—N1—C4	−171.95 (9)
N1—C1—C2—N2	−173.69 (9)	C4^i—C3—N1—C1	137.76 (10)
O1—C1—N1—C3	176.58 (10)	C4^i—C3—N1—C4	−54.61 (12)
C2—C1—N1—C3	−4.88 (15)	C3^i—C4—N1—C1	−136.92 (9)
O1—C1—N1—C4	9.51 (15)	C3^i—C4—N1—C3	54.59 (12)

Symmetry code: (i) −x, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H21···O1^ii	0.92 (1)	2.39 (1)	3.2219 (15)	151 (1)

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