tert-Butyl 4-(2-diazoacetyl)piperazine-1-carboxylate

The title crystal structure, C11H18N4O3, is the first diazoacetamide in which the diazoacetyl group is attached to an N atom. The piperazine ring is in a chair form and hence the molecule has an extended conformation. Both ring N atoms are bonded in an essentially planar configuration with the sum of the C—N—C angles being 359.8 (2) and 357.7 (2)°. In the crystal structure, the O atom of the diazoacetyl group accepts two H atoms from C—H donors, thus generating chains of weak hydrogen-bonded R 2 1(7) rings.

The title crystal structure, C 11 H 18 N 4 O 3 , is the first diazoacetamide in which the diazoacetyl group is attached to an N atom. The piperazine ring is in a chair form and hence the molecule has an extended conformation. Both ring N atoms are bonded in an essentially planar configuration with the sum of the C-N-C angles being 359.8 (2) and 357.7 (2) . In the crystal structure, the O atom of the diazoacetyl group accepts two H atoms from C-H donors, thus generating chains of weak hydrogen-bonded R 2 1 (7) rings.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LH5033).
Diffraction data were first collected at ambient temperature, yielding a structure with a massively disordered sixmembered ring. At 105 K the ring is completely ordered in a well defined chair conformation, Fig. 1.
The diazoacetyl moiety is not an uncommon functional group in organic molecules, however only 15 occurrences were found in the Cambridge Structural Database (Version 5.31 of November 2009; Allen, 2002), and none where, as here, the group is attached to a N atom. In only two structures the group sits on a non-aromatic ring (Miller et al., 1991;Fenlon et al., 2007).
In a model molecule like trimethylamine the N atom is located about 0.45 Å above the plane defined by the three C atoms.
In the crystal structure, the O atom of the diazoacetyl group accepts two H atoms from C-H donors, thus generating chains of hydrogen-bonded R 1 2 (7) rings (Bernstein et al., 1995).

Experimental
A 2.5 ml vial containing tert-butyl 4-(2-diazoacetyl)piperazine-1-carboxylate (10.8 mg) and dichloromethane (1000 ml) was capped and a pinhole (0.5 mm) was made in the cap to allow for vapour diffusion of solvents. This vial was placed inside a 25 ml vial containing n-pentane (8 ml) that was subsequently capped and stored in the dark at ambient temperature for approximately 48 hours, affording bright yellow plate-shaped crystals.

Refinement
Coordinates were refined for H1 (bonded to C1), which is involved in the shortest intermolcular interaction. Other H atoms were positioned with idealized geometry and fixed C-H distances set to 0.98 Å (methyl) or 0.99 Å (methylene). Free rotation was permitted for the methyl groups. U iso values were 1.2U eq of the carrier atom or 1.5U eq for methyl groups.
supplementary materials sup-2 Figures  Fig. 1. The asymmetric unit of (I), with atomic numbering indicated, together with selected atoms of neighbouring molecules connected by weak hydrogen bonds shown as dotted lines (see Table 1, symmetry operations are -x,1/2+y,1/2-z for O', -x,-1/2+y,1/2-z for H1" and H32"). Displacement ellipsoids are shown at the 50% probability level with H atoms as spheres of arbitrary size.

Special details
Experimental. Crystallized from dichloromethane and n-pentane.
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 F 2 against ALL reflections.