2-tert-Butyl 4-methyl 3,5-dimethyl-1H-pyrrole-2,4-dicarboxylate

In the title molecule, C13H19NO4, except for two C atoms of the tert-butyl group, the non-H atoms are almost coplanar (r.m.s. deviation = 0.2542 Å). In the crystal, molecules are linked into centrosymmetric dimers by two intermolecular N—H⋯O hydrogen bonds, forming an R 2 2(10) ring motif.

In the title molecule, C 13 H 19 NO 4 , except for two C atoms of the tert-butyl group, the non-H atoms are almost coplanar (r.m.s. deviation = 0.2542 Å ). In the crystal, molecules are linked into centrosymmetric dimers by two intermolecular N-HÁ Á ÁO hydrogen bonds, forming an R 2 2 (10) ring motif.

Hong-Xin Cai and Zhao-Po Zhang Comment
Schiff bases containing pyrrole units have been extensively investigated due to their excellent coordination abilities (Wu et al., 2003;Wang et al., 2008). As part of our studies on bis(pyrrol-2-yl-methyleneamine) ligands, the crystal structure of the title compound is reported here.
In the title molecule ( Fig. 1), except for C12 and C13 atoms of the tert-butyl, the non-hydrogen atoms are almost coplanar (r.m.s. deviation of the non-hydrogen atoms being 0.2542 Å). In the crystal, the molecules are linked into centrosymmetric dimers by two intermolecular N-H···O hydrogen bonds (Table 1), forming a R 2 2 (10) ring motif (Fig. 2).

Refinement
The H atoms were positioned geometrically (N-H = 0.86 Å, C-H = 0.96 Å) and refined as riding with U iso (H) =1.2U eq (N) or 1.5U eq (methyl C).  The molecular structure shown with 30% probability displacement ellipsoids.

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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )
x y z U iso */U eq C1