3-[Bis(dimethylamino)methylene]-1,1-diphenylurea

In the title compound, C18H22N4O, the C=N and C—N bond lengths in the CN3 unit are 1.3179 (11), 1.3551 (11) and 1.3737 (11) Å, indicating double- and single-bond character, respectively. The N—C—N angles are 115.91 (8), 118.20 (8) and 125.69 (8), showing a deviation of the CN3 plane from an ideal trigonal–planar geometry. The bonds between the N atoms and the terminal C-methyl groups all have values close to a typical single bond [1.4529 (12)–1.4624 (12) Å]. The dihedral angle between the phenyl rings is 79.63 (4)°. In the crystal, the molecules are connected via weak C—H⋯O hydrogen bonds, generating chains along [100].

In the title compound, C 18 H 22 N 4 O, the C N and C-N bond lengths in the CN 3 unit are 1.3179 (11), 1.3551 (11) and 1.3737 (11) Å , indicating double-and single-bond character, respectively. The N-C-N angles are 115.91 (8), 118.20 (8) and 125.69 (8), showing a deviation of the CN 3 plane from an ideal trigonal-planar geometry. The bonds between the N atoms and the terminal C-methyl groups all have values close to a typical single bond [1.4529 (12)-1.4624 (12) Å ]. The dihedral angle between the phenyl rings is 79.63 (4) . In the crystal, the molecules are connected via weak C-HÁ Á ÁO hydrogen bonds, generating chains along [100].
Therefore, it proved to be important to determine the hitherto unknown crystal structure of the free ligand, to enable comparative investigations. According to the structure analysis, the C1-N3 bond in the title compound is 1.3179 (11)  1), generating a chain along the ab-plane (Fig. 2). On the other hand, intermolecular C-H···N hydrogen bonds play no prominent role in the stabilization of the crystal structure.

Experimental
The title compound was obtained by heating two equivalents (60.4 mmol) of N′,N′,N′′,N′′-tetramethylguanidine with one equivalent (30.2 mmol) N,N-diphenylcarbamoyl chloride in acetonitrile for three hours under reflux. After cooling to room temperature the precipitated N′,N′,N′′,N′′-tetramethylguanidinium chloride was filtered off and the solvent was removed. The residue was redissolved in diethylether and the insoluble part was filtered off. After evaporation of the solvent a colorless solid was been obtained. The title compound crystallized from a saturated acetonitrile solution after several days at 273 K, forming colorless single crystals. Yield: 7.6 g (81%)

Refinement
The hydrogen atoms of the methyl groups were allowed to rotate with a fixed angle around the C-N bond to best fit the experimental electron density, with U iso (H) set to 1.5 U eq (C) and d approximation, with U iso (H) set to 1.2 U eq (C).

Figure 1
Molecular structure of the title compound with displacement ellipsoids at the 50% probability level.