Crystal structure of 3-mesityl-1-[(pyridin-2-yl)methyl]-3,4,5,6-tetrahydropyrimidin-1-ium bromide monohydrate

In the title hydrated salt, C19H24N3 +·Br−·H2O, the values of the N—C bond lengths within the tetrahydropyrimidinium ring indicate delocalization of the N=C double bond. In the cation, the dihedral angle formed by the pyridine and benzene rings is 14.97 (12)°. In the crystal, ions and water molecules are linked by O—H⋯Br, O—H⋯N, C—H⋯Br and C—H⋯O hydrogen bonds into chains running parallel to the b axis.


Related literature
Hydrogen-bond geometry (Å , ).  (Dunsford & Cavell, 2014). It would be of interest to explore whether the introduction of ring expanded NHCs to a chelating framework will result in new chelating complexes displaying novel reactivity and enhanced catalytic activities. To the best of our knowledge, no report on chelating NHC metal complexes has been presented. Following our interest in the development of ring-expanded NHCs based on substituted 1,4,5,6-tetrahydropyrimidine and their metal complexes (Mao et al., 2012), and with the intention of synthesizing chelating ringexpanded NHC metal complexes, we synthesized the chelating NHC precursor, 3-methyl-1-(pyridin-2-ylmethyl)-3,4,5,6tetrahydropyrimidin-1-ium bromide and determined the structure of its monohydrate derivative. Research on the synthesis of carbene-metal complexes containing this ligand is currently in progress.
The molecular structure of the title compound is shown in Figure 1. As expected, the values of the bond distances within the pyrimidinyl ring indicate delocalization of the N═C bond that extends from N2 to N3 through C10, resulting in the increased acidity of the proton on C10 and convenient formation of a carbene functionality. In the cation, the benzene and pyridine rings form a dihedral angle of 14.97 (12)°. In the crystal structure, ions and water molecules are linked by O -H···N, O-H···Br, C-H···Br and C-H···O hydrogen bonds (Table 1) forming chains parallel to the b axis.
Infrared detection showed the disappearance of the carbonyl group. The mixture was then put into an ice-bath, and NaBH 4 (120 mmol, 4.54 g) was added portion-wise for 1 h, before being warmed up to room temperature and then heated to 70 °C overnight. The solvent was evaporated and the residue was poured into a mixture of water (20 ml) and CH 2 Cl 2 (20 ml). The resulting suspension liquid was filtered and the filtrate was extracted by CH 2 Cl 2 (10 ml) for 3 times. The combined organic phase was evaporated and the residue obtained was dissolved in methanol (10 ml Hexahydropyrimidine (5 mmol, 1.48 g) was dissolved in DME (20 ml). NBS (5 mmol, 0.89 g) was added portion-wise and the resulting mixture was stirred at room temperature for 3 h, during which time a white precipitate formed. The precipitate was filtered and washed with DME. Crystallization of the precipitate from CH 2 Cl 2 /diethyl ether (1:1 v/v) afforded the title product as colourless crystals.

S3. Refinement
The water H atoms could be located in a difference Fourier map, but only one of them (H1B) could be refined freely. The second H atom (H1A) was refined using a rigid-body approximation, with O-H constrained to be 0.9 Å, and with U iso (H) = 1.5 U eq (O). All other H atoms were placed geometrically and refined as riding, with C-H = 0.93-0.97 Å, and with U iso (H) = 1.2 U eq (C).

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