Crystal structure of trans-dichloridobis[N-(5,5-dimethyl-4,5-dihydro-3H-pyrrol-2-yl-κN)acetamide]palladium(II) dihydrate

The synthesis and crystal structure of the complex trans-[dichlorido-bis(N-(4,5-dihydro-5,5-dimethyl-3H-pyrrol-2-yl)acetamide)]palladium(II) dihydrate is described.


Chemical context
The [2 + 3]-cycloaddition of nitrones with nitriles is one of the most important routes for the synthesis of 1,2,4-oxadiazolines (Bokach et al., 2011). However, there are some limitations for this method, as only electrophilically activated nitriles react with nitrones under harsh conditions and/or long reaction times (Eberson et al., 1998;Lasri et al., 2008). The coordination of nitriles to a suitable metal atom becomes a convenient methodology and facile metal-mediated route for the synthesis of a large number of compounds, inaccessible directly by pure organic chemistry (Bokach et al., 2011). The N-O bond cleavage of oxadiazoline rings can be promoted by thermal heating to furnish the derived ketoimine complexes (Lasri et al., 2011). Moreover, the oxadiazoline ligands are opened by N-O bond cleavage to form pyrrolylbenzamide derivatives in which the N atoms of the pyrrolyl moieties coordinate to the palladium atom in the trans positions (Lasri et al., 2009).

Supramolecular features
In the asymmetric unit, both the N2 and N4 atoms act as hydrogen-bond donors for the O3 atom of a water molecule ( Table 1). The water molecule including the O3 atom also acts as a hydrogen-bond donor to Cl2 and to a second water molecule (O4) which, in turn, forms hydrogen bonds with the Cl1 and O3 atoms of neighboring metal complexes. A view of the crystal packing ( Fig. 2) shows that the molecules are organized in such a way that hydrogen bonds form double layers of metal complexes parallel to the bc plane, mainly connected by weak van der Waals interactions.

Synthesis and crystallization
A solution of bis(1,2,4-oxadiazoline) palladium(II) (complex 1; 100 mg, 0.206 mmol; Lasri et al., 2009) in CHCl 3 (10 mL) was refluxed for one week. The solvent was then removed in vacuo and the resulting solid was washed with three 10 mL portions of diethyl ether and dried under air to give a yellow  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
Packing diagram of the title compound viewed down the c axis.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. Dashed lines indicate hydrogen bonds solid. The 1 H and 13 C NMR spectra in CDCl 3 of the obtained solid show the presence of a mixture of compounds. However, the pyrrolylacetamide product 2 was isolated by mechanical separation of the crystals obtained from slow evaporation of an acetone/toluene (30:1 v/v) solution. The IR spectrum of 2 shows strong (NC O) and (N C) vibrations at 1729 and 1644 cm À1 , respectively, and (NH) at 3300 cm À1 .

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The amine and water hydrogen atoms were located in a difference-Fourier map and refined isotropically. All other hydrogen atoms were positioned geometrically and constrained to ride on their parent atoms, with C-H = 0.96-0.97 Å , and with U iso = 1.2 U eq (C) or 1.5U eq (C) for methyl H atoms. A rotating model was applied to the methyl groups. The maximum electron density is located 0.97 Å from atom Pd1 and the minimum electron density is located 0.95 Å from atom Pd1. Two outliers (102 and 002) were omitted in the last cycles of refinement.  Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXS2014/7 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015); molecular graphics: SHELXL2014/7 (Sheldrick, 2015); software used to prepare material for publication: APEX3 (Bruker, 2016) and PLATON (Spek, 2015).

trans-Dichloridobis[N-(5,5-dimethyl-4,5-dihydro-3H-pyrrol-2-yl-κN)acetamide]palladium(II) dihydrate
Crystal data Special details 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.