Synthesis and crystal structure of trans-dichlorido[3-methyl-1-(4-vinylbenzyl)-1H-imidazol-3-ium-2-yl-κC 2](4-phenylpyridine-κN)palladium(II)

In the title compound, [Pd(C11H9N)(C13H14N2)Cl2], the PdII ion is coordinated by two Cl anions, one carbene C atom and one pyridine N atom in a slightly distorted square-planar geometry. In the crystal, the molecules are linked through weak C—H⋯Cl hydrogen bonds into a tape structure.


Chemical context
In the last few years, palladium complexes with N-heterocyclic carbene ligands (Pd-NHCs) have received attention, inter alia as catalysts for cross-coupling in organic synthesis (Hadei et al., 2005;Nasielski et al., 2010;Valente et al., 2010Valente et al., , 2012. NHC complexes derived from vinyl imidazolium salts are of growing significance in organometallic transformations because of their potential as precursors in heterogeneous catalysis, biocompatibility, anti-microbial activity and fuel cell applications (Dani et al., 2015;Ghazali-Esfahani et al., 2013;Anderson & Long, 2010;Kim et al., 2005;Kuzmicz et al., 2014;Seo & Chung, 2014;Li et al., 2011). The crystal structures of 1methyl-3-(4-vinylbenzyl) imidazolium hexafluoridophosphate and silver complexes with 1-methyl-3-(4-vinylbenzyl) imidazole as a carbene ligand have been reported previously (Lu et al., 2009(Lu et al., , 2010. Here we report on the crystal structure of a new type of Pd-NHC complex belonging to the group of PEPPSI (pyridine-enhanced precatalyst preparation stabilization and initiation) catalysts, which are stable towards air and moisture, and have the advantage of being easy to synthesize and handle (Hadei et al., 2005).

Structural commentary
In the title compound, the Pd II ion coordinates the fivemembered NHC ligand with a Pd1-C4 bond length of 1.9532 (16) Å and the 4-phenylpyridine ligand with a Pd1-N3 ISSN 2056-9890 bond length of 2.0938 (14) Å . The two mutually trans Cl ions fulfil the coordination sphere (Fig. 1). Bond angles in the soformed distorted square-plane are all close to 90 with the C4-Pd1-Cl angles slightly less than 90 and the others slightly more. The C4-Pd1-N3 angle shows an expected value 179.52 (6) , while Cl1-Pd1-Cl2 exhibits a slightly distorted angle of 176.789 (17) , probably due to the steric influence of the aromatic rings (Sevinçek et al., 2007). The dihedral angle between the N1/C4/N2/C3/C2 and C6-C11 rings in the NHC ligand is 77.90 (5) .

Supramolecular features
In addition to dispersion interactions, the crystal of title compound 4 shows ainteraction between the C19-C24 phenyl rings of neighbouring molecules with a centroidcentroid distance of 3.9117 (11) Å (Fig. 2). Two weak nonclassical C-HÁ Á ÁCl hydrogen bonds are detected (Table 1). No C-HÁ Á Á contacts are present in the crystal packing diagram of compound 4 (Fig. 3).

Synthesis and crystallization
General: Solvents and chemicals were purchased from commercial suppliers and used as received. The imidazolium salts 1 and 2 were prepared according to previously reported The molecular structure of the title compound (4). All non-H atoms are represented as displacement ellipsoids drawn at the 50% probability level and H atoms as small spheres with arbitrary radii.

Figure 2
The dimer of the title compound (4) linked through theinteraction.
procedures (Kim et al., 2005;Lu et al., 2009). The title compound 4 was synthesized according to the carbene silver(I) route, as shown in Fig. 4. Transmetallation of the ligand from the tetrameric silver complex 2 gave the chloridobridged palladium dimer 3. Cleavage of the dimer with phenylpyridine afforded complex 4 in excellent yield. With its vinyl groups it can serve as a precursor in co-polymerization reactions with e.g. styrene to form polymeric materials with catalytic properties.
[PdCl 2 (bmim)] 2 (3). A 100 ml Schlenk flask was charged with 2 (7.0 g, 20.5 mmol), 50 ml of dry CH 2 Cl 2 and Pd(PhCN) 2 Cl 2 (7.8 g, 20.5 mmol). The mixture was stirred for 48 h at room temperature, during which time the solution changed colour to cloudy light brown. It was filtered through Celite and the filtrate was reduced to ca 10 ml. Upon addition of n-hexane, a light-brown solid was formed, which was collected on a frit and dried under vacuum to give 5.97 g (yield 78%).
[PdCl 2 (bmbim)(4-Phenylpyridine)] (4). 4-Phenylpyridine (0.085 g, 0.55 mmol) was added to a 40 ml solution of 3 (0.25 g, 0.26 mmol) in dry CH 3 CN and stirred at ambient temperature for 24 h, during which time the solution changed colour to clear yellow. The mixture was filtered through Celite and all solvents were evaporated. The solids were dissolved in CH 2 Cl 2 and, upon addition of n-hexane, a yellow solid was formed, which was collected on a frit and dried under vacuum to give 0.153 g (93%) of 4.
Single crystals of 4 suitable for X-ray diffraction were obtained by slow diffusion of n-hexane into a saturated CH 2 Cl 2 solution of the compound.

Refinement details
Crystal data and structure refinement details are summarized in Table 2. H atoms were treated as riding, with C-H = 0.95-0.99 Å , and with U iso (H) = 1.2U eq (C). Synthesis pathway of the title compound (4).