Synthesis and crystal structure of [Pd{C6H4(CH2NHCH2Ph)-2-κ2 C,N}(μ-I)]2

The binuclear molecules of the title complex show weak intermolecular C—H⋯Pd interactions, whereas the amine N—H functional groups are not involved in hydrogen bonding.

Over the past few years, our group has been interested in the synthesis, reactivity and applications in organic synthesis of orthopalladated derivatives of dibenzylamine. We have reported the first general method for the cyclopalladation of primary and secondary amines by using Pd(OAc) 2 . The acetato-bridged complexes were transformed into the corresponding halido-bridged complexes by anion metathesis reactions, which were used for further reactivity studies (Vicente et al., 1997).
Herein we report the synthesis and crystal structure of a iodido-bridged complex [Pd{C 6 H 4 (CH 2 NHCH 2 Ph)-2}(-I)] 2 . This is a rare example of a cyclopalladated complex containing bridging iodido ligands and one of the few Ĉ N-cyclopalladated iodido-bridged complexes characterized by X-ray diffraction.

Structural commentary
The complex crystallizes in the centrosymmetric monoclinic space group P2 1 /n with one molecule in the asymmetric unit. ISSN 2056-9890 The molecular structure can be described as a nearly planar dipalladium subunit of the type (C-N)Pd(-I) 2 Pd(C-N) (Fig. 1). Both palladium atoms adopt a slightly distorted square-planar coordination environment, the mean deviations of the Pd-N-C-I-I planes being larger for Pd2 (0.0868 Å ) than for Pd1 (0.0301 Å ). The highest deviation from the average coordination plane occurs for C22 (0.1261 Å ). The more distorted square-planar geometry of Pd2 is further evidenced by the smaller dihedral angle between the planes N1-Pd1-C2 and I1-Pd1- I2 [5.53 (16) ] compared to that of N2-Pd2-C22 and I1-Pd2- I2 [8.29 (16) ]. The structural differences around both Pd II atoms are consistent with the presence of two N-H stretching bands at 3261 and 3201 cm À1 in the infrared spectrum of the solid.
Owing to the cisoid arrangement of the C,N-cyclopalladated ligands, one of the iodine atoms of the Pd 2 I 2 unit is trans to two carbon atoms (I1) whereas the other is trans to two nitrogen atoms (I2). Consequently, the Pd-I bond lengths of the I atoms trans to N [2.5959 (5) and 2.5801 (4) Å ] are shorter than those of the I atoms trans to C [2.7504 (5) and 2.7030 (5) Å ] because of the greater trans influence of the aryl ligands compared to that of the amino ligands. Similar values for these bond lengths and also for the C-Pd [1.986 (5), 1.991 (4) Å ] and N-Pd [2.104 (4), 2.809 (4) Å ] bond lengths have been found in the five structures of iodido-bridged cyclopalladated complexes reported so far (see Database survey). Selected torsion angles are collated in Table 1.
One of the methylenic hydrogen atoms of the cyclopalladated dibenzylamine moiety coordinating to Pd1 participates in the formation of a non-classical intramolecular C-HÁ Á ÁI hydrogen bond (Fig. 1, Table 2).

Supramolecular features
There are no hydrogen-bonding interactions involving the two NH groups. The most remarkable intermolecular interaction observed in the crystal structure is a weak hydrogen bond between the arylic hydrogen placed in position 3 of the phenylene ring attached to Pd2 (H16) and the Pd2 atom of the adjacent molecule. This interaction gives rise to the formation of a chain arrangement of molecules along the b axis (Fig. 2). Although the Pd-H bond length [2.760 (2) Å ] is slightly shorter than the sum of the van der Waals radii of Pd and H (2.83 Å ) (Bondi, 1964), it seems to direct the arrangement of the molecules in the crystal structure. In this context it is interesting to compare the arrangement of the molecules in  Table 1 Selected torsion angles ( ).

Figure 2
A view of the molecular packing of the title compound. Dotted lines indicate C-HÁ Á ÁPd contacts. H atoms not involved in the interactions have been omitted for clarity.

Figure 1
The molecular structure of the title complex, with displacement ellipsoids at the 50% probability level. The black dashed line indicates the intramolecular C-HÁ Á ÁI hydrogen bond (see Table 2 for numerical details).

Synthesis and crystallization
To a suspension of the complex [Pd{C 6 H 4 (CH 2 NHCH 2 Ph)-2}-(-OAc)] 2 (Vicente et al., 1999) (800 mg, 1.106 mmol) in acetone (30 ml) solid NaI (1000 mg, 6.022 mmol) was added and the resulting mixture was stirred for 3 h. The solution was filtered through a plug of MgSO 4 , and the filtrate was concentrated to ca 5 ml. Diethyl ether was added (25 ml), the solvent was partially removed (to ca 5 ml), and n-pentane was added (25 ml) to precipitate the title complex as an orange solid, which was collected and air-dried. Single crystals of the compound suitable for X-ray analysis were obtained by slow diffusion of n-pentane into a solution of the compound in CHCl 3 at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. C and N atoms were subjected to DELU commands (Sheldrick, 2015), and five reflections were omitted from the final refinement due to poor agreement between measured and calculated intensities. All H atoms associated with C atoms could be located in difference-Fourier maps. However, they were relocated at geometrically idealized positions and were allowed to ride on the parent atoms with C-H = 0.95 Å (aromatic) and 0.99 Å (CH 2 ) and U iso (H) = 1.2U eq (C). Hydrogen atoms bound to N atoms were discernible from a difference-Fourier map and were subsequently refined with N-H distance restraints [target value 0.87 (2)   Computer programs: APEX2 and SAINT (Bruker, 2013), SHELXS97 and SHELXTL (Sheldrick, 2008) and SHELXL2013 (Sheldrick, 2015). program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).