Dichlorido{(E)-2,4,6-trimethyl-N-[phenyl(2-pyridyl)methylidene]aniline-κ2 N,N′}palladium(II)

The title complex, [PdCl2(C21H20N2)], contains a PdII atom in a slightly distorted square-planar coordination environment defined by two N atoms from one 2,4,6-trimethyl-N-[phenyl(2-pyridyl)methylidene]aniline ligand and two Cl atoms, forming a five-membered ring (N—Pd—N—C—C).

Financial support from the Ministry of Economic Affairs, Taiwan, is appreciated.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: PK2244).

Comment
Recently, palladium-catalyzed Suzuki-Miyaura reactions involving cross-coupling of aryl halides with aryl boronic acids have emerged as the most important synthetic methods for the preparation of biaryl compounds (Miyaura et al., 1995;Na et al., 2004;Rajagopal et al., 2002;Li 2003;Tomioka et al., 2004;Nicolaou et al., 2005). Thus, because of its utility as an important synthetic methodology, a significant amount of research focus had been devoted to designing improved catalysts for the Suzuki-Miyaura cross-coupling reaction. It is noteworthy that there has been a continuing interest in the further development of more efficient and selective catalytic systems for the synthesis of biaryls. However, only a few examples of N,N' pyridyl-imine palladium complexes have been reported as catalysts in coupling reaction (Lai et al., 2005;Pelagattia et al., 2005). Herein, we report the synthesis and crystal structure of the title palladium (II) complex that is certainly a potential catalyst in cross-coupling reactions.
The structure of the title compound is a mononuclear configuration with the metal center bound to two N atoms (one from the imine group and one from the pyridine ring) and two Cl atoms (Fig. 1). The coordination geometry around Pd II atom is slightly distorted square planar, and the distances of Pd(1)-N(1) and Pd(1)-N(2) are 2.025 (2) and 2.033 (2) Å, respectively. It is noticed that the trans angles (N2-Pd-Cl1 and N1-Pd-Cl2) in the PdN 2 Cl 2 core do not deviate more than 8° from the ideal value of 180°. Moreover, the planes of the pyridine (N1-C1-C2-C3-C4-C5) and phenyl rings (C8-C9-C10-C11-C12 and C13-C14-C15-C16-C17-C18) are close to perpendicular, and the dihedral angles between them are 80.9 (3) and 82.8 (3)°, respectively. All bond distances and bond angles lie within normal ranges, which are essentially similar to the pyridyl-imine palladium (II) complex (Hsueh et al., 2006;Zhang et al., 2008).

Refinement
All H atoms were initially located in a difference Fourier map. The methyl H atoms were then constrained to an ideal geometry with C-H distances of 0.96 Å and U iso (H) = 1.5U eq (C), but each group was allowed to rotate freely about its C-C bond. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C-H distances in the range 0.95-1.00 Å and U iso (H) = 1.2U eq (C).  Fig. 1. A view of the molecular structure of the title compound with displacement ellipsoids shown at the 30% probability level.

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.
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 Rfactors(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.