cis-Dichloridobis[tris(2-methylphenoxy)phosphane-κP]palladium(II)

In the title compound, [PdCl2(C21H21O3P)2], the Pd atom adopts a slightly distorted square-planar coordination geometry, with pairs of the equivalent ligands in cis positions. Adjacent molecules are linked by weak C—H⋯Cl hydrogen bonds. The crystal structure is additionally stabilized by π–π stacking interactions between the aromatic rings [shortest centroid–centroid distance = 3.758 (4) Å].

In the title compound, [PdCl 2 (C 21 H 21 O 3 P) 2 ], the Pd atom adopts a slightly distorted square-planar coordination geometry, with pairs of the equivalent ligands in cis positions. Adjacent molecules are linked by weak C-HÁ Á ÁCl hydrogen bonds. The crystal structure is additionally stabilized bystacking interactions between the aromatic rings [shortest centroid-centroid distance = 3.758 (4) Å ].
Cg1 denotes the centroid of ring C11-C16; Cg2 of ring C41-C46. CgÁ Á ÁCg is the distance between ring centroids. The interplanar distance is the perpendicular distance of CgI from the ring J plane. The offset is the lateral displacement of ring I relative to ring J. The planes of the I and J rings are parallel.

Izabela Błaszczyk, Anna M. Trzeciak and Andrzej Gniewek Comment
Palladium complexes with phosphito ligands are frequently used as catalyst precursors in carbon-carbon bond-forming reactions. The Sonogashira reaction has attracted a lot of attention as an efficient way to produce phenylated alkines (Sonogashira et al., 1975). In this paper we report crystallization of a palladium(II) complex with tritolylphosphito ligands, the title compound, which has recently proved its high catalytic activity in a copper-free Sonogashira reaction with iodobenzene and phenylacetylene as substrates and imidazolium ionic liquids as the reaction medium (Błaszczyk et al., 2009).
The Pd atom of the title compound is four-coordinated in a square-planar geometry (Fig. 1). The molecule adopts the cis configuration in the solid state. The angles between adjacent ligands deviate only slightly from the expected value of 90° (Table 1). The Pd-Cl1 and Pd-Cl2 bond distances are within a range typical for palladium complexes: 2.298-2.354Å (Orpen et al., 1989). The measured Pd-P bond lengths 2.22-2.24Å are also commonly observed in such a kind of complexes (Sabounchei et al., 2000;Trzeciak et al. 2001).
In the crystal structure, the molecules of the title complex are linked by a few weak hydrogen interactions of the C-H···Cl type (Desiraju & Steiner, 1999). The C17 and C45 atoms act as hydrogen-bond donors, via H17A and H45, to the Cl i or Cl ii atom [symmetry codes: (i) x -1, y, z; (ii) -x + 1, -y + 1, -z + 1], respectively, as an acceptor ( Table 2). The observed C-H···Cl distances are similar to the values of the N-H···Cl hydrogen bonds identified for Cl bonded to a transition metal (Aullón et al., 1998).
Additionally, the C11-C16 and C41-C46 aromatic rings are engaged in π-π stacking contacts, which further assist in the stabilization of the crystal structure (Table 3). Even though the distance of the centroids and the offset of the interacting rings may first appear to be somewhat large, it is however well known that energetically favorable non-bonded aromatic interactions are generally observed at such phenyl ring centroid separation distances (McGaughey et al., 1998).

Experimental
The title compound was prepared according to the previously reported procedure (Błaszczyk et al., 2009): tris(2-methylphenyl)phosphite (0.96 ml, 3.0 mmol) was slowly added to the solution of PdCl 2 (cyclooctadiene) (0.144 g, 0.6 mmol) in benzene (5 ml). A change of color from yellow to pale yellow was observed. The solution was stirred at room temperature for 45 minutes. The solvent was evaporated in vacuo. The white product was recrystallized from a mixture of benzene and diethyl ether. Yield: 0.25 g, 48%.

Refinement
All H atoms were positioned geometrically and refined using a riding model with aromatic C-H = 0.95Å and U iso (H) = 1.2U eq (C). The methyl groups were refined with C-H = 0.98Å and U iso (H) = 1.5U eq (C). The highest residual peak and the deepest hole in the final difference map are located 0.83 and 0.77Å from the C51 and Pd atom, respectively.

Figure 1
The molecular structure and atom numbering scheme of the title compound. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.

cis-Dichloridobis[tris(2-methylphenoxy)phosphane-κP]palladium(II)
Crystal data  Special details Experimental. The crystal was placed in the cold stream of an open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100 K. Analytical numeric absorption correction was carried out with CrysAlis RED (Oxford Diffraction, 2010) using a multifaceted crystal model (Clark & Reid, 1995). 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 > 2σ(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.