Di-μ-chlorido-bis{[2-(di-tert-butylphosphanyl)biphenyl-3-yl-κ2 C 3,P]palladium(II)} dichloromethane disolvate

The asymmetric unit of the title compound, [Pd2Cl2(C20H26P)2]·2CH2Cl2, contains one half-molecule of the palladium complex and a dichloromethane solvent molecule. In the complex, two PdII atoms are bridged by two Cl atoms, with the other two coordination sites occupied by a C atom of the biphenyl system and a P atom, resulting in a distorted square-planar coordination geometry of the PdII atom and a cyclometallated four-membered ring. The Pd2Cl2 unit is located about an inversion center. The planes of the rings of the biphenyl system make a dihedral angle of 66.36 (11)°.

The asymmetric unit of the title compound, [Pd 2 Cl 2 (C 20 H 26 P) 2 ]Á2CH 2 Cl 2 , contains one half-molecule of the palladium complex and a dichloromethane solvent molecule. In the complex, two Pd II atoms are bridged by two Cl atoms, with the other two coordination sites occupied by a C atom of the biphenyl system and a P atom, resulting in a distorted square-planar coordination geometry of the Pd II atom and a cyclometallated four-membered ring. The Pd 2 Cl 2 unit is located about an inversion center. The planes of the rings of the biphenyl system make a dihedral angle of 66.36 (11) .  We would like to acknowledge the University of Johannesburg for financial assistance.
The title compound crystallizes as a dichloromethane solvate, with half a molecule of the complex in the asymmetric unit, in which the the two Pd centres are bridged by two chlorides and are part of a constrained four-membered ring along with two carbon atoms of a phenyl ring and a phosphorus atom (Fig. 1). The four-membered rings are trans across the planar Pd 2 Cl 2 unit, the planar Pd 2 Cl 2 unit being on the center of inversion at 1/2, 0, 0. The coordination around the palladium atom is distorted square planar, with the angles around the metal deviating significantly from orthogonallity yet very planar. The smallest of the angles around the metal centre is 68.84 (10)° and is similar to that previously reported dinuclear cyclopalladate, 68.89 (3)° (Christmann et al., 2006) and of related ortho-metallated Pd-structures from literature (Sole et al., 2004;Mohr et al., 2006;Bennett et al., 2010). The other angles around the Pd centers are 85.85 (11), 95.0 (2) and 106.44 (3)° all probably due to steric hindrance caused by tert-butyl groups. The Pd-C distance (1.978 (3) Å) is shorter than the Pd-P distance (2.2327 (9) Å) which is in good agreement with the Pd-P separation in similar four-membered compounds with a sp 2 -hybridized carbon. The carbon-phosphorus distance that is part of the constrained ring is significantly shorter [1.824 (3) Å] compared to the other two [1.860 (3) and 1.879 (4) Å] as observed in most cyclopalladates. The planes of the phenyl rings of the biphenyl moiety have a dihedral angle of 66.36 (11)°.

Experimental
(2-Biphenyl)-di-tert-butylphosphine (597 mg, 2 mmol) was added to the solution of lithium chloride (170 mg, 4 mmol) and palladium chloride (355 mg, 2 mmol) in 2:1 methanol-dichloromethane (15 ml) under argon. The mixture was heated under reflux under argon for 1 h. The solvent was evaporated in vacuo. To the residue was added dichloromethane (15 ml) and water (10 ml) and the mixture stirred for 30 minutes. The organic phase was separated, dried (anhydrous sodium sulfate) and the solvent evaporated to leave a residue (823 mg) which was chromographed over silica gel (Davisil,20 g) using 5% methanol in dichloromethane as mobile phase. The eluent (120 ml) was evaporated to leave 1 as a colourless The title compound was also obtained in essentially quantitative yield by reacting the above phosphine with an equimolar amount of (cis, cis-1,5-cyclooctadiene) palladium (ll)-chloride in dichloromethane under reflux (1 hr) or at room temperature (18 hrs).

Figure 1
The molecular structure and atom-numbering scheme for (I), with displacement ellipsoids drawn at the 50% probability level. Hydrogen atoms have been omited for clarity. The assymetric unit only has only half a molecule of the palladium complex, the other half generated by the symetry operator -x, -y, -z. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.16 e Å −3 Δρ min = −1.09 e Å −3

Special details
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 > σ(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. >>> The Following ALERTS were generated <<< Format: alert-number_ALERT_alert-type_alert-level text 232_ALERT_2_C Hirshfeld Test Diff (M-X) Pd1 -Cl1.