Bis(2,4-dimethoxyphenyl)(phenyl)phosphine selenide

In the title molecule, C22H23O4PSe, the P atom has a distorted tetrahedral environment formed by the selenide atom [P=Se = 2.1219 (5) Å] and three aryl rings. The orientations of the methoxy groups in the two 2,4-dimethoxyphenyl ligands are distinct, as seen from the torsion angles: C—C—O—C = 14.7 (3) and 175.97 (17)° in one ligand, and −9.1 (2) and 5.1 (3)° in the other. In the crystal, weak intermolecular C—H⋯Se interactions link the molecules into zigzag chains propagated in [010].

In the title molecule, C 22 H 23 O 4 PSe, the P atom has a distorted tetrahedral environment formed by the selenide atom [P Se = 2.1219 (5) Å ] and three aryl rings. The orientations of the methoxy groups in the two 2,4-dimethoxyphenyl ligands are distinct, as seen from the torsion angles: C-C-O-C = 14.7 (3) and 175.97 (17) in one ligand, and À9.1 (2) and 5.1 (3) in the other. In the crystal, weak intermolecular C-HÁ Á ÁSe interactions link the molecules into zigzag chains propagated in [010].

Related literature
For background to studies aimed at understanding the transition metal-phosphorus bond, see: Muller et al. (2006); Roodt et al. (2003) Tolman (1977. As part of this systematic investigation we are now also studying selenium-bonded phosphorus ligands, see: Muller et al. (2008). For the synthesis of ortho-substituted arylalkylphosphanes, see: Riihimä ki et al. (2003). For a description of the Cambridge Structural Database, see: Allen (2002 Table 1 Hydrogen-bond geometry (Å , ).

Comment
There has been extensive development in understanding the transition metal phosphorous bond by various groups, including our own, with various techniques such as single-crystal X-ray crystallography, multi nuclear NMR and IR (Roodt et al., 2003). As part of this systematic investigation we are now also studying selenium bonded phosphorus ligands (see Muller et al., 2008) This way there is no steric crowding effect, albeit crystal packing effects, as normally found in transition metal complexes with bulky ligands, e.g. in trans-[Rh(CO)Cl{P(OC 6 H 5 ) 3 } 2 ] cone angles variation from 156° to 167° was observed for the two phosphite ligands (Muller et al., 2006). The J( 31 P-77 Se) coupling can also be used as an additional probe to obtain more information regarding the nature of the phosphorous bond. Reported here is the first single-crystal structure of the compound PPh(2,4-OMe-C 6 H 3 ) 2 to date (Cambridge Structural Database; Version 5.31, update of August; Allen, 2002).
Crystals of the title compound, (I), packs in the P2 1 /c (Z=4) space group with the molecules lying on general positions.
All geometrical features of the molecule (Allen, 2002) are as expected with the selenium atom and the three aryl groups adopting a distorted arrangement about phosphorous (see Fig. 1 and Table 1). The cone angle was found to be 176.9° when the Se-P distance is adjusted to 2.28 Å (the default value used in Tolman, 1977) Two different orientations for the methoxy moieties are noted and is probably due to some weak interactions (Table 1) forcing it into the conformations observed.

Experimental
PPh(2,4-OMe-C 6 H 3 ) 2 were prepared either by direct ortho metallation of anisole with BuLi followed the addition of the appropriate chlorophosphine or by metal/halogen exchange between BuLi and 1-bromo-2,4-dimethoxybenzene followed by the addition of PPhCl 2 according to established methods (Riihimäki et al. 2003).
Eqimolar amounts of KSeCN and the PPh(2,4-OMe-C 6 H 3 ) 2 compound (ca 0.04 mmol) were dissolved in the minimum amounts of methanol (10 -20 ml). The KSeCN solution was added dropwise (5 min.) to the phosphine solution with stirring at room temperature. The final solution was left to evaporate slowly until dry to give crystals suitable for a single-crystal X-ray study.

Refinement
The aromatic and methylene H atoms were placed in geometrically idealized positions (C-H = 0.93 -0.98 Å) and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (C) respectively, with torsion angles refined from the electron density for the methyl groups. The highest residual electron density was located 0.64 Å from H25.