Bis(2-methoxyphenyl)(phenyl)phosphine selenide

The title compound, C20H19O2PSe or SePPh(2-OMe-C6H3)2, crystallizes with two distinct orientations for the methoxy groups. The Se=P bond is 2.1170 (7) Å and the cone angle is 176.0°. Intramolecular C—H⋯Se interactions occur. In the crystal, molecules are linked by intermolecular C—H⋯Se interactions.

The title compound, C 20 H 19 O 2 PSe or SePPh(2-OMe-C 6 H 3 ) 2 , crystallizes with two distinct orientations for the methoxy groups. The Se P bond is 2.1170 (7) Å and the cone angle is 176.0 . Intramolecular C-HÁ Á ÁSe interactions occur. In the crystal, molecules are linked by intermolecular C-HÁ Á ÁSe interactions.

Comment
The evaluation of the electronic parameter of tertiary phosphines is a study that spans over several decades, and even today attracts attention due to its importance. As part of a systematic investigation we are studying selenium bonded phosphorus ligands (see Muller et al. 2008) to give insight on the nature of these ligands. 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 angle variations from 156° to 167° was observed for the two phosphite ligands (Muller, et al. 2006). Using the geometries obtained from the selenium bonded phosphorus ligands and the 31 P NMR J( 31 P-77 Se) couplings, it would be possible to obtain more information regarding the nature of the phosphorous substituted ligands.
Geometrical parameters of the molecule are as expected (Allen, 2002). Selenium atom and the three aryl groups adopt a distorted tetrahedral arrangement about phosphorous (Fig. 1). The cone angle of 176.0 ° can be calculated for the Se-P distance adjusted to 2.28 Å (the default value from Tolman, 1977). The cone value observed in the title compound is close to the value 178 (7) ° calculated from data of 5 metal bonded phosphines extracted from Cambridge Structural Database (Version 5.31, update of August; Allen, 2002).
Two different orientations for the methoxy moieties might be explained by some weak interactions (Table 2) forcing them into the conformations observed.

Experimental
PPh(2-OMe-C 6 H 4 ) 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-methoxybenzene followed by the addition of PPhCl 2 according to established methods (Riihimäki et al. 2003).
Eqimolar amounts of KSeCN and the PPh(2-OMe-C 6 H 4 ) 2 compound (ca. 0.04 mmol) were dissolved in the minimum amounts of methanol (10 -20 mL). The KSeCN solution was added drop wise (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. The aromatic and methylene H atoms were placed in geometrically idealised 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 1.01 Å from Se. Fig. 1. View of (I) (50% probability displacement ellipsoids). H atoms have been omitted for clarity. For the C atoms, the first digit indicates the ring number and the second digit indicates the position of the atom in the ring.