8-(Diphenylphosphanyl)quinoline

The title compound, C21H16NP, is a known P—N chelator and various crystal structures of its metal complexes have been reported. However, no crystallographic evidence of the free ligand has been given to date. The phenyl rings are almost orthogonal to one another [dihedral angle = 88.9 (1)°], and they are twisted from the mean plane of the quinoline by 80.5 (1) and 76.3 (1)°.


Experimental
Crystal data

Comment
Bearing both imine and phosphine moieties, 8-quinolylphosphine derivatives are good chelators for transition metals. (Hudali et al., 1979) Their complexes have important photochemical and photophysical properties and are widely used in chemical industry (catalysis, functional materials, etc). (Canovese et al., 2008;Qin et al., 2009;Tsukuda et al., 2009). For the specific example of the 8-(diphenylphosphino)quinoline, although crystallographic evidence of various of its metal complexes exists (Suzuki, 2004;Suzuki et al., 2009, Canovese et al., 2008, this is the first report of the free ligand structure (Figure 1).
It is worth mentioning the almost orthogonal position of the phenyl rings to one another (88.9 (1)°), and their tilt with respect to the mean plane of the quinoline by 80.5 (1)° and 76.3 (1)°, maximizing the intramolecular CH/π interactions. The structure is also stabilized by intermolecular CH/π interactions between the proton H3 of the quinolyl ring and the π system of an adjacent phenyl (H3···Cg 2.8 Å, C3-H3···Cg 170 (1)°). It is also to be noted the short contact of 2.9 Å, at the limit of the van der Waals radius (3.0 Å), between the phosphorus atom and the quinolyl hydrogen H2 of an adjacent molecule.

Experimental
The title compound, 8-(diphenylphosphino)quinoline, was synthesized by the reaction of 8-(trifluoromethylsulfonyl)quinoline with tetrakis-triphenylphosphine palladium in presence of zinc cyanide, as a byproduct of 8-cyanoquinoline (Lord et al. 2009). 8-(Trifluoromethylsulfonyl)quinoline (2.0 g, 7.3 mmol), zinc cyanide (0.54 g, 4.6 mmol) and tetrakis-triphenylphosphine palladium (0.84 g, 0.73 mmol) were taken in dry DMF (15 ml) and refluxed under nitrogen for 2 h. The reaction mixture was cooled and poured into water (150 ml). Aqueous H 2 SO 4 (2M) (15 ml) was added and the mixture was stirred for 5 min. This was then extracted with EtOAc (2 x 100 ml), washed with brine and dried over anhydrous MgSO 4 . Evaporation of the solvent gave a brown gummy solid. This was subjected to column chromatography on SiO 2 with 30% EtOAc in n-hexane as eluent. The first band contained the title compound. Solvent evaporation at room temperature gave off-white X-ray quality crystals.

Refinement
The H atoms were positioned geometrically (C-H 0.95 Å) and included in the refinement in the riding model approximation; their temperature displacement parameters were set to 1.2 times the equivalent isotropic temperature factors of the parent site. Fig. 1. The molecular structure of the title compound (30% probability displacement ellipsoids).

Special details
Experimental. X-ray crystallographic data for I were collected from a single-crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Platform diffractometer, equipped with a Bruker SMART 4 K Charged-Coupled Device (CCD) Area Detector using the program APEX2 and a Nonius FR591 rotating anode equiped with a Montel 200 optics The crystal-to-detector distance was 5.0 cm, and the data collection was carried out in 512 x 512 pixel mode. The initial unit-cell parameters were determined by a least-squares fit of the angular setting of strong reflections, collected by a 10.0 degree scan in 33 frames over four different parts of the reciprocal space (132 frames total). One complete sphere of data was collected, to better than 0.80Å resolution. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq P1 0.85952 (