Crystal structure of triphenylphosphoniummethylenetrifluoroborate

The synthesis, characterization and structural analysis of triphenylphosphoniummethylenetrifluoroborate are presented.

There are many examples of zwitterionic organotrifluoroborates containing ammonium moieties, but very few containing phosphonium groups have been reported (see Database survey). Phosphonium trifluoroborates have been shown to enhance the hydrolytic stability of the RBF 3 moiety (Wade et al., 2010.) In this context we synthesized Ph 3 PCH 2 BF 3 and report herein its crystal structure.
The B-F bond lengths fall within normal ranges for organotrifluoroborate compounds. The methylene C-P bond length [1.787 (4) Å ] and the C-B bond length [1.636 (4) Å ] also fall within the normal range for similar compounds (Allen et al., 1987). In terms of the surrounding angles, the B and P atoms appear to be sp 3 hybridized. The methylene carbon is predominantly sp 3 hybridized, but has a distorted tetrahedral geometry with a P1-C1-B1 angle of 119.7 (2) .

Supramolecular features
In the crystal, two weak C-HÁ Á ÁF hydrogen bonds between the meta hydrogen atoms on the triphenylphosphonium rings and the trifluoroborate moiety (Table 1) fall within the range of distances observed in other triphenylphosphonium trifluoroborates (Wade et al., 2010) and form chains of R 2 2 (16) rings along the [100] axis (Fig. 2). These chains are further stabilized by herringbone edge-to-face weak C-HÁ Á Á interactions (Fig. 3).

Synthesis and crystallization
Potassium iodomethyltrifluoroborate (1.00 g, 4.04 mmol) and triphenylphosphine (1.11 g, 4.23 mmol) were combined in a pressure flask containing a stir bar under nitrogen, and anhydrous THF (25.0 mL) was added. The flask was sealed and heated to 343 K for 18 h. The reaction was cooled to room temperature and the solvent was removed in vacuo. The residue was washed with Et 2 O (3 x 10 mL) and the resulting solid was dissolved in a minimal amount of acetone and the product was precipitated with water and collected by filtration, to afford a white solid (0.63 g, 1.82 mmol, 45%.) X-ray quality crystals were grown by slow diffusion of pentane into a solution of the title compound dissolved in dichloromethane.  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
Part of the crystal structure, showing weak C-HÁ Á ÁF hydrogen bonds as dashed lines.

Figure 3
Part of the crystal structure, showing weak C-HÁ Á Á interactions along [100] as dashed lines. Only the H atoms involved in these interactions are shown.

Crystal data
C 19 H 17 BF 3 P M r = 344.10 Triclinic, P1 a = 9.514 (2)  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.