( E )-2-{ 2-[ 4-( Trifluoromethyl ) phenyl ]-ethenyl }-1 , 3 , 2-benzodioxaborole

The title compound, (I), is one of a series of 2-styrylboronate esters prepared in a study of hydroboration reactions of alkynes, with a variety of para substituents (Wiesauer, 1997). We have previously reported the structure of the parent compound with no substituent in the para position (Clegg et al., 2001). The title compound is the tri ̄uoromethyl analogue. Structures have also been determined for the SMe (Yuan et al., 1990), OMe (Nguyen et al., 2002) and Me (Clegg et al., 2004) derivatives.

Molecules of the twinned and disordered title compound, C 15 H 10 BF 3 O 2 , are essentially planar with a high degree of conjugation. The molecular geometry is similar to that of closely related analogues. Molecules pack parallel in the triclinic crystal structure, with some %-stacking interaction.

Comment
The title compound, (I), is one of a series of 2-styrylboronate esters prepared in a study of hydroboration reactions of alkynes, with a variety of para substituents (Wiesauer, 1997). We have previously reported the structure of the parent compound with no substituent in the para position (Clegg et al., 2001). The title compound is the tri¯uoromethyl analogue. Structures have also been determined for the SMe (Yuan et al., 1990), OMe (Nguyen et al., 2002) and Me (Clegg et al., 2004) derivatives.
The molecule of the title compound ( Fig. 1) is approximately planar, except for the F atoms of the CF 3 group (which is disordered), with a high degree of conjugation. The r.m.s. deviation of the ordered atoms from their mean plane is 0.147 A Ê ; this is rather greater than for the corresponding methyl-substituted compound and the parent compound. All torsion angles for non±F atoms are close to 0 and 180 , the largest corresponding to twists of about 5 and 9 around the BÐC and CÐC bonds linking the alkene double bond to the benzodioxaborole (Bcat) group and the tri¯uoromethylphenyl group (Table 1). As well as these small twisting distortions, the molecule is slightly bowed along its length.
The molecular geometry of this series of compounds has been discussed in the previous paper (Clegg et al., 2004). The molecular structure, with atom labels and 50% probability ellipsoids for non-H atoms. Minor disorder component atoms are not labelled.
All the molecules in the triclinic crystal structure are parallel, with a separation of about 3.66 A Ê between pairs of adjacent molecules, indicating some %-stacking interaction (Figs. 2 and 3). This is different from the herring-bone packing arrangement found in other compounds in this series and typical of many planar organic molecules.
Extinction correction: SHELXTL Extinction coef®cient: 0.04 (2) H atoms were positioned geometrically and re®ned with a riding model, with CÐH = 0.95 A Ê and with U iso (H) = 1.2U eq (C). The triuoromethyl group is disordered, the two components being rotated by about 60 from each other around the CÐC bond, with occupancy factors that re®ned to 0.883 (9):0.117 (9); restraints were applied to the geometry and displacement parameters. The crystal was found to be non-merohedrally twinned by 180 rotation about the [001] reciprocal lattice vector, with approximately equal contributions of the two components. The twinning was resolved with the aid of the programs ROTAX (Cooper et al., 2002) and ROTWIN (Pink & Young, 2000), and involved the re®nement of six twin-component parameters applied to groups of re¯ections with different degrees of overlap; because of the twinning, equivalent re¯ections could not be merged before the re®nement. The combination of twinning and disorder leads to relatively high R factors.  The overlap of adjacent molecules related by inversion symmetry, seen in projection normal to the mean plane of one molecule. One molecule is shown with ®lled bonds, and the other with hollow bonds.

Figure 3
The crystal packing, viewed along the a axis.