( E )-2-[ 2-( 4-Methylphenyl ) 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 methyl analogue. Structures have also been determined for the SMe (Yuan et al., 1990), OMe (Nguyen et al., 2002) and CF3 (Clegg et al., 2004) derivatives.

Molecules of the title compound, C 15 H 13 BO 2 , are essentially planar with a high degree of conjugation. Pairs of molecules related by inversion symmetry show %-stacking interactions, and the overall packing is a herring-bone pattern. The molecular geometry is similar to that of closely related analogues.

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 methyl analogue. Structures have also been determined for the SMe (Yuan et al., 1990), OMe (Nguyen et al., 2002) and CF 3 (Clegg et al., 2004) derivatives.
The molecule of the title compound ( Fig. 1) is essentially completely planar except for the H atoms of the methyl group, with a high degree of conjugation. The r.m.s. deviation of all non-H atoms from their mean plane is 0.071 A Ê . All torsion angles for non-H atoms are close to 0 and 180 , the largest corresponding to a twist of about 7 around the BÐC bond linking the alkene double bond to the benzodioxaborole (Bcat) group (Table 1). This almost completely planar arrangement is found also for the other derivatives mentioned above.
Bond lengths and angles are typical of compounds in which Bcat is attached to an alkene double bond; these include not only the derivatives with different para substituents, but also the compounds (Bcat)CH C(R)(Cl), where R is either Me or Et (Bayer et al., 2002), the symmetrically substituted alkene (Bcat) 2 C C(Bcat) 2 (Gu et al., 2001), two Bcat-substituted cyclopentadienes (Avent et al., 2003), and several alkenes and dialkenes with two or more Bcat groups Clegg et al., 1996). Steric interaction, particularly between Bcat groups, forces some of these molecules to adopt nonplanar forms, which has minor effects on the degree of conjugation and hence on some bond lengths.
Centrosymmetric pairs of molecules of the title compound show extensive overlap (Fig. 2) and a separation of about 3.57 A Ê , indicating some %-stacking interaction. These dimeric units are further assembled into a herring-bone pattern in the overall crystal packing (Fig. 3), as is commonly found for planar organic molecules.

Re®nement
Re®nement on F 2 R[F 2 > 2'(F 2 )] = 0.042 wR(F 2 ) = 0.108 S = 1.06 2697 re¯ections 165 parameters H-atom parameters constrained  The overlap of two parallel molecules related by inversion symmetry, seen (a) from above and (b) from the side. One molecule is shown with ®lled bonds, and the other with hollow bonds.

Figure 3
The crystal packing, viewed along the a axis. H = 0.95 (aromatic and ole®nic) or 0.98 A Ê (methyl), and with U iso (H) = 1.2U eq (C) (1.5U eq for methyl groups).