A new polymorph of tri(p-tolyl)boroxine

A new orthorhombic polymorph of tri(p-tolyl)boroxine (Pmn2(1)) with relatively short intermolecular B-O distances of 3.321 angstrom was crystallized from CDCl3 at ambient temperature. The crystal structure of the orthorhombic polymorph of tri(p-tolyl)boroxine shows the shortest intermolecular B-O contact yet found in boroxines. The cell dimensions of the orthorhombic polymorph of tri(p-tolyl)boroxine are a = 21.888(4) angstrom, b = 9.304(2) angstrom, and c = 4.7804(10) angstrom. The structural features of the orthorhombic polymorph of tri(p-tolyl)boroxine are quite different from a previously reported monoclinic (Beckett et al., J. Organomet. Chem. 1997, 535, 33-41) but similar to that of tri(p-bromophenyl)boroxine (Avent et al., Coll. Czech. Chem. Commun. 2002, 67, 1051-1060). Obviously, electronic effects of substituents on the boron centers influence the structural features of substituted boroxines less than discussed in earlier reports (Boese et al., Angew. Chem. 1987, 99, 239-241).