STERIC EFFECT OF ALLYL SUBSTITUENT ON THE MOLECULAR-STRUCTURES OF ALLYLTITANIUM COMPLEXES

The crystal structures of a series of allyltitanium complexes have been determined by X-ray crystallography. Crystals of (C5H5)2Ti(1,3-dimethylallyl) (1) are monoclinic, space group P2(1)/n, with a = 13.353(2), b = 7.674(1), c = 25.543(2) angstrom, beta = 90.92(1)-degrees, and Z = 8. Crystals of (C5H5)2Ti(2-methylallyl) (2) are orthorhombic, space group Pbca, with a = 15.299(4), b = 25.797(2), c = 12.014(1) angstrom, and Z = 16. The unit cells of 1 and 2 each contain two molecules in a crystallographic asymmetric unit. The coordination geometry of a non-substituted allyltitanium compound was determined for (C5H5)(C5Me5)-Ti(allyl) (3) with the mixed ancillary ligands since (C5H5)2Ti(allyl) (4) includes the packing disorder. Crystals of 3 are orthorhombic, space group Pnma, with a = 9.633(1), b = 12.743(1), c = 12.718(1) angstrom, and Z = 4. The molecular structure exhibits a crystallographic mirror symmetry. All the crystal structures were refined by the full-matrix least-squares to the R indices of 0.062, 0.051, and 0.065 for 1, 2, and 3, respectively. The allyl groups are eta-3-coordinated to the metal with a mirror symmetry. Detailed comparisons of these complexes revealed the remarkable steric effect by the methyl substituents of the allyl ligands on the coordination geometries of allyl ligands to titanium atom. Complex 1 has the longest Ti-C(1) and Ti-C(3) bonds, while complex 2 has the longest Ti-C(2) bond. The shortest Ti-allyl bonds were seen in complex 3.