Performance of the semiempirical PM3 (tm) method in the geometry optimization of transition metal complexes

The geometries of three different sets of transition metal compounds are optimized with the semiempirical PM3 (tm) method. The systems under test are: (i) products of cyclometallation, like [Pd{C6H4[CH(Me)NH2]}Br(PPh3)], (ii) molecular dihydrogen complexes, like [W(CO)3(H2)(PR3)2], and (iii) H-BR2 σ complexes of titanium, like TiCp2(HBcat)2 (cat = O2C6H4). The results are compared with available X-ray and neutron diffraction data, as well as with ab initio molecular orbital and density functional theory results published in the literature. The performance of the PM3 (tm) method ranges from excellent in the case of dihydrogen complexes to very poor in the case of H-BR2 complexes.