Geometry and electronic structure of titanacycloalkenes

A number of titanacycloalkenes, H2TiC2H2, HTiC3H3, H2TiC4H4, and HTiC5H5, h ave been studied using ab initio techniques. Vibrational frequencies were c omputed at the RHF, MP2, BLYP, and B3LYP levels. Both a LANL2DZ pseudopoten tial and an all-electron TZV basis set was used for each method. The electr onic structure of the systems of interest is characterized in terms of natu ral resonance theory (NRT) and the atoms in molecules (AIM) analysis. All r ings are planar except for titanabenzene, HTiC5H5, H2TiC2H2 has C-2v symmet ry and has single Ti-C bonds. HTiC3H3, unlike the isovalent cyclobutadiene and silacyclobutadiene, has C-2v symmetry and shows significant electron de localization. In H2TiC4H4 the TIC ring is planar with equivalent single Ti- C bonds and has C-2v symmetry. HTiC5H5 has a boat-shaped geometry where the angle between the CTiC plane and the plane formed by the neighboring four carbon atoms is nearly 90 degrees. AIM analysis isolates a weak critical po int between Ti and the para-C atom, and NRT analysis confirms the weak bond ing interaction.