Geometry and Electronic Structure of Titanacycloalkenes

A number of titanacycloalkenes, H₂TiC₂H₂, HTiC₃H₃, H₂TiC₄H₄, and HTiC₅H₅, have been studied using ab initio techniques. Vibrational frequencies were computed at the RHF, MP2, BLYP, and B3LYP levels. Both a LANL2DZ pseudopotential and an all-electron TZV basis set was used for each method. The electronic structure of the systems of interest is characterized in terms of natural resonance theory (NRT) and the atoms in molecules (AIM) analysis. All rings are planar except for titanabenzene, HTiC₅H₅. H₂TiC₂H₂ has C_2v symmetry and has single Ti−C bonds. HTiC₃H₃, unlike the isovalent cyclobutadiene and silacyclobutadiene, has C_2v symmetry and shows significant electron delocalization. In H₂TiC₄H₄ the TiC₄ 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°. AIM analysis isolates a weak critical point between Ti and the para-C atom, and NRT analysis confirms the weak bonding interaction.