This dataset contains DFT calculations that were carried out in conjunction with experimental investigation of a cationic phenoxyimine yttrium complex as an isoprene polimerization catalyst. Calculations were performed using the Gaussian 09 D.01 suite of programs.Electronic structure calculations were performed at the DFT level using the B3PW91 functional. The Stuttgart-Cologne small-core quasi-relativistic pseudopotential ECP28MWB and its available basis set including up to the g function were used to describe yttrium. Similarly, silicon and phosphorus were represented by a Stuttgart-Dresden-Bonn pseudopotential along with the related basis set augmented by a d function of polarization (αd(P) = 0.387 and αd(Si) = 0.284). Other atoms were described by a polarized all-electron triple-ζ 6-311G(d,p) basis set. Bulk solvent effect of toluene or THF was simulated using the SMD continuum model. The Grimme empirical correction with the original D3 damping function was used to include the dispersion correction as a single-point calculation. Transition-state optimization was