Investigation of Spin–Flip Reactions of Zr + CH₃CN by Relativistic Density Functional Theory

To explore the details of the reaction mechanisms of Zr atoms with acetonitrile molecules, the triplet and singlet spin-state potential energy surfaces have been investigated. Density functional theory (DFT) with the relativistic zero-order regular approximation at the PW91/TZ2P level has been applied. The complicated minimum energy reaction path involves four transition states (TS), stationary states 1–5 and one spin inversion (indicated by ⇒): 3Zr + NCCH3 → 3Zr-η1-NCCH3 (31) → 3TS1/2 → 3Zr-η2-(NC)CH3 (32) → 3TS2/3 → 3ZrH-η3-(NCCH2) (33) → 3TS3/4 → CNZrCH3 (34) ⇒ 1TS4/5 → CN(ZrH)CH2 (15). The minimum energy crossing point was determined with the help of the DFT fractional-occupation-number approach. The spin inversion leading from the triplet to the singlet state facilitates the activation of a C—H bond, lowering the rearrangement-barrier by 78 kJ/mol. The overall reaction is calculated to be exothermic by about 296 kJ/mol. All intermediate and product species were frequency and NBO analyzed. The species can be rationalized with the help of Lewis type formulas.