Theoretical Study on the Reaction Mechanism for the Formation of 2-Methylpyridine Cobalt(I) Complex from Cobaltacyclopentadiene and Acetonitrile

Using B3LYP level calculations, the reaction of acetonitrile with cobaltacyclopentadiene complex in singlet and triplet electronic states, to give pyridine cobalt complexes, was studied. While the most favorable path for the singlet reaction passes through a [4 + 2] cycloaddition transition state., the most favorable triplet reaction follows the reaction mechanism through azacobaltacycloheptatriene. Since the transition state for the singlet reaction path is lower in energy than those for the triplet reaction path, the singlet reaction seems to be more favorable. However, the reactant in the triplet state is more stable than that in the singlet state, suggesting that the two-state reactivity (TSR) mechanism with spin changes is followed. Determination of energy minimum crossing points between singlet and triplet energy surfaces led to the conclusion that the TSR mechanism is more favorable than both the singlet- and triplet-state (single-state reactivity) (SSR) mechanisms. Comparison of a reaction profile between trimerization of acetylene and cocyclotrimerization of acetonitrile with two acetylene molecules in the presence of the CpCo catalyst is also made.