Insights into the Fluxional Processes of Monomethylcyclohexenyl Manganese Tricarbonyl

Multiple fluxional processes of 6-monomethylcyclohexenylmanganese tricarbonyl [(6-MeC6H8)Mn(CO)3, complex 1] and 5-monomethylcyclohexenylmanganese tricarbonyl [(5-MeC6H8)Mn(CO)3, complex 2] have been explored using density functional theory (DFT) computations. The contributions of four agostomers—1, 2, 3, and 4—to the (MeC6H8)Mn(CO)3 exchange processes were revealed. The computational results demonstrated that the 1, 2-agostic isomerization only occurred via the η4-diene hydride transition state (TS-1-2, 14.0 kcal/mol), which is consistent with the experimentally proposed high-energy exchange process (16.0 kcal/mol). Excellent agreement is observed (R2 = 0.9862) when comparing the computed and experimentally observed variable temperature 1H NMR chemical shifts. With these results, important insights into the role of agostic interaction in the homogeneous catalysis process could be made, especially with regard to transition metal catalyzed C-H activation.