Insights into the Fluxional Processes of Monomethylcyclohexenyl Manganese Tricarbonyl.

Multiple fluxional processes of 6-monomethylcyclohexenylmanganese tricarbonyl [(6-MeC 6 H 8 )Mn(CO) 3 , complex 1 ] and 5-monomethylcyclohexenylmanganese tricarbonyl [(5-MeC 6 H 8 )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 (MeC 6 H 8 )Mn(CO) 3 exchange processes were revealed. The computational results demonstrated that the 1, 2-agostic isomerization only occurred via the η 4 -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 (R 2 = 0.9862) when comparing the computed and experimentally observed variable temperature 1 H 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.