Experimental and Theoretical Study of the Hydride Migration to Ethylene in an Electron-Rich Cobalt Complex
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Abstract
The kinetics and energetics of β-migratory insertion in the electron-rich cobalt ethylene hydride complex [(PMe3)3Co(H)(C2H4)] (1) were studied with experimental and theoretical techniques. The activation parameters were established in toluene solution using 1H magnetization transfer methods. Data obtained over the temperature range 265−290 K gave ΔH⧧ = 16.4 ± 0.6 kcal mol-1 and ΔS⧧ = 8 ± 2 cal mol-1 K-1. The structural and energetic parameters have also been determined by DFT electronic structure calculations. The global minimum thus obtained is in agreement with the experimental findings. The same holds true for the activation energies for migratory insertion as well as for β-elimination. Comparison of the activation parameters with those for other complexes suggests an increase of the barrier of migratory insertion with increasing electron richness of the metal center, which destabilizes species with agostic metal−H−C interactions. It is proposed that there may even be cases where an agostic structure is not an intermediate.
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