| Abstract
| - The free energies of reaction and the activation energies are calculated, with DFT (B3PW91) andsmall RECP (relativistic core potential) for uranium, for the reaction of Cp2UNMe and Cp2UO withMeC⋮CMe and H3Si−Cl that yields the corresponding addition products. CAS(2,7) and DFT calculationson Cp2UO and Cp2UNMe give similar results, which validates the use of DFT calculations in thesecases. The calculated results mirror the experimental reaction of [1,2,4-(CMe3)3C5H2]2UNMe withdimethylacetylene and [1,2,4-(CMe3)3C5H2]2UO with Me3SiCl. The net reactions are controlled by thechange in free energy between the products and reactants, not by the activation energies, and thereforeby the nature of the UO and UNMe bonds in the initial and final states. A NBO analysis indicates thatthe U−O interaction in Cp2UO is composed of a single U−O σ bond with three lone pairs of electronslocalized on oxygen, leading to a polarized U−O fragment. In contrast, the U−NMe interaction in Cp2UNMe is composed of a σ and π component and a lone pair of electrons localized on the nitrogen,resulting in a less polarized UNMe fragment, in accord with the lower electronegativity of NMe relativeto O. The strongly polarized U(+)−O(-) bond is calculated to be about 70 kcal mol-1 stronger than theless polarized UNMe bond.
- The net reactions are exoergic and the thermodynamic control is traced to the strength and nature of the Cp2UO and Cp2UNMe bonds.
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