Uranium complexes are capable of producing some of the most extraordinary reactions, which are most of the time impossible to form with other type of metals (e.g. main group, lanthanides or transition metals). This is mainly due to the oxophilicity, Lewis acidity, and highly reducing nature of U(III) congeners. A new paradigm of such reaction is the addition of different alkynes to NUIII(DME) complexes, leading to the immediate formation of vinyl bridged dinuclear complexes of uranium (IV).Based on those experimental observations, DFT (B3PW91) calculations were conducted, for the prediction of a reasonable reaction pathway. The most thermodynamically favoured and kinetically accessed mechanism consists of two steps: first, oxidation and subsequent formation of the activated dinuclear alkyldiyne complex, followed by cyclization, or C-C coupling, to form the corresponding vinyl bridged dinuclear uranium complex (IV). Alternate pathways, like cyclization of the alkyldiyne in the monomer, were examined as well, in order to conclude which one will be the most favoured one. Moreover, we have investigated a possible C-H activation process, to verify the correctness of our predicted mechanism, which was found to be kinetically less accessible and thermodynamically unfavored than the first one. In sum, our calculations highlight the generality of this particular mechanism and shed light to different ways of extending the applicability of our mechanism to less active olefins.

Theoretical insights into the general mechanism of alkyne dimerization catalyzed by U(IV) complexes

245th National Meeting (2013)

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