Abstract
Quantum chemical calculations by using density functional theory at the B3LYP level have been carried out to elucidate the reaction course for the addition of ethylene to [OsO~2~(CH~2~)~2~] (1). The calculations predict that the kinetically most favorable reaction proceeds with an activation barrier of 8.1 kcal mol^−1^ via [3+2] addition across the OOsCH~2~ moiety. This reaction is −42.4 kcal mol^−1^ exothermic. Alternatively, the [3+2] addition to the H~2~COsCH~2~ fragment of 1 leads to the most stable addition product 4 (−72.7 kcal mol^−1^), yet this process has a higher activation barrier (13.0 kcal mol^−1^). The [3+2] addition to the OOsO fragment yielding 2 is kinetically (27.5 kcal mol^−1^) and thermodynamically (−7.0 kcal mol^−1^) the least favorable [3+2] reaction. The formal [2+2] addition to the OsO and OsCH~2~ double bonds proceeds by initial rearrangement of 1 to the metallaoxirane 1 a. The rearrangement 1→1 a and the following [2+2] additions have significantly higher activation barriers (>30 kcal mol^−1^) than the [3+2] reactions. Another isomer of 1 is the dioxoosmacyclopropane 1 b, which is 56.2 kcal mol^−1^ lower in energy than 1. The activation barrier for the 1→1 b isomerization is 15.7 kcal mol^−1^. The calculations predict that there are no energetically favorable addition reactions of ethylene with 1 b. The isomeric form 1 c containing a peroxo group is too high in energy to be relevant for the reaction course. The accuracy of the B3LYP results is corroborated by high level post‐HF CCSD(T) calculations for a subset of species.