Mechanistic investigation of cis and trans oxidative addition to acetylacetonato-1,5-cyclooctadieneiridium(I)

Abstract

Density functional theory (DFT) calculations of the oxidative addition of CH3I, as well as Hg(CN)2, to [Ir(acac)(cod)] are described (acac=acetylacetone). Both cis and trans oxidative addition mechanisms are considered and compared to experimental data. The DFT calculated thermodynamically most stable oxidative addition products are trans-[Ir(acac)(cod)(CH3)(I)] and cis-[Ir(acac)(cod)(HgCN)(CN)]. The steric demand of the cod ligand leads to a distorted octahedral trans-[Ir(acac)(cod)(CH3)(I)] complex, with the CCH3-Ir-I angle deviating by more than 20° from 180°, as expected for real octahedral geometry. However, the steric demand of the cod ligand does not lead to any cis transition state for the [Ir(acac)(cod)]+CH3I reaction, rather the trans transition state is energetically favoured, as is generally found for oxidative addition of CH3I to square planar complexes. On the other hand, oxidative addition of Hg(CN)2 to [Ir(acac)(cod)], occurs via a concerted three-centre cis transition state structure. The concerted three-centre cis transition state structure is confirmed by the existence of a ring critical point, as obtained by the Bader’s quantum theory of atoms in molecules analysis of the cis transition state structure. Both trans addition of CH3I to [Ir(acac)(cod)] as well as cis addition of Hg(CN)2 to [Ir(acac)(cod)], are in agreement with experimental observation.