Simplification through complexity: the role of Ni-complexes in catalysed diyne– cyclobutanone [4+2+2] cycloadditions, a comparative DFT study

A series of density functional theory (DFT) experiments carried out on selected nickel((0))-catalysed diyne-cyclobutanone [4+2+2] cycloadditions provided quantitative confirmation of proposed multistep mechanisms, while clarifying the catalytic role of Ni in the reactions. Geometric and energetic results of the Ni-catalysed process were compared to the one-step non-catalysed complement. Results show the first oxidation to be the rate-determining step, with the intramolecular reaction being the preferred one of the two competing pathways. Ligand-identity is also shown to greatly influence reaction barriers, leading to large deviation in product yields, in direct agreement with experimental observations.