Simulation of UV/visible absorption spectra of (α-diimine)nickel(II) catalysts by time-dependent density functional theory

The metal-to-ligand charge-transfer excited states of (α-diimine)-Ni^II catalysts were simulated using time-dependent density functional schemes for three reaction intermediates: the active site with a methyl group to mimic the growing alkyl chain, the corresponding π-complex formed with an ethylene molecule, and the product where the propyl chain displays a γ-agostic interaction. The simulations provide a basis for analyzing the experimental data in terms of charge-transfer and enable one to assess the variations of the spectra upon modifications of the bidentate ligand. Moreover, the impact of the atomic basis set and exchange-correlation functionals on the electronic absorption spectra was addressed in view of a more systematic use on new late transition metal catalysts.