Multi-tier electronic structure analysis of Sita's Mo and W complexes capable of thermal or photochemical N2 splitting

An emerging approach for the activation of the nitrogen molecule is the light‐driven splitting of the N‐N bond . Less than ten examples for complexes capable of N 2 photoactivation are currently known, and the underlying photophysical and photochemical processes after light absorption are largely unresolved. All complexes have a central [M(μ‐η 1 :η 1 ‐N 2 )M] unit with symmetric ligand spheres around the metals. For several of these complexes, small modifications of the ligand sphere result in thermal rather than photochemical activity. Herein, we analyse the electronic structures and computed UV‐vis spectra of four complexes: two thermally and two photochemically active complexes, each either involving Mo or W. The analysis of electronic structures and spectra is based on the molecular orbitals, difference densities and the charge‐transfer numbers provided by TheoDORE. We find that the spectra of the photochemically active complexes contain excitations with more ligand‐to‐metal charge‐transfer character and higher intensity, providing a plausible explanation for light‐induced nitrogen splitting.