AVVISO DI SEMINARIO

prof. Edwin Otten

(Università di Groningen - Olanda)

Complexes with Non-Innocent Ligands: New Avenues in Catalysis

The role of ‘supporting’ ligands in organometallic chemistry has in the past largely focused on controlling the stereo-electronic environment around the central metal center; key elementary steps that break or make bonds in many catalytic cycles rely on the reactivity of the metal (e.g., oxidative addition / reductive elimination). There is increasing interest in ligands that play a much more ‘active’ role in catalysis: incorporating reactivity of the ligand(s) into a catalytic cycle has the potential to open up new mechanistic pathways and lead to distinctly different, new (catalytic) reactivity.

In this presentation, the chemistry of ruthenium complexes with a de-aromatized pincer ligand will be described. Their reaction with the C≡N bond of nitriles leads to formation of new Ru-N and (ligand)C-C bonds. Based on this, we developed efficient oxa-Michael addition catalysis to unsaturated nitriles. A key feature of the mechanism of this challenging transformation involves metal-ligand cooperative activation of the nitrile. Secondly, the chemistry of complexes with formazanate ligands, which are nitrogen-rich analogues of the well-known β-diketiminates, will be discussed. The presence of low-lying π^*-orbitals in the backbone leads to multiple stable oxidation states of these ligands (L^-/2-/3-), and results in unusual electronic structures in both main group and transition metal compounds.