Sequential Oxygenation of Bis(β-diketiminate) on a Selective Diruthenium Platform

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Catalysis

Background:

• Diruthenium complexes with redox-active ligands are of interest for catalytic applications.
• Understanding dioxygen activation mechanisms is crucial for developing oxidation catalysts.

Purpose of the Study:

• To synthesize and characterize isomeric diruthenium(III)-bis(β-diketiminate) species.
• To investigate the dioxygen activation capabilities of these novel complexes.
• To elucidate the mechanism of oxygenation and identify key intermediates.

Main Methods:

• Synthesis and isolation of isomeric {(acac)2RuIII}2(μ-L2-) complexes (1-trans/1-cis).
• Spectroscopic characterization including EPR and UV-Vis spectrophotometry.
• Oxygenation studies with O2 and 18O2 labeling to form mixed-valent (2) and isovalent (3) complexes.
• Computational studies (MOs, Mulliken spin densities) to understand ligand noninnocence.

Main Results:

• First synthesis of isomeric diruthenium(III)-bis(β-diketiminate) species (1).
• Complex 1 undergoes two-step oxygenation to form mixed-valent (2) and isovalent (3) complexes.
• Identification of a short-lived blue intermediate, proposed as a valence tautomer, facilitating oxygen activation.
• Kinetic studies reveal pseudo-first-order rate constants for the 1 -> 2 conversion.

Conclusions:

• The redox-noninnocent phenylene-linked bis(β-diketiminate) ligand plays a critical role in dioxygen activation.
• A valence tautomeric intermediate is key to the observed oxygenation pathway.
• The diruthenium system provides a platform for studying ligand-assisted oxygen activation mechanisms.