Mimicking Extradiol Dioxygenase Reactivity on Iridium.

Area of Science:

• Organometallic Chemistry
• Bioinorganic Chemistry
• Catalysis

Background:

• Extradiol dioxygenases cleave benzenediol (catechol) or aminophenols via oxygen insertion.
• Proposed mechanisms involve d6 alkylperoxide intermediates, but regiospecificity is rare in synthetic models.
• Understanding these mechanisms is key to developing new catalytic processes.

Purpose of the Study:

• To synthesize and characterize third-row metal analogues of enzymatic intermediates in dioxygenase reactions.
• To investigate the mechanisms of oxygen atom insertion and ring expansion using synthetic iridium complexes.
• To explore the role of ligand design in achieving regiospecific oxygenations.

Main Methods:

• Synthesis of a dioxygenated iridium complex (2).
• Triggered conversion of complex 2 to a paramagnetic metallatrioxolane (3) via H• abstraction.
• Photolysis of complex 2 to yield oxygen atom-inserted products (4 and 5), including a ring-expanded product.

Main Results:

• Generated three iridium complexes (2, 3, 4, 5) mimicking enzymatic intermediates.
• Demonstrated H• abstraction to form a reduced metallatrioxolane (3).
• Achieved ring expansion via photolysis, yielding reduced ring-expansion products (4, 5), including a novel ortho ester ligand binding mode.

Conclusions:

• The synthetic complexes provide valuable models for extradiol dioxygenase mechanisms, particularly for Co(II)-accepting variants.
• Ligand design, incorporating a catechol-like substrate, enhances metal affinity and enables access to key intermediates.
• These findings offer insights into regiospecific aerobic oxygenations and the design of biomimetic catalysts.