Diiron oxo reactivity in a weak-field environment

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Bioinorganic Chemistry

Background:

• Diiron complexes with bridging oxo ligands are crucial in various biological and catalytic processes.
• Understanding the reactivity and electronic properties of these species is key to designing new functional materials.
• The Pacman dipyrrin ligand platform offers a unique scaffold for stabilizing dinuclear metal centers.

Purpose of the Study:

• To synthesize and characterize novel diiron complexes derived from a dinucleating cofacial Pacman dipyrrin ligand.
• To investigate the reactivity of these diiron complexes, particularly their protonation and oxidation states.
• To quantify the basicity of diiron μ-oxo and related species and understand factors influencing it.

Main Methods:

• Synthesis of diiron complexes via concomitant deprotonation and metalation using Fe2(Mes)4.
• Characterization through chemical transformations including hydrolysis, oxidation, and reduction.
• Quantification of basicity using pKa studies of conjugate acids and computational analysis.

Main Results:

• Formation of a diiron complex (dmx)Fe2(Mes)2, which upon reaction with water yields the diiron μ-oxo complex (dmx)Fe2(μ-O).
• Isolation of diferric and mixed-valent species, demonstrating control over oxidation states.
• Quantification of the basicity of (dmx)Fe2(μ-O) (pKa = 15.3(6)) and its solvent-ligated adduct (pKa = 26.8(6)), showing increased basicity with ligand coordination.
• Computational determination of a low pKa (-1.8(6)) for the conjugate acid of a diferric bridging hydroxide, indicating reduced basicity.

Conclusions:

• The study successfully synthesized and characterized a series of diiron complexes with a Pacman dipyrrin ligand.
• The basicity of the bridging oxo ligand is significantly influenced by the iron oxidation state and coordination environment.
• These findings highlight the intricate relationship between oxidation state and reactivity in diiron μ-oxo systems.