Rapid nitrite reduction enabled by secondary sphere hydrogen bonds within non-heme iron complexes

Area of Science:

• Bioinorganic Chemistry
• Coordination Chemistry
• Catalysis

Background:

• Non-heme iron complexes are crucial in biological systems.
• Nitrite reduction is a key biochemical process.
• Understanding ligand effects on iron complex reactivity is vital.

Purpose of the Study:

• To investigate the role of secondary sphere hydrogen bonds in modulating the reactivity of non-heme iron complexes.
• To compare the nitrite reduction activity of two electronically analogous iron complexes with and without hydrogen bond donors.
• To elucidate the structural and electronic factors influencing the stability of the resulting Fe(III)2(μ-O)2 core.

Main Methods:

• Synthesis and characterization of two non-heme iron(II) complexes: TPA^NHPh and TPA^Me.
• Kinetic studies of nitrite reduction to nitric oxide.
• Spectroscopic analysis (e.g., UV-Vis, NMR) of the iron complexes and reaction intermediates.
• Structural comparison of the Fe(III)2(μ-O)2 cores formed by both complexes.

Main Results:

• The TPA^NHPh complex, featuring secondary sphere H-bond donors, rapidly reduces nitrite to nitric oxide.
• The TPA^Me complex, lacking H-bond donors, reduces nitrite four orders of magnitude slower.
• Both complexes form Fe(III)2(μ-O)2 diamond cores.
• H-bonding interactions weaken Fe-O bonds and alter the electronic structure of the Fe2O2 core, impacting reductive stability.

Conclusions:

• Secondary sphere hydrogen bonds dramatically enhance the rate of nitrite reduction by non-heme iron complexes.
• H-bonding influences the electronic structure and stability of the Fe(III)2(μ-O)2 core.
• This study underscores the importance of non-covalent interactions in designing efficient bioinspired catalysts.