Exploring secondary-sphere interactions in Fe-N H complexes relevant to N₂ fixation.

Area of Science:

• * Inorganic Chemistry
• * Organometallic Chemistry
• * Catalysis

Background:

• * Secondary sphere interactions are vital in metalloenzymes and synthetic catalysts.
• * Developing synthetic nitrogen fixation catalysts with secondary sphere design is challenging.
• * Previous studies on [EPR3]FeN2 catalysts suggested a hydride termination pathway.

Purpose of the Study:

• * To investigate synthetic iron complexes incorporating secondary sphere hydrogen-bond acceptors for nitrogen fixation.
• * To explore the role of remote amine sites in ligand design for iron-catalyzed nitrogen fixation.
• * To provide mechanistic insights into catalyst deactivation pathways.

Main Methods:

• * Synthesis of new tris(phosphine)silyl ligands with remote tertiary amine hydrogen-bond acceptors.
• * Characterization of iron complexes with these ligands, including Fe-N2 and Fe-H species.
• * Reactivity studies involving nitrogenous substrates and proton/electron sources.

Main Results:

• * Novel iron complexes ([SiPNMe3] and [SiPiPr2P^NMe]) featuring tertiary amine hydrogen-bond acceptors were synthesized.
• * The ligand conformation (boat vs. chair) adapted based on substrate coordination and hydrogen-bonding capability.
• * Reactivity studies confirmed rapid formation of catalytically inactive Fe-H species, supporting a hydride termination pathway.

Conclusions:

• * The incorporated amine functionality in iron complexes can lead to catalyst deactivation via a hydride pathway.
• * Ligand design incorporating secondary sphere elements is crucial for understanding and controlling nitrogen fixation catalysis.
• * This work provides a foundation for designing more efficient and stable synthetic nitrogen fixation catalysts.