Trisilylation of a Formal Cr(-I) Bis-dinitrogen Complex

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• The direct synthesis of nitrogen-containing chemicals from dinitrogen (N₂) is a long-standing goal in chemistry.
• Electrophilic attack on coordinated N₂ ligands is a primary strategy for forming nitrogen-element bonds.
• Previous studies on metal complexes with multiple N₂ ligands typically resulted in N₂ extrusion, limiting derivatization to a single N₂ ligand.

Purpose of the Study:

• To achieve the simultaneous functionalization of two dinitrogen ligands on a single metal center.
• To explore the electrophilic functionalization of a mononuclear chromium bis-dinitrogen complex.
• To understand the electronic structure requirements for dual N₂ ligand functionalization.

Main Methods:

• Synthesis and characterization of a mononuclear formal chromium(-I) bis-dinitrogen complex supported by a PCP-pincer ligand.
• Electrophilic treatment of the bis-dinitrogen complex with trimethylsilyl chloride (TMSCl) and trimethylsilyl triflate (TMSOTf).
• Detailed electronic structure analysis using highly correlated wave function-based ab initio methods.

Main Results:

• Electrophilic silylation of both N₂ ligands was achieved using TMSCl, yielding a Cr(IV) complex with diazenido and hydrazido units from a Cr(II) bis-diazenido intermediate.
• A Cr(IV) monohydrazido species was formed in a 1:1 ratio with the dual functionalized product.
• Reaction with TMSOTf produced a Cr(III) hydrazido complex, indicating a different reaction pathway.
• A key requirement for dual N₂ functionalization is noncompetitive eight-electron M-(N₂)₂ π-backdonation.

Conclusions:

• This study reports the first successful functionalization of two dinitrogen ligands on a single metal center.
• The findings provide critical insights into the electronic structure prerequisites for achieving multiple N₂ ligand derivatization.
• The work paves the way for designing novel dinitrogen complexes capable of more complex nitrogen fixation transformations.