New Scandium Borylimido Chemistry: Synthesis, Bonding, and Reactivity

Area of Science:

• Organometallic Chemistry
• Rare Earth Chemistry
• Inorganic Chemistry

Background:

• Borylimido complexes are a relatively underexplored class of organometallic compounds.
• Understanding their reactivity is crucial for developing new synthetic methodologies.

Purpose of the Study:

• To synthesize and characterize the first borylimido complex of a rare earth metal.
• To investigate the reactivity of this complex, particularly in C-H and C≡C bond activation.
• To elucidate the bonding and mechanistic aspects using theoretical calculations.

Main Methods:

• Combined synthetic, mechanistic, and theoretical (DFT) studies.
• Thermolysis of a methyl-borylamide precursor to generate the transient borylimido complex.
• In situ reactions with various substrates (e.g., pyridine, DMAP, alkynes).
• Computational analysis including QTAIM and NBO.

Main Results:

• Successful synthesis of the rare earth borylimido complex (NacNac^NMe)Sc{NB(NAr'CH)₂}.
• Demonstration of reversible cyclometalation and C-H activation (sp³, sp²) with substrates.
• Observation of irreversible sp C-H activation and [2+2] cycloaddition with alkynes.
• DFT calculations revealed stronger metal-nitrogen bonding in borylimides compared to arylimides.
• Borylimides exhibit more exothermic and strongly activating reactions than arylimides.

Conclusions:

• The first rare earth metal borylimido complex was synthesized and characterized.
• This complex exhibits diverse reactivity, including novel substrate activation pathways.
• Borylimido ligands offer unique electronic properties, leading to enhanced reactivity compared to arylimides.
• Theoretical studies provide insights into bonding and reaction mechanisms.