Reversible alkene binding and allylic C-H activation with an aluminium(i) complex

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Redox Chemistry

Background:

• Monomeric aluminium(I) complexes are reactive species.
• Understanding reversible substrate binding is crucial for catalysis.
• Main group element reactivity often differs significantly from transition metals.

Purpose of the Study:

• To investigate the reactivity of a monomeric molecular aluminium(I) complex with alkenes.
• To characterize the structure and reversibility of alkene binding.
• To explore the potential for C-H bond activation and catalytic cycles.

Main Methods:

• Reaction of aluminium(I) complex 1 with various alkenes (ethylene, propylene, allylbenzene, norbornene).
• Thermodynamic analysis using Van't Hoff plots to quantify binding.
• Structural characterization via single crystal X-ray diffraction.
• Computational studies (DFT) to elucidate reaction mechanisms.

Main Results:

• Formation of reversible alkene-bound metallocyclopropane complexes.
• Reversibility attributed to positive reaction entropy, disfavored at higher temperatures.
• Alkene binding involves a reversible Al(I) to Al(III) redox process.
• Under forcing conditions, metallocyclopropanes undergo irreversible allylic C-H activation to form aluminium(III) allyl hydride complexes.

Conclusions:

• Demonstrated a rare example of redox-based main group reactivity with reversible substrate binding.
• Identified a reaction network where alkene dissociation is necessary for C-H activation.
• Highlighted implications for developing redox-based catalytic cycles using main group compounds.