Isolable Three-Coordinate Base-Stabilized Alumylene: A Precursor of Persistent Acceptor-Free Monomeric Aluminum Oxide

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry

Background:

• Alumylenes, low-valent aluminum species, are reactive intermediates.
• Stabilization of low-valent main group elements is crucial for their isolation and study.

Purpose of the Study:

• To synthesize and characterize a monomeric alumylene stabilized by both phosphine and N-heterocyclic carbene (NHC) ligands.
• To investigate the reactivity and electronic properties of this novel alumylene complex.

Main Methods:

• Synthesis of the target alumylene complex.
• Experimental techniques including NMR spectroscopy and X-ray crystallography.
• Density Functional Theory (DFT) calculations to understand electronic structure and bonding.

Main Results:

• Isolation of a monomeric alumylene (2) featuring both phosphine and NHC ligands.
• Experimental and theoretical evidence for the lability of the NHC ligand above -20 °C.
• Alumylene 2 displays enhanced reactivity and nucleophilicity compared to monophosphine-ligated analogues.
• Reaction with nitrous oxide (N2O) at -90 °C yields a stable bis-ligated aluminum oxide (15).

Conclusions:

• The combination of phosphine and NHC ligands can stabilize a reactive alumylene.
• Ligand lability plays a key role in the observed high reactivity.
• This work opens avenues for utilizing low-valent aluminum species in synthesis.