Alumazene adducts with pyridines: synthesis, structure, and stability studies

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Alumazenes are organoaluminum compounds with unique ring structures.
• Lewis acid-base adducts are crucial for understanding reactivity and bonding.
• The electronic and steric properties of ligands influence adduct formation and stability.

Purpose of the Study:

• To synthesize and characterize Lewis acid-base adducts of the alumazene [2,6-(i-Pr)2C6H3NAlMe]3 (1) with pyridine (py) and 4-dimethylaminopyridine (dmap).
• To investigate the structural, spectroscopic, and thermodynamic properties of these adducts.
• To compare the Lewis basicity of pyridine and dmap towards the alumazene.

Main Methods:

• Synthesis and structural characterization of alumazene adducts using X-ray diffraction.
• Spectroscopic analysis including NMR spectroscopy.
• Thermodynamic studies using the static tensimetric method (vapor pressure-temperature dependence).
• Quantum chemical computations (B3LYP/6-31G*) to model adducts and their properties.

Main Results:

• Four adducts were synthesized: 1(py)2 (2), 1(py)3 (3), 1(dmap)2 (4), and 1(py)(dmap) (5).
• Bisadducts (2, 4, 5) adopted trans isomers, while the trisadduct (3) showed an unexpected cis-cis isomer.
• Coordination of Lewis bases disrupted the planarity of the alumazene ring.
• dmap exhibited higher basicity compared to pyridine, indicated by shorter Al-N bond distances and lower pyramidality at Al.
• Bisadducts were stable in solution, but trisadduct 3 was labile, converting to 2.
• Thermodynamic data revealed decreasing Al-N bond distances and increasing bond dissociation energies with increasing pyridine ligand number in the gas phase.

Conclusions:

• The study successfully synthesized and characterized novel alumazene adducts, providing insights into their structural diversity.
• The findings highlight the influence of Lewis base structure on adduct geometry and stability.
• dmap is confirmed as a stronger Lewis base than pyridine for this alumazene system.
• Thermodynamic and computational results offer a comprehensive understanding of adduct formation and dissociation.