Chiral Bis(oxazoline) Ligand-Supported Alkyl Aluminum Cations

Alkyl aluminum cations have shown high Lewis acidity and capability of catalyzing challenging organic transformations, however, the related chiral catalyst is scarcely documented. Herein, we report the generation of a series of weakly solvated or Lewis base-stabilized alkyl aluminum cationic complexes bearing chiral bis(oxazoline) ligands. The increase of steric hindrances at the ligand backbone and the aluminum center were found to significantly increase the complex stability. In the Gutmann-Beckett experiment and fluoride ion affinity calculation, these complexes display Lewis acidity greater than B(C6F5)(3) and the reported tetra-coordinate aluminum cation. Preliminary catalytic studies revealed that the aluminum cation catalysts can effectively promote hydroboration of ketone and hydrosilylation of un-activated olefin, despite only poor ee values were obtained.

Automated summary

This study reports the generation of stable chiral alkyl aluminum cationic complexes with high Lewis acidity and catalytic ability in organic transformations.