(2-Phosphinophenyl)aluminum Dichloride Complexes as Intramolecular Al/P Frustrated Lewis Pairs for Ketone, Ester, and Imine Activation.

(2-Phosphinophenyl)aluminum dichloride complexes were synthesized and their frustrated Lewis pair (FLP) reactivity was investigated. Selective mono-substitution of AlCl₃ with lithioarenes was achieved by introducing sterically demanding substituents-tert-butyl, ethyl, or PCy₂-at the 6-position of the phenylene linker, effectively suppressing over-substitution and enabling successful isolation of the target complexes. Single-crystal X-ray diffraction and NMR spectroscopic analyses confirmed the formation of a four-membered P-Al-C-C core structure. These complexes function as Al/P-based FLPs capable of activating simple carbonyl and imine compounds, including aliphatic ketones, prop-2-ynoate esters, and N-arylimines. The mechanism of carbonyl activation by these Al/P FLPs was elucidated through density functional theory (DFT) calculations.