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

Abstract (2‐Phosphinophenyl)aluminum dichloride complexes were synthesized and their frustrated Lewis pair (FLP) reactivity was investigated. Selective mono‐substitution of AlCl 3 with lithioarenes was achieved by introducing sterically demanding substituents— tert ‐butyl, ethyl, or PCy 2 —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.