Reactions of an Al–P-Based Frustrated Lewis Pair with Carbonyl Compounds: Dynamic Coordination of Benzaldehyde, Activation of Benzoyl Chloride, and Al–C Bond Cleavage with Benzamide

Treatment of the Al/P-based frustrated Lewis pair (FLP) Mes₂PC­(CHPh)­Al­(CMe₃)₂ (<b>1</b>) with benzaldehyde afforded the adduct <b>2</b> with a five-membered AlCPCO heterocycle. The carbonyl oxygen atom is bound to aluminum and the carbonyl carbon atom to phosphorus. <b>2</b> is dynamic in solution at room temperature, which results in a fast equilibration of the enantiomeric molecules by cleavage of the P–C and fast rotation about the Al–O bond. Benzoyl chloride and <b>1</b> yielded three products (<b>3</b>–<b>5</b>). Quinoid structures were formed by C–Cl bond activation, chlorine abstraction, and loss of aromaticity in the benzoyl phenyl group. Alkylation of the <i>p</i>-C atom by an AlCMe₃ group completed the transformation and resulted concomitantly in the formation of derivatives with Al–Cl bonds. The complexes may be described as a ketene molecule coordinated to FLP <b>1</b>. Benzamide reacted as a proton donor and gave cleavage of the Al–C bond to the vinylic carbon atom of <b>1</b>. An alkenylphosphine, Mes₂PC­(H)C­(H)­CMe₃, and a dinuclear amidate complex with two dialkylaluminum groups bridged by two chelating ligands were isolated