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 (1) with benzaldehyde afforded the adduct 2 with a five-membered AlCPCO heterocycle. The carbonyl oxygen atom is bound to aluminum and the carbonyl carbon atom to phosphorus. 2 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 1 yielded three products (3–5). Quinoid structures were formed by C–Cl bond activation, chlorine abstraction, and loss of aromaticity in the benzoyl phenyl group. Alkylation of the p-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 1. Benzamide reacted as a proton donor and gave cleavage of the Al–C bond to the vinylic carbon atom of 1. An alkenylphosphine, Mes2PC­(H)C­(H)­CMe3, and a dinuclear amidate complex with two dialkylaluminum groups bridged by two chelating ligands were isolated.