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.