Dehydrochlorination of Carboxylic Acid Chlorides by an Aluminum/Phosphorus‐Based Frustrated Lewis Pair and the Formation of Ketene Adducts

The Al/P‐based frustrated Lewis pair (FLP)Mes 2 P–C(=CH–Ph)–Al(CMe 3 ) 2 ( 1 ) reacted with carboxylic acid chlorides [Cl–C(=O)Me, Cl–C(=O)Et, Cl–C(=O)CH 2 CMe 3 ] by dehydrochlorination. The released hydrogen chloride molecules were captured by one equivalent of the FLP 1 to yield the previously published HCl adduct, Mes 2 P(H) + –C(=CH–Ph)–Al(Cl)(CMe 3 ) 2 – ( 3 ). This remarkable reaction resulted in the formal generation of ketenes, R (H)C=C=O, which were trapped by a second equivalent of 1 via the coordination of the C=O groups to the Lewis acidic aluminum and the Lewis basic phosphorus atoms ( 4 to 6 ). Five‐membered AlC 2 PO heterocycles were formed, which had an exocyclic C=C double bond. Quantum chemical DFT calculations were performed to study the thermodynamic driving forces of the adduct formation and to identify reactive intermediates with respect to a mutual activation of this process by phosphorus and aluminum atoms.