Carbonyl Bond Cleavage by Complementary Active Sites

Abstract

We have studied the size-selective reactivity of Aln– clusters with formaldehyde to determine if carbonyl bonds may be broken by complementary active sites. Gas phase experiments reveal that Aln–, where n = 8–12, react with formaldehyde to form Aln–2CH2–, which demonstrates that the carbonyl bond is broken in the reaction with the cluster, while Al13– is found to be resistant to reaction. The most likely leaving group is determined to be Al2O. We also found n = 15–19 to be reactive with the products being a mix of Aln–2CH2– and Aln(OCH2)m–. Theoretical investigations find that the adjacent Lewis acid and Lewis base sites stabilize the resonance structure in which the carbonyl is reduced to a single bond which encourages carbonyl cleavage. A transition state analysis of the cleavage of the carbonyl bond confirms the size selective cleavage of the carbonyl bond and supports the importance of complementary Lewis acid–Lewis base active sites in governing the reactivity.