An ab initio computational study on the reaction of organotin enolates: Comparison of highly coordinated tin reagent with noncoordinated reagent

An ab initio computational study revealed the mechanism of the reaction bet ween tin enolates and aldehydes or organic halides in both cases with and w ithout a bromide anion as a coordinating ligand to tin. The calculations sh owed the stabilization of tin compounds by complexation with the bromide an ion. The order of stabilization is tin bromide > tin enolate > tin alkoxide . In the reaction of tin enolate with aldehyde, a noncoordinated tin enolat e gave the cyclic transition state in sled-form while the acyclic transitio n state which leads to deactivation of the reaction process is shown in the use of a highly coordinated enolate. This open structure is ascribed to th e bromide anion-coordinated tin which is reluctant to coordination by carbo nyl oxygen in aldehyde. In both cases with and without ligands, synclinal a rrangements between carbonyl C = O in aldehyde and vinyl C = C in enolate a re observed. The reaction of tin enolates with organic halides proceeds thr ough two steps involving alkylation in S(N)2 mode and destannylation with f ormation of bromostannane. The system of high-coordinated tin enolate is fa vored both kinetically and thermodynamically. The high nucleophilicity of h igh-coordinated tin enolate is due to coordination of an anionic ligand.