HIGHLY CONTROLLED CHEMOSELECTIVITY OF TIN ENOLATE BY ITS HYBRIDIZATION STATE - ANIONIC COMPLEX OF TIN ENOLATE COORDINATED BY TETRABUTYLAMMONIUM BROMIDE AS HALO SELECTIVE REAGENT

The control of reactivity and/or selectivity of organotin(IV) enolates has been studied by means;of a high coordination method in which the hybridization state of tin was effectively changed. An anionic tin com plex, five-coordinated tin enolate 1(h), was formed by the coordinatio n of bromide anion from tetrabutylammonium bromide (Bu4NBr) to neutral four-coordinated. tin(TV) enolates 1(e) The highly coordinated enolat es which attained a marked change in chemoselectivity have higher nucl eophilicity to organic halides. In addition, they showed low nucleophi licity toward carbonyl moieties by the coordination of the bromide ani on, whereas carbonyl addition readily proceeds using the usual four-co ordinated tin enolate. NMR studies revealed the generation of HMPA- or bromide-anion-coordinated tin enolates in equilibrium between four-co ordinated enolate Ic(e) and five-coordinated enolate Ic(h), showing a considerable upfield shift delta(Sn-119) and increasing values of the coupling constants (1)J(Sn-119-C-13). I, detailed NMR analyses of high ly coordinated tin enolate, it was shown that the contribution of high ly coordinated species 1(h) to the equilibrium between 1(e) and 1(h) b ecame more significant as the added amount of ligands such as Bu4NBr o r HMPA was increased. Considering these results, it was assumed that t he: bromide-anion-coordinated tin enolate was generated, which showed a unique reactivity and selectivity. The effective control of chemosel ectivity in the intermolecularly competitive reaction between organic halides and carbonyl compounds was demonstrated using two types of tin enolates, four-coordinated enolate and highly coordinated anionic eno late; halide displacement reaction exclusively took place using the br omide-anion-coordinated enolate, and the usual four-coordinated enolat es reacted with only carbonyl compounds.