SYNTHESIS AND SOLUTION-STATE CHARACTERIZATION BY GRADIENT-ENHANCED 2DMULTINUCLEAR NMR-SPECTROSCOPY OF A FLUORINE-BRIDGED DIMETHYLTIN(IV) SALICYLALDOXIMATE DERIVATIVE

The reaction of [(Me2Sn)(2)(Me2SnO)(ONZOH)(HONZO)(ONZO)] (HONZOB = o-H ON=CHC6H4OH, salicyl-aldoxime) with ammonium fluoride yields a fluorot ris(dimethyltin) disalicylaldoximate complex, compound 4, containing o ne seven-coordinate and two five-coordinate tin atoms, with a fluoride anion bridging the five-coordinate tin atoms. Though 4 can be obtaine d in a crystalline form, its crystals are unsuitable for X-ray analysi s. its structure has been completely characterized in solution by 1D H -1, C-13, Sn-119, and F-19 NMR spectra and 2D gradient-assisted H-1-Sn -119 and H-1-C-13 HMQC and HMBC NMR spectra. In solution, 4 is involve d in an equilibrium with several species. It is shown that the Sn(2)-F -Sn(3) moiety of 4 is the reactive site amenable to nucleophilic subst itution with weak nucleophiles like water and methanol, The preservati on of the splitting of the (1)J(Sn-119/117(3)-F-19) coupling but not t he (1)J(Sn-119/117(2)-F-19) coupling evidences a reaction intermediate where the entering nucleophile is bound to the Sn(2) tin atom whereas the fluorine is still linked to the Sn(3) atom. Overall, mu(2)-nucleo philic substitutions on compound 4 with hydroxylated nucleophiles shou ld be viewed as addition-elimination reactions.