Synthesis and Solution State Characterization by Gradient-Enhanced 2D Multinuclear NMR Spectroscopy of a Fluorine-Bridged Dimethyltin(IV) Salicylaldoximate Derivative.

The reaction of [(Me(2)Sn)(2)(Me(2)SnO)(ONZOH)(HONZO)(ONZO)] (HONZOH = o-HON=CHC(6)H(4)OH, salicylaldoxime) with ammonium fluoride yields a fluorotris(dimethyltin) disalicylaldoximate complex, compound 4, containing one seven-coordinate and two five-coordinate tin atoms, with a fluoride anion bridging the five-coordinate tin atoms. Though 4 can be obtained in a crystalline form, its crystals are unsuitable for X-ray analysis. Its structure has been completely characterized in solution by 1D (1)H, (13)C, (119)Sn, and (19)F NMR spectra and 2D gradient-assisted (1)H-(119)Sn and (1)H-(13)C HMQC and HMBC NMR spectra. In solution, 4 is involved 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 substitution with weak nucleophiles like water and methanol. The preservation of the splitting of the (1)J((119/117)Sn(3)-(19)F) coupling but not the (1)J((119/117)Sn(2)-(19)F) 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, &mgr;(2)-nucleophilic substitutions on compound 4 with hydroxylated nucleophiles should be viewed as addition-elimination reactions.