DIRECT NMR SPECTROSCOPIC EVIDENCE FOR SOLVATED TRIORGANOSTANNYL CATIONS

Solutions of tributyl- and triphenylstannyl perchlorates have been stu died by NMR spectroscopy. Solvent-induced changes in Sn-119, and Cl-37 line widths as well as Sn-C scalar couplings indicate the existence o f an equilibrium between tetrahedral and trigonal bipyramidal arrangem ents. Bipyramidal forms are favoured if the solvent donicity is increa sed, including structures in which the solvent molecules occupy the tw o axial positions of the five-coordinate trigonal bipyramid. This situ ation is unequivocally demonstrated by the presence of Sn-119-P-31 cou pling using hexamethylphosphoramide-d18 as solvent.