X-ray diffraction and gradient-assisted 2D H-1-Sn-119 HMQC NMR studies on the structure of condensation complexes of salicylaldoxime and dimethyltin(IV) oxide

Reaction of dimethyltin(IV) oxide with salicylaldoxime in the molar ratio 3:2 or 1:1 in refluxing toluene/ethanol (4/1) affords reaction mixtures which, upon crystallization from alcohols TOH (T = Me, Et, n-Pr, i-Pr), generate compounds with three dimethyltin and two salicylaldoximate moieties. These compounds obey the formula [(Me(2)Sn)(Me(2)SnO)(Me(2)-SnOT)(HONZO)(ONZO)], where HONZOH represents salicylaldoxime, o-HON=CHC6H4OH. X-ray diffraction analysis of the compounds at room temperature (T = Me, compound 3; T = Et, 4; T = n-Pr, 5; T = i-Pr, 6) reveals that all structures contain one seven-coordinate tin atom bound to two nitrogen and three oxygen atoms in the equatorial plane of a pentagonal bipyramid, the two methyl groups being in apical positions. The two other tin atoms are five-coordinate with a trigonal-bipyramidal geometry having the two methyl groups and a common oxygen atom in the equatorial positions and, in apical positions, two further oxygen atoms, of which the trifurcated alkoxy oxygen atom bridges these tin atoms. Reaction of dimethyltin(IV) oxide with salicylaldoxime in the molar ratio 1:1 in refluxing benzene generates, after solvent evaporation, compound 2b, obeying the formula [(Me(2)Sn)(2)(Me(2)SnO)-(HONZO)(ONZO)(HONZO)]. The solution-state structures of the alkoxy-bridged compounds 3-6, investigated by gradient-assisted 2D H-1-Sn-119 HMQC as well as H-1-C-13 HMQC and HMBC NMR spectroscopy, are the same as those in the solid state. The bonding mode of the third ligand (i.e. HOZNO) of compound 2b has been elucidated.