Macrocyclic Diorganotin Complexes of γ-Amino Acid Dithiocarbamates as Hosts for Ion-Pair Recognition

The dimethyl-, di-n-butyl-, and diphenyltin(IV) dithiocarbamate (dtc) complexes [{R2Sn(L-dtc)}x] 1−7 (1, L = L1, R = Me; 2, L = L1, R = n-Bu; 3, L = L2, R = Me, x = ∞; 4, L = L2, R = n-Bu; 5, L = L3, R = Me, x = 2; 6, L = L3, R = n-Bu, x = 2; 7, L = L3, R = Ph, x = 2) have been prepared from a series of secondary amino acid (AA) homologues as starting materials: N-benzylglycine (α-AA derivative = L1), N-benzyl-3-aminopropionic acid (β-AA derivative = L2), and N-benzyl-4-aminobutyric acid (γ-AA derivative = L3). The resulting compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR (1H, 13C, and 119Sn) spectroscopy, thermogravimetric analysis, and X-ray crystallography, showing that in all complexes both functional groups of the heteroleptic ligands are coordinated to the tin atoms. By X-ray diffraction analysis, it could be shown that [{Me2Sn(L2-dtc)}x] (3) is polymeric in the solid state, while the complexes derived from L3 (5−7) have dinuclear 18-membered macrocyclic structures of the composition [{R2Sn(L3-dtc)}2]. For the remaining compounds, it could not be established with certainty whether the structures are macrocyclic or polymeric. A theoretical investigation at the B3LYP/SBKJC(d,p) level of theory indicated that the α-AA-dtc complexes might have trinuclear macrocyclic structures. The macrocyclic complexes 5−7 have a double-calix-shaped conformation with two cavities large enough for the inclusion of aliphatic and aromatic guest molecules. They are self-complementary for the formation of supramolecuar synthons that give rise to 1D molecular arrangements in the solid state. Preliminary recognition experiments with tetrabutylammonium acetate have shown that the [{R2Sn(L3-dtc)}2] macrocycles 6 and 7 might interact simultaneously with anions (AcO−), which coordinate to the tin atoms, and organic cations (TBA+), which accommodate within the hydrophobic cavity (ion-pair recognition).