Interaction of ethyltrichlorostannane with N,N-dimethylamides of O- trimethylsilyl-α-hydroxyacids

Reactions of ethyltrichlorostannane with N,N-dimethylamides of 2-(trimethylsilyl)glycolic (2a), 2(S)-lactic [(S)-2b] and mandelic (2c) acids led to the first representatives of tin(IV) O,O-monochelates containing the five-membered SnOCC(O) monoanionic chelate cycles as a result of the substitution of one halogen atom. According to the X-ray data, in the case of the derivatives of glycolic and mandelic acids, the isolated complexes have dimeric structures {EtCl₂Sn[OCH(R)C(O)NMe₂]}₂ [R = H (3a), Ph (3c)] with the bridge oxygen atoms and hexacoordinated tin atoms. By contrast, in the case of the derivative of lactic acid (S)-2b, the product of the reaction is the cationic-anionic complex 2EtCl ₂Sn[OCH(Me)C(O)NMe₂]·HCl (4), which is the adduct of two molecules of the respective monomeric complex with HCl. In addition, N,N-dimethylamide of O-triethylstannylglycolic acid (5) with tetracoordinated tin is described. To analyze the stability of complex 4, the experimental charge density study and the quantum chemical calculations [PBE0/6-311G(d,p)] were carried out. Topological analysis of the experimental and calculated electron density distribution functions allowed us to conclude that the strong O-H···O bond with pronounced covalent contribution stabilizes the dimeric structure of 4 to a greater extent than the bridged Sn-Cl bonds.