Studies of organometallic compounds The five-membered ring structure of organotin containing dicarboxylic esters

Abstract

Bis[(1,2-dialkoxycarbonyl)ethyl]tin dihalides (II) were synthesized by the direct method; the reaction between tin foil and dialkyl halosuccinates in the presence of accelerators. Besides the main products, [(1,2-dialkoxycarbonyl)ethyl] tin hydroxydibromide (III) was obtained as by-product. It was considered that (II) had two stereoisomers with a six-coordination containing 2 five-membered ring structures in which the oxygen atom of the CO at the γ-position with respect to the tin atom was coordinated to the tin atom. These isomers could be isolated with appropriate solvents and the by-products (III) on the basis of IR or NMR spectra, had the five-coordination with tridentate ligand in which the CO group at the γ-position was coordinated to the tin atom and another CO group in the β-position formed a hydrogen bond to the OH group. However, only one product (unstable in the air) was obtained by the direct reaction between other dialkyl halodibasic acid esters and tin foil. The properties of the direct reaction products were compared with those of hydrostannation of the unsaturated dicarboxylic ester with tri-n-butyltin hydride and of the subsequent bromination. The brominated products were considered to have the five-membered ring structure with the CO at the γ-position coordinated to the tin atom, also on the basis of IR and NMR spectra. In view of these observations, it is concluded that those coordinations where the CO at the γ-position coordinates to the tin atom must be caused by the electronegativity of the attached halogen atoms.