117Sn, 119Sn–proton long-range coupling constants in the 1H nuclear magnetic resonance spectra of alkylhalogenostannanes

Abstract

¹ H N.m.r. spectra of methyl- and ethyl-halogenostannanes have been recorded in [²H]chloroform and [²H₆] dimethyl sulphoxide and the parameters obtained by accurate analysis. Large differences in the ¹H parameters in the two solvents are found, especially for di- and tri-halogeno-derivatives. Long-range Sn–H coupling constants increase with electronegativity and with the number of halogen atoms, and correlations similar to those obtained for J(¹³C–H) can be determined for these coupling constants. The spectra for dimethyl sulphoxide solutions and the comparison with those for CDCl₃ of methylhalogenostannanes provide information about the s-orbital distribution of tin in the Sn–C bonds, it being assumed that the Fermi contact mechanism is the main contribution to longrange tin–proton coupling constants, known geometries of complexes between methyltin halides and sulphoxide being used. In the case of ethyltin derivatives complications arise from the anomalous coupling constants of tin with α-protons which seem very sensitive to the nature of the groups linked to tin.