The effect of ligands, solvent and temperature on the reactions of allyltin(IV) compounds with singlet oxygen

The reaction of singlet oxygen with a variety of allyltin compounds CH₂=CHCH₂SnR₃ (R₃ = Me₃, Bu₃, allyl₃, (cyclo-C₆H₁₁₃, Ph₃, allylBu₂, Bu₂Cl, Bu₂OAc, allylCl₂, allylCl₂bipy) has been investigated, and the allylperoxytin compounds, 3-stannylallyl hydroperoxides, and 4-stannyl-1,2-dioxolanes which result from M-ene, H-ene and cycloaddition processes, respectively, have been identified by NMR spectroscopy. As the tin centre becomes more electropositive, as indicated by the ¹³C NMR shift of the allylic CH₂ group, the proportion of the M-ene reaction increases, and when δCH₂ is above about 23.7, the allylperoxytin compound is the only product. An exception to this rule is tetraallyltin, δCH₂ 16.13, which similarly shows only the M-ene reaction. This is tentatively ascribed to the special effect of hyperconjugation between the C---Sn σ-bond and the remaining π-systems.

A polar solvent favours the M-ene reaction. The cycloaddition reaction is favoured by low temperature, and at − 70°C in a non-polar solvent it may become the major route.

Diallylmercury and allylmercury chloride react with singlet oxygen to show only the M-ene reaction, but also undergo extensive photosensitized decomposition. With 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), allylmercury chloride shows only the M-ene reaction.