Synthesis, stability, and reactions of 10-Sn-5 tin ate complexes bearing four tin-carbon bonds

Article abstract of DOI:10.1016/0022-328X(95)05634-2

The monocyclic organostannates (o-C₆H₄C(CF₃)₂O)SnR₂(p-CH₃C₆H₄)^-Li⁺(2a-Li⁺(R = Me), 2b-Li^- (R = ^tBu)) bearing four Sn-C bonds, which can be prepared from the reaction of tetracoordinate tin 3a (R = Me) and 3b (R = ^tBu) with p-CH₃C₆H₄Li, were found to be thermally stable but were unstable to moisture giving 3 quantitatively upon aqueous workup. These ate complexes were inert toward some typical electrophiles such as p-methoxybenzaldehyde, but were reactive enough toward 1,3-bis(methoxycarbonyl)pyridinium chloride (8) to give corresponding alkylated(arylated) dihydropyridines (9). These are quite unique examples in the respect that organostannanes bearing four Sn-C bonds, which have been known to be reluctant to form compounds of higher coordination numbers, formed stable pentacoordinate ate complexes and showed unique reactivity which differed from that of lithium reagents such as p-CH₃C₆H₄Li which could have formed upon dissociation from the ate complexes. The reaction of 3a with ⁿBuLi gave complex mixtures after treatment with water indicating that the expected ate complexes (o-C₆H₄C(CF₃)₂O)SnMe₂(ⁿBu)^-Ki^-(2c-Li⁺) was thermally unstable and existed in an equilibrium with a ring-opened structure 5c.