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

Abstract

The monocyclic organostannates ( o- C 6H 4C(CF) 3) 2O)SnR 2(p-CH 3C 6H 4) −Li +( 2a−Li +(R = Me), 2b−1Li + (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-CH 3C 6H 4Li, 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-CH 3C 6H 4Li 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- C 6H 4C(CF 3) 2O)SnMe 2 ( nBu) −Ki +( 2c−Li + ) was thermally unstable and existed in an equilibrium with a ring-opened structure 5c.