Novel zwitterionic heterocycles containing hypervalent tin

The reactions of (E)-2-chloro(dimethyl)stannyl-3-diethylboryl-N,N-dimethyl-2-pentenylamine 2, containing penta-coordinate tin, with lithium diethylamide, -diiso-propylamide, -bis(trimethylsilyl)amide, with N-lithiated azoles (pyrrole, 1,2,4-triazole), and C-lithiated azoles (N-methylimidazole, thiazole and 4-methylthiazole) were studied. Most of the products 3–11 correspond closely to those obtained previously from (E)-2-chloro(dimethyl)stannyl-3-diethylboryl-2-pentene 1. However, there is a tendency for the increase in the coordination number of tin in the 1,2,5-azoniastannaboratole derivative 3, the 1,3-stannaborole derivative 4, the bis(trimethylsilyl)amide 5 and the N-pyrrolylborane 6. In the products derived from 1,2,4-triazole (7), N-methylimidazole (8), thiazole (9, 10) and 4-methyl-thiazole (11), the coordinative N–Sn bonding with the dimethylamino group is strong, as indicated by multinuclear magnetic resonance data in solution (1H-, 11B-, 13C-, 14/15N-, 119Sn-NMR), and by X-ray structural analysis of 11 in the solid state. In the cases of 10 and 11, zwitterionic structures are formed, in which tin is linked to nitrogen, and boron to carbon of the thiazole. These compounds can be classified as carbene–borane adducts.