Sieburth_1990_Pest.Sci_29_215

All of the Group IV elements, C, Si, Ge, Sn and Pb, form four tetrahedrally disposed bonds and could be considered as replacements for each other. Because the atomic radius increases linearly with increasing row number, this replacement can also be considered as a probe of steric effects. The use of silicon, with its high natural abundance and non-toxic nature, has received the most attention. Examples of silicon-for-carbon exchange can be found for all major classes of insecticides, including carbamates, phosphates, pyrethroids, as well as DDT and juvenile hormone analogs. Generally, the silicon analogs retain insecticidal activity. A silicon analog of MTI-800 (dimethyl-4-ethoxyphenyl-I-(3-(4-fluoro-3-phenoxyphenyl)propyl)silane) is a broad spectrum insecticide. This silane was used as a starting point for building new silane analogs as potential insecticides. Two analogs were particularly noteworthy. A silane with a cyclopropyl group was found to be non-toxic to Trichoplusia ni (cabbage looper) while the corresponding carbon compound was a potent insecticide. An analog containing a silicon-hydrogen bond, a structural feature reported to be unstable in vivo, was found to be significantly insecticidal both topically and in foliar tests. The latter compound suggests that biologically active silanes can encompass broader structural types than previously anticipated.