Stereochemically non-rigid silanes, germanes, and stannanes. Part 2. Silylcyclopentadienes

Abstract

Reactions of chiorosilanes with cyclopentadienyl or related anions have been used to synthesize 5-silyl-, 5-chloro-silyl-, 5-dichlorosilyl-, 5-trichlorosilyl-, 5-methylsilyl-, and methyl-5-silyl-cyclopenta-1,3-diene (1)–(6), respectively, and 1 -silylindene (7). Infrared and mass-spectral data have been obtained and assigned. Intra-molecularrearrangements in compounds (1)–(7) have been investigated using ¹³C as well as ¹H n.m.r. spectroscopy. Compounds (1)–(3) and (5) undergo degenerate metallotropism above –25 °C, (6) exhibits ready non-degenerate rearrangement, while for (4) and (7) slow-limiting spectra are observed below 50 °C. The effect of increasing Cl substitution at the Si atom on the olefinic carbon resonances in the ¹³C n.m.r. spectra for (1)–(4) has been examined, leading to an assignment which when related to temperature-dependent non-symmetrical collapse in this region provides new and compelling evidence for a 1,2-metallotropic shift as the mechanism for intramolecular non-rigidity. Slow formation of stereochemically rigid ‘2-’ and ‘3-’ isomers by prototropic shifts has been fully characterized for compounds (1) and (5) using ¹H n.m.r. spectroscopy.