Stereochemical non-rigidity in germylcyclopentadiene and related derivatives of germane

Abstract

The compounds germylcyclopentadiene (I), germyl(methyl)cyclopentadiene (II), methylgermylcyclopentadiene (III), bis(cyclopentadienyl)germane (IV), and germylindene (V) have been synthesised through reaction of halogenogermanes with appropriate hydrocarbon anions. Using variable-temperature ¹H n.m.r. spectroscopy, it has been found that while compounds (I)–(IV) are fluxional at 35 °C, the onset of similar behaviour for (V) occurs only at 175 °C. For compounds (I) and (II), spin coupling between protons at Ge and on the C₅ ring could be resolved (a) below –20 °C. establishing the identity of the species present at the slow-exchange limit in each case, and (b) above 50 °C, providing novel evidence for an intramolecular, metallotropic shift as the mechanism for rearrangement. I.r. and Raman spectra for compounds (I)–(V) have been partly assigned, with ν[Ge–C(ring)] near 370 cm^–1; mass spectra show fragmentation patterns indicating extensive transfer of H from Ge to the organo-group. Heating compound (I) results in partial prototropic rearrangement to 2- and 3-germyl isomers; several reactions of (I), including those with HCl and Me₃SnH, have been investigated.