RESUMEN
The synthesis of persistent sila- and germacyclopentadienyl (silolyl- and germolyl-) radicals by careful stoichiometric reduction of the corresponding halides with potassium is reported. The radicals were characterized by EPR spectroscopy and trapping reactions. The reduction of tris(trimethylsilyl)silyl-substituted halides was successful while smaller substituents (i. e., t-Butyl, Ph) gave the corresponding dimers. The EPR spectroscopic parameter of the synthesized tetrolyl radicals indicate only small spin delocalization to the butadiene unit due to cross-hyperconjugation. Silolyl- and germolyl anions are unavoidable byproducts and are isolated in the form of their potassium salts and characterized by X-ray crystallography. The comparison of the molecular structures of two closely related potassium silolides provided an example for different coordination of the potassium cation to the silolyl anion (η1 vs. η5 coordination) that triggers the switch between delocalized and localized states.
RESUMEN
The addition of 2,6-dimethylphenyl isocyanide and t-butyl isocyanide to tetramesityldisilene was examined. In both cases, the initially formed product is an iminodisilirane; however, the iminodisiliranes are unstable under the reaction conditions and react with a second equivalent of the isocyanide to give either a 3-silaazetidine or a novel bicyclic double enamine, respectively. Taken together with the previous examples in the literature, the results demonstrate that subtle differences in the steric bulk of the disilene or the electronic effects of the isocyanide can lead to dramatic differences in the reaction pathway.
RESUMEN
An unusual germole-to-silole transformation is described. As key intermediates hetero-fulvenes are formed which rearrange to more stable bicyclic carbene analogues. The so-formed germylenes undergo a reductive elimination yielding elemental germanium and siloles. In contrast, the analogous silylenes are stable at ambient conditions and were identified by MS spectrometry and NMR spectroscopy supported by the results of quantum mechanical calculations. These bicyclic silylenes are stable derivatives of the global minimum of the C4 Si2 H6 potential energy surface.
RESUMEN
The synthesis of a new type of silylene 1 is reported. It adopts a bicyclo[2.1.1]hexene structure in which a hafnocene group is incorporated. The silylene is stabilized by homoconjugation with the remote CâC double bond. This is indicated by its highly shielded 29Si NMR chemical shift (δ29Si = -155) and is firmly established by its experimental molecular structure from XRD analysis. The results of a detailed bonding analysis based on DFT calculations suggest for model compounds of silylene 1 and for its heavier germanium, tin, and lead homologues uniformly electronic structures of carbene analogues that are stabilized by homoconjugation. This stabilization mode is equivalent to a σ2, π-coordination of the butadiene ligand to the element atom as it is typical for zirconocene or hafnocene butadiene complexes.
RESUMEN
The synthesis of a bicyclic germylene from the reaction of a germole dianion with hafnocene dichloride is reported. This germylene is stabilized by a homoconjugative interaction of the dicoordinated germanium atom with a remote C=C double bond. First reactivity studies revealed its nucleophilic character and resulted in the synthesis of bimetallic hafnium/iron and hafnium/tungsten complexes with a germylene group linker.
RESUMEN
By reactions of magnesium oligosilanides with SbCl3, a number of oligosilanylated antimony compounds were obtained. When oligosilanyl dianions were used, either the expected cyclic disilylated halostibine was obtained or alternatively the formation of a distibine was observed. Deliberate formation of the distibine from the disilylated halostibine was achieved by reductive coupling with C8K. Computational studies of Sb-Sb bond energies, barriers of pyramidal inversion at Sb, and the conformational behavior of distibines provided insight for the understanding of the spectroscopic properties.