ORGANOMETALLIC CHEMISTRY .24. CONTINUED SEARCH FOR ELUSIVE PERSISTENT TRIVALENT ORGANOSILYL CATIONS - THE CLAIMED TRIMETHYLSILYL CATION REVISITED - ATTEMPTED PREPARATION OF CYCLIC AND HALOGEN-BRIDGED ORGANOSILICENIUM IONS

Comparison of ab initio/IGLO calculated H-1, C-13, and Si-29 NMR chemical shifts with the experimental data on trimethylsilyl perchlorate and related derivatives supports the conclusion that no long-lived persistent trimethylsilicenium ion has been observed in solution. Attempts were made to prepare 5-methyl-5H-dibenzo[b,f]silepinium ion to probe whether cyclic aromatically stabilized silicenium could be prepared under stable ion conditions. The attempts were unsuccessful, and the related perchlorate was found to be a covalent compound. Similarly the products of hydride abstraction of 1-methyl- and 1-phenyl-substituted tetraphenylsilole were also found to be covalent perchlorates in contrast to a reported study wherein ionization was claimed. Both silepinium and silole perchlorates are covalent in nature with no manifestation of aromatic and antiaromatic character, respectively, indicating very little Si-O bond polarization. Attempted preparation of sila-substituted cyclic halonium ions resulted only in donor-acceptor complex formation and decomposition. In the case of the (bromomethylsilyl)diphenylcarbenium ion, there is little indication of bromine bridging.