Preparation and structure of silacycloheptatriene

Abstract

MNDO for 5. AMI does appear to produce Sn-C bonds in stannocene that are somewhat too short, ranging from about 2.49 to 2.62 Á as compared to the experimental values which range from roughly 2.58 to 2.75 Á. The centroid-centroid angle for 4, 120°, is also smaller than that of the X-ray structure18 (144°a nd 148°), although it is close to that derived from the GED study, 125°.19 As the gas phase is the closest model to AMI, the discrepancy may be due to forces in the solid state not present in isolated systems, such as preferential packing arrangements.The highest occupied orbitals of stannocene have been predicted by X" calculations23 to be the nearly degenerate 6a2 and 9b220 with the tin lone pair next highest in energy. Extended Huckel calculations reverse this ordering.20 The Xa calculations, however, appear to be in accord with the UV PES spectrum of 4,23 and in good agreement with the Xa calculations, AMI predicts the nearly degenerate Cp ring MOs as the highest occupied MOs. AMI does, unfortunately, overestimate the IP of stannocene, predicting a first ionization potential of 8.49 eV as compared to the experimentally observed value of 7.57 eV.23 Overestimation of IPs in methods using the core approximation25 is a common problem26 due to the fact that repulsions between the valence and subvalence AOs are not specifically accounted for in these methods. ConclusionsThe AMI formalism has been successfully extended to tin. In almost all cases, AMI performs better than MNDO. The AMI results for organometallic species are especially promising.(25) The valence electrons are assumed to move in a fixed core of the nuclei and inner shell electrons.(26) Dewar, M.

Chemistry of silepins and their analogs containing group 14 elements

“…Its 1 H-NMR spectra remained unchanged over a wide temperature range (−122 °C to +30 °C), with the two methyl resonances as a singlet, indicating a rapid ring inversion. 5 For the much more sterically congested 9,9-dimethyl-9H-tribenzo[b,d,f]silepin, there was no line broadening observed for the two methyl resonances even at 200 °C, indicating a very rigid system in solution. 6 The boat conformation of the sila-2,4,6-heptatriene ring is also evident from several X-ray crystallographic studies.…”

Formation of silacycles via metal-mediated or catalyzed Si-C bond cleavage

“…Oshima and coworkers [28][29][30] developed this ring expansion of siletane into an efficient method to synthesize various five-and sixmembered silacycles with less toxic alkali metals (Scheme 2). Later, Sakurai and co-workers [31] developed a similar carbene insertion reaction to synthesize silepine 11 (eq. (2)).…”

A novel synthesis of stable 3H-pyrrolizine fused diazaborepin

“…[1][2][3][4][5][6] Heteropines incorporated heteroatoms such as B,7,8 Al, 9 Ga, 10,11 Si, 12,13 Ge, 14 Sn, 15 P, 16,17 As, 18 Bi, 18 and Se. 14 B-heteropine, denoted as borepin with a heterocyclic ring containing only boron and carbon atoms was used by Letsinger et al 19 in 1955.…”