Stannylene , calculations

It has become common to classify all molecular compounds, which fulfill the above characteristics, as carbene analogs 9,13>. As a consequence, compounds of divalent silicon, germanium, tin, and lead may be regarded as carbene-like and are therefore called silylenes, germylenes, stannylenes, and plumbylenes. In contrast to carbenes they have one property in common the energetically most favorable electronic state is the singlet 1a2 found by experiments and calculations 9). 

Unsubstituted or 2,3-disubstituted stannoles can be prepared from the palladium-catalyzed reaction of an alkyne with the stable stannylenes [(Me3Si)2CH]2Sn and CH2C(SiMe3)2 2Sn . The mechanism has been traced by the isolation of intermediates,235 and by ab initio calculations (Equation (78)).236... 

Spectroscopic studies and quantum-chemical calculations of short-lived germylenes, stannylenes and plumbylenes... 

Quantum-chemical calculations are employed extensively for the interpretation of experimentally observed spectra. Increasing accuracy of modern quantum-chemical methods in the prediction of spectral characteristics, geometries and energies allows one to a certain extent to fill the gaps in experimental data available for germylenes, stannylenes and plumbylenes. Therefore we review in Section X the results of quantum-chemical studies of germylenes, stannylenes and plumbylenes. 

Quantum-chemical studies showed that the ability to form complexes with Lewis bases decreases on going from silylenes to stannylenes and increases in the following series of n-donor agents amines < phosphines < arsines < stibines189. This series somewhat differs from that proposed based on experimental data188. Calculations were successfully used to predict the absorption maxima shifts on complexation of silylenes with amines190. 

Quantum-chemical calculations have been used to probe all the characteristic chemical reactions of CAs (at least in the case of silylenes and germylenes). The theoretical studies cover intramolecular rearrangements, insertions into 0-bonds, additions to double and triple bonds and dimerizations. Note that experimental data on the mechanisms of these reactions are still scarce and the results of theoretical studies are needed to understand the main trends in the reactivity of germylenes, stannylenes and plumbylenes. 

This review shows that despite the huge amount of information accumulated on fundamental structural, electronic and spectral characteristics of germylenes, stannylenes and plumbylenes, many gaps still exist in this area. Modem quantum-chemical calculations partially help to fill these gaps, but reliable experimental data are needed. 

Use of ab initio calculations to assign the singlet-singlet transitions in spectroscopic studies of small germylenes, stannylenes and plumbylenes has now become standard... 

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