Silenes computations

Aromatic rings containing, s/j2-hybridized silicon atoms also constitute members of the silene family. Interest in these compounds largely focuses on the possible delocalization of electron density in the rings, the extent to which they display aromatic character, and their relative stabilities. Raabe and Michl6 have reported much data, which will not be repeated here other computational studies are reported in Section III.D. A few interesting additions to our knowledge of these systems have been reported in recent years. 

This review describes the current status of silenes (silaethylenes, silaethenes), molecules which contain a silicon-carbon double bond. The heart of the material is derived from a computer-based search of the literature which we believe reports all silenes that have been described to date, either as isolated species, chemically trapped species, proposed intermediates (in reactions where some experimental evidence has been provided), or as the result of molecular orbital calculations. Ionized species... 

Silenes have been the object of numerous theoretical studies. It now seems generally agreed that the silicon-carbon tt bond strength is 35-36 kcal/mol or roughly half that of the carbon-carbon tt bond. It should be noted that whereas the inclusion of d orbitals does improve the computed geometry, the tt bond strength is unchanged. 

In this section we will review the computational studies on reactions of silylenes, mainly addition and insertion reactions. Some reactions, in particular the following isomeriz-ations of silylenes to the corresponding multiply bonded species, were discussed above (a) to silaethylene in Section V.A.l.a.v, (b) to substituted silenes in Section V.A.l.b.iv, (c) to disilenes in Sections V.A.2.d and f, (d) to silanimines in Section Y.A.3, (e) to silanephos-phimines in Section V.A.4, (f) to silanones in Section V.A.5, (g) to silanethiones in Section V.A.6, (h) to silynes in Section V.B.l, (i) to disilynes in Section V.B.2, (j) to aromatic compounds in Section VI.A and to antiaromatic compounds in Section VI.D. 

The only computation of an addition path of this type dealt with the addition of HCl to silene and identified a transition state for electrophilic addition296. It seems likely to us that a more thorough search will identify a nucleophilic attack path with an even more favorable transition state. 

Summary The thermal rearrangement of silylamides into l,l-bis(trimethylsUyl)-2-amino-2-trimethylsilyloxysilenes and their subsequent trapping by 2,3-dimethyl-1,3 -butadiene were investigated both computationally and experimentally, with focus on the geometric and electronic structure of these silenes. 

These experiments provide us with ample data for further computational investigations. We feel confident that silenes 6 are formed, but how does the subsequent trapping reaction and the formation of 8 proceed Moreover, one may ask whether there is a direct electronic influence of the A-phenyl groups on the reactivity of the silene or whether these groups have an indirect influence caused solely by their steric bulk B3LYP/6-31G(d) computations show that they force the amino... 

Computational studies of the thermal reactions of silene (Me3Si)2Si C(OSiMe3)(t-Bu) with silyl-substituted acetylenes, bis(trimethylsilyl)butadiyne, t-butyldimethylsilylacet-ylene, and bis(trimethylsilyl)acetylene report substituent effects in the reactivity of the silene. A regioselective migration of a sulfonyl group for the synthesis of functionalized pyrroles can be controlled with high selectivity for the formation of both a- and / -(arylsulfonyl)methyl pyrroles. 

---