Potentially Aromatic Silylenes

Veszpr6mi and coworkers suggested that silylenes such as 95 and 96 are also potentially aromatic and that therefore they should be good candidates for synthesis. The formal trisilylene 95 is calculated to be by 30.5 kcalmoC (CCSD/6-31G //MP2/6-31G 16.5 kcalmoC at MP2/6-31G //MP2/6-31G ) more stable than the isomeric aromatic 41 (see Section III.H. for a discussion on 41 and 42). Similarly, the silylene 96a is by 8.9 kcalmol-l more stable than 2-silapyridine 42 (MP2/6-311G V/MP2/6-311G ). 96a and 42 are separated by a high barrier of 56 kcalmoC, similar to the barrier of 54 kcalmoC that separates 75d from 90 (see Section V.A.2.a). The 96-42 stability order is reversed upon methyl substitution 96b is by 5.6 kcalmol less stable than the methyl-substituted (on Si) 42. 

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Besides the applications of the electrophilicity index mentioned in the review article [40], following recent applications and developments have been observed, including relationship between basicity and nucleophilicity [64], 3D-quantitative structure activity analysis [65], Quantitative Structure-Toxicity Relationship (QSTR) [66], redox potential [67,68], Woodward-Hoffmann rules [69], Michael-type reactions [70], Sn2 reactions [71], multiphilic descriptions [72], etc. Molecular systems include silylenes [73], heterocyclohexanones [74], pyrido-di-indoles [65], bipyridine [75], aromatic and heterocyclic sulfonamides [76], substituted nitrenes and phosphi-nidenes [77], first-row transition metal ions [67], triruthenium ring core structures [78], benzhydryl derivatives [79], multivalent superatoms [80], nitrobenzodifuroxan [70], dialkylpyridinium ions [81], dioxins [82], arsenosugars and thioarsenicals [83], dynamic properties of clusters and nanostructures [84], porphyrin compounds [85-87], and so on. 

An ab initio computational study has predicted that 87r-homologs (129 and 130) of planar aromatic carbenes and silylenes will form twisted 6 2-geometries, providing palladium complexes with Mobius-aromatic chiral character, and present an opportunity to design potentially chiral monodentate metal coordination. ... 

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