SILYLENES WITH AROMATIC CHARACTER

Surprising thermal and chemical stability of the cyclic silylene (29) may be explained by an enhanced aromaticity. This can be seen by comparison with its percursor (30) the difference in length between the single N—C (1.415 A) and double C=C (1.322 A) bonds in (30) decreases in (29) (N—C 1.400 A, =C 1.347 A) to imply an increased delocalization. Also the Si—N bond length increases in (29) only by 0.056 A (from 1.697 A to 1.753 A) instead of the 0.080-0.100 A typical for transition from tetra- to dicoordinate silicon this may indicate developing partial Si= N double bond character in (29) <94JA269l>. 

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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