Silole dianions

In contrast to the case of the silole dianion and similar to the case of ger-mole dianion (Section 2.3.2.5), stannole dianion 68 [Li+(Et20)]2 has both Li ions above and below the plane being pentahaptocoordinated to the SnC4 five-membered ring. " The stannole ring is nearly planar and the endocyclic C-C bonds are... 

The known silole dianions are coordinated to the metallic counter ions either by rj5,rj5-bonding10a 82 or by r/1, r/ -bondinglob (Figures 8c and 8d). Pyramidality at Si is, of course, not a problem for the silole dianions where the Si is dicoordinated, and the known dianions are all planar (Figures 8c and 8d). The structural and magnetic properties of the silole dianions are consistent with charge delocalization and aromatic character of these species, as shown by the data collected in Table 7. 

The parent silole dianion C-C4H4S/ 2 and its lithiated complexes... 

Yitzhak Apeloig and Miriam Kami 4. Higher congeners of the silolyl anion and silole dianion... 

Dehydrocoupling of 1 catalyzed by <50 mol% (i.e., M-H/Si-H < 0.5) of Red-Al yielded 2 as light yellow powders. Polymers with molecular weights (Mw) of 4600 and 4100 were isolated in 86 and 78% yields when 15 mol% and 50 mol% of Red-Al were used, respectively. Polymer yields and molecular weights when 15 mol% of Red-Al was used were higher compared to polymers obtained when 50 mol% of Red-Al was used. Products from the reaction of 1 with 15 mol% 25 mol%, and 50 mol% Red-Al were separated by preparative GPC and were characterized by NMR spectroscopy. Shorter oligomers such as silole dimer or trimer were not found in products. However, when 100 mol% of Red-Al (i.e., M-H/Si-H = 1) was used, the formation of silole dianion 333 was observed without forming 2 [Eq. (6)]. 

The activated anionic intermediate could lose both a dihydrogen molecule and a hydride ion (this hydride may participate again in the catalytic cycle) sequentially to form a silylene type of silole. If the activated anionic intermediate accepts another hydride ion, a silole dianion 3 will be formed after losing two dihydrogen molecules. The silylene type of silole will then either self-couple or keep inserting into the Si-H bond of 1, forming 2 (Fig. 1). 

Dilithiosilanes have been known. 1,1-Dilithiosilanes are interesting species and silole dianion was first reported. ... 

Silole dianions, which are of current interest as aromatic species [1 - 3], behave as nucleophiles in simple displacement reactions, generally yielding simple trapping products [4 - 6]. However, the reaction of l,l-dilithio-2,3,4,5-tetraphenylsilole (1) with l,l-dichloro-2,3-diphenylcyclopropene (2) takes a most unexpected course, leading to ring-opening of the cyclopropene ring and ultimate formation of a tetracyclic disilapentalene and a stable bis-silole diradical [7]. 

The dicoordinated silicon in the aromatic silole dianion 574 resonates at an nnexpectedly low field for a sUyl dianion (5 Si = 68.5 ppm) . The diffeent chanical shifts in the solid state (5 Si = 87.3 ppm) and in solntion suggest diffaent structures. While in the solid state a structuie 574a is proven by an X-ray structure, in solution a highly symmetric structure 574b seems to dominate . According to ab initio calculations both isomers show indications of cyclic conjugation . ... 

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