Cyclosilanes Cyclotrisilanes

Although homonuclear cyclosilanes have been known for a long time, it is only recently that the smallest members of this series, the cyclotrisilanes, have become available [1], Cyclotrisilanes 1 are obtained by reductive halogen elimination from ort/zo-disubstituted diaryldichlorosilanes [2, 3] or, in particular cases, from hexaalkyl-l,3-dichlorotrisilanes [4]. 

Hexakis(2,6-dimethylphenyl)cyclotrisilane, the first known stable three-membered cyclosilane, was prepared in 1982 by Masamune and coworkers from dichlorobis(2,6-dimethylphenyl)silane by the reductive dechlorination with lithium naphthalenide in low yield34. Other cyclotrisilanes bearing substituents of comparable steric bulk have been synthesized analogously. The chemistry of the cyclotrisilanes presently known has recently been reviewed35. 

A well established method for the preparation of metalated silanes is the cleavage of Si-Si a-bonds by alkali metals [1]. The reaction of arylsubstituted cyclosilanes yields the corresponding a,(0-dilithiated oligosilanes. Whereas the reaction of cyclopenta- and cyclotetrasilanes with lithium is well known [2, 3], a metal mediated cleavage of a cyclotrisilane was not described up to now. Here we report the reaction of cyclotrisilane 1 with lithium, which affords, depending on the conditions, either 1,3-dilithiotrisilane 2-Li or l,2-dilithiodisilane3-Li. 

Reaction of 3a with an equimolar amount of (BusSiNa at -78°C with subsequent warming to room temperature leads to a mixture of various cyclosilanes. The cyclotrisilane 8 is the major component (59%), other products are the cyclotrisilane 9 (5%) and the cyclotetrasilanes 10 (8%), 11 (25%) and 12 (3%) [2] The all-c/s -cyclotetrasilane is not formed. At higher temperature (65°C) 3a reacts with U3SiNa mainly to the cyclotrisilane 9 (74 %) and not at all to the cyclotrisilane 8. The yields of the cyclotetrasilanes are not significantly temperature-dependent. 

A class of polysilanes which can be envisioned as analogous to the cycloalkanes is the cyclosilanes, of which cyclotrisilane (1), cyclotetrasilane (2), cyclopentasilane (3), and cyclohexasilane (4) would be examples. Although existence of these simple cyclosilanes has not been documented in the... 

Organosilicon compounds containing chains of silicon atoms in a cycle will be named as derivatives of cyclic silicon compounds having the formula (SiH2) and will be called cyclotrisilanes, cyclotetrasilanes, etc., according to the number of members in the ring they will have the generic name cyclosilanes. Cyclosilanes will be numbered in the same way as are carbon compounds of a similar nature. Therefore, the compound... 

As already shown above for cyclotrisilanes, ohgosilanyl dianions are convenient building blocks for the synthesis of cyclosilanes with different substitution pattern [47, 96, 108]. l,l,2,2-Tetrakis(trimethylsilyl)tetramethylcyclotetrasilane which forms in the oxidative coupling of the 1,4-dipotassium compound (Scheme 8) can... 

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