Trisilanes reductive

In review OW,7 only four types of synthetic methods are introduced for stable disilenes as shown in Scheme 1 (1) photolysis of linear trisilanes (method A), (2) photolysis of cyclic trisilanes (method B), (3) reductive dehalogenation of dihalosi-lanes (method C), and (4) reductive dehalogenation of 1,2-dihalodisilanes (method D). 

When 1,1,1,3,3,3-hexaphenyltrisilane (la) is used as a starting material in the reaction with two or three equivalents of TfOH respectively, the trisilanes lb and Ic can be isolated after reduction with LiAlHq. Compound la with four equivalents of TfOH and subsequent reaction with LiF yields Id (see... 

This simple electrochemical method seems to be the most practical way to produce these trisilanes. Knowing that the reduction potentials of dichlorosilanes are much less cathodic than that of Me3SiCl, we can assume that the dichlorosilanes are first reduced to monochlorosilyl anions which are then trapped by the Me3SiCl, present in large excess, rather than by the dichlorosilane (Eq. 10). 

Up-to-date, a variety of disilenes have been reported, owing to the improvement of several synthetic methods. For example, the photolysis of cyclic trisilanes (Scheme 5) and the reduction of dihalosilanes or 1,2-dihalodisilanes (Scheme 6) were found to be useful approaches to the corresponding stable silylenes when the precursors are available as stable compounds. 

One exceptional reaction involving oxidative addition onto divalent palladium complexes has been reported. The spiro trisilane 21 is reacted with Cq3-al-lyl)CpPd(II) complexes at room temperature to afford Tris(organosilyl) CpPd(IV) complexes 23 in good yields (Eq. 7) [21]. The reaction maybe rationalized by oxidative addition of one of the two Si-Si bonds of 21, subsequent reductive elimination with formation of the Si-allyl bond giving mono(si-lyl)CpPd(II) complexes, and then oxidative addition of another Si-Si bond in the molecule onto the Pd(II). 

All known isolable two-coordinated silylenes are cyclic monomers stabilized by bulky substituted amino groups at silicon and in most cases supplemented by a Huckel-type delocalized electron system. They were obtained by reduction of the corresponding dihalogenated derivates [1]. Attempts to synthesize analogous pyrido- ornaphtho-l,3,2A, -diaminosiloles by the same route gave small amounts of the desired pure product or they failed [Id, 2]. This prompted us to investigate (i) the photolysis of bis(trimethylsilyl)diaminosilanes and (ii) the thermolysis of recently reported disilanes [3] and of the trisilanes as alternative methods to prepare stabilized low-coordinated silicon compounds. 

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