Silicon—mercury bonds

The formation of mercury-silicon bonds has been observed in the reaction of the mercury halides HgCP, HgBr2 and Hg2Cl2 with decamethylsilicocene, Cp 2Si. The reaction products are a consequence on single or double insertion reactions. An example of a product is shown as 2. ... 

The first mercury(I) silyl complex [(Me3SiMe2Si)3Si]2Hg2 was prepared by the reaction of an excess of (Me3SiMe2Si)3SiH with (t-Bu)2Hg. The solid structure of the complex displays linear Si—Hg—Hg—Si fragment with regular metal-silicon bond lengths... 

When a thin film prepared from poly[(tetraethyldisilanylene)bis(2,5-thienylene)] was irradiated in air with a 6-W low pressure mercury lamp bearing a Vycor filter, the absorption maximum near 340 nm disappeared within 40 min. Poly[(tetraethyldisilanylene)(2,5-thienylene)] also exhibited a rapid UV change when its thin film was irradiated. IR spectra of the resulting films reveal strong absorption bands due to Si-O-H and Si-O-Si bonds at 3300 and 1100 cm [. The formation of the Si-O-H and Si-O-Si bonds can be best explained by the reaction of the silyl radicals generated by homolytic scission of the silicon-silicon bonds in the polymer backbone with oxygen in air. The other polymers are also photoactive,... 

Examples of carbene insertions into the carbon-silicon bond of SCBs have been known since 1967, when Seyferth studied the behavior of SCBs exposed to dichlorocarbene, which was generated by thermolytic activation of phenyl(bromodichloromethyl)mercury <1967JA1538>. The reaction produces a mixture of products arising from Si-C and C-H bond insertions, with the major products being the ring-expanded silacyclopentanes that result from Si-C bond insertions (Scheme 30). 

Previously, trifluorosilyl groups have been bound to phosphorus (40) and silicon via the SiF (g), fluorine-bond insertion-mechanism (41). The new compound HgCSiFs) is readily hydrolyzed, but it can be stored for long periods of time in an inert atmosphere. It is a volatile, white solid that is stable up to at least 80°C. The preparation of bis(trifluoro-silyDmercury, of course, raises the possibility of (a) synthesis of the complete series of trifluorosilyl, "silametallic compounds, as had previously been done for bis(trifluoromethyl)mercury by using conventional syntheses, and (b) transfer reactions similar to those in Section II, as well as (c) further exploration of the metal-vapor approach. The compound Hg(SiF.,)j appears also to be a convenient source of difluoro-silane upon thermal decomposition, analogous to bis(trifluoromethyl)-mercury ... 

The major synthetic routes to transition metal silyls fall into four main classes (1) salt elimination, (2) the mercurial route, a modification of (1), (3) elimination of a covalent molecule (Hj, HHal, or RjNH), and (4) oxidative addition or elimination. Additionally, (5) there are syntheses from Si—M precursors. Reactions (1), (2), and (4), but not (3), have precedence in C—M chemistry. Insertion reactions of Si(II) species (silylenes) have not yet been used to form Si—M bonds, although work may be stimulated by recent reports of MejSi 147) and FjSi (185). A new development has been the use of a strained silicon heterocycle as starting material (Section II,E,4). 

The reaction of heterocyclic lithium derivatives with organic halides to form a C-C bond has been discussed in Section 3.3.3.8.2. This cannot, however, be extended to aryl, alkenyl or heteroaryl halides in which the halogen is attached to an sp2 carbon. Such cross-coupling can be successfully achieved by nickel or palladium-catalyzed reaction of the unsaturated organohalide with a suitable heterocyclic metal derivative. The metal is usually zinc, magnesium, boron or tin occasionally lithium, mercury, copper, and silicon derivatives of thiophene have also found application in such reactions. In addition to this type, the Pd-catalyzed reaction of halogenated heterocycles with suitable alkenes and alkynes, usually referred to as the Heck reaction, is also discussed in this section. 

Germylene insertion into germacyclobutanes to give 1,2-digermacyclopentanes has already been described (Scheme 88). However, the tetraethyl derivative (95) is better made via the mercury derivative (Scheme 162). Like its silicon counterpart, (95) is slowly oxidized at room temperature, and inserts sulfur, selenium and bromine in the Ge—Ge bond. While (95) is less stable than the 1,2-digermacyclohexane, dichlorocarbene inserts into the /3-C—H bond of both rings, and not the Ge—C bond (Scheme 163) (69JOM(16)227). 

The allyl-metal bond is usually broken very readily by electrophilic reagents and allyl groups are cleaved from mercury, boron, silicon, germanium, tin, and lead much more easily than are the saturated alkyl groups. Kinetic studies, however, have not been very numerous such studies are reviewed in this chapter. 

The chemistry of a class of organometallic compounds that contain a linkage between two different metallic and/or metalloidal elements has recently been the subject of considerable study (195, 207), but only very little interest has been shown in such compounds with the silicon-silicon-metal bond. Only a few derivatives of mercury and alkali metals are known. 

Lewis acids based on boronic acid derivatives or main group elements such as mercury, tin and silicon form strong bonds to anions with considerable covalency, exemplified by hydride sponge and the anticrowns. 

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