Silicon-transition metal bonds hydrogen

Complexes with Hydrogen-Bridged Silicon-Transition Metal Bonds... 

When the silicon-transition-metal bond is reasonably strong, hydrogen attached to the metal may be replaced (mode 4b in Fig. 2) by halogens (entries 26,27, and 30) or deuterium (entry 29). In the case of the ruthenium example, halogenation can be followed by reductive elimination of RsSiH (226). 

Structure//was one of the first known examples of hydrogen bridges between a transition metal and a main-group element other than boron. There are many interesting features in syntheses, bonding properties, and reactions of silicon-transition-metal compounds which can only be outlined in this article, which covers the literature up to 1973. But any survey achieves its aim if it stimulates further interest and research in its specific area. 

Two closely related reactions, (a) and (b), illustrated by Eq. (12) (Rj = HPhj, Etj, Phj, CI3, CljPh) and (13), of silicon hydrides with transition metal complexes generate compounds with Si—M bonds with elimination of hydrogen (a) cleavage of metal-metal bonds and (b) reaction with transition metal hydrides. Reactions discussed in this section are relevant to... 

In addition to activation of sihcon bonds by fluoride ions as discussed in Section 2.4, silicon-silicon, silicon-carbon, silicon-hydrogen, and silicon-nitrogen bonds are activated by transition metal salts and transition metal complexes. Thus, hydrolysis of silicon-carbon bonds such as in phenyltrimethylsilane 81 can be induced by... 

Most of the above reactions occur via a mechanism involving intermediates with a metal-silicon bond (i.e. silicometallics) and a metal-hydrogen bond, accompanied (or sided) only occasionally by compounds containing metal-carbon bonds (i.e. organometallics) that are characteristic of the key intermediates of transition-metal-catalyzed transformations of organic compounds (for recent reviews, see Refs [11, 13]). 

Use of a hydrosilane instead of molecular hydrogen in combination with a transition metal has opened the door leading to hydrosilylation and dehydrogenative silylation of unsaturated bonds. Thus, replacement of hydrogen by a hydrosilane is a reasonable strategy to improve serious issues in hydroformylation of alkenes. Along this line, some types of silylcarbonylation were extensively studied by Murai and his co-workers. However, the silicon moiety always attaches to the oxygen atom of incorporated GO molecule (Scheme 1). 

There are countless examples of the interactions of various atoms and molecules with the clean Si(100) surface. In addition these adsorbate-surface interactions can differ with deposition conditions, such as the rate of deposition or temperature of the sample. For example, even the simplest adsorbate, hydrogen, can etch the surface at room temperature and also form a variety of ordered structures at elevated sample temperatures [57]. A number of adsorbates can form ordered structures commensurate with the surface (e.g. Ag [58], Ga [59], Bi [60]), most transition metals react with the surface to form silicides (e.g. Ni [61], Co [62], Er [63]), halogens can etch the surface at room temperature (e.g. F2 [64], CI2 [65], Br2 [66]), some molecules dissociate on the surface (e.g. PH3 [67], B2H6 [68], NH3 [37]) and other molecules can bond to the silicon in different adsorption configurations but remain intact (e.g. Benzene [69], Cu-phthalocyanine [70], C60 [71]). A detailed review of a number of adsorbate-Si(lOO) interactions can be found in [23,72] and a more specific review relating to organic adsorbates can be found in [22]. As an example of an adsorbate-silicon system we shall here consider the adsorption of a molecule that our group has extensive experience with phosphine. 

The reaction is catalysed by many transition-metal complexes, and a mechanism for the hydrosilylation of an alkene under transition-metal catalysis is depicted in Figure Si5.7. Initial coordination of the alkene to the metal is followed by cis addition of the silicon-hydrogen bond. A hydride migratory insertion and elimination of the product silane complete the cycle. 

Instead of adding two hydrogen atoms to an alkynyl silane we could add H and SiMe3 to a simple alkyne by hydrosilylation (addition of hydrogen and silicon). This is a cis addition process catalysed by transition metals and leads to a tram (E-) vinyl silane. One of the best catalysts is chloroplatinic acid (H2PtCl6) as in this formation of the E-vinyl silane from phenylacetylene. In this case photochemical isomerization to the Z-isomer makes both available. Other than the need for catalysis, this reaction should remind you of the hydroboration reactions earlier in the chapter. The silicon atom is the electrophilic end of the Si-H bond and is transferred to the less substituted end of the alkyne. 

With one exception (the Me/Cl exchange in Table I), all redistributions of siloxanes catalyzed by transition metals observed to date occur only when at least one silicon-hydrogen bond is present in the molecule. We have established that hexamethyldisiloxane (EE) and hexamethylcyclotri-siloxane (D3) are completely inert under the same conditions that cause extensive redistribution of hydridosiloxanes. 

Since silene is an unstable species, various transition metal-silene complexes coordinated by the silicon-carbon double bond have been reported. In 1970, Pannel reported the formation of silene by irradiation of an iron complex (Eq. 6) [8]. He obtained an iron-TMS complex that was apparently formed from silene and an iron-hydride complex generated from the starting iron complex by /3-hydrogen elimination [8]. Wrighton confirmed the existence of tungsten-and iron-silene complexes by examination of NMR spectra obtained at low temperature (Eqs. 7 and 8) [9]. 

To examine the reactivity of a zirconium-silicon bond, Mori et al. synthesized a zirconium-silicon complex from Cp2ZrCl2 and Ph/BuSiLi (1 equiv.) and investigated the reactivity of this complex [ 14]. Furthermore, they found that the reaction of Cp2ZrCl2 with 2 equivalents of Me2PhSiLi gave disilylzirconocene, which was easily converted into a zirconium-silene complex via /J-hydrogen elimination (Scheme 1) [15]. This is the first example of the formation of an early transition metal-silene complex. In this chapter, the reactivity of the zirconium-silene complex is described. 

Germanium forms a wide range of compounds with hydrogen, silicon, the heavier group 14 elements, some main group metals, and transition metals. Catenated hydrides, Ge H2 +2, have already been discussed. The majority have carbon bonded to Ge and are included in the next article (see Germanium Organometallic Chemistry). 

On the other hand, in Hume-Rothery s classification of the elements boron is one of two placed in its own box as neither metal, intermediate element, or nonmetal (12). Indeed, there are properties of boron and features of boron chemistry that are similar to those of transition metals. The electronegativity of boron is less than that of hydrogen as is the electronegativity of most transition metals. This property is also common to other nonmetals past the first row (e.g., silicon). There is, however, one crucial difference between boron and other elements such as silicon. Because it lies to the left of carbon, boron has fewer valence electrons than valence orbitals. Elements with this electronic feature are usually found to exhibit metallic bonding in the elemental state but... 

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