From Disilanes

There are three plausible primary processes for the decomposition of Si2H( as shown in equations (35)-(37), with the formation of SiH2, SiH3, and H atoms, respectively. 

The information on the decomposition of various disilanes and trisilanes including Si2Hj is summarized in Table 1. The Arrhenius parameters available in the literature for the primary decomposition of various silanes are given in Table 2. For Si2Hg, the E value was 205.02 kJ mor and the log A value was 14.5 as measured by Bowrey and Purnell.  

Ring and coworkers studied the pyrolysis of Si2Fj, Si2H5F, Si2H,Cl, 

TABLE 2, Arrhenius Parameters for the Primary Decomposition of Silanes 

The ratio can be evaluated from the product yield ratio, SiH33 SiH4. 

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Deposition from disilane (Si2H6) in anRF induction heated reactor at 850°C.[ 1... 

Silylated triphosphanes and triphosphides, synthesis, 31 188-194 yields, 31 194 Silylenes, 29 2-6 addition reactions, 29 4-6 to butadiene, 29 4 to ethylene, 29 4 to hexadienes, 29 5 mechanism, 29 4 nitric oxide scavenging, 29 4 complexes, 25 37, 51, 116, 118 as catalyst intermediates, 25 118 extrusion from disilanes, 25 114, 118 halides, 3 225 from hydridosilanes, 25 14 insertion into element-hydrogen bonds, 29 3-4... 

The oxidation potential decreases in the order Si—Si Si—Ge>Ge—Ge>Si—Sn> Ge—Sn >Sn—Sn in accord with the ionization potential (7P) of the corresponding dimetal. Anodic generation of silicenium ions from disilanes was also reported. The reduction potentials of silicenium ions were determined by cyclic voltammetry of neutral precursor disilanes49. The reduction potential shifted to the negative direction as the center element changed from C to Ge as shown in equation 44. 

Without a doubt, a complete picture of the dynamics of dissociative chemisorption and the relevant parameters which govern these mechanisms would be incredibly useful in studying and improving industrially relevant catalysis and surface reaction processes. For example, the dissociation of methane on a supported metal catalyst surface is the rate limiting step in the steam reforming of natural gas, an initial step in the production of many different industrial chemicals [1]. Precursor-mediated dissociation has been shown to play a dominant role in epitaxial silicon growth from disilane, a process employed to produce transistors and various microelectronic devices [2]. An examination of the Boltzmann distribution of kinetic energies for a gas at typical industrial catalytic reactor conditions (T 1000 K)... 

Disilylcarbodiimide polymers 33 are obtained from disilanes 32 and cyanamide in the presence of triethylamine. ... 

Silicon-based polymers form a dimensional hierarchy from disilanes, to crystal silicon, and through polysilanes, ladder polymers, siloxenes, polysilane alloys, clusters, and amorphous silicons and include unsaturated systems, such as polysilenes, hexasilabenzenes, and so on. Their properties depend basically on the network dimensions and can vary from conducting (metallic) and semiconducting to insulating. 

During the 1960s and 1970s, clean methods were developed for the generation of silylenes [5]. It required many years, however, for woricers in the field to recognize the connection between the most useful reactions for the production of silylenes, extrusion from disilanes and siliranes, and reactions that efficiently consume them, insertions into cr-bonds and addition to r-bonds. Yet staring us in the face was a phenomenon quite different from carbene chemistry nearly all silylene reactions are reversible [6]. This provides a compact framework within which to present a selection of the reactions that lead to silylenes and those reactions that consume them, as shown in Scheme 1. 

The reaction of the enantiomerically enriched silyllithium compound 4 [prepared from disilane (/J)-12] with cyclopropylmethyl chloride occurs with retention of the configuration [(/ )-14], while, for cyclopropylmethyl bromide and iodide, mainly Inversion of the configuration [(S)-14] was observed. The products of the radical reaction (15) indicate a racemization at the silicon center. 

Summary The silylenes MeSiNMe2 and MeSiNH(iPr) can be thermally generated from disilanes. In rapid copyrolytic gas phase reactions between disilanes and trapping reagents the intermediate silylenes and dienes or heterodienes furnish a variety of five-membered unsaturated silicon heterocycles in 35-65 % yield. 

Cleavage of disilanes Triorganosilyl anions are generated in situ from disilanes and this salt. It is a better reagent than TB AF for inducing cleavage of the disilanes. 

The reported values of quantum yields for each of the above processes are 0.61, 0.18, 0.21, respectively. Of course these quantum yields are not necessarily applicable if excitation energy is different. For example, according to the recent theoretical thermochemical data given by Ho and co-workers (14,15) the reaction enthalpy for the formation of a silylsilylene and two hydrogen atoms from disilane (decomposition (b)) is about 166 kcal/mol, which is equivalent to the photon energy at 172 nm. On the other hand, the dissociative excitation of disilane can be effected with even longer wavelength of up to... 

The transition structure for the insertion of H(H3Si)Si into H2 is shown in Figure 50b. The calculated barrier is very low, 1.9 kcal mol -1 at MP4SDTQ/MC-311G //MP2/ 6-31G, and the reaction is exothermic by 53.4 kcal mol -1 199 The reverse reaction, i.e. the elimination of H2 from disilane, is the lowest energy process for the decomposition of H3SiSiH3199. 

The gas-phase pyrolysis of disilane and silane is also likely to involve this rearrangement process. The original proposal60, that the thermal elimination of H2 from disilane is a three-center process leading to silylsilylene, was subsequently modified67 in response to the results of chemically activated disilane decomposition. It was concluded that both the... 

This abstraction experiment is significant in its own right, since it is apparently one of the first direct observations of a surface reaction via an Eley-Rideal process. Abstraction appears to be temperature-independent down to 123 K, suggesting that abstraction is unactivated or that the incident H atoms do not equilibrate with the surface before abstraction occurs. Both suggestions are probably true. A low activation barrier for abstraction from a Si surface (4.5 kcal/mol) has been measured by Abrefah and Olander [37], and a low barrier for abstraction from disilane (2.4 kcal/mol) has been... 

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