Silicon compounds overview

In this review we have chosen to limit the scope to nucleophilic substitution at silicon. A short overview is given of material covered in detail in our previous review in The Chemistry of Organic Silicon Compounds 1, with recent advances covered in greater depth. 

J. Y. Corey, "Historical overview and comparison of silicon with carbon", in "The chemistry of organic silicon compounds" (Eds. S. Patai and Z. Rappoport), John Wiley Sons, 1989, p. 1. 

This chapter will give first an overview of silyl cations. Thereafter, very briefly, hypervalent silicon compounds will be discussed. Strictly speaking, the concept of hypervalent silicon compounds is part of Lewis base catalysis and will be discussed there in detail. However, since in this type of reaction a Lewis base forms in situ with a silicon atom containing reagent or SiCh an intermediate, which functions as a Lewis acid to activate substrates during the reaction, we also give here a few examples. Notably, silicon is a semimetal. Hence, we leave it up to the reader to decide whether silicon catalysts should be considered as organocatalysts. 

Compounds which accommodate agostic interactions of Si-H moieties with transition metals may also be considered as a special type of higher-coordinated silicon compounds. A few reviews on this matter are also available [36]. These include a recent general overview [37] and further publications on selected sub-topics such as platinum compounds [38] or niobium and tantalum complexes [39]. Complexes of this type are also discussed in comparison to C-H and H-H interactions with lanthanides [40]. 

Due to the numerous overviews on the chemistry of hypercoordinated silicon compounds, the present review is primarily focused on the structural and synthetic aspects. Spectroscopic and other properties as well as (potential) applications are only briefly mentioned in selected cases. Nevertheless, the literature on higher-coordinated silicon complexes published in the past 5 years should be covered comprehensively, while relevant older literature is also considered. 

In this review we focused on the most recent literature, while at the same time trying to provide a comprehensive overview on the synthetic routes, structures, ligand types, and donor atoms in higher-coordinated silicon compounds. The... 

Organometallic polymer precursors offer the potential to manufacture shaped forms of advanced ceramic materials using low temperature processing. Polysilazanes, compounds containing Si-N bonds in the polymer backbone, can be used as precursors to silicon nitride containing ceramic materials. This chapter provides an overview of the general synthetic approaches to polysilazanes with particular emphasis on the synthesis of preceramic polysilazanes. 

In the following section, we provide a brief review of the structures of the major semiconductor surfaces for which the adsorption and reaction chemistry will be covered in this chapter. This includes the (100) and (111) crystal faces of silicon and germanium. Chapter 1 of this book also provides a brief overview of the structure of the silicon surface. The surface structures of compound semiconductors, including GaAs and InP, can be quite complex and are not covered here. A number of reviews describe the structure of these surfaces much more extensively [5,6,25-29], and the reader is referred to those references for more detail. 

M-C as propagating species, 4, 1008 monomer coordination and insertion reactions, 4, 1010 monomer insertion regio- and stereochemistry, 4, 1015 overview, 4, 1005-1166 regioirregular insertions, 4, 1023 stereocontrol mechanism, 4, 1018 stereocontrol symmetry rules, 4, 1020 stereoregular polymers, 4, 1016 in Ru-Os heterodinuclear compounds, 6, 1046 in Ru-Os mixed-metal clusters, 6, 1064 semiconductor growth, conventional precursors, 12, 2 with silicon, 3, 514... 

Hafnium complexes with bis(cyclopentadienyl)s, 4, 731 in carbometallations, overview, 10, 255 in C-C bond formation, 10, 424 in ethylene polymerization, 4, 1139 for isotactic polypropylene, 4, 1126 metal-metal bonds, 4, 755 mixed-valence compounds, 4, 755 with pyridyl amines, for olefin polymerization, 4, 1094 in Ru-Os heterodinuclear compounds, 6, 1046 with silicon, 3, 515... 

This section presents a brief overview of a few other compounds that have not been described in previous sections. Because it can function as a nonmetal, silicon forms sihcides with several metals. These materials are often considered as alloys in which the metal and silicon atoms surround each other in a pattern that may lead to unusual stoichiometry. Examples of this type are Mo3Si and TiSi2. In some sihcides, the Si-Si distance is about 235 pm, a distance that is quite close to the value of 234 pm found in the diamond-type structure of elemental silicon. This indicates that the structure contains Si22-, and CaSi2 is a compound of this type. This compound is analogous to calcium carbide, CaC2 (actually an acetylide that contains C22- ions (see Chapter 10)). 

This list of compounds with silicon in the whole range of its coordination numbers and environments, including their synthesis and the investigation of their chemistry gives an impressive overview of organosilicon research currently going on worldwide. 

The assignment of configuration and the measurement of enantiomeric purity is a necessary step in any stereochemical study. Both the physical and chemical techniques used have been described in detail in the case of carbon compounds (92, 93). In this section we give a brief overview of their application to organo-silicon stereochemistry. 

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