Silicon-carbon compounds

Silicon carbide, the simplest silicon-carbon compound, is especially stable. Its typical form, p SiC, has a diamond structure with a lattice constant a = 435 pm (the value for diamond is 356 pm). Each Si atom is surrounded by four C atoms, and every C atom, by four Si atoms. The density (3.17 g/cm ) is lower than that of diamond (3.51 g/cm ) the greater atomic weight of sihcon is more than compensated by its greater lattice constant. The melting point of SiC is 2700 °C (partial decomposition) that of diamond is 3500 ""C. 

Silicon (3), which resembles metals in its chemical behavior, generally has a valence of +4. In a few compounds it exhibits a +2 valence, and in silicides it exists as a negative ion and largely violates the normal valency rules. Silicon, carbon, germanium, tin, and lead comprise the Group 14 (IVA) elements. Silicon and carbon form the carbide, SiC (see Carbides). Silicon and germanium are isomorphous and thus mutually soluble in all proportions. Neither tin nor lead reacts with silicon. Molten silicon is immiscible in both molten tin and molten lead. 

At one time it was felt that it would be possible to produce silicon analogues of the multiplicity of carbon compounds which form the basis of organic chemistry. Because of the valency difference and the electropositive nature of the element this has long been known not to be the case. It is not even possible to prepare silanes higher than hexasilane because of the inherent instability of the silicon-silicon bond in the higher silanes. 

The 13C-NMR spectra of 4-7, 9-11 show a close similarity to the spectral data of analogous carbene complexes. The shift differences between the metal carbonyls of the silylene complexes and the related carbon compounds are only small. These results underline the close analogy between the silicon compounds 4-7, 9-11 and Fischer carbene complexes. This view is also supported by the IR spectral data. On the basis of an analysis of the force constants of the vco stretching vibration,... 

An ab-initio calculation for (OC)5Cr = Si(OH)H shows parallels to the parent carbon compound. However, the electron deficiency at the silicon atom is significantly higher compared to the carbene complex. The LUMO of the Cr=Si... 

C. Eabom and R. W. Bott, Synthesis and reactions of the silicon-carbon bond, Organo-metallic Compounds of the Croup IV Elements, ed. A. G. MacDiarmid, Vol. 1, Part 1. Marcel Dekker, New York (1968). 

Silicon compounds can also act as Lewis acids, whereas carbon compounds typically cannot. Because a silicon atom is bigger than a carbon atom and can expand its valence shell by using its d-orbitals, it can accommodate the lone pair of an attacking Lewis base. A carbon atom is smaller and has no available d-orbitals so in general it cannot act as a Lewis acid. An exception to this behavior is when the carbon atom has multiple bonds, because then a Tt-bond can give... 

Carbon forms ionic carbides with the metals of Groups 1 and 2, covalent carbides with nonmetals, and interstitial carbides with d-block metals. Silicon compounds are more reactive than carbon compounds. They can act as Lewis acids. 

B. The Synthesis of Compounds with Silicon-Carbon-Transition Metal... 

Silenes with a wide range of structures have been synthesized over the years, from the simplest possible compound, H2Si=CH2, which has a transient existence, to species that contain four complex groups attached to the ends of the silicon-carbon double bond, e.g., (Me3Si)MesSi=C... 

Silicon-carbon thermoset, 10 5 Silicon casting, 22 506-507 Silicon charge-coupled devices, 19 150-151 Silicon chips, 9 694-695 Silicon criystal lattice, 23 33 Silicon compounds titanium in, 25 55—56... 

Although carbon and silicon both belong to the same group of periodic table and many of the silicon compounds resemble carbon compounds, but the chemical reactivity of silicon in organosilicon compounds is more comparable to that of hydrogen because many nucleophilic displacements at... 

Organic groups were detected on the surface after grinding of silica in the presence of organic solvents. Silicon-carbon bonds are also formed by nucleophilic attack on the siloxane bonds with lithium organic compounds. This reaction is analogous to the dissolution of silica with alkali hydroxides. 

The importance of carbon-centred radical cyclizations in organic chemistry has been documented in the large number of papers published each year and numerous reviews and books dealing with this subject. In Chapter 7 the reader can find a collection of such processes mediated by organosilanes. The silicon-centred radical cyclizations have instead received very little attention, although there has been a growing interest in silicon-containing compounds from a synthetic point of view, due to their versatility and applicability to material science. As we shall see, this area of research is very active and some recent examples show the potentiality of silyl radical cyclization in the construction of complex molecules. 

Early estimates for the Si NMR chemical shift of silylium ions were based on an empirical correlation between NMR and Si NMR chemical shifts of iso-structural silicon and carbon compounds, and predicted for trimethylsilylium a Si NMR chemical shift within the range 225-275. ... 

It reacts with carbon monoxide to form a compound with a silicon carbon bond ... 

---