Singly bonded silicon compounds

B. T. Luke, J. A. Pople, M.-B. Krogh-Jespersen, Y. Apeloig, J. Chandrasekhar, and P. v. R. Schleyer,/. Am. Chem. Soc., 108,260 (1986). A Theoretical Survey of Singly Bonded Silicon Compounds. Comparison of the Structures and Bond Energies of Silyl and Methyl Derivatives. 

B. Larger Non-cyclic Singly Bonded Silicon Compounds... 

The lightest member of the series, containing silicon, has only just been reported in 2004. The compound RSiSiR (R = Si(Pr(SitBu3)2) has an Si=Si bond length of 2.06 A, some 3.8% shorter than an Si=Si double bond, and 13.5% shorter than an Si Si single bond. The compound is trans-bent with an Si-Si =Si angle of 137°. 

In Group 4A the effect of size is reflected in the dramatic differences between the chemistry of carbon and that of silicon. The chemistry of carbon is dominated by molecules containing chains of C—C bonds, but silicon compounds mainly contain Si—O bonds rather than Si—Si bonds. Carbon forms a wide variety of stable compounds with strong C—C single bonds. Silicon also forms compounds with chains of Si—Si bonds. 

The ultrahigh vacuum STM was used to investigate the addition of the 2,2,6,6-tetramethyI-l-piperidinyloxy (TEMPO) radical to the dangling bond of Si(l 0 0)-2 X 1 surface. ° ° The TEMPO can bond with a single dangling bond to form stable Si-O coupling products, in contrast to the thermal decomposition of TEMPO-silicon compounds. Semiempiiical and DFT calculations of TEMPO bound to a three-dimer silicon cluster model yielded... 

The single-bond compounds between Si, Ge, and Sn and chalcogens (S, Se, Te) are reactive and used as synthetic intermediates in the synthesis of organic compounds, organochalcogen compounds, organo-silicon, -germanium and -tin compounds, and transition metal-chalcogen complexes and clusters. 

Compounds that arc formally analogous to carbon compounds arc found to have quite different structures. Thus carbon dioxide is a gaseous monomer, hot silicon dioxide is an infinite single bonded polymer. In a similar manner, /ym-diok arc unstable relative to ketones ... 

Carbon- and silicon-element single bonds in 4-coordinated carbon and silicon compounds. Polarities of the bonds. 

Most of the organosilicon compounds contain bonds between the silicon and carbon atom. In the following paragraph the structural chemistry of the Si—C single bond is discussed, mostly in compounds with tetracoordinate silicon and tetracoordinate carbon atoms. The structural chemistry of the Si—C bond in compounds where the carbon coordination state is different, is also discussed. The Si—C bond is markedly polarized and the increase of the bond ionicity by attaching different substituents to either the silicon or the carbon atoms may affect its length. The electronic and steric effects are discussed later. 

The coordination of donors lengthens the Si=N bond and leads to pyramidalization at the silicon centre, as can be seen from the deviation of the sum of angles around the silicon atom from 360° (see examples in Table 17). Coordination of silanimines to transition metal centres also increases the silicon-nitrogen bond length to 1.66-1.69 A, which corresponds to a Si—N single bond. It has already been mentioned above that these metal compounds are best described as metallacycles349,350. 

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