Silicon and tin

Aryl silicon compounds can be prepared by metal-catalysed reaction of halides with silanes, as in the rhodium-catalysed reaction below. The mechanistic details of this reaction (probably) differ from the palladium-catalysed borane reaction. (NOTE triethoxy silane is extremely toxic ) 

Useful alternative preparations of stannanes include palladium-catalysed decarboxylation of stannyl esters. ° Trialkylstannyl and trialkylsilyl anions are highly reactive and will displace halogen without the use of a catalyst. It is possible to directly silylate indoles and pyrroles via electrophilic substitution.  

The relatively high stability of carbon-silicon/-boron/-tin bonds allows the metaT to be carried through many heterocyclic syntheses as an inert substitutent some examples are shown below.  

Silicon and tin are both subject to ipra-replacement by electrophiles, via an electrophilic addition/metal elimination mechanism analogous to other aromatic substitutions, but at a much faster rate than the corresponding replacement of hydrogen. /pra-substitutions also take place on heterocycles and, in the case of electron-rich systems, probably via the same type of mechanism. 

4-Trimethylsilyl-pyridines will also react with aldehydes under fluoride catalysis an intramolecular example is shown below.  

There appear to be no well-characterized Co111—Si bonded compounds. Interactions with silicates, particularly on surfaces, are through oxygen atoms. The use of the complex [Co(en)2(LL)]Cl3 (where LL = (MeO SiC C C NHCt Ct NTy permits bonding of the substitution-inert CoN6 species to a silica surface.549 

There are few well-established examples of Co111—Sn bonds. Stannanes R3SnH react with OEP complexes (124) or the divalent Co(OEP) to form Co(OEP)SnR3.550 This is also accessible from R3SnCl and [CoT(OEP)]. The structure shows a square-pyramidal Co displaced 0.777 A out of the porphyrin plane and towards the Sn, which is 2.510(2) A distant from the Co111 center. 

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New lands (1864) was the first to predict correctly the existence of a missing element when he calculated an atomic weight of 73 for an element between silicon and tin, close to the present value of 72.61 for germanium (discovered by C. A. Winkler in 1886). However, his method of detecting potential triads was unreliable and he predicted (non-existent) elements between... 

Germanium was predicted as the missing element of a triad between silicon and tin by J. A. R. Newlands in 1864, and in 1871 D. I. Mendeleev specified the properties that ekasilicon would have (p. 29). The new element was discovered by C. A. Winkler in 1886 during the analysis of a new and rare mineral argyrodite, AggGeSfi " he named it in honour of his country, Germany. By contrast, tin and lead are two of the oldest metals known... 

C. J. Evans and S. Karpel. Orgcnotin Compounds in Modem Technology. Journal of Organomelallic Chemistry Libraty, 16 Elsevier, Amsterdam, 1985, 280 pp. S. J. Blunden. P. a. Cusack and R. Hiu., The Industrial Uses of Tin Chemicals. Royal Society of Chemistry, London, 1985, 346 pp. K. Das, S. W. Ng and M. Gielen, Chemistry and Technology Oxford University Press, Oxford, 1992, 608 pp. 

By an analogous route, the cyclization of chiral (z-amino imines 197, bearing the proper tw-functionality in the o -alkyl chain, will lead to 3-substituted 1,2-diaminocycloalkanes 198. The intermolecular and intramolecular addition of allylic silicon and tin compounds to a-amino azomethine compounds should also be investigated. 

Finally, because of the close relationship between silicon and tin, carbonyl compounds such as phenylacetaldehyde afford with the commercially available bis[bis(trimethylsilyl)amino]tin(II) 561, which is prepared by reaction of li-HMDS 492 with SnCl2, the N,N-bis(trimethylsilylated)enamine 562, in 85% yield, and SnO [131, 132] (Scheme 5.41). 

By explicitly showing the relationship between the elements, Mendeleyev was able to predict the existence and properties of elements that had not yet been discovered. He theorized, for example, that an undiscovered element should fall between silicon and tin on the periodic table. In 1880, German chemist Clemens Winkler isolated a new element, which he named germanium, that had exactly the properties that Mendeleyev predicted. 

Carbon-Carbon Bond-Forming Reactions of Compounds of Boron, Silicon, and Tin... 

In contrast to the transition metals, where there is often a change in oxidation level at the metal during the reaction, there is usually no change in oxidation level for boron, silicon, and tin compounds. The synthetically important reactions of these three groups of compounds involve transfer of a carbon substituent with one (radical equivalent) or two (carbanion equivalent) electrons to a reactive carbon center. Here we focus on the nonradical reactions and deal with radical reactions in Chapter 10. We have already introduced one important aspect of boron and tin chemistry in the transmetallation reactions involved in Pd-catalyzed cross-coupling reactions, discussed... 

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