Silicon germanium halides

The crux of organic mechanistic stereochemistry may be the Walden inversion, the inversion of stereochemistry about a four-coordinate carbon atom by nucleophilic attack of, for example, a hydroxide ion on an alkyl halide. Many reactions of inorganic molecules follow the same mechanism. In contrast, the dissociative mechanism of tertiary halides to form tertiary carbocatanion intermediates is essentially unknown among the nonmetallic elements silicon, germanium, phosphorus, etc. The reason for this is the generally lower stability of species with coordination numbers of less than 4, together with an increased stability of five-coordinate intermediates. This difference is attributable to the presence of d orbitals in the heavier elements (Chapter 18). 

Reduction of halides (X) with zinc and hydrochloric acid. bles carbon and tin resembles silicon Germanium resem-... 

Of all the reactions studied, only the synthesis of nitrogen oxides and acetylene in arcs or plasma torches and that of ozone in glow and corona discharges are of major importance. In addition, a few small-scale preparations of inorganic compounds have been developed, e.g. synthesis of hydrazine and of hydrides and halides of silicon, germanium, tin, lead, phosphorus or arsenic 3> ... 

The reaction of the appropriate halides with diazomethane is an elegant laboratory-scale method for the synthesis of halomethyl derivatives of silicon, germanium, tin, and lead.1-4 However, good yields are obtained only with the following types ... 

All of the binary tetrahalides of carbon, silicon, germanium, and tin have been made, and many mixed halides (of the type SiCl2F2) have also been characterized. Except for SnF4 (the most saltlike of the group), all of the tetrahalides are volatile. It is interesting (and not easily explained) that aside from CF4 and SiF4, the tetrahalides of silicon boil at lower temperatures than those of carbon. 

Nucleophilic carbenes have been reported to react with Eewis acidic group 14 complexes with the isolation of neutral or ionic compounds via simple adduct formation or displacement of a halide ion. > The range of carbene complexes of silicon, germanium, tin, and lead, as well as some related cyclopropenylidene complexes are described below. 

Analogous to the mentioned halides of silicon, germanium, and tin, beryllium chloride, (as its adduct with THF) react with 62 in ether at low temperature to form tetrazenide 65, as in Eq. (82). Compound 65... 

In the benzoin condensation, one molecule of aldehyde serves as an electrophile. If a carbanion is generated from protected cyanohydrins, a-aminonitriles or dithioacetals, it can react with electrophiles such as alkyl halides, strongly activated aryl halides or alkyl tosylates to form ketones. Amongst other electrophiles which are attacked by the above carbanions are heterocyclic A -oxides, carbonyl compounds, a,p-unsaturated carbonyl compounds, a,3-unsaturated nitriles, acyl halides, Mannich bases, epoxides and chlorotiimethyl derivatives of silicon, germanium and tin. 

Azarian, D., Dua, S. S., Eaborn, C., Walton, D. R. M. Reactions of organic halides with R3MMR3 compounds (M = silicon, germanium, tin) in the presence of tetrakis(triarylphosphine)palladium. J. Organomet. Chem. 1976,117, C55-C57. 

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