Silicon, or Germanium Compounds

Chemical and stereochemical properties of compounds with silicon- or germanium-transition metal bonds. E. Colomer and R. J. P. Corriu, Top. Curr. Chem., 1981, 96, 79-107 (68). 

Colomer, E., and Corriu, R. J. P. Chemical and Stereochemical Properties of Compounds with Silicon or Germanium-Transition Metal Bonds, 96, 79-110 (1981). 

Chemical and Stereochemical Properties of Compounds with Silicon or Germanium-Transition Metal B(nids... 

Silicon and germanium hydrides react with cobalt, manganese and rhenium carbonyls affording complexes having a silicon (or germanium)-metal bond. These reactions, described previously for inactive compounds have been used in the synthesis of optically active silyl and germyl-transition metals ... 

Most of the reactions of silicon or germanium organic compounds proceed photochemically via a radical mechanism or via a cycloaddition mechanism (Chapters 4 and 6). There are few examples of nucleophilic addition of RSi or RGe to Cgo [118,119]. Reaction of silyUithium derivatives RjSili or germyllithium derivatives RjGeLi with different alkyl- and aryl-substituents R yields mainly the 1,2-adduct 28 or the 1,16-adduct 29 1,4-addition and dimerization of two fullerene-units was also found as a minor pathway. One example is given in Scheme 3.15. 

Similarly, a primary — CH2F fluorine adjacent to silicon is shielded by about 50 ppm compared to the respective hydrocarbon, with similar tin or germanium compounds being shielded slightly less. The value of -277 ppm observed for tetrakis(fluoromethyl)silane has the largest chemical shift known for a single carbon-bound fluorine (Scheme 3.40). 

Silicon and germanium compounds of the R4- MX (X = halogen n = 2,4) series interact with bases (B) forming complexes of 1 1 and 1 2 composition (the latter are more stable) in which the coordination number of M is 5 or 6, respectively. However, there exist several intramolecular complexes of Si and Ge in which the coordination number of M is 7. 

For the carbon, silicon, and germanium compounds considered here, this should not lead to exceptionally large errors, because H for M substitution generally changes BDEs by 4 kcal/mol or less. 

Many of the results reviewed here suggest that a replacement of the usual alkyl or aryl substituents by silyl substituents in unsaturated silicon and germanium compounds may be rewarding. As we noted, silyl substituents do tilt the properties of silylenes, silyl radicals, and sequential BDE trends toward those in carbon chemistry. They have already been shown to stabilize disilenes with respect to dissociation to two silylenes, and this may be crucial to the further development of digermene and distannene chemistry. 

Electron diffraction determinations " Intermolecular contacts in Table 11 Silicon-transition-metal compounds in Table 10 Averaged two-bond contacts between oxygen and silicon or germanium Mes = 2,4,6-trimethylphenyl See the text... 

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