Silicon complexes with germanium

Fischer-type carbenes are known as potential carbene transfer reagents to electron-rich and electron-deficient alkenes. Little is known about the chemistry of carbene complexes with silicon substituents at the carbene C-atom, whereas complexes with germanium, tin, or lead have not yet been prepared. The tungsten-carbene complexes 6 react with an excess of ethyl vinyl ether to give l,2-diethoxy-l-(trialkylsilyl)cyclopropanes 7." Only the f-isomers were formed and similar results can be achieved by using the corresponding molybdenum or chromium complexes. On the other hand, no reaction takes place with 2,3-dihydrofuran or ethyl ( )-but-2-enoate. ... 

Thus, several complexes with platinum-silicon or germanium bonds have been obtained ... 

Complexes with silicon (or germanium)-transition metal bonds in which silicon or germanium is optically active are very stable both chemically and optically. 

X-ray investigations have indicated a very similar structure of the free ligand as compared to their complexes with silicon (see Sect. 4.4.3) and germanium 2 21. 

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. 

Complexes with type I.II ligands are usually referred to as boron (tin, germanium, silicon, antimony)-capped macrobicyclic dioximates (oximehydrazonates, azineoximates). Their abbreviated... 

W. Petz, Transition Metal Complexes with Derivatives of Divalent Silicon, Germanium, Tin, and Lead as Ligand", Chem. Rev. 1986, 86, 1019. 

In the analysis of a number of materials (e.g., silicon- and germanium compounds and volatile reagents) traces of boron are pre-concentrated and boron is then separated by volatilization of the matrix. Mannitol, which forms a non-volatile complex with boric acid, is added to retain all the boron present in the residue [20]. Boron is fairly volatile in acidic media. While boron traces are determined in chlorosilanes, it is advisable to add some chlorotriphenylmethane [21], which forms a non-volatile compound with boron thus preventing its volatilization, when the matrix is evaporated. Ref. 21 is not cited. 

Phenylfluorone also forms coloured complexes with many metals, e.g., Sn, Sb, Ti, Fe(III), Nb, and Ta. Low concentrations of arsenic, silicon, and fluoride do not interfere in the formation of the germanium complex. Citric and oxalic acids are used to mask Mo, V, Sn, and Ti [19,20]. Preliminary separation of germanium as GeCU by extraction or distillation renders the phenylfluorone method specific for germanium. 

An evoked possibility of n-type doping of diamond with sulphur [219] has aroused an interest for the electronic properties of this element in diamond. It is now well established that, as expected from the properties of chalcogens in silicon and germanium, S behaves in diamond as a deep donor, with an ionization energy of 1 eV for S°, predicted from the ab initio DFT calculations [177]. However, the existence of S-related complexes with native defects or impurities like B is a possibility which could explain some appealing experimental results ([37], and references therein). 

A disadvantage of the method depicted in Scheme 8.2 is the low yield of the tetragermabutadiene of merely 10%. Very recently, we have found that the reaction of the germanium(II) chloride dioxane complex with the Grignard compound 31 affords compound 30 in one step and in a yield of more than 30%. We will next investigate whether 30 can participate in similar reactions to those of its silicon analogue 6. 

The metalloid elements include boron, silicon, germanium, arsenic, antimony, tellurium, and astatine. Ligand exchange reactions complete much faster for silicon complexes when compared with carbon complexes because the silicon atom can form a hypervalent transition state that carbon cannot. 

By variation of the substitution pattern of the amidinate ligands and of the silicon or germanium coordination centers, we obtained a number of compounds with a variable degree of Si/Ge-N hypervalent interaction, i.e. compounds with essentially no bones and ones with very strong element-nitrogen bonds ( double bonds ) are formed, providing tetra-, penta- or hexa-coordinated species [4], New or newly structurally characterized examples of silicon amidinate complexes with pentacoordinate silicon are obtained (Eq. 1 Table 1). 

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