Pentacoordinate germanium complexes

Quite recently, it was established that the formation of the pentacoordinated germanium and tin compounds EF4(CH2CH=CH2) from EF3(CH2CH=CH2) (E = Ge, Sn) by the addition of F is exothermic148. The nucleophilicity of the allylic y-carbon is much enhanced when the pentacoordinated EF4(CH2CH=CH2) is formed. These results are qualitatively similar to those found for the reaction of the corresponding silicon compound. The pentacoordinated Ge and Sn complexes have a significant Lewis acidity which allows them to form stable hexacoordinated intermediates in the course of the reaction. 

Holmes and his coworkers described a number of pentacoordinated anionic germanium complexes containing a spirocyclic framework with methyl, phenyl, halogen or hydroxyl ligand at the acyclic site307,332,333. Reaction of an organogermanium trichloride with a catechol or thiocatechol derivative in the presence of triethylamine, followed by a metathetical exchange, led to desired products as illustrated by the formation of the phenyl-substituted derivatives 90 and 91 (equation 16)333. 

Tacke and his coworkers have recently reported the synthesis and structural characterization of a series of pentacoordinated anionic germanium complexes based on the Ge04C ligand framework340-344. The route to these compounds involves the reaction of (chloromethyl)trimethoxygermane with a secondary amine in the presence of triethy-lamine, followed by an exchange with two equivalents of bidentate ligands, such as aromatic 1,2-diols or a-hydroxycarboxylic acids, as shown for the synthesis of 114340 (equations 22 and 23). 

Among neutral pentacoordinate intramolecular germanium complexes, compounds containing a C,0-chelating ligand have been most extensively studied. 

Holmes and his coworkers described a number of pentacoordinated anionic germanium complexes containing a spirocyclic framework with methyl, phenyl, halogen or hydroxyl ligand at the acyclic Reaction of an organogermanium trichloride with... 

Various monocyclic and bicyclic pentacoordinate anionic germanium and tin complexes are known which possess bidentate dianionic oxo and related ligands, such as aliphatic or aromatic 1,2-diols, a-hydroxy carboxylic acids and their thio analogues (for early references see References 191, 307-309). Anionic mono- and bis-chelated germanium and... 

SCHEME 6. Relationship between trigonal bipyramid and rectangular pyramid for pentacoordinated spirocyclic germanium and tin complexes... 

P-diketones, a pentacoordinate structure of these complexes was proposed in which the central germanium atom acquires the TBP geometry. 

Hypervalent compounds of organic germanium, tin and lead derivatives 1007 TABLE 14. X-ray data for pentacoordinate anions in chelate triphenyltin complexes... 

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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