Polygermane

Soluble and weU-characterized polygermane homopolymers, (R Ge), and their copolymers with polysdanes have been prepared by the alkaH metal coupling of diorgano-substituted dihalogermanes (137—139), via electrochemical methods (140), and by transition-metal catalyzed routes (105), as with the synthesis of polysdanes. 

Recently increasing interest is evident in polymers bearing group 14 atoms. Polygermane and germane-silane polymers show properties such as semiconductivity, photoconductivity... 

The method for preparation of polygermanes by reduction of organodichlorogermanes with alkali metals was replaced by electroreduction of organodichlorogermanes and silanes on magnesium cathodes214. The conditions were mild and safe and the product had a satisfactorily defined weight distribution. Ge—Ge and Ge—Si bonds are successfully created. The following test reactions have been performed to show that conditions are indeed favorable for metal-metal bond formation ... 

Polygermanes and germane-silane polymers were prepared similarly. Polygermanes from the electroreduction of dichlorophenylbutylgermane showed typically a molecular weight of Mn = 19900 (10% yield). Germane-silane copolymers showed similar M values. The Ge/Si ratio in mixed polymers was roughly proportional to the ratio of monomers... 

TABLE 27. Oxidation of polygermanes and reduction of the oxidized form215... 

Since the field was last reviewed,1 a number of linear and cyclic oligogermanes have been reported, as have a number of new methods for the synthesis of polygermanes. The Ge-Ge single bond length is typically considered to be approximately 2.45 A, which is twice the atomic radius of germanium. 

Singly bonded oligo- and polygermanes undergo various electron-transfer processes. The digermacyclohex-... 

The testing of germanium halide derivatives of other bulky substituents such as Bu did not afford (GeBu% species. Instead, a variety of polygermane species with interesting structures were isolated [38]. The use of the more bulky -CMeEt2... 

Polymer or polymer network with a skeletal strueture that does not inelude carbon atoms. Note Examples include polyphosphazenes, polysilieates, polysiloxanes, polysilanes, polysilazanes, polygermanes, polysulfides, ete. 

Much of the interest in the polysilanes, polygermanes, and polystannanes involves their sigma delocalization and their sigma-pi delocalization when coupled with arenes or acetylenes. This is not unexpected since silicon exists as a covalent network similar to diamond. In exhibiting electrical conductivity, germanium and tin show more typical metallic bonding. Some polystannanes have been referred to as molecular metals. ... 

Very intense and sharp near-UV absorption bands due to radical ions of polysilanes [53a,b] and polygermanes [53c] were observed by nanosecond pulse radiolysis. Broad visible and IR absorption spectra due to the radical ions of polysilyne [54] and polygermyne [54] were also observed. Very systematic pulse radiolysis studies on many different kinds of polysilanes [55] have been made by our improved nanosecond pulse radiolysis system over a wide range of... 

Berry and co-workers have reported a new method for the synthesis of moderate to high molecular weight polygermanes in very high yields by the catalytic coupling of tertiary germanes.83 This ruthenium-catalyzed process appears to be the first example of a catalytic demethanative coupling, in which element-element bonds are produced with the concurrent elimination of CH4 [Eq. (58)]. 

The catalyst, Ru(PMe3)4(GeMe3)2, is active at levels as low as 0.01 mol%, depending on monomer purity. As the catalyst is prepared from the reaction of HGeMe3 with Ru(PMe3)4Me2, this more readily obtainable ruthenium complex can be used directly in the polymerization as a convenient catalyst precursor. The properties of the polygermanes prepared with either complex appear to be identical. 

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