Polygermanes preparation

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. 

Figure 1. Polycyclic polysilanes and polygermanes prepared via reductive coupling of RMX3 or RX2M-MX2R...

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. 

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... 

Like polysilanes, polygermanes can be decomposed and volatilized by exposure to radiation of the appropriate frequency. They have been considered for microlitho-graphic applications.42,43 Because they are more difficult and more expensive to prepare, and have no obvious advantages over polysilanes, they have not found much use to date in this type of application. 

A very efficient catalytic process for the high-yield preparation of permethylated polygermanes 9 starting from trimethylgermane was reported by Berry and coworkers65 (Scheme 6, Table 2, entries 12 and 13). In the catalytic cycle, element-element bonds are produced and methane is eliminated. The proposed mechanism for the formation of linear and branched polygermanes is shown in Schemes 7 and 8. 

TABLE 2. Representative examples for the preparation of polygermanes using different methods... 

C-O bond cleavage is most efficiently set up in strained systems, e.g. in oxiranes [26] and oxetanes [27], whereas 0-0 bond cleavage in cyclic peroxides [28] and C-S [29] and C-Se [30] bond rupture occur efficiently even in unstrained compounds. Si(Ge)-Hal bond cleavage [31] has become a valuable reaction, e.g. in the preparation of network polysilanes and polygermanes [32]. 

A magnesium sacrificial anode is also effective for the synthesis of Si-Ge and Ge-Ge bonds. This method is quite successful for the preparation of polygermanes and germane-silane copolymers [Eq. (49)] [183]. Polygermanes were also prepared by conventional electrochemical reduction of dihalogermanes using a Pt cathode and an Ag anode [184]. 

The usual procedure in preparations of polysilanes and polygermanes is to circulate the simple hydride through an ozonizer-type discharge until practically all of it has decomposed and the gas being circulated is principally hydrogen. The product hydrides are trapped out in a suitable cold trap in the gas circuit. If the desired product vapors were allowed to circulate continually through the discharge, the product would... 

The triphenylgermylmetallic reagents are very versatile precursors of polygermanes. Of particular interest is the possibility of preparing un-symmetrically substituted digermanes 151,151a). As might be anticipated,... 

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