Germanium halides—

Gep2 is formed as a volatile white solid (mp 110°) by the action of Gep4 on powdered Ge at 150-300° it has a unique structure in which trigonal pyramidal [GePsI units share 2 P atoms to form infinite spiral chains (Pig. 10.2). Pale-yellow GeCl2 can be prepared similarly at 300° or by thermal decomposition of GeHCls at 70°. Typical reactions are summarized in the scheme  

GeBr2 is made by reduction of GeBr4 or GeHBr3 with Zn, or by the action of HBr on an excess of Ge at 400° it is a yellow solid, mp 122°, 

The ternary Ge halides, MGeX3 (M = Rb, Cs X = Cl, Br, I) are polymorphic with various distorted perovskite-like (p. 963) structures which reflect the influence of the nonbonding pair of electrons on the Ge centre. Thus, at room temperature, rhombohedral CsGel3 has three Ge-I at 275 pm and three at 327 pm whereas in the high-temperature cubic form (above 277°C) there are six Ge-I distances at 320 pm as a result of position changes of the Ge atoms (reversible order-disorder transition). Again, RbGel3 has a lemon-yellow, orthorhombic form below —92° an intermediate, bordeaux-red orthorhombic perovskite form (—92° to —52°) a black rhombohedral form (—52° to —29°) and 

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In order to test the generality of the synthesis, the reaction of (CzFsljHg with Gel was assessed. This reaction required a higher temperature, 135°, before it proceeded measurably. (Pentafluoroethyl)ger-manium triiodide was the only (perfluoroethyl)germanium halide produced, in 54% yield (15). From this reaction, perfluoroethyl iodide was also isolated (in 30% yield). The reactions of GeBr4 with (CF3)2Hg and (C2F5)2Hg were similar in nature (16). 

D. Reduction and Oxidation of Germanium Halides (see also Section XI)... 

Addition of an excess of organolithium or organomagnesium reagents to germanium halides results in the deplacement of the halide ions and the formation of tetra-alkyl and -arylgermanium compounds. Representative examples of these reactions are shown in equations 4 and 5, respectively. 

Common methods for the formation of germanium-carbon bonds, including reactions of germanium halides with organolithium or Grignard reagents, are still used and have yielded some interesting new compounds. In addition, several novel methods for Ge-C bond formation have also been developed since the field was last reviewed. 

The triphenylmethyl-substituted germanium halide 31 can be prepared in modest yield using GeCl4 and contains a formally seven-coordinate germanium metal center (Scheme 9). The structure of 31 (Figure 2, Table 11) is a tricapped tetrahedral structure where all the three Ge-O distances are shorter than the sum of the van der Waals radii (3.62 A). A series of hypervalent germanium halides 32-34 can be prepared, as shown in Scheme 10.95 The fluoride 32 is hexacoordinate, whereas the chloride 33 and bromide 34 are pentacoordinate. 

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... 

Other transition metal anions fail in giving the expected compounds . Germanium halides react more easily but are useless for the preparation of optically active compounds. Indeed, optically active bromo-germanes are not known, and chlorogermanes rapidly racemize in ether or tetrahydrofuran. ... 

With SiHsI phosphine probably forms silylphosphine and with (CH3)2BBr, crystalline H2PB(CH3>2 Germanium halides do not react with phosphine... 

The alkoxides of both oxidation states were obtained by metathesis of germanium halides (chlorides and iodides) with alkali alkoxides [1488, 1142, 857, 1535]. The yields can be increased by application of GeCl4 solvates with Py or NH3 or amines [3, 222] (method 5) and also by alcohol interchange of ethoxides (method 6) or alcoholysis of Ge[Si(NR3)2]2 [568, 1543] (method 4). The application of alkali alkoxides in the preparation of Ge(OR)4is possible in contrast to that of analogous derivatives of Sn(IV) and Zr due presumably to the much lower stability of corresponding alkoxogermanates the intermediate products of the corresponding reactions because of stability — of the tetrahedral coordination for Ge. The direct electrochemical preparation of Ge(OEt)4... 

The anionic polymerization of tris(pentafluorophenyl)germanium halide (49) was reported by Bochkarev et alJ58 to give Ge-based polymers (50 Scheme 6.14), a 9-Cascade germane[3] (2,3,5,6-tetrafluorogermanylidyne) pentafluorobenzene. These poly-... 

Catenated germanium halides are rare, in contrast to Si. The well-characterized polygermanium Ge2CU, a colorless solid, has been prepared. " An improved method involves passing GeCU at low pressure through a microwave discharge. ... 

Formation of Germanium-Transition and Inner Transition Metal Bond 5.8.4.3. from Germanium Halides... 

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