Divalent germanium compounds

Several organogermanium structures have recently been reported, and are herein included to up-date the literature surveyed. 

Interest in sterically hindered Group IVA ethers and thio-ethers continues, with the structure of [(C(iH5CH2)3Ge]2S (190) being added to those already reported (Section V). The Ge—S—Ge moiety is nonlinear (106.6°) and the overall structure is similar to that of [(CfiH5)3Ge]2S (113). 

Three cyclic organogermanium structures have appeared, embracing three-, four-, and six-membered ring systems. A triangular Ge3 

Finally the structure of [(CH3)5C5]2Ge(II) elucidated by electron diffraction (74) has been retracted (188). In the same report appears preliminary electron diffraction data on (T7-C5H4CH3)2Ge(II), an angu- 

The quality of the available data are generally of a reliable standard, particularly the more recent X-ray diffraction studies. Caution, however, must be exercised when evaluating much of the earlier gas phase work, in view of limitations in both contemporary instrumentation and experimental methods which usually require implicit assumptions about molecular geometry. Such data are generally best assessed in groups, and reliance given to systematic trends rather than absolute values. 

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Chalcogenation of a divalent germanium compound with styrene sulfide has been examined as an alternative route to the first free germanethione Tbt(Tip)Ge = S 165142 (Scheme 32) and later on allowed the synthesis of new base-stabilized germanethiones 187 and 188156 [Eq. (37)]. Phenyl isocyanate also may serve as a sulfur source leading to 165, which was evidenced by electronic spectroscopy and underwent a subsequent [2 + 2] cycloaddition with phenyl isocyanate157 (Scheme 36). 

Cyclic compounds containing Si2E2 rings (10.56, E = S, Se) are also formed from the reaction of a stable silylene with sulfur or selenium [eqn (10.37)]. The reaction of the divalent germanium compound Ge[N(SiMe3)2]2 with... 

Other divalent germanium compounds include salts of GeClj, such as the substituted pyrazolyl complexes [Ge2(pz )3][GeCl3] (8-XXII) which is obtained in the reaction of Ba(pz )2 with GeCl2-dioxane.148 There are also a sulfide, GeS, several thiolato complexes,149 and a white to yellow hydroxide of no definite stoichiometry that is converted by NaOH to a brown material that has Ge—H bonds. 

Kobayashi prepared a novel germanium-containing polymer, poly(germanium enolate), by reaction of a divalent germanium compound, germylene, with a cyclic a, -unsaturated ketone in the presence of a catalytic amount of a lithium compound (Scheme 11.65) [91[. 

It is apparent from most of the examples previously described that the most common formal oxidation state found for the Group 14 element is E(IV) (E = Ge, Sn, Pb). Relatively few examples of divalent germanium, tin, or lead complexes have been described, and of these, many are not well characterized. Cobalt-containing compounds are no exception in this regard and there appears to be only one report in the literature that describes a species of this type, viz. [Ge Co(CO)4 2], 67, although the precise structure of this complex is unknown (77). Two main synthetic routes are described, Eqs. (4) and (S), the starting complex in the latter reaction being... 

A truly divalent germanium complex with a Cr—Ge bond is found in the macrocycle-containing compound (tmtaa)Ge—Cr(CO)5174 in which the local geome-... 

Divalent germanium has been used as a reducing agent for the determination of mercury in soils and sediments (Zelyukova et al., 1987). In alkaline solution, also organic mercury compounds were reduced. The detection limit can be estimated at about... 

For group 14, whereas divalent carbon and silicon (carbenes and silylenes) are typically highly reactive, divalent germanium is considerably more stable. Divalent tin salts are quite stable, although still relatively reducing. By contrast, divalent lead salts are very stable and tetravalent lead compounds are potent oxidants the cleavage of vicinal diols by lead tetraacetate is a good example of the latter ... 

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