Germylene

Cyclic Si-, Ge-, Sn- and Pb-analogs of carbenes and alkenes 99EJI373. Germylenes and germanium double-bonded species in heterocyclic organoger-manium chemistry 99KGS1155. 

Direct spectroscopic studies and calculations of cyclic silylene-to-silene and germylene-to-germene interconversions 99IZV2027. 

It is interesting to note that no examples are known for a retro-reaction of this dimerization. Such a reaction has been observed, however, for germylene complexes and for stannylene complexes, in some cases an equilibrium between uncomplexed and base-stabilized compounds has been found. 

Whether these results will also have an impact on the theory of metallaallenes is difficult to predict at least for the compounds Cp (CO)2Mn = M = Mn(CO)2Cp, (M = Ge, Sn, Pb) a linear structure is established and also linear p-carbido complexes are known [198], Recently, a germanium compound has been synthesized which is directly comparable with 22. In this case, the starting material for the synthesis is not a monomeric base adduct, but a dimeric germylene complex which is cleaved by Na2Fe(CO)4 in pyridine to form 72 [199],... 

Scheme 9 Saturated and unsaturated carbenes, silylenes and germylenes...

The chemistry of germanium(II) amidinates has been summarized in a review article by Kiihl under the title "N-Heterocyclic germylenes and related... 

A bis(chelate) structure was found for the closely related germylene [MeC(NPr )2]2Ge, which was also made from GeCl2(dioxane) and 2 equivalents of the lithium amidinate (colorless crystals, 81%). The same synthetic approach was used to make bis(amidinato) metal dichlorides of silicon and germanium in high yields (83-95%). Rapid oxidative addition of chalcogen atom sources (styrene sulfide and elemental Se) to the germylene derivatives resulted in a series... 

Another germaallene was also reported in 1998 by Okazaki et al. Initially, the report of a germaallene trap with chalcogens, alkylidenetelluragermirane 86a, appeared in 1997. The germylene precursor 82 is made in situ from dichloroger-mane 81 and two equivalents of lithium naphthalenide (Scheme 23). The addition... 

A number of close carbene analogues - silylenes and germylenes - have also been generated, stabilized in inert matrices and studied using the IR spectroscopic technique. 

In contrast to diazido compounds [102] and [104], which throw off two azido groups and form silylene and germylene, photodecomposition of silyl azide [105] led to the generation of aminosilylene [107] via isomerization of initially formed nitrene [106] (Maier et al., 1989b). The IR spectrum of the... 

It has become common to classify all molecular compounds, which fulfill the above characteristics, as carbene analogs 9,13>. As a consequence, compounds of divalent silicon, germanium, tin, and lead may be regarded as carbene-like and are therefore called silylenes, germylenes, stannylenes, and plumbylenes. In contrast to carbenes they have one property in common the energetically most favorable electronic state is the singlet 1a2 found by experiments and calculations 9). 

The stability of molecules depends in the first place on limiting conditions. Small, mostly triatomic silylenes and germylenes have been synthesized successfully at high temperatures and low pressures, 718). Their reactions can be studied by warming up the frozen cocondensates with an appropriate reactant, whereas their structures are determined by matrix techniques 17,18). In addition, reactions in the gas phase or electron diffraction are valuable tools for elucidating the structures and properties of these compounds. In synthetic chemistry, adequate precursors are often used to produce intermediates which spontaneously react with trapping reagents 7). The analysis of the products is then utilized to define more accurately the structure of the intermediate. 

Bis(amido)-germylene and -stannylene react with [Pt(COD)2] to give the platinum(O) complexes [Pt(M NTMS 2)3], M = Ge or Sn.78 The stannylene complex has a trigonal-planar structure with Pt—Sn bond lengths of 2.47-2.50 A.79... 

A variety of preparation methods are known for transient germanium-chalcogen double bond species some of them seemed to be useful also for the synthesis of kinetically stabilized systems. Indeed, the reaction of a germylene with an appropriate chalcogen source was found to be one of the most versatile and general methods for the synthesis of stable germanium-containing heavy ketones (Scheme 21). 

Most of them were prepared by the direct chalcogenation of the corresponding germylenes 92, 94, and 97 thermodynamically stabilized with the heteroatom... 

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