Germylene compounds

This is confirmed by a very similar homologous germylene compound [85] that has two annulated quinoxaline units on an eight-membered germylene ring system. There, the germanium centre is sufficiently electron deficient to ligate a chloride anion, i.e. it acts as an electrophile not as a nucleophile. 

Figure 1.22 Calculated occupancy of the carbene center in modei carbene, siiyiene, and germylene compounds [13].

Poly(germaniiim enolate) (186) has been synthesized as shown in Scheme 46.2 0,261 jjj order to form a polymeric material, a,P-unsaturated carbonyl compound was required to react with a germylene in the presence of a lithium catalyst such as LiCl or LiR. It was believed that initial formation of a germyl anion species was achieved by coordination of the Li catalyst to the germylene compound. 

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],... 

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. 

Compared with the corresponding organosilicon compounds, the Ge derivatives are less stable and decompose at lower temperatures21. Thermolysis mechanisms as deduced from gas-phase studies are consistent with the presence of germylenes as intermediates. 

Interest in divalent compounds of germanium has increased steadily over the past several years, and many new species have been prepared. In particular, unsymmetrical heteroleptic species GeLL have become much more prevalent. Several reviews covering the synthesis and chemistry of germylenes have appeared, and the... 

The addition reaction of germylenes to unsaturated compounds is well known.331 Addition of germylene 50 to tetramethylbutatriene furnishes a germacyclopropane with two exocyclic C=G double bonds (Equation (271)).332 A sterically encumbered diarylgermylene undergoes addition to the C-G triple bond of an electron-poor alkyne to yield a germacyclopropene (Equation (272)).333... 

The other important type of reaction leading to the formation of two bonds between a metal and four-atom fragment is addition of carbenoids, i.e. germylenes and stannylenes, to a-dicarbonyl and related compounds. The process can be classified as redox (4 + 1) cycloaddition since the dicarbonyl fragment is reduced while the carbenoid is oxidized. Formally the simplest example of such reactions is the interaction of methylglyoxal with activated tin metal to give a cyclic stannylene, Sn(II) enediolate (see Scheme 34) <83CL1825>. 

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