Germylenes dimerization

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],... 

The formation of transient 1,2-digermacyclobutadiene 9179 was postulated in the reaction of TsiGeCl LiCT 3THF78 with Mg in the presence of diphenylacetylene. This reaction could involve the formation of the digermyne intermediate 92 generated from 93 formed by dimerization of the germylene anion radical 94 [Eq. (18)]. 

Intramolecular Lewis base complexation of the germanium atom also did not appear to be a valuable alternative to overcome the lability of these elusive intermediates, since the germanones expected from oxidation of the base-stabilized germylenes 140131 (with Me3NO) and 141132 (with 02, DMSO, or pyridine oxide) either rearrange as already mentioned [Section VI,A,4, Eq. (33)]131 or dimerize to digermadioxetane 160132 [Eq. (35)]. 

Quantum-chemical calculations have been used to probe all the characteristic chemical reactions of CAs (at least in the case of silylenes and germylenes). The theoretical studies cover intramolecular rearrangements, insertions into 0-bonds, additions to double and triple bonds and dimerizations. Note that experimental data on the mechanisms of these reactions are still scarce and the results of theoretical studies are needed to understand the main trends in the reactivity of germylenes, stannylenes and plumbylenes. 

Experimental aspects of the dimerization of germylenes, stannylenes and plumbylenes were discussed in a review363. Relations between the characteristics of ER2 (E = C, Si, Ge, Sn, Pb R = H, F) and the structure of their dimers E2R4 were studied theoretically by Trinquier and coworkers364-367. 

X-ray crystallographic analysis of the orange single crystals, which were obtained after the removal of inorganic salts and naphthalene, has revealed that the structure of the orange crystal is that of the digermene ( )-Tbt(Mes)Ge=Ge(Mes)Tbt 10, the dimer of the germylene Tbt(Mes)Ge 2225. The details of the structural analysis of 10 will be discussed later. 

Photolysis of mononuclear chlorogermyl metal carbonyl complexes yields binuclear bis(/r-germylene) metal carbonyl compounds (equation 53). The dimerization is believed to occur through a radical process8. 

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