Germanium germylenes

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

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 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... 

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). 

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). 

Other five-membered germanium heterocycles were prepared by the Lewis acid-catalyzed C-H insertion of a germylene (Equation (15)),26 thermal dissociation of a germaketenethioacetal and trapping of the resulting germy-lene 11 (Equation (16)),27 and from the zircona-bicyclic complexes 12 and 13 (Scheme 2 and Equation (17)).28... 

Oxadative addition reactions of germylenes are a versatile method for the formation of germanium-pnictogen bonds.147-156 Reaction of germylenes with diazabutadienes yields [4+ 1]-cycloaddition products (Equation (115)),148... 

A germanium-nitrogen complex containing two Ge atoms disposed in an acyclic array was obtained via the formation of the intermediate germylene [(Me3Si)2N]GeCl, which was converted into a germanium(iv) adduct via an insertion reaction (Scheme 19).157... 

Germylenes can be released thermally in the presence of a transition metal complex leading to the formation of a germanium-metal bond (Equation (193)).239 The reaction occurs at room temperature when a germylsilane is used as the synthon (Equation (194)).240... 

The electronic properties of germanium have led to an interest in incorporating the element into extended polymeric chains due to the intrinsic properties of the polymers themselves or in their use as precursors for material synth-esis. Catalytic co-polymerization of the germylene Ge[N(SiMe3)2]2 with various substituted acetylenes leads to... 

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... 

Efforts to prepare germanium analogs of alkynes which contain Ge-Ge triple bonds have also met with some success.382-385 Reduction of the germylene 163 with a slight excess ( 5%) of potassium metal affords the germyne 172 (Equation (322)), which contains only one substituent at each germanium and a Ge-Ge distance of 2.2850(6) A... 

Germylene 185 can be reduced with substoichiometric amounts of KCg to give the cyclotrigermenyl radical 186, which has been structurally characterized (Equation (329)), while reaction of 185 with an excess (2 equiv.) of KC8 produces 187 which is the germanium analog of the allyl anion (Equation (330)).400 The structure of 187 has been obtained as well. 

As said previously, germylenes are obtained from digermenes 69 and 74 in solution60,63 and from tetrasilyldigermene 85 by photolysis.57 A similar phenomenon has already been reported,3 4,7,8 this phenomenon depending on the substituents on germanium. 

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)]. 

Reaction of germylenes with elemental chalcogens (sulfur, selenium, tellurium) also allowed the synthesis of stable >Ge = E species. This was first exemplified by the isolation of terminal chalcogenido complexes of germanium 170152 and 171-173153 (Scheme 34). Stabilization in these cases is achieved by intramolecular complexation of the metal atom by Lewis bases. 

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