Dichlorogermylene

The first member of the new class of stable radicals, (t-Bu2MeSi)3Si 43, was synthesized by the one-electron oxidation of the silylsodium derivative (t-Bu2MeSi)3SiNa with dichlorogermylene-dioxane complex GeCl2 diox in Et20 (Scheme 2.35). ... 

The GeCNS ring resulted similarly10- from a dichlorogermylene reaction with an adamantylimidethione. In the ring, angles are close to 90°, Ge-C = 200.8 pm and Ge-N = 181.3 pm. 

Diethyl-1,3,2-dithiagermolane (336) reacts with the chromium pentacarbonyl complex of dichlorogermylene (in the form of solvate with THF) to give a cyclic germylene complex (337) which can be further stabilized with an additional nitrone ligand <87JOM(33i)ii>. 

A detailed examination of the reactivity of organo-aluminium derivatives of 0,0-bifunctional ligands has been undertaken,559 and the effect of substituents on the reversible rearrangements of chlorophosphane-dichlorogermylene ylides to trichloro-germylphosphanes has been investigated.560... 

The synthesis of the first cyclotrisilenes has required a longer time than for the cyclotrigermenes due to the lack of suitable stable silylenes, in contrast, for example, to the well-known dichlorogermylene-dioxane complex25. Therefore, the preliminary preparation of the silylene precursors, which can generate silylenes in situ, was necessary for the successful synthesis of cyclotrisilenes. Until now, only two examples of cyclotrisilenes have been reported in the literature, of which only one was structurally characterized. 

Trichlorogermane reactions involving participation of dichlorogermylene are not oxidation-reduction reactions in the usual sense of this term, though they are described by Gen/GeIV transfers. At the same time, the reductive properties of trichlorogermane can be illustrated by the reduction of nitrobenzenes to anilines. 

This reaction, inaptly named condensation reaction43, proceeds either by a nucleophilic substitution mechanism or by insertion of dichlorogermylene into the C—Cl bond. The nucleophilic substitution mechanism is doubtful. In accordance with quantum-chemical calculations, the negative charge in the anion GeCh- is distributed on chlorine atoms and a movement of anion to the cation from the rear results in Cl- loss and GeCl2 formation39. 

The insertion reaction can be easily modeled by using the dioxane complex of dichlorogermylene24,49. Kinetic investigation of the reaction with benzyl chloride was carried out50. The experimental data were in line with kinetic equation 9, which involves participation of a free dichlorogermylene in the insertion step (in dioxane solution, where the equilibrium is shifted to the left, the insertion reaction does not occur). 

The radical pathway in the hydrogermylation of isobutene is confirmed by formation of the oligomer 13, whose structure also testifies to a dichlorogermylene participation (equation 16)57. 

A concerted 1,6-cycloaddition of dichlorogermylene to d.v-hexatriene resulting in 1,1-dichloro-l-germacyclohepta-3,5-diene (22) was found for the first time (equation 24)63 67. 

It is noteworthy that the product of a possible 1,4-cycloaddition of dichlorogermylene to hexatriene, i.e. l,l-dichloro-2-vinyl-l-germacyclo-3-pentene, was not observed at all in the reaction mixture. 

Dichlorosilylene and dichlorogermylene are formed in the gas phase at 500-550 °C and can be trapped with 1,3-butadienes with the formation of substituted l,l-dichloro-2,5-dihydrometalloles 154 <2001RJC1438>. 

The mechanism of the formation of a three-membered unsaturated ring was clarified later, when this reaction was reexamined by the same authors in detail . They found that the reaction of dichlorogermylene-dioxane complex with one equivalent of f-BusSiNa in THF at —78 °C led to the formation of c ,frawi-l,2,3-trichloro-l,2,3-tris(tri-terf-butylsilyl)cyclotrigermene 7 in 98% yield (Scheme 4). The cis,trails conformation of 7 was established by NMR spectroscopy and X-ray analysis (Figure 3). Treatment of 7 with two equivalents of f-Bu3SiNa in TFIF at —78°C cleanly produced cyclotrigermene 5 (Scheme 4), which gives evidence that 7 is a precursor for 5. 

As shown by calculations, the carbenoid mechanism of dichlorogermylene insertion in ordinary C—Cl bond begins by electrophilic attack of the vacant p-orbital of the Ge atom on the electrons of the bond . The vacant p-orbital does not interact with the unpaired electrons of the chlorine atoms. When the distance between the reactants decreases and becomes close to the value of the C—Cl bond length, inactivated transfer of Cl to the germylene center occurs with formation of a radical pair, followed by its recombination. The closer the components of the radical pair, the smaller the probability of radicals movement away from one another. The theoretical interest concerning the details of the germylene insertion mechanism is continuing. Thus, a quantum-chemical examination of... 

Participation of dichlorogermylene was assumed to play the key role in these reactions, as shown in equation 32. Theoretical examination of the GeCL interaction with ethylene showed that formation of a three-membered cycle with a Ge-atom is energetically not profitable, and therefore asymmetric tt-complex 32 could be the intermediate instead of germacyclopropane 33 . Recent computations (DFT, Gaussian 94) confirmed the formation and calculated the geometry of such a complex in detail . The primary formation of 34 and 30 in commensurable amounts was confirmed by observing the Ge—H bond in the IR and NMR spectra of the reaction mixture after distillation and by the easy transformation of 34 to 30 under the reaction conditions . 

Figure 33 The structure of 3-dichlorogermylene-l,3-benzothiazole (Reproduced by permission from Angew. Chem. Internat. Edn., 1973, 12, 1002)...

---