Dichlorogermylene complexes

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). ... 

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>. 

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 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 complex . 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. 

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. 

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 . 

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