Spirocyclic germanes via transannular insertion reactions of vinyl germylenes into Si-Si bonds

Tetryl-Tetrylene Addition to Phenylacetylene

Phenylacetylene adds [Ar*GeH2 -SnAr'], [Ar*GeH2 -PbAr'] and [Ar'SnH2 -PbAr*] at rt in a regioselective and stereoselective reaction. The highest reactivity was found for the stannylene, which reacts immediately upon addition of one equivalent of alkyne. However, the plumbylenes exhibit addition to the alkyne only in reaction with an excess of phenylacetylene. The product of the germylplumbylene addition reacts with a second equivalent of alkyne and the product of a CH-activation, a dimeric lead acetylide, were isolated. In the case of the stannylplumbylene the trans-addition product was characterized as the kinetically controlled product which isomerizes at rt to yield the cis-addition product, which is stabilized by an intramolecular Sn-H-Pb interaction. NMR chemical shifts of the olefins were investigated using two- and four-component relativistic DFT calculations, as spin-orbit effects can be large. Hydride abstraction was carried out by treating [Ar'SnPhC=CHGeH2 Ar*] with the trityl salt [Ph3 C][Al(OC{CF3 })4 ] to yield a four membered ring cation.

Cascade-Reaction Leading to an Intramolecular [2 + 4] Cycloaddition of a Phenyl Group by a Reactive Ge═Si Double Bond

The reaction of GeCl₂·dioxane with 2 equiv of the thiolate LiSHyp [Hyp = Si(SiMe₃)₃] yields the germanide (12-crown-4)₂Li[Ge(SHyp)₃] (1). A small structural variation in the substituent leads to a completely different result because the reaction of GeCl₂·dioxane with 2 equiv of the thiolate KSHyp^Ph₃ [Hyp^Ph₃ = Si(SiMe₃)₂(SiPh₃)] in toluene yields the unexpected compound [Ph₃Si][Me₃Si]Ge[{(C₆H₅)Ph₂Si}{SiMe₃}₂SiS]Si[SSiMe₃] (2) in high yield. The reaction cascade to give 2 includes several rearrangement reactions and an intramolecular [2 + 4] cycloaddition of a phenyl ring. The syntheses and molecular structures of both compounds are presented, together with quantum-chemical calculations and NMR measurements, to enlighten the reaction mechanism behind the formation of 2.

1,2- and 1,1-Migratory Insertion Reactions of Silylated Germylene Adducts

The reactions of the PMe₃ adduct of the silylated germylene [(Me₃Si)₃Si]₂Ge: with GeCl₂·dioxane were found to yield 1,1-migratory insertion products of GeCl₂ into one or two Ge–Si bonds. In a related reaction, a germylene was inserted with tris(trimethylsilyl)silyl and vinyl substituents into a Ge–Cl bond of GeCl₂. This was followed by intramolecular trimethylsilyl chloride elimination to another cyclic germylene PMe₃ adduct. The reaction of the GeCl₂ mono-insertion product (Me₃Si)₃SiGe:GeCl₂Si(SiMe₃)₃ with Me₃SiC≡CH gave a mixture of alkyne mono- and diinsertion products. While the reaction of a divinylgermylene with GeCl₂·dioxane only results in the exchange of the dioxane of GeCl₂ against the divinylgermylene as base, the reaction of [(Me₃Si)₃Si]₂Ge: with one GeCl₂·dioxane and three phenylacetylenes gives a trivinylated germane with a chlorogermylene attached to one of the vinyl units.

Reactions of GeCl2 with the Thiolate LiSC(SiMe3 )3 : From thf Activation to Insertion of GeCl2 Molecules into C-S Bonds

The reaction system GeCl₂ ⋅dioxane/LiSTsi (Tsi=C(SiMe₃ )₃ ) opens a fruitful area in germanium chemistry, depending on the stoichiometry and solvent used during the reaction. For example, the reaction of GeCl₂ ⋅dioxane in toluene with two equivalents of the thiolate gives the expected germylene Ge(STsi)₂ in excellent yield. This germylene readily reacts with hydrogen and acetylene, however, in a non-selective way. By using an excess amount of the thiolate and toluene as the solvent, the germanide [Ge(STsi)₃ ][Li(thf)] is obtained. Performing the same reaction in thf leads to a C-H activation of thf to give (H₇ C₄ O)Ge[STsi](μ² -S)₂ Ge[STsi]₂ , in which the thf molecule is still intact. Using a sub-stoichiometric amount of the thiolate leads to the heteroleptic compound [ClGe(STsi)]₂ and to the insertion product (thf)Ge[S-GeCl₂ -Tsi]₂ , in which additional GeCl₂ molecules insert into the C-S bonds of Ge(STsi)₂ . The synthesis and the experimentally determined structures of all compounds are presented together with first reactivity studies of Ge(STsi)₂ .