Hydrometallation of iPr2 N-Ge(CMe3 )(C≡C-CMe3 )2 with H-M(CMe3 )2 (M=Al, Ga) affords alkenyl-alkynylgermanes in which the Lewis-acidic metal atoms are not coordinated by the amino N atoms but by the α-C atoms of the ethynyl groups. These interactions result in a lengthening of the Ge-C bonds by approximately 10 pm and a comparably strong deviation of the Ge-CC angle from linearity (154.3(1)°). This unusual behaviour may be caused by steric shielding of the N atoms. Coordination of the metal atoms by the amino groups is observed upon hydrometallation of Et2 N-Ge(C6 H5 )(C≡C-CMe3 )2 , bearing a smaller NR2 group. Strong M-N interactions lead to a lengthening of the Ge-N bonds by 10 to 15 pm and a strong deviation of the M atoms from the MC3 plane by 52 and 47 pm, for Al and Ga, respectively. Dual hydrometallation is achieved only with HAl(CMe3 )2 . In the product, there is a strong Al-N bond with converging Al-N and Ge-N distances (208 vs. 200 pm) and an interaction of the second Al atom to the phenyl group. Addition of chloride anions terminates the latter interaction while the activated Ge-N bond undergoes an unprecedented elimination of EtN=C(H)Me at room temperature, leading to a germane with a Ge-H bond. State-of-the-art DFT calculations reveal that the unique mechanism comprises the transfer of the amino group from Ge to Al to yield an intermediate germyl cation as a strong Lewis acid, which induces β-hydride elimination, with chloride binding being crucial for providing the thermodynamic driving force.

Treatment of alkynyl-arylchlorogermanes ArylnGe(Cl)(C[triple bond, length as m-dash]C-(t)Bu)3-n (n = 1, 2) with HM(t)Bu2 (M = Al, Ga) yielded mixed Al or Ga alkenyl-alkynylchlorogermanes via hydrometallation reactions. Intramolecular interactions between the Lewis-basic Cl atoms and the Lewis-acidic Al or Ga atoms afforded MCGeCl heterocycles. The endocyclic M-Cl distances were significantly lengthened compared to the starting compounds and indicated Ge-Cl bond activation. Dual hydrometallation succeeded only with HGa(t)Bu2. One Ga atom of the product was involved in a Ga-Cl bond, while the second one had an interaction to a C-H bond of a phenyl group. In two cases treatment of chlorogermanes with two equivalents of HAl(t)Bu2 resulted in hydroalumination of one alkynyl group and formation of unprecedented Ge-H functionalized germanes, Aryl-Ge(H)(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2)[double bond, length as m-dash]C(H)-(t)Bu] (Aryl = mesityl, triisopropylphenyl). The Al atoms of these compounds interacted with the α-C atoms of the alkynyl groups. Ph(Cl)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2}[double bond, length as m-dash]C(H)-(t)Bu] reacted in an unusual Cl/(t)Bu exchange to yield the tert-butylgermane Ph((t)Bu)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C{Al((t)Bu)(Cl)}[double bond, length as m-dash]C(H)-(t)Bu]. Quantum chemical calculations suggested the formation of a germyl cation as a transient intermediate.

A series of alkenylhydrogermanes, RR′(H)Ge‐C(AlR′′2)=C(H)‐tBu [4a, R = R′ = Mes, R′′ = tBu; 4b, R = R′ = Mes, R′′ = CH(SiMe3)2; 5a, R = R′′ = tBu, R′ = CH2CH2tBu; 5b, R = tBu, R′ = CH2CH2tBu, R′′ = CH(SiMe3)2], was synthesized by hydroalumination of the respective alkynylgermanes, RR′(H)Ge‐C≡C‐tBu 3, with R′′2Al–H [R′′ = tBu, CH(SiMe3)2]. In the solid state compound 5b showed a contact between Al and the Ge bound H atom (293 pm) which according to quantum chemical calculations results in Ge–H bond activation. In case of less bulky substituents on Al (5a, R′′ = tBu) a mixture of isomers was observed that reacted with Et2NH to yield the simple Lewis acid‐base adduct [(tBu)(tBuCH2CH2)(H)Ge‐C(AltBu2)=C(H)‐tBu](HNEt2) (6). 6 features a dihydrogen bond (Ge–H···H–N) as evident from typical downfield (N–H) and high‐field (Ge–H) shifts in the NMR spectrum, red shifts of νGe‐H and νN‐H in the IR spectrum, a short H···H contact (210 pm) in the solid state and a bond critical point between both H atoms. The presence of a hard Lewis‐acidic Al atom in geminal position to the Ge–H bond in 5a facilitates reactions with Ph2CO, OC4H8N‐C≡N and Ph–NCO under surprisingly mild conditions by hydrogermylation of the heteronuclear π‐bonds and formation of four‐membered Ge–O/N–Al–C (7, 9) or six‐membered Ge–N–C–O–Al–C (8) heterocycles. Reaction with Ph–C≡C–H afforded the cis‐addition product 10, in which the α‐C atom of the new alkenyl group showed a close contact [258.3(2) pm] to the Al atom.

Hydroalumination of the dialkynylgermane Ph2Ge(C≡CtBu)2 (1) and the digermanes Phn(tBuC≡C)3–nGe–Ge(C≡CtBu)3–nPhn (2a: n = 2; 2b: n = 1) with two equivalents of H–AltBu2 or H–AlEt2 yielded the mixed Al/Ge compounds Ph2Ge[C(AltBu2)=CH‐tBu]2 (3), [Ph2GeC(AltBu2)=CH‐tBu]2 (4a), and [Ph2GeC(AlEt2)=CH‐tBu]2 (4b). Reactions of 2b with both aluminum hydrides afforded inseparable mixtures of products. 3 reacted with heterocumulenes by retrohydroalumination. Phenyl isocyanate gave insertion of the C=N group into the resulting Ge–C(≡C–tBu) bond (5), whereas the NCS and NCN groups of phenyl isothiocyanate and a carbodiimide inserted into Al–Cvinyl bonds (6 and 7) with unaffected terminal Ge–C≡C–tBu moieties. The generation of 5 represents the first example of the insertion of a heterocumulene into a Ge–C bond, which may be favored by the activation of the isocyanate group by the Lewis acidic Al atom and the increased polarity of the N=C=O fragment as determined by NBO calculations. The reactions of the digermanes 4 with heterocumulenes were unselective and afforded inseparable mixtures. Treatment of 4a with the azide (4‐tBu)C6H4CH2–N3 led interestingly to reductive coupling of two azide molecules, and the hexazene complex (tBuC6H4CH2N3–N3C6H4tBu)(AltBu2)2 (8) was isolated in moderate yield. Six nitrogen atoms form a dianionic chain, which coordinated two AltBu2 fragments by formation of two joint AlN4 heterocycles.

Alkenylchlorosilanes functionalized by coordinatively unsaturated Al atoms, R′′(R′)Si(Cl)C(AltBu 2 )=C(H)R 5 [R = tBu, cHex, 1-Ad, Ph, 3,5-(F 3 C) 2 C 6 H 3 ; R′ = Mes, Ph, 4-tBuC 6 H 4 , 4-tBuOC 6 H 4 , 4-Et 2 NC 6 H 4 , tBu; R′′ = Mes, CH(SiMe 3 ) 2 , tBu], were obtained in good yields by hydroalumination of the respective alkynylchlorosilanes R′′(R′)Si(Cl)C≡C-R 3 with t Bu 2 Al-H. They feature four-membered, close to planar SiCAlCl heterocycles by intramolecular Al-Cl interactions. The activation of the Si-Cl bonds results in bond lengthening from about 209 pm in 3 to 220 to 225 pm in compounds 5. The 29 Si NMR resonances show an increasing shift to a lower field and range from δ = 24.0 for 5a [R = tBu, R′ = R′′ = Mes] to δ = 68.1 for 5j [R = R′ = R′′ = [a]