Hydroalumination of Oligoalkynylgermanes and ‐digermanes – Reactions with Heterocumulenes by Al–C or Ge–C Bond Activation and Formation of a Hexazenedialuminum Complex

Abstract

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.