Influence of anellation in unsaturated heterocyclic diaminogermylenes

The influence of anellation on the properties and structures of heterocyclic diaminogermylenes was studied. Benzo- and pyrido-anellated cyclic germylenes 1,2-C6H4[N(CH2' BU)](2)Ge (1) and 2,3-C5H3N[N(CH2' BU)](2)Ge (2) were synthesised by dilithiation of aromatic ortho-diamino compounds C5H3X[N(CH2' Bu)](2) (X = CH, N) with BuLi and subsequent reaction with GeCl2(dioxane), the non-anellated but analogously N,N ' -disubstituted C2H2[N(CH2' Bu)](2)Ge (3) was obtained by reductive metalation of N,N'-dineopentyl-glyoxal diimine with lithium and cyclisation with GeCl2(dioxane). Crystal structure determinations on 1-3 give evidence on their monomer nature and lack of interactions between Ge(II) and the basic pyridine N-atom in 2. Spectroscopic data and structures of anellated and non-anellated compounds were compared. The sensitivity to distortions of bond lengths in the germylene 3 as compared to 1 and 2 may hint to a lower stability of the non-anellated diazagermoline-2-ylidene pi -system as compared with the 10 pi -system in the anellated compounds 1 and 2, which are favoured by the intrinsic stability of the o-arenediimine fragment. (C) 2001 Elsevier Science Ltd. All rights reserved.