Three-membered cyclic digermylenes stabilised by an N-heterocyclic carbene

Treatment of potassium salts of silole dianions with donor stabilised germanium dichlorides gave the anticipated silagermafulvenylidenes R(2)Si = Ge(Do) (R(2)Si = 1-silacyclopentadiendiyl, Do = N-heterocyclic carbene (NHC)) only as transient intermediates in a side reaction. They were detected by NMR spectroscopy and, in one case, the formal dimer, 2,4-disila-1λ(3),3λ(3)-digermetane, was isolated. The main products of these reactions are sila-bis-λ(3)-germiranes, i.e. directly interconnected digermylenes that are part of a three-membered ring. The structural data, supported by the results of density functional calculations confirm the digermylene nature of these products with a long inner cyclic Ge–Ge bond that decreases the inherent high ring strain in silagermiranes.