An N-Heterocyclic Germylene and Stannylene with a 1,1’-Ferrocenylene Backbone and Dimesitylboryl N-Substituents

The diaminoferrocene derivative fc[NH(BMes₂)]₂ (1H₂; fc=1,1’-ferrocenylene, Mes=mesityl) was prepared from fc(NH₂)₂ and Mes₂BCl and used for the preparation of the N-heterocyclic tetrylenes fc{[N(BMes₂)]₂E} (1E, E=Ge, Sn) via the sodium amide fc[NNa(BMes₂)]₂ (1Na₂), which was obtained from 1H₂ and NaN(SiMe₃)₂. 1H₂ is inert towards LiN(SiMe₃)₂ or nBuLi. Its reaction with nBuLi in the presence of TMEDA afforded the TMEDA-coordinated lithium amide 1Li₂(TMEDA)₂. Crystallisation of 1Na₂ from THF furnished the adduct 1Na₂(THF)₃. The reaction of 1Na₂ with Me₃SiCl afforded 1(SiMe₃)₂. Attempts to obtain the thiourea fc{[N(BMes₂)]₂C=S} (1C=S) from 1Na₂ and Cl₂C=S were not successful. 1C=S is accessible from fc(NH₃)Cl₂, which is transformed to fc[(NH)₂C=S] (2) by reaction with Cl₂C=S and NEt₃ (4 equiv.), followed by conversion of 2 to fc{[N(SiMe₃)]₂C=S} (3) with Me₃SiCl and NEt₃ (2 equiv.) and subsequent reaction of 3 with Mes₂BCl. All new compounds except 1Na₂ and 2 were structurally characterised by single-crystal X-ray diffraction. The N-boryl substituents of 1E compete efficiently with the Eᶦᶦ atom for nitrogen π-donation, causing comparatively long Eᶦᶦ−N bonds and small Eᶦᶦ bond angles. 1C=S contains a four-membered BNCS ring due to intramolecular adduct formation involving the Lewis basic S atom and a Lewis acidic B atom.