Two different co-ordination modes of hydrazide ligands in silicon and germanium compounds
Abstract
The compounds SiCl4 and GeCl4 reacted with Me2NNMeLi in hexane to form dichlorobis(trimethylhydrazido)-silane, SiCl2(NMeNMe2)21 and tetrakis(trimethylhydrazido)germane, Ge(NMeNMe2)42 in 51 and 50% yield, respectively. The liquid 1(m.p. 6 °C) and solid 2(m.p. 73 °C) decompose at temperatures greater than 100 and 140 °C, respectively. Both compounds can be slowly vaporised at ambient temperature in high vacuum. They have been characterised by spectroscopic techniques including NMR (1H, 13C, 29Si), IR, mass and high-resolution mass spectrometry. Evidence for higher co-ordination of the silicon atom occurs from the 29Si chemical shift (δ–44.0). The crystal structure of 1 shows the Nβ atoms of the hydrazide ligands interacting with the silicon atom resulting in a 4 + 2 co-ordination, whereas no Nβ⋯ Ge interactions are detectable in the structure of 2. While the geometry at the Nα atom in 1 is completely planar, that of the corresponding atom in 2 is slightly pyramidal. Ab initio calculations have been carried out for the model systems SiCl2(N2H3)21a, GeCl2(N2H3)21b(both C2v), and Si(N2H3)42a and Ge(N2H3)42b(both S4) up to the MP2/6-31G* level of theory. The results lead to the prediction that the germanium compound analogous to 1 should have Nβ⋯ Ge interactions which are even stronger than the Nβ⋯ Si ones in 1.