2 DIFFERENT COORDINATION MODES OF HYDRAZIDE LIGANDS IN SILICON AND GERMANIUM COMPOUNDS

The compounds SiCl4 and GeCl4 reacted with Me(2)NNMeLi in hexane to fo rm dichlorobis(trimethylhydrazido)silane, SiCl2(NMeNMe(2))(2) 1 and te trakis(trimethylhydrazido)germane, Ge(NMeNMe(2))(4) 2 in 51 and 50% yi eld, respectively. The liquid 1 (m.p. 6 degrees C) and solid 2 (m.p. 7 3 degrees C) decompose at temperatures greater than 100 and 140 degree s C, respectively. Both compounds can be slowly vaporised at ambient t emperature in high vacuum. They have been characterised by spectroscop ic techniques including NMR (H-1, C-13, Si-29), IR, mass and high-reso lution mass spectrometry. Evidence for higher co-ordination of the sil icon atom occurs from the Si-29 chemical shift (delta - 44.0). The cry stal structure of 1 shows the N-beta atoms of the hydrazide ligands in teracting with the silicon atom resulting in a 4 + 2 co-ordination, wh ereas no N-beta ... Ge interactions are detectable in the structure of 2. While the geometry at the N-alpha atom in 1 is completely planar, that of the corresponding atom in 2 is slightly pyramidal. Ab initio c alculations have been carried out for the model systems SiCl2(N2H3)(2) 1a, GeCl2(N2H3)(2) 1b (both C-2v), and Si(N2H3)(4) 2a and Ge(N2H3)(4) 2b (both S-4) up to the MP2/6-31G level of theory. The results lead to the prediction that the germanium compound analogous to 1 should ha ve N-beta ... Ge interactions which are even stronger than the N-beta ... Si ones in 1.