beta-donor interactions as secondary bonds in dichlorobis(dimethylaminoxy)silane and -germane

The compounds Cl2Si(ONMe2)(2) and Cl2Ge(ONMe2)(2) were prepared by the reac tion of the appropriate tetrachlorides with N,N-dimethylhydroxylamine in th e presence of 2,6-lutidine as an auxiliary base. The compounds were obtaine d as crystalline solids and characterised by elemental analysis, IR and NMR spectroscopy (nuclei H-1, C-13, N-15, O-17, and Si-29). Their molecular st ructures were determined by single-crystal X-ray diffraction. The compounds are isostructural and both show the presence of weak secondary bonds betwe en the nitrogen and silicon centres (beta-donor bonds), as is indicated by the small angles SiON [1.02.8(1) and 103.7(1)degrees] and GeON [102.0(1)deg rees], and the distances Si...N (2.438 and 2.450 Angstrom) and Ge...N (2.51 9 and 2.520 Angstrom). The conformation is anti-gauche in both compounds (o ne O-Si-O-N torsion angle being about 180 degrees, the other 60 degrees), b ut the strength of the beta-donor interaction is not significantly affected by the different antisubstituents at the nitrogen centres, although such b ehaviour was expected from earlier studies carried out on ClH2SiONMe2. The beta-donor interactions are also weaker than those found in ClH2SiONMe2.