The silicon effect in metallic silylamides

Abstract

The alkoxysilazane tBuO-SiMe2-N(H)-CMe3 (1), which has a tert-butyl substituent at nitrogen and the corresponding trimethylsilyl derivative tBuO-SiMe2-N(H)-SiMe3 (2) can be transformed to amides of divalent transition metals. While (tBuO-SiMe2-N-CMe3)2Ni is blue and has a paramagnetism of 3.25 B.M., the corresponding (tBuO-SiMe2-N-SiMe3)2Ni is red and has a paramagnetism of 2.41 B.M. If Ni is substituted by Co the differences in B.M. of the two derivatives are even greater (4.05 B.M. versus 1.86 B.M.). The dilithium salt Me2Si(NCMe3)2Li2 reacts smoothly with PbCl2 to yield the metallacycle Me2Si(NtBu)2Pb, while in the case of the more silicon-rich amide Me2Si(NSiMe3)2Li2 a hetero-metallic amide [Me2Si(NSiMe3)2]2PbLi2 is obtained from the reaction with PbCl2. The latter procedure may be used to synthesize similar heterometallic silylamides. If in hexamethyldisilazane two of the methyl groups are substituted by t-butoxy-groups, an alkoxysilazane (tBuO)SiMe2-N(H)-SiMe2(OtBu) originates, which has chelating capabilities. A number of divalent metallic elements can be bound to the nitrogen, replacing hydrogen. All derivatives of the general formula [Me2Si(OtBu)]2N-M-N[(OtBu)SiMe2]2, M=Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Ba, behave as molecular compounds with no further organic base linked to the metallic element M. A comparision of different structures shows that the ligand [Me2Si(OtBu)]2N can adopt quite different chemical bonding.