Bis[[diphenyl(piperidinomethyl)silyl]methyl]cadmium and -magnesium.

The homoleptic and monomeric metal alkyls bis[[diphenyl(piperidinomethyl)silyl]methyl]cadmium, [Cd(C(19)H(24)NSi)(2)] or [Cd[CH(2)SiPh(2)(CH(2)NC(5)H(10))](2)], (I), and bis[[diphenyl(piperidinomethyl)silyl]methyl]magnesium, [Mg(C(19)H(24)NSi)(2)] or [Mg[CH(2)SiPh(2)(CH(2)NC(5)H(10))](2)], (II), (CH(2)NC(5)H(10) is piperidinomethyl) are isostructural, and the molecules exhibit crystallographically imposed C(2) symmetry. The metal centres are located on special positions and, for each structure, half of the molecule is located in the asymmetric unit. The metal centres are intramolecularly coordinated and stabilized by two piperidinomethyl groups (side-arm donation). The Si-C and M-C bonds (M is Cd or Mg) are shortened compared with the corresponding non-metallated compounds, indicating stabilization by the diffuse polarizable Si centres (alpha effect). The C-M-C angle is 140.53 (12) degrees in (I) and 123.39 (11) degrees in (II).