Synthesis and crystal structures of three silicon complexes with N-[(2-hy-droxy-naphthalen-1-yl)methyl-idene]alanine

The reaction of the Schiff base ligand N-[(2-hy-droxy-naphthalen-1-yl)methyl-idene]alanine, H₂ L, with di-chloro-diorganosilicon compounds, Cl₂SiR ₂, yields silicon complexes LSiR ₂. The crystal structure analyses of (RS)-dimethyl{N-[(2-oxidonaphthalen-1-yl)methyl-idene]alaninato}silicon, C₁₆H₁₇NO₃Si, (1), (RS)-di-ethenyl{N-[(2-oxidonaphthalen-1-yl)methyl-idene]alaninato}silicon, C₁₈H₁₇NO₃Si, (2), and (RS)-methyl-{N-[(2-oxidonaphthalen-1-yl)methyl-idene]alaninato}phenylsilicon chloroform hemisolvate, 2(C₂₁H₁₉NO₃Si)·CHCl₃, (3), allow a detailed analysis of the coordination geometries of the penta-coordinated silicon complexes. All three complexes adopt a distorted trigonal-bipyramidal coordination geometry. The apical positions in these coordination polyhedra are occupied by the oxygen atoms O1 and O2, whereas the equatorial positions are occupied by the nitro-gen atoms N1 and the carbon atoms of the organic groups at the silicon atom. In all three compounds, the O3 oxygen atoms inter-act in bifurcated C-H⋯O inter-actions with the imine hydrogen atoms, leading to stable zigzag chains. Differences between the three structures are found in the support of this inter-action via other C-H⋯O or aryl inter-actions. While 1 exhibits π-π stacking, 2 and 3 shows C-H⋯π contacts. This study demonstrates the ability of the H₂ L ligand to form hypercoordinate silicon complexes.