Synthesis and structure of new anionic five-coordinate silicon complexes derived from α-hydroxy acids and 1-methylpiperazine-2,5-dione

Abstract

Anionic five-coordinate complexes with two bis-O,O’-chelating ligands bearing α-hydroxy acid moieties, dicyclohexylammonium salts \(\text{Cy}_{2}\text{NH}_{2}{^+}\{\text{PpnCH}_2\text{Si}[\text{OCR}_2\text{C}\text{(O)O]}_2\}^-\) (Cy is cyclohexyl, PpnCH₂ is 4-methyl-2,5-dioxopiperazin-1-ylmethyl, R = Me, Ph), were synthesized by esterification of alkoxysilane PpnCH₂Si(OMe)₃ with α-hydroxy acids (dimethyl- and diphenylgylcolic acids) in the presence of dicyclohexylamine. The five-coordinated state of the silicon atom in the resulting compounds in solution was confirmed by ²⁹Si NMR spectroscopy. According to the X-ray diffraction data, the synthesized compounds contain the SiCO₄ coordination unit.