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

nionic five-coordinate complexes with two bis- O , O ’-chelating ligands bearing α-hydroxy acid moieties, dicyclohexylammonium salts Cy_2NH_2^+{PpnCH_2Si[OCR_2C(O)O]_2}^- (Cy is cyclohexyl, PpnCH 2 is 4-methyl-2,5-dioxopiperazin-1-ylmethyl, R = Me, Ph), were synthesized by esterification of alkoxysilane PpnCH 2 Si(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 29 Si NMR spectroscopy. According to the X-ray diffraction data, the synthesized compounds contain the SiCO 4 coordination unit.