Zwitterionische Bis[vic-arendiolato(2 –)] [(morpholinio)alkyl]silicate: Synthese sowie strukturelle Charakterisierung in Lösung und im Kristall / Zwitterionic Bis[vic-arenediolato(2 –)] [(morpholinio)alkyl]silicates: Synthesis and Structural Characterization in Solution and in the Crystal

Abstract

The zwitterionic A5-spirosilicates bis[1,2-benzenediolato(2–)][(morpholinio)methyl]silicate (1), bis[2,3-naphthalenediolato(2–)][(morpholinio)methyl]silicate (2; isolated as 2 • CH3CN), bis[1,2-benzenediolato(2–)][3-(morpholinio)propyl]silicate (3) and bis[2,3-naphthalenediolato(2 –)][3-(morpholinio)propyl]silicate (4; isolated as 4·1/2CH3CN) have been synthesized by various methods including Si – C bond cleavage reactions. The crystal structures of 2 • CH3CN and 4 · 1/2 CH3CN have been determined. 1,2 • CH3CN, 3 and 4 · 1/2 CH3CN have also been characterized by solution-state (1H, 13C, 29Si) and solid-state NMR spectroscopy (29Si CP/MAS). The pentacoordinate silicon atoms of the zwitterions 1-4 are surrounded by four oxygen atoms and one carbon atom. In the crystal, the coordination polyhedra around the silicon atoms of 2 • CH3CN (two crystallographically independent zwitterions and two crystallographically independent acetonitrile molecules) can be described as nearly ideal trigonal bipyramids, with the carbon atoms occupying equatorial sites. The crystal structure of 2 • CH3CN is considerably influenced by intermolecular N – H···N hydrogen bonds between the zwitterions and the acetonitrile molecules. The coordination polyhedron observed for the silicon atom in the crystal of 4 · 1/2 CH3CN can be described as a distorted square pyramid, with the carbon atom in the apical position. The crystal structure of 4 · 1/2 CH3CN is considerably governed by intermolecular N –H···O hydrogen bonds between the zwitterions which form infinite chains in the crystal. The 29Si chemical shifts (δ = – 75,5 to – 85,8) observed for 1,2 • CH3CN, 3 and 4 · 1/2 CH3CN in solution ([D6]DMSO) and in the crystal are typical of pentacoordinate silicon of the type SiO4C. For all compounds very similar 29Si chemical shifts have been observed for the solution and solid state [⊿(δ29Si) ≤ 0,9] indicating that the zwitterions 1-4 do also exist in solution.