Lewis Acid–Base Adducts of α-Amino Isobutyric Acid-Derived Silaheterocycles and Amines

Authors:
Open Access
Publisher website
Google Scholar
Abstract
The 1:1 stoichiometric reactions of α-amino isobutyric acid (H2Aib) and diaminosilanes of the type SiRR′(NR1R2)2 (SiMe2(imidazol-1-yl)2, SiMe2(NHnPr)2, and SiRR′(pyrrolidin-1-yl)2 with R,R′ = Me,Me, Me,H, Me,Vi, and Et,Et) afforded the pentacoordinate silicon complexes (Aib)SiRR′(HNR1R2) with the release of one equivalent of HNR1R2. Single-crystal X-ray diffraction analyses confirmed the coordination of the N-donor Lewis base (i.e., imidazole, n-propylamine, and pyrrolidine, respectively) in an axial position of the distorted trigonal-bipyramidal Si-coordination sphere, trans to the carboxylate O atom of the Si-chelating Aib-dianion. The N–H moieties of the adduct-forming Lewis bases are involved in N–H⋯O hydrogen bonds with carboxylate groups of adjacent complex molecules, thus supporting the supramolecular structures of these adducts. The equatorially bound NH group of the Aib-dianion is involved in N–H⋯O hydrogen bonds in most cases, and it gives rise to residual dipolar coupling of the 14N nucleus with its directly bound atoms C and Si, thus causing characteristic shapes of both the 29Si and 13C NMR signals of these two atoms in the solid-state spectra. In contrast to the adduct-formation reactions, the analogous conversion of H2Aib and SiMe2(NHtBu)2 did not afford an amine adduct. Instead, a second equivalent of H2Aib entered the reaction, and the ionic silicon complex [tBuNH3]+[(Aib)2SiMe]− was obtained and characterized by crystallography and solution NMR spectroscopy.
Funding Information
  • European Union (European Social Fund, ESF) (100670490-AP2)
  • federal state of Saxony (Sächsische Aufbaubank, SAB, Dresden, Germany) (100670490-AP2)

This publication has 54 references indexed in Scilit: