%0 Journal Article
%A Tacke, Reinhold
%A Heermann, Joachim
%A Pülm, Melanie
%A Richter, Ingo
%D 1998
%T (Ammoniomethyl)bis[salicylato(2−)-O1,O2]silicates:
Zwitterionic Spirocyclic λ5Si-Silicates with Two
Six-Membered SiO2C3 Ring Systems
%U https://acs.figshare.com/articles/journal_contribution/_Ammoniomethyl_bis_salicylato_2_-_i_O_i_sup_1_sup_i_O_i_sup_2_sup_silicates_Zwitterionic_Spirocyclic_sup_5_sup_i_Si_i_-Silicates_with_Two_Six-Membered_SiO_sub_2_sub_C_sub_3_sub_Ring_Systems/3781467
%R 10.1021/om9709852.s001
%2 https://ndownloader.figshare.com/files/5892432
%K zwitterionic spirocyclic λ 5 Si
%K enantiomer
%K MAS
%K acetonitrile
%K carboxylate oxygen atoms
%K configuration
%K 29 Si NMR studies
%K trimethoxy
%K CH
%K CN
%K O 2
%K silicate
%K Si O 4 C skeleton
%K racemate
%K crystal
%K silicon
%K SiO
%X The zwitterionic spirocyclic
λ5Si-silicate
(morpholiniomethyl)bis[salicylato(2−)-O1,O2]silicate (5) was synthesized by reaction of
trimethoxy(morpholinomethyl)silane and
dimethoxy(morpholinomethyl)phenylsilane, respectively, with salicylic acid
(molar ratio 1:2) in
acetonitrile at room temperature.
Bis[salicylato(2−)-O1,O2][(2,2,6,6-tetramethylpiperidinio)methyl]silicate (6) was obtained analogously, starting
from trimethoxy[(2,2,6,6-tetramethylpiperidino)methyl]silane. Compound 5 was
isolated as a crystalline product consisting of
enantiomorphic crystals, each containing exclusively zwitterions with
the same absolute
configuration. Crystallization of this product from acetonitrile
yielded the crystalline solvate
5·CH3CN (crystals containing a 1:1
mixture of enantiomers with opposite absolute configuration). Compounds 5 (Δ-enantiomer),
5·CH3CN (racemate), and 6
(racemate) were
structurally characterized by single-crystal X-ray diffraction.
The spirocyclic frameworks
of 5 and 6 are built up by two six-membered
SiO2C3 ring systems. The zwitterions in
the
crystal of 5, 5·CH3CN, and
6 contain a pentacoordinate (formally negatively charged)
silicon
atom (SiO4C skeleton) and a tetracoordinate
(formally positively charged) nitrogen atom.
The coordination polyhedra around the silicon atoms are distorted
trigonal bipyramids, the
axial positions being occupied by the carboxylate oxygen atoms.
Solid-state MAS NMR
studies revealed the following isotropic 29Si chemical
shifts: δ −120.6 (5), −123.1
(5·CH3CN), −120.4 (6). The zwitterion 6 exists
also in solution (CDCl3; 1H, 13C,
and 29Si NMR
studies).
%I ACS Publications