Basizität und ²⁹Si‐NMR‐spektroskopische Untersuchungen von Ethoxysiloxanen

Abstract

Die Ethoxysiloxane der Typen (RMe2SiO)3SiOEt, Me3−n(R3SiO)nSiOEt[(Me3SiO)3SiO]n(Me3SiO)3−nSiOEt (n = 1−3) und (Me3SiO)3Si[OSi(OSiMe3)2]2OET wurden dargestellt. Die relative Basizität der (Si)OEt‐Gruppe und die 29Si‐NMR‐chemischen Verschiebungen des Si(OEt)‐Signals wurden bestimmt. Sowohl die relativen Basizitäten als auch die 29Si‐NMR‐chemischen Verschiebungen sind von der Art und Anzahl der Siloxygruppen abhängig. Basizität und 29Si‐NMR‐chemische Verschiebungen der jeweiligen Verbindungstypen stehen in direkter Beziehung zueinander.

Hybrid Disila-Crown Ethers as Hosts for Ammonium Cations: The O–Si–Si–O Linkage as an Acceptor for Hydrogen Bonding

“…The ligands were prepared using methods described in the literature (see Scheme 2) [11,15]. Subsequent reaction of these ligands with NH4PF6 in anhydrous dichloromethane yielded the respective complexes [NH4(1,2-disila [18]crown-6)]PF6 (3) The ability of these systems to form a hydrogen bond has been discussed since the early sixties, especially by the group of West. Early examinations order the affinity to form hydrogen bonds in the sequence R 3 COCR 3 > R 3 COSiR 3 >> R 3 SiOSiR 3 according to IR-spectroscopic and thermodynamic studies, as well as NMR experiments [16][17][18].…”

“…Recrystallization of equimolar ratios of salt and an appropriate crown ether from organic and/or aqueous solution yields crown ether complexes with the general formula [M(CE)]A, where M = H 3 O + or NH 4 + , CE = crown ether, and A = anion. Mainly crown ethers of the [18]crown-6 type are used, but the anion structure varies with…”

“…For this reason, hydrogen bonding towards hydronium cations could not be performed. However, the incorporation of a guest turned out to be successful in the use of ammonium hexafluorophosphate as the salt and 1,2-disila [18]crown-6 (1), as well as 1,2-disila-benzo [18]crown-6 (2) as the ligands of choice. The ligands were prepared using methods described in the literature (see Scheme 2) [11,15].…”

“…The resulting colorless blocks were analyzed via XRD. 3 crystallizes in the non-centrosymmetric monoclinic space group P2 1 as an enantiopure product very similar to the corresponding potassium complex [K(1,2-disila [18]crown-6)PF 6 ] according to the lattice constants [11].…”

“…The hydrogen bonding data for 3 and related compounds-based on the representation in Scheme 2. Synthesis of 1,2-disila [18]crown-6 and 1,2-disila-benzo[18}crown-6 [11,15]. Compound 3 is a rare example combining hydrogen bonding situations towards etheric oxygen atoms, as well as partially silicon substituted oxygen atoms in the same molecule.…”