Synthesis and solid-state NMR structural characterization of polysiloxane-immobilized thiol and thiol-amine ligands

Thiol and thiol-amine ligand systems that are immobilized in a polysiloxane matrix have been synthesized via the sol-gel process by hydrolytic condensation of mixtures of Si(OEt)(4) and (MeO)(3)Si(CH2)(3)SH, as well as (EtO)(3)Si(CH2)(3)NH2 or (MeO)(3)Si(CH2)(3)NH(CH2)(2)NH2 for thiol-amine systems. In these systems, most of the amine groups can be protonated by aqueous acid solution. Solid-state Si-29 nuclear magnetic resonance (NMR) spectra confirm the fact that these materials, in analogy to polysiloxane-immobilized amine systems, undergo leaching of small oligomers containing ligand groups when they are treated with aqueous acid. N-15 NMR spectra indicate that the amine groups in these systems may be involved in hydrogen bonding with silanols or with other ligand groups. C-13-detected and Si-29 detected T-1(H) values were measured on the polysiloxane-immobilized thiol system, thiol-monoamine system and thiol-diamine system. The T-1(H) results suggest that the ligand groups in these systems are evenly distributed in the polysiloxane networks.