Nondestructive immobilization of cobalt and copper Schiff base complexes in silica aero- and xerogels was achieved via the sol−gel method using a precursor N,N‘-ethylenebis(salicylidenaminato) (salen) ligand modified with pendant silyl ethoxy groups. Aerogels were obtained by semicontinuous extraction of the wet gels with supercritical CO₂ and xerogels by conventional drying. Cobalt and copper(salen) containing silica gels were characterized by FTIR, UV−vis, and XPS spectroscopy, laser ablation-ICP-MS, and EPR studies. Aero- and xerogel incorporated salen compounds exhibited similar spectroscopic properties to cobalt/copper(salen) precursors and known metal(salen) compounds. BET measurements confirmed the importance of supercritical CO₂ drying in maintaining the mesoporous structure of the aerogel. Laser ablation-ICP-MS and EPR studies of the aerogels showed that a uniform distribution of the isolated metal(salen) complex was achieved via molecular mixing using the sol−gel method. Stability of these materials was demonstrated by thermogravimetric analyses in air and leaching studies conducted under typical liquid-phase oxidation conditions. XPS analyses showed surface relative atomic concentrations in the modified gels to be similar before and following leaching studies.

Base-catalyzed H/D-exchange for α- and β-isophorone (1 and 2, resp.) was monitored by NMR spectroscopy to identify the number and nature of reactive sites. Results show that α-isophorone (1) undergoes H/D exchange at up to four different sites depending on reaction conditions. β-Isophorone (2), on the other hand, exhibits activity at two sites, predominantly at the α-position, under comparable conditions. Quantum-chemical calculations indicate that the thermodynamically more-stable anions formed upon proton abstraction from isophorone are not favored kinetically in all cases. Thermodynamically unfavorable H/D-exchange at the α-position in 1, which is observed experimentally, is explained via intermediate formation of γ-isophorone (3) with subsequent conjugation to the α-isomer. Differences observed in the reactivities of the two isomers and differences in reactivity of 1 under various conditions in reactions involving proton abstraction as an initial step may be partly explained on the basis of these results.