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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.

Aminodimethylalanes R1R2NAlMe2 (R1 = 2,6-i-Pr2C6H3, 2,6-Me2C6H3; R2 = SiMe3, Si(i-Pr)Me2, Si(t-Bu)Me2, Si(2,4,6-Me3C6H2)Me2) are prepared in high yield via reaction of the respective amine R1R2NH with trimethylaluminum in n-hexane. Further reaction of (2,6-i-Pr2C6H3)N(SiMe3)AlMe2 with 2 equiv of trimethyltin fluoride in toluene affords the aminoalane difluoride (2,6-i-Pr2C6H3)N(SiMe3)AlF2. An X-ray structural determination of (2,6-i-Pr2C6H3)N(SiMe3)AlMe2 shows it to be dimeric with bridging methyl and terminal amino groups. The aminoalane difluoride (2,6-i-Pr2C6H3)N(SiMe3)AlF2 is trimeric with a six-membered alternating aluminum−fluorine ring. Terminal fluorine atoms are located above and below the ring. Reactions of aminoalanes R1R2NAlMe2 with 2 equiv of trimethyltin fluoride in THF yield the monomeric THF adducts R1R2NAlF2·THF.

Several novel routes for the immobilization of modified Cu(salicylaldimine) complexes on commercially available silica are described. New pulse electron paramagnetic resonance (EPR) and electron-nuclear double resonance sequences, which provide more detailed information than that available previously, in combination with continuous wave EPR, allow a definitive assignment of the geometry at the copper center in the immobilized Cu(salicylaldimine). Immobilization of the modified Cu(salicylaldimine) on silica was followed in situ by monitoring the intensity of the characteristic free- and metal-coordinated imine bands as a function of time using attenuated total reflectance IR spectroscopy. On the basis of these studies, the outcome of the Schiff base condensation of Cu-bis(salicylaldehyde) with gamma-aminopropyl-modified silica gel is shown to provide immobilized trans-O(2)N(2)- and O(3)N-coordinated immobilized Cu(salicylaldimine)-type compounds. In addition, trans-O(2)N(2)- or O(3)N-coordinated copper centers are selectively prepared on silica by controlling the aminopropyl modifier loading, thus opening a route to compounds not available by conventional synthesis. The O(3)N-coordinated Cu(salicylaldimine)-type compound on silica was investigated as a precursor for the synthesis of a tethered chiral Cu(salicylaldimine) via reaction of the coordinated carbonyl group with (R)-(+)-alpha-methylbenzylamine. Supported Cu(salicylaldimine) was also prepared via the immobilization of the appropriate silylethoxy-modified homogeneous precursor on silica gel. Precursors and silica-supported Cu(salicylaldimine) materials have been fully characterized. Comparisons are drawn with related Cu(salicylaldimine) immobilized in silica aerogels.