Mesoporous silicates are excellent materials for supported catalysis due to their ease of functionalization, tunable pore size and high surface areas. Mesoporous silicates have been utilized in a variety of applications such as drug delivery scaffolds and catalyst supports. Functionalization of the surface can be achieved by either grafting of alkoxy silanes or co-condensation of the organosilane with the inorganic silica source.
My research in this area can be divided into two components. In the first, we address the significant issue of metal contamination after reactions that are catalyzed by transition metals. In the second, we examine the design of new catalysts based on organic/inorganic composites.
Ruthenium catalyzed processes such as olefin metathesis or asymmetric hydrogenation, are often underutilized due to the difficulty of removing the ruthenium by-products. Attempts to remove ruthenium involve treating the solution with a scavenging reagent followed by silica chromatography. Often these scavenging agents are expensive phosphines or toxic agents like lead tetra-acetate. SBA-15 functionalized with aminopropyl triethoxysilane displays a high affinity for ruthenium. Furthermore, it can be utilized to remove ruthenium by-products from olefin metathesis or hydrogenation reactions without the need for silica chromatography.
We have also prepared sulfur-functionalized mesoporous silicates that have a high affinity for palladium. The materials after loading prove to be active catalysts for a variety of palladium catalyzed processes such as Suzuki-Miyaura and Sonogashira couplings. The catalysts are recyclable with moderate loss of activity and structure...
There is currently a great interest in the field of porous organosilica
materials because of the high surface areas (> 1000 m²/g) and narrow pore size
distributions which are beneficial for applications such as chromatography, chiral
catalysis, sensing or selective adsorption. Periodic mesoporous organosilicas
(PMOs) represent an interesting class of hybrid silica materials because of the
wide variety of bridging organic groups which can be incorporated within the
precursors [(OR)3Si-R-Si(OR)3] giving rise to materials with exceptional
We have synthesized and characterized various aromatic PMOs
composed of supporting structural monomers (phenylene- or biphenylenebridged)
and functional stilbene monomers (cis and trans) (1, 2). The effect of
the different synthetic procedures and varying amounts of functional stilbene
monomer on the properties of the materials was examined. The functional transstilbene
component was determined to be well distributed in a phenylene-bridged
PMO using P123 as a pore template from TEM techniques with Os staining. The
trans-stilbene linkers were completely transformed to aryl aldehydes through
ozonolysis with dimethylsulfide workup. Further transformation of the carbonyl
functionality to an aryl imine showed a moderate level of success.
Enantiomeric forms of a novel...
Chapter 1 constitutes a review of current methods of aromatic substitution focusing on Directed ortho Metalation (DoM) and Directed remote Metalation (DreM). The field of mesoporous silica is reviewed in Chapter 2, focusing on the preparation, characterization, and application of mesoporous silicates.
Chapter 3 presents an introduction of phosphorus based Directed Metalation Groups (DMGs). The development of the directed ortho metalation (DoM) reaction of the tetraethyl phosphorodiamidate DMG is described. In addition to being one of the most powerful DMGs, migration of the OPO(NEt2)2 group to the ortho and remote positions is demonstrated, constituting new reactions as well as affording new organophosphorus compounds.
Attempts to improve the synthetic utility of the DMG led to the discovery and optimization of a two new nickel-catalyzed cross coupling reactions, which is described in Chapter 4. Both the OPO(NEt2)2 and OCONEt2 DMGs are demonstrated to undergo cross coupling reactions with aryl boronic acids.
By means of DoM and cross coupling tactics, the concise synthesis of a chiral binaphthol bridged silasesquioxane is described. Chapter 5 explores new methods to prepare chiral periodic mesoporous organosilica (PMO) materials using this monomer. PMOs are prepared by the co-condensation of a relatively small amount of chiral binaphthyl dopant which acts to twist the bulk prochiral biphenylene framework.; Thesis (Master...