New porous materials from polymeric and molecular building blocks for applications in catalysis

This thesis describes the synthesis of porous materials from well-defined dendritic polymers and “single-source precursor” molecules. This work was undertaken in order to obtain novel materials whose properties can be precisely controlled by virtue of the “nanoscale” building blocks employed.; Four new carbosilane dendrimers terminated with 12, 24, 36 and 72 benzyl groups have been synthesized and characterized by matrix-assisted laser desorption/ionization - time of flight (MALDI-TOF) mass spectrometry. These dendrimers were capped with Cp*Ru+ to yield polycations containing charges of 12+, 24+, 36+ and 72+. The charged dendrimers were characterized by electrospray ionization (ESI) mass spectrometry and full resolution of individual isotopic distributions was achieved. The first-generation, ruthenium-containing dendrimer (G1-Ru₁₂) was also characterized by single crystal X-ray diffraction.; Second and third generation alkoxysiyl-terminated carbosilane dendrimers, Si[CH₂CH₂CH₂Si(CH₂CH₂Si(OEt) ₃)₃]₄ (G2-(OEt) ₃₆) and Si{lcub}CH₂CH₂CH₂Si[CH ₂CH₂CH₂Si(CH₂CH₂Si(OEt) ₃)₃]₃{rcub}₄ (G3-(OEt )₁₀₈), were hydrolyzed in THF and benzene to yield monolithic gels. The resulting xerogels, X-G2_THF, X-G3_THF, X-G2_benz and X-G3 _benz, respectively, have surface areas of 325 − 800 m 2/g, a high degree of Si-OH functionality and a spectroscopically well-define surface. The surface area of the xerogels increase with increasing dendritic radii, suggesting that the dendrimer building blocks of (for example) X-G2_benz are compressed onto one another to a greater extent than the corresponding dendrimers that comprise X-G3_benz. Post gellation processing produced xerogels with surface areas as high as 1300 m2/g. These aerogel-like materials were treated with Ti(O iPr)₄ and Ti[OSi(OtBu) ₃]₄ to yield the corresponding Ti-impregnated gels. These gels were shown to be highly active catalysts for the epoxidation of cyclohexene.; The synthesis of mesoporous, multicomponent oxides (denoted UCB1 ), based on the use of several molecular precursors in conjunction with block copolymer templates, has been achieved using a new synthetic protocol. This method is illustrated for materials with the compositions ZrO₂•4SiO ₂, Ta₂O₅•3SiO₂, Fe₂O ₃•6SiO₂, and AlPO₄ by employing the precursors Zr[OSi(OtBu)₃]₄, (EtO) ₂Ta[OSi(OtBu)₃]₃, Fe[OSi(OtBu)₃]₃•THF and [Al(OiPr)₂O₂P(O tBu)₂]₄, respectively, and block polyalkylene oxide copolymers.; A new metal-siloxide (Mg[OSi(OtBu) ₃]₂) complex has been prepared. This molecule undergoes clean thermolytic conversion to MgO•2SiO₂ gels in toluene solution. The monolithic gels were processed to obtain high surface area xerogels and aerogels.