Modification of mesoporous silicas

Mesoporous silicas were post-synthetically modified with organometallic complexes in order to produce well defined supported meal centres.The first part of this thesis describes the synthesis of mesoporous silicas MCM-41(A), MCM-41(B) and A1MCM-41 using surfactant templates, MESLC using liquid crystal templates and KMES from an aged gel mixture. The mesoporous materials were characterised by a combination of methods (PXRD, IR spectrometry, MAS NMR, TEM and BET surface area measurements) which resulted in the identification of porous silicas with a hexagonal lattice of pores of 22 - 36 Å and internal surface areas of 848 - 1646 m2g-1. The second part of this thesis describes the post-synthetic modification of mesoporous silicas with the organometallic species trimethylgallium, diethylzinc, Pd(allyl)cp, Pd(CH3CN)2(NO2)Cl and Pd(PPh3)3. MCM-41(A) was modified with trimethylgallium in a direct and indirect vapour phase reaction. MCM-41(B), KMES and MESLC were modified with trimethylgallium via vapour phase reactions. The interaction of trimethylgallium with mesoporous silicas was monitored by EXAFS and led to the loss of one methyl group and surface attachment of diemthylgallium via two silanol groups for MCM-41(A) at 100°C, and MCM-41(B) and KMES at 200°C, and via two silanol groups for MESLC at 200°C. The modification of MCM-41(A), MCM-41(B), KMES and MESLC by diethylzinc resulted in the loss of one ethyl group and interaction of the monoethylzinc species with the silica surface via three silanol groups for MCM-41(A), MCM-41(B) and KMES, and via two silanol groups for MESLC.MCM-41(A), KMES AND MESLC were modified by Pd(allyl)cp leading to the formation of Pd-cp subunits attached to the silica surface via two silanol groups for MCM-41(A) and KMES, and via one silanol group for MESLC. MCM-41(A) was also modified with Pd(CH3CN)2(NO2)Cl leading to the loss of two acetonitrile groups and the anchoring of a Pd(NO2)Cl subunit to the surface of the silica via two silanol groups.