An investigation of catalyst/cocatalyst/support interactions in silica-supported olefin polymerization catalysts based on Cp*TiMe3*

Catalytic consequences of open and closed grafted Al(III)-calix[4]arene complexes for hydride and oxo transfer reactions

“…In addition, the slightly lower rate for 6-SiO 2 (450) relative to 6-SiO 2 (800) suggests that a high degree of silica dehydroxylation may promote monodentate attachment of open precursors to the silica surface, because bidentate grafting is expected to synthesize MPV-inactive sites within a closed configuration. A monodentate mode of attachment of the open Al(III) sites to silica within catalyst 6 is consistent with studies of previous investigators who have grafted Me 3 Al on silica (23)(24)(25), and a recent detailed 27 Al NMR spectroscopic analysis of the binding of Et 3 Al on silica, which shows the predominant grafted species to contain two ethyl ligands on aluminum (40). Scott et al have notably shown within this regard that a silica dehydroxylation temperature of 800°C promotes greater monodentate grafting of organometallic complexes relative to a lower temperature of 500°C (23, 24).…”

“…Other notable examples of grafted metal cations on the silica surface include noncalixarene grafted Al(III) sites on silica using an aluminum-methyl precursor complex (23)(24)(25), and an elegant solid-phase version of the Sharpless homogeneous epoxidation catalyst (see below). This latter example employs open grafted Ta (V) active sites, which were shown to be highly enantioselective for epoxidation of allylic alcohols (26 Fig.…”

Methylalumoxane – History, Production, Properties, and Applications

“…182,183 Monomeric Me 3 Al could react with either one or two hydroxy groups on the surface, leading to the respective –AlMe 2 and =AlMe species on the surface (Figure 11a). As mentioned earlier, Me 3 Al occurs predominantly in its dimeric form, Me 6 Al 2 , which similarly could react with hydroxy groups on the surface 184. In this case, either bridging or terminal Me groups can be eliminated to enable end‐ and side‐on attachment of the Me 5 Al 2 fragment.…”

Catalysis using multifunctional organosiliceous hybrid materials

“…The post-synthesis anchoring of AlMe 3 onto hybrid supported materials implied the formation of methylene-bridged bimetallic complexes, (RSiO) 2 Cp*TiCH 2 AlMe 2 , which is accompanied by the passivation of the silica surface by methyl groups (Scheme 12). 33 In this class of supported hybrids, the influence of surface acidity on catalyst activity is important due to the strong interaction between surface silanol groups with metallic species. This was studied by Sa ´nchez and Iglesias et al who confirmed the positive effect of acid sites present on the surface of the solid, as a function of Si/Al ratios of the supports, over anchored chiral palladium or nickel complexes, catalyzing alkene and imine hydrogenation processes (Scheme 13).…”