Trityl-spaced aminosilica

To test the performance of the trityl-spaced aminosilica, Ti, Zr, and Hf constrained-geometry-inspired catalysts (CGCs) were grafted to the amine sites (Fig. 20.3) [14-18]. 

The synthesis of these materials starts with the reaction of chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane (Cp -silane) with the snrface amine groups. It was shown that the percentage of amine sites reactive toward the Cp -silane was significantly better for the trityl-spaced material than traditionally prepared aminosilica (77% reacted amines vs. 29% reacted amines) [19]. Also, once the Cp -silane moiety was reacted with the trityl-spaced amines, the percentage... 

The benzyl-spaced aminosilica was also used as a scaffold on which to anchor CGC-inspired catalysts [19]. As in the trityl-spaced study, the aminosilica was first reacted with Cp -silane. For the benzyl-spaced materials, complete conversion of the amine groups through reaction with the Cp -silane did not occur however, the amine conversion for this material was twice the amine conversion for the traditionally grafted material (63% reacted amines vs. 29% reacted amines) [19]. When the grafted, metallated catalyst was tested for polymerization of ethylene, the benzyl-spaced catalyst again outperformed the traditionally grafted material, although it was somewhat less active than the trityl-spaced immobilized catalyst. 

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