The reactions of molecular transition metal complexes with extended oxide surfaces such as silica and alumina can be used to create highly-dispersed catalysts with a high degree of active site uniformity, via ligand substitution. Traditionally, such reactions have involved the major functional groups on the native oxide surfaces, namely the hydroxyls and the oxo groups. For example, the reactions of AlMe3 and GaMe3 with silica result in the formation of M-O bonds (M = Al, Ga) primarily via protonolysis by surface hydroxyls, with release of methane, as well as a minor reaction involving cleavage of Si-O-Si (siloxane) bridges with transfer of methyl to Si. Recently, we demonstrated that oxide surfaces modified with other types of functional groups such as halides are capable of immobilizing and activating transition metal complexes by non-protolytic ligand metathesis reactions. For example, Me3SiOReO3 reacts irreversibly with chlorinated silica to form grafted perrhenates, liberating Me3SiCl, while MeReO3 reacts with chlorinated alumina to form MeReO2Cl+ while transferring an oxo to the alumina surface. Such reactions allow us to access new types of active sites and new types of catalytic activity that are inaccessibly by conventional routes.

Synthesis of supported metal catalysts using molecular precursors and halide metathesis reactions

253rd National Meeting (2017)

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