Supported Metal Complexes—Molecular Analogues Bonded to Surfaces

Supported Metal Complexes—Molecular Analogues Bonded to Surfaces 

The simplest supported catalysts are mononuclear metal complexes, exemplified by industrial supported metallocene catalysts, used (with promoters) for alkene polymerization these are the so-called single-site catalysts that are finding wide industrial applications (Kristen, 1999 Kaminsky, 1999 Roscoe et al., 1998). The most common supports are metal oxides and zeolites. The metals in these complexes range from oxophilic (e.g., Zr and Ta) to noble (e.g., Rh). Supported metal complexes are stabilized by ligands—in addition to those provided by the support—such as hydride (H), hydrocarbons, and carbonyl (CO). In a typical supported metal complex, the metal is present in a positive oxidation state. Although some such complexes are relatively stable, most are, befitting their roles as catalysts, highly reactive and air- and moisture-sensitive. 

In the following paragraphs, methods of preparation and characterization of structurally simple supported metal complexes are summarized, and examples are presented that illustrate characterization data and support general conclusions about structure, bonding, reactivity, and catalysis. 

Many syntheses of supported metal complexes involve simply the reaction of an organometallic precursor in an organic solvent with a support surface alternatively, a gas-phase precursor may be used in the absence of a solvent. The surface reactions are typically analogous to molecular reactions known from solution organometallic chemistry. The surface chemistry has been reviewed (Lamb, Gates, and Knozinger, 1988 Basset, Lefebvre, and Santini, 1998), and only a few examples are given here. 

In other preparations, oxidative addition of an O-H ligand of an oxide support surface to a metal center of an organometallic complex leads to anchoring of the metal complex to the support (Lamb, Gates, and Knozinger, 1988). 

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II. Supported Metal Complexes—Molecular Analogues Bonded to Surfaces... 

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