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Surface organometallic chemistry aims to understand the interactions of organometallic complexes with surfaces at the molecular level. In comparison with traditional surface science, surface organometallic chemistry uses more of the tools and concepts of molecular chemistry (e.g., preparation using well-defined precursors, characterization by NMR spectroscopy, structure-activity relationships). When the organometallic complexes of interest are catalytically active, surface organometallic chemistry is also referred to as “heterogeneous molecular catalysis.”
The general approach is to anchor or graft an organometallic complex to a surface via a direct bond between the metal and a surface atom. This direct bonding distinguishes surface organometallic species from other supported homogeneous species (i.e., those that are tethered, encapsulated, encaged, entrapped, or otherwise immobilized). From the perspective of surface organometallic chemistry, the surface behaves as a ligand for the organometallic species rather than as only a support material. Alternatively, the surface can be viewed as chemically modified by grafted metal complexes.
The aims of surface organometallic chemistry are (1) to prepare materials that exhibit the most useful characteristics of both heterogeneous catalysts (e.g., high activity, facile product separation) and homogeneous catalysts (e.g., high selectivity, better knowledge of mechanism), (2) to create unique catalytic species with unprecedented properties, and (3) to provide well-characterized models for a variety of heterogeneous catalysts.[1] Although the surface organometallic chemistry approach has produced interesting examples of unique chemical reactivity, to date it has not led to processes of practical significance.
General Preparation
[edit]Support materials include oxides (e.g., silica, alumina, zirconia, zeolites) and metals (e.g., rhodium, platinum). Typically the support material is pre-treated to ensure surface homogeneity, and then it is reacted with a well-defined metal complex often introduced in solution or in the gas phase (e.g., sublimation, chemical vapor deposition).
Examples
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A specific example involves the formation of tantalum alkylidene and tantalum hydride species supported on silica. These species show interesting reactivity with alkanes, including alkane metathesis.[2]
Related surface organometallic species also can mediate olefin metathesis, among other reactions.
History
[edit]The foundations of surface organometallic chemistry date to the 1960s and 1970s with emerging ideas about molecular approaches to understanding heterogeneous catalysis. [3]
References
[edit]- ^ Sautet, P. and Delbecq, F. “Catalysis and Surface Organometallic Chemistry: A View from Theory and Simulations” Chemical Reviews 2010, 110, 1788-1806. DOI 10.1021/cr900295b
- ^ Basset, J.-M.; Candy, J.-P.; Coperet, C. “Surface Organometallic Chemistry” chapter 12.10 in Comprehensive Organometallic Chemistry III; Elsevier: Amsterdam, 2007. ISBN 9780080445908
- ^ Basset, J. M. and Ugo, R. “On the Origins and Development of ‘Surface Organometallic Chemistry’” chapter 1 in Modern Surface Organometallic Chemistry; Wiley-VCH: Weinheim, 2009. ISBN 978-3-527-31972-5