Chemistry

A Probe of Homogeneity

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Science  25 Nov 2011:
Vol. 334, Issue 6059, pp. 1035
DOI: 10.1126/science.334.6059.1035-a

One of the commonly touted advantages of homogeneous catalysis is that the catalyst structure is well defined. Dissolved molecules—as distinct from extended crystalline (or in some cases noncrystalline) surfaces—can be characterized and modified with high precision, and their interactions with substrates can be modeled in sharp detail, all in the service of optimizing their performance. Of course, such a path toward optimization relies critically on the knowledge that the active catalyst is in fact dissolved. If aggregated particles prove responsible for some or all of the catalytic activity, the implications of modifying the catalyst structure become far less clear. Esfandiari and Blum explore this question in the context of an olefin metathesis catalyst widely used for polymerization. Because the catalyst is only partially soluble in the medium, the appearance of the reaction mixture raises the possibility of activity at the solid-liquid interfaces. However, by carefully applying fluorescence microscopy with (submicrometer) single-particle resolution, the authors determine that nascent polymer does not accumulate at the sites of undissolved catalyst particles; rather, the data are consistent with fully homogeneous catalysis in the surrounding solution.

J. Am. Chem. Soc. 133, 18145 (2011).

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