Catalytic alkene polymerization is one of the world's largest applications of homogeneous, organotransition metal chemistry.  A consistently troubling aspect of industrial catalysts concerns the number of catalyst active sites–how much of the catalyst is acting to make product? Such questions are particularly troublesome for very sensitive catalysts, such as organometallic polymerization catalysts.  In order to quantitate active site counts in catalytic polymerization reactions, we have developed a chromophore-quench labeling strategy in which all actively propagating metal-alkyls are labeled with a UV chromophore.  The quench-labeling approach must label the polymers and stop the catalytic reaction;  several of these reagents have been developed and the data are compared with alternative methods for counting active site counts.  Applications of quench-labeling and other techniques reveal unusual active site counts, rate laws, and catalyst resting state for imino-amido hafnium catalysts.

Mechanistic features of catalytic alkene polymerization as revealed by chromophore-quench labeling

2019 Spring National Meeting

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