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Long Group Published in Chem. Eur. J.

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The Long Group published their research “Mechanochemical Formation, Solution Rearrangements, and Catalytic Behavior of a Polymorphic Ca/K Allyl Complex” in Chemistry—A European Journal. Authors Brian Long and Alicia Doerr, graduate student, collaborated with Vanderbilt University and the University of Rochester. 

Without solvents present, the often far‐from‐equilibrium environment in a mechanochemically driven synthesis can generate high‐energy, non‐stoichiometric products not observed from the same ratio of reagents used in solution. Ball milling 2 equiv. K[A´] (A´ = [1,3‐(SiMe3)2C3 H3]– ) with CaI2  yields a non‐stoichiometric calciate, K[CaA´3], which initially forms a structure (1) likely containing a mixture of pi‐ and sigma‐bound allyl ligands. Dissolved in arenes, the compound rearranges over the course of several days to a structure (2) with only  η3‐bound allyl ligands, and that can be crystallized as a coordination polymer. If dissolved in alkanes, however, the rearrangement of 1 to 2 occurs within minutes. The structures of 1 and 2 have been modeled with DFT calculations, and 2 initiates the anionic polymerization of methyl methacrylate and isoprene; for the latter, under the mildest conditions yet reported for a heavy Group 2 species (one‐atm pressure and room temperature).

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Doerr Selected for Prestigious Symposium

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Alicia Doerr, graduate student in the Long Group, has been selected to take part in the ACS national meeting’s symposium entitled “Excellence in Graduate Polymer Research.” This annual symposium is organized by the POLY division and held at Spring national meetings of the ACS to recognize outstanding graduate students in polymer science and engineering, foster networking and exposure, and help develop the careers of future leaders in the field of polymers. This symposium was started in 2004 and includes both oral and poster sessions with presentations exclusively from graduate students.

Due to this meeting’s hybrid nature, the ACS POLY division created an independent web page to highlight the accomplishments of these graduate scientists. 

Doerr’s research explores the field of redox-switchable catalysis which has gained considerable interest in recent years, enabling catalytic reactivity/selectivity to be oscillated based on the redox-state of the ligand or active metal center. Unfortunately, though a myriad of redox-switchable catalysts have been developed for the ring opening polymerization of cyclic esters, very few fundamental structure-catalytic performance studies have been conducted that ascertain how systematic changes in ligand structure affect the catalytic performance.

This work describes studies used to determine how changes in the placement and number of redox-active moieties, ligand denticity, and active metal center identity impacts the catalytic performance.

The results of these studies reveal that the proximity of the redox-active moiety to the active metal center may influence both catalyst activity and redoxswitchability. Conversely, the number of redox-active moieties present within the ligand scaffold may not play a crucial role in the catalysts’ switchability. Lastly, when Ti-/ Zr-centered analogues of these catalysts were compared it was revealed that the choice of metal center may dramatically influence both catalyst activity and redox-switchable.