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Bismuth provides catalytic surprises

Lewis acidic perfluoroalkylphosphinates prove to be inexpensive, stable catalysts for a range of industrial organic reactions

by Stephen K. Ritter
December 5, 2016 | A version of this story appeared in Volume 94, Issue 48

A research team led by Berthold Hoge of Bielefeld University has gone into a little-used corner of the periodic table to develop a new set of highly active catalysts—bismuth perfluoroalkylphosphinates—that could be useful in industrial organic synthesis (Chem. Eur. J. 2016, DOI: 10.1002/chem.201604914). Although bismuth is a rare heavy metal, and the heaviest stable element in the periodic table to boot, it’s relatively inexpensive as a by-product of copper, lead, and tin mining. And unlike most heavy metals, its salts have remarkably low toxicity—most are less toxic than table salt. With those attributes, chemists are increasingly attracted to bismuth salts as Lewis acid catalysts to replace corrosive and toxic industrial catalysts such as boron trifluoride. Some examples such as bismuth triflate, Bi(SO3CF3)3, have already been successfully tested. But they are moisture sensitive. Hoge and his team found that switching to fluoroalkylphosphinates creates air- and moisture-stable compounds without altering the Lewis acidity. To make bismuth(III) catalysts, the researchers treated commercially available Bi(C6H5)3 with perfluoroalkyl­phosphinic acid, (C2F5)2P(O)OH. To make an unprecedented bismuth(V) catalyst, they treated Bi(C6H5)3Cl2 with Ag[(C2F5)2PO2]. Hoge and his colleagues showed that these bismuth phosphinates are versatile in mediating a range of carbon-carbon bond-forming reactions, including Friedel-Crafts alkylation and the Diels-Alder reaction.


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