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Unsymmetrical Twist For NH-Acidic Amines

Framing an amine nitrogen with two different electron-withdrawing perfluoroalkyl groups yields a new weakly coordinating species

by Stephen K. Ritter
April 7, 2014 | A version of this story appeared in Volume 92, Issue 14

Amines or imides with two strongly electron-withdrawing groups, HNRR´, which are referred to as NH-acids, are popular molecules because they form very weakly coordinating anions. These species are essential components of some olefin polymerization catalysts and lithium-ion batteries. Researchers led by Julius F. Kögel and Jörg Sundermeyer at Philipps University, in Marburg, Germany, have devised a new member of this compound class (shown) that is unprecedented for bearing two different sterically demanding and strongly electron-withdrawing substituents: a pentafluorophenyl group and a perfluorinated tert-butyl group ­(Inorg. Chem. 2014, DOI: 10.1021/ic5001717). Among NH-acids, the most prominent example is bis(trifluoromethylsulfonyl)imide, HN(SO2CF3)2. In the past, chemists have made NH-acids with one SO2CF3 group paired with a C6F5 group or with a pair of pentafluorophenyl groups, but not with two different perfluorocarbon groups. The Marburg team prepared the new compound in three steps starting from pentafluoroaniline and hexafluoroacetone and studied the thermal, spectroscopic, and structural properties of its alkaline and alkaline-earth salts. The researchers suggest the new NH-acid will be useful in preparing ionic liquids, as a component of lithium-ion battery electrolytes, and as a weakly coordinating ligand in metal complexes.


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