Back Cover Article in European Journal of Inorganic Chemistry

Authors: Luisa Waag-Hiersch, Jan Mößeler, Ulrich Schatzschneider

Abstract: Rhodium(III) azide half-sandwich complexes of general formula [Rh(Cp*)(N₃)(bpy^R,R)]CF₃SO₃ with R = H, OCH₃ were prepared in three steps in an overall yield of 55–65 %. Their stability strongly depends on the 4,4′-substituent on the 2,2′-bipyridine (bpy) ligand and increases in the order COOCH₃ < H < OCH₃. Consequently, no stable product could be isolated for the complex with the methyl ester substituent. The title compounds easily underwent cycloaddition reactions with ethyl 4,4,4-trifluoro-2-butynoate in acetonitrile at room temperature in the absence of catalyst. The resulting triazolate products were simply isolated by precipitation in 65–75 % yield. The trifluoromethyl group enabled facile monitoring of the reaction by ¹⁹F NMR spectroscopy. Kinetic studies with solution IR spectroscopy revealed pseudo-first-order rate constants of 2.4 to 3.8 × 10^–3 s^–1, and the reactions were accelerated by the presence of electron-donating groups at the 4,4′-position of the bpy coligand. These values are of a similar magnitude as those for the Staudinger ligation utilized for bio(macro)molecule functionalization.

Link: http://onlinelibrary.wiley.com/doi/10.1002/ejic.201700199/abstract